Ubuntu Manpage: This documentation describes BackupPC version 4.4.0, released on 20 Jun 2020.

Provided by: backuppc_4.4.0-8build1_amd64

BackupPC Introduction

This documentation describes BackupPC version 4.4.0, released on 20 Jun 2020.

Overview
BackupPC is a high-performance, enterprise-grade system for backing up Unix, Linux, WinXX, and MacOSX
PCs, desktops and laptops to a server's disk. BackupPC is highly configurable and easy to install and
maintain.

Given the ever decreasing cost of disks and raid systems, it is now practical and cost effective to
backup a large number of machines onto a server's local disk or network storage. For some sites this
might be the complete backup solution. For other sites additional permanent archives could be created by
periodically backing up the server to tape.

Features include:

• A clever pooling scheme minimizes disk storage and disk I/O. Identical files across multiple backups
of the same or different PC are stored only once, resulting in substantial savings in disk storage
and disk writes.

• Compression provides additional reductions in storage, depending on the type of data being backed up.
The CPU impact of compression is low since only new files (those not already in the pool) need to be
compressed.

• A powerful http/cgi user interface allows administrators to view the current status, edit
configuration, add/delete hosts, view log files, and allows users to initiate and cancel backups and
browse and restore files from backups.

• The http/cgi user interface has internationalization (i18n) support, currently providing English,
French, German, Spanish, Italian, Dutch, Polish, Portuguese-Brazilian, Chinese, Polish, Czech,
Japanese, Ukrainian, and Russian.

• No client-side software is needed. On WinXX the standard smb protocol is used to extract backup data.
On linux, unix or MacOSX clients, rsync, tar (over ssh/rsh/nfs) or ftp is used to extract backup
data. Alternatively, rsync can also be used on WinXX (using cygwin), since rsync provides for
efficient transfers and allows incremental backups to detect almost all changes.

• Flexible restore options. Single files can be downloaded from any backup directly from the CGI
interface. Zip or Tar archives for selected files or directories from any backup can also be
downloaded from the CGI interface. Finally, direct restore to the client machine (using smb or tar)
for selected files or directories is also supported from the CGI interface.

• BackupPC supports mobile environments where laptops are only intermittently connected to the network
and have dynamic IP addresses (DHCP). Configuration settings allow machines connected via slower WAN
connections (eg: dial up, DSL, cable) to not be backed up, even if they use the same fixed or dynamic
IP address as when they are connected directly to the LAN.

• Flexible configuration parameters allow multiple backups to be performed in parallel, specification
of which shares to backup, which directories to backup or not backup, various schedules for full and
incremental backups, schedules for email reminders to users and so on. Configuration parameters can
be set system-wide or also on a per-PC basis.

• Users are sent periodic email reminders if their PC has not recently been backed up. Email content,
timing and policies are configurable.

• BackupPC is Open Source software hosted by GitHub.

BackupPC 4.0
This is the first release of 4.0, which is a significant rewrite of BackupPC. This section provides a
short overview of the changes and features in 4.0.

Here's a short summary of what has changed in V4:

• No use of hardlinks (except temporarily to do atomic renames). Reference counting is handled at the
application level in a batch manner (hardlinks will still remain for any legacy V3 backups).

• Backups are stored as "reverse deltas" - the most recent backup is always filled and older backups
are reconstituted by merging all the deltas starting with the nearest future filled backup and
working backwards.

This is the opposite of V3 where incrementals are stored as "forward deltas" to a prior backup
(typically the last full backup or prior lower-level incremental backup, or the last full in the case
of rsync).

• Since the most recent backup is filled, viewing/restoring that backup (which is the most common
backup used) doesn't require merging any deltas from other backups.

• The concepts of incr/full backups and unfilled/filled storage are decoupled. The most recent backup
is always filled. By default, for the remaining backups, full backups are filled and incremental
backups are unfilled, but that is configurable.

• Uses full-file MD5 digests, which are stored in the directory attrib files. Each backup directory
only contains an empty attrib file whose name includes its own MD5 digest, which is used to look up
the attrib file's contents in the pool. In turn, that file contains the metadata for every file in
that directory, including each files's MD5 digest.

• The Pool layout still supports chains to handle md5 collisions. While collisions can be constructed
and are now well-known, they are highly unlikely in the wild. Pool files are never renamed or moved,
unlike V3.

• Any backup can be deleted (deltas are merged into next older backup if it is not filled).

• The reverse deltas allow "infinite incrementals" - no need for a full backup if you are willing to
trade speed for the risk that a file change will not be detected if the metadata (eg, mtime or size)
doesn't change.

• An rsync "full" backup now uses --checksum (instead of --ignore-times), which is much more efficient
on the server side - the server just needs to check the full-file checksum computed by the client,
together with the mtime, nlinks, size attributes, to see if the file has changed. If you want a more
conservative approach, you can change it back to --ignore-times, which requires the server to send
block checksums to the client.

• The use of rsync --checksum allows BackupPC to guess a potential match anywhere in the pool, even on
a first-time backup. In that case, the usual rsync block checksums are still exchanged to make sure
the complete file is identical.

• Uses a modified rsync called rsync_bpc (currently based on rsync-3.0.9) on the server side (in place
of File::RsyncP), with a C code interface to the BackupPC storage. So the whole data path for rsync
is now in compiled C code, which is much faster than perl.

• Due to the use of rsync-3.X, acls and xattrs are supported, and many other useful options (but not
all) are supported. Rsync protocol 30 supports the efficient incremental file list, which
significantly improves memory usage and startup time. It also supports MD5 full-file checksums,
which match BackupPC's new digest. That allows a full-file digest to be checked as easily as an
mtime on the server side.

• Significant portions of the BackupPC code are now compiled C code in a new module called BackupPC::XS
that is dynamically linked to perl.

Here is a more detailed discussion:

• Completely new backup storage. No hardlinks! Backups are stored as reverse deltas, with the most
recent backup always filled. Prior backup "n" contains the changes relative to prior backup "n+1".

• Since every backup is based on the last filled backup, the concept of incremental levels is removed.

• Example: let's assume backup #4 is the most recent, and therefore filled, and backups #0..3 are not
filled.

Backups #0..3 store just the necessary reverse changes needed to reconstruct those backups, relative
to the next backup.

- To view/restore backup #4, all the information is stored in backup #4.
- To view/restore backup #3, backup #4 (the filled one), is merged with the deltas in #3.
- To view/restore backup #2, backup #4 (the filled one), is merged with the deltas in #3 and #2
- etc.

When a new backup is started (#5), we begin by renaming backup #4 to #5. At that instant, backup #4
storage is now empty (which means backups #4 and #5 are currently identical). As the backup runs,
changes are made to #5 with the changed/new files in place, and the opposite changes are added to
backup #4, to keep the "view" of backup #4 unchanged.

After the backup is done, #5 is now the filled version of the latest backup, and #4 contains the
changes necessary to turn #5 back into the state when backup #4 was done. If there are no changes
detected in the new backup, the storage tree for #4 will be empty. If just one file changed, the new
file will be below #5, and the prior file will be below #4 (well, technically not quite true, since
files aren't stored below the backup trees; more correctly, the attrib file in #5 will point to the
new pool file, and the attrib file in #4 will point to the old pool file).

• The concepts of incr/full backups and unfilled/filled storage are now decoupled. The most recent
backup is always filled (whether or not the last backup was a full or incr). Certain older backups
can be filled for convenience to make restoring old backups faster (because fewer backups need to be
merged), and are used to specify expiry schedules.

• When a backup starts, there are several different cases that determine how the backups are stored and
whether prior deltas are stored:

1. No existing backups: create a new backup #0 and do a full backup in place (ie: no prior deltas
are stored).

2. V3 backups exist, but no V4 backups. The last V3 backup is duplicated into V4 format, and a full
backup is done in place (ie: no prior deltas are stored).

3. Last V4 backup is a full, or more than $Conf{FillCycle} since last filled backup. The last
backup is duplicated to create a new filled backup, and the new backup is done in place (ie: no
prior deltas are stored).

4. There are V4 backups and it's less than $Conf{FillCycle} since last one is filled. Renumber the
last backup to #n+1, and put the reverse deltas in initially empty backup tree #n.

5. CompressLevel has toggled on/off between backups. This isn't well tested and it's very hard to
support efficiently. We treat this as a brand new (empty) backup in place, that is therefore
filled. That way we won't need to merge between backups with compress on/off.

6. Last backup was a V4 partial. If prior V4 backup is filled (and not partial), then just do
another in-place backup. Otherwise, treat as case 4. When complete (whether successful or
another partial), delete the prior deltas in #n, which merges the cumulative changes into #n-1.

• The treatment of a "Partial" backup has changed. Unlike in V3 where partials are removed prior to
the next backup, in V4 partials are kept and are used as the starting point for the next backup. See
case 6 above. If the new backup fails, if no files have been backed up, the empty backup #n is
removed.

• Backups are stored as mangled directory trees, but each directory only contains an "attrib" file.
The attrib file is zero-length, and its name includes the MD5 digest so the contents can be looked up
in the pool.

The attrib contents in the pool contains the directory contents: for each file, that means the
metadata, xattrs and the MD5 digest of the file contents.

• A modified rsync called rsync_bpc, based on rsync 3.0.9, is used on the server side, with a C code
layer that emulates all the file-system OS calls to be compatible with the BackupPC store. That
means for rsync, the data path is now fully in compiled C, which should mean a significant speedup.
It also means many (but not all) of the rsync options are supported natively.

• Significant parts of the BackupPC storage and pooling code have been written in C (the same code is
used in the server rsync_bpc). BackupPC::FileZIO, BackupPC::PoolWrite, BackupPC::Attrib,
BackupPC::AttribCache and BackupPC::PoolRefCnt (reference counting and storage) are all replaced with
BackupPC::XS, a C-code perl extension.

• Extended attributes (xattr) are supported. Rsync is configured to "store acls using xattr", meaning
both acls and xattrs are supported.

• infinite incrementals with rsync are supported. The most recent backup is always filled, so an
incremental will still leave the most recent backup filled.

• any V4 backup can be deleted - dependencies are merged into the next older backup if it isn't already
filled.

• file digests are full-file MD5. Collisions are much more unlikely than V3, but still possible.
Duplicates are implemented with an extension to the 16 byte MD5 digest (ie: 16 bytes for plain file,
17 bytes for next 255 duplicates etc).

• V4 pool files are stored in a new hierarchy, two levels deep, with 7 bits at each level (ie: 128
directories at top-level, and each with 128 directories at next level).

• V4 pool files are never moved or renamed.

• Inodes for hardlinked files are stored in each backup tree. This makes backing up hardlinks
accurate, compared to V3, and provides for consistent inode numbering across backups.

• zero-sized files or empty attribute files don't get written or pooled.

• the elimination of hardlinks means that reference counting has to be maintained by the BackupPC code.
This is one of the riskiest area in terms of development and testing. Reference counts are
maintained per-backup, per-host, and for the whole pool.

Each operation that changes reference counts (eg: doing a new backup, deleting a backup, or
duplicating (filling) a backup) creates one or more poolRefDelta files in that client's backup
directory (ie: TopDir/pc/HOST/NNN). These files are lists of MD5 digests, and corresponding counts
deltas.

Each night, BackupPC_nightly runs BackupPC_refCountUpdate, which, for each host, updates the per-host
reference count database with the new deltas. It then combines all the per-host reference count
files to create the global pool reference count database.

BackupPC_refCountUpdate can run concurrently with backups. If you still have V3 backups and pool,
BackupPC_nightly still needs to run and check for old V3 pool files that can be deleted. But since
there are no new V3 backups happening, BackupPC_nightly can run concurrently with backups.

• There is a new utility BackupPC_fsck that can check/fix the per-host and global reference counts.
The per-host reference count database is verified by parsing all the attrib files in each backup
tree. The global reference count database is verified by combing all the per-host reference count
databases and comparing them.

BackupPC_fsck cannot run when BackupPC is.

• When BackupPC_refCountUpdate updates the overall reference counts, it removes pool files that have a
reference count of zero. To avoid race conditions, it uses a two-phase process. It first flags
files that have zero reference counts using one of the file attributes. The next time it runs
(typically 24 hours later), any flagged files that still have zero reference count are then removed.
The rest of the code knows not to use flagged pool files to avoid race conditions.

• Progress indication: a simple status that shows the number of files processed so far. It's hard to
convert that to a percentage, since the total isn't known until the end of the backup. But knowing
the number of files is quite helpful, since you can get an idea of the expected total based on the
prior backups, or knowing what configuration you have changed (ie: adding a large new tree).

• BackupPC_link is removed since it is no longer used.

• Since files are no longer stored in backup trees, browsing the backup trees is even harder than V3
(where you just had to deal with mangling). A new utility BackupPC_ls acts like "ls -l", showing
accurate directory listings of files, together with the MD5 digests.

BackupPC_ls can be given either an explicit hostname, number, and unmangled path, or can be given the
full (mangled) path, which makes it easier to use directory completion. It should be possible to
configure tcsh and bash, together with some new hooks in BackupPC_ls, to give a more natural
file/directory completion.

BackupPC_zcat also can take just the MD5 digest (which you can paste from BackupPC_ls). Currently
BackupPC_zcat doesn't support the tree parsing that BackupPC_ls does (it can only zcat actual files),
but that should be easy to rectify.

• Configuration for expiry: since full/incr are decoupled from filled/unfilled, expiry is a bit
trickier.

The convention for expiry parameters is "FullKeepPeriod/FullKeepCnt" etc refer to Filled backups, and
"IncrKeepPeriod/IncrKeepCnt" refer to Unfilled backups.

• V3 migration: nothing specific is needed. V4 can browse/view/restore V3 backups. When you install
V4, no changes are made to any V3 backups. If you are upgrading from V3, be sure to set
$Conf{PoolV3Enabled} to 1 so the old V3 pool is searched for matching files.

• When you install V4, it will notice that the V3 pool exists. Running configure.pl should set
$Conf{PoolV3Enabled} to 1 in that case, but you should be sure to check that.

• When a V4 backup is first done, BackupPC_backupDuplicate is run to duplicate the most recent V3
backup to create a new V4 backup. A "filled" view of the most recent V3 backup is used to create
a "filled" V4 backup tree.

This step could be time consuming, since every file needs to be read (as a V3 file) and written
as a V4 file. However, the V4 pooling code knows about the V3 pool, so it will move the V3 pool
file into the V4 pool. So this duplication process doesn't burn a lot of pool storage space, but
every file still needs to be read (to compute the MD5 digest) and "written" (really just
matching/linking).

• Expiry: all the V3 + V4 backups are considered on a combined basis for expiry checking.

• On a clean new V4 install, the steps of computing and checking V3 digests is eliminated.

• Downgrading V4->V3: Not tested and not recommended. In theory you can remove any new V4 backups,
remove the V4 pool itself, and you should be able to re-install V3 and still have access to your
original full working V3 store (except for any V3 backups that V4 might have routinely removed
based on normal backup expiry configuration).

However, any V3 pool files moved to V4 will no longer be in the V3 pool. So subsequent V3
backups will burn more storage as files get re-added to the old V3 pool.

Hopefully downgrading isn't necessary...

• Optimizations: the C code implementation should give a significant performance advantage, as well as
the more flexible.

Potential V4 optimizations that are planned, but not yet implemented, include:

• rsync-bpc doesn't support checksum caching.

• rsync-bpc with --ignore-times actually reads each unchanged file three times, and writes it once
(normal rsync reads twice and writes once; the extra one is due to compression). Some careful
optimization can eliminate two reads and the write. The final read can be eliminated with
checksum caching.

• BackupPC_refCountUpdate, BackupPC_fsck, BackupPC_backupDuplicate, BackupPC_backupDelete are all
single-threaded.

Backup basics
Full Backup
A full backup is a complete backup of a share. BackupPC can be configured to do a full backup at a
regular interval (typically weekly). BackupPC can be configured to keep a certain number of full
backups. Exponential expiry is also supported, allowing full backups with various vintages to be
kept (for example, a settable number of most recent weekly fulls, plus a settable number of older
fulls that are 2, 4, 8, or 16 weeks apart).

Incremental Backup
An incremental backup is a backup of files that have changed since the last successful backup.

Rsync is the best option for BackupPC. Any files whose attributes have changed (ie: uid, gid, mtime,
modes, size) since the last full are backed up. Deleted, new files and renamed files are detected by
rsync incrementals.

For SMB and tar, BackupPC uses the modification time (mtime) to determine which files have changed
since the last backup. That means SMB and tar incrementals are not able to detect deleted files,
renamed files or new files whose modification time is prior to the last lower-level backup.

BackupPC can also be configured to keep a certain number of incremental backups, and to keep a
smaller number of very old incremental backups.

BackupPC "fills-in" incremental backups when browsing or restoring, based on the levels of each
backup, giving every backup a "full" appearance. This makes browsing and restoring backups much
easier: you can restore from any one backup independent of whether it was an incremental or full.

Partial Backup
When a full or incremental backup fails or is canceled, the most recent backup is labeled "partial".
Prior to V4, that backup was incomplete, and would be deleted when the next backup completed.

In V4 a partial backup denotes that the last backup is incomplete. However, since V4 does backup
updating in place, it represents the best and latest backup. A partial backup can be browsed or used
to restore files just like a successful full or incremental backup. And it will be used as the
starting point for the next backup attempt.

Identical Files
BackupPC pools identical files. By "identical files" we mean files with identical contents, not
necessary the same permissions, ownership or modification time. Two files might have different
permissions, ownership, or modification time but will still be pooled whenever the contents are
identical. This is possible since BackupPC stores the file metadata (permissions, ownership, and
modification time) separately from the file contents.

Prior to V4, identical files were stored using hardlinks. In V4+, hardlinks are eliminated (except
for temporary atomic renames), and reference counting is done at the application level.

Backup Policy
Based on your site's requirements you need to decide what your backup policy is. BackupPC is not
designed to provide exact re-imaging of failed disks. See "Some Limitations" for more information.
However, with rsync and tar transports for linux/unix clients, plus full support for special file
types, extended attributes etc, likely means an exact image of a linux/unix file system can be made.

BackupPC saves backups onto disk. Because of pooling you can relatively economically keep several
weeks or months of old backups.

At some sites the disk-based backup will be adequate, without a secondary offsite cloud, disk or tape
backup. This system is robust to any single failure: if a client disk fails or loses files, the
BackupPC server can be used to restore files. If the server disk fails, BackupPC can be restarted on
a fresh file system, and create new backups from the clients. The chance of the server disk failing
can be made very small by spending more money on increasingly better RAID systems. However, there is
still the risk of catastrophic events like fires or earthquakes that can destroy both the BackupPC
server and the clients it is backing up if they are physically nearby.

Some sites might choose to do periodic backups to tape or cd/dvd. This backup can be done perhaps
weekly using the archive function of BackupPC.

Other users have reported success with removable disks to rotate the BackupPC data drives, or using
rsync to mirror the BackupPC data pool offsite.

In V4, since hardlinks are not used permanently, duplicating a V4 pool is much easier, allowing
remote copying of the pool.

Resources
BackupPC home page
The BackupPC project page is at:

https://backuppc.github.io/backuppc

This page has links to the current documentation, github project source and general information.

Github
BackupPC development is hosted on github:

https://github.com/backuppc

Releases for BackupPC and the required packages BackupPC-XS and rsync-bpc are available at:

https://github.com/backuppc/backuppc/releases
https://github.com/backuppc/backuppc-xs/releases
https://github.com/backuppc/rsync-bpc/releases

BackupPC Wiki
BackupPC has a Wiki at <https://github.com/backuppc/backuppc/wiki>. Everyone is encouraged to
contribute to the Wiki. Anyone with a Github account can edit the Wiki.

Mailing lists
Three BackupPC mailing lists exist for announcements (backuppc-announce), developers (backuppc-
devel), and a general user list for support, asking questions or any other topic relevant to BackupPC
(backuppc-users).

The lists are archived on SourceForge:

https://sourceforge.net/p/backuppc/mailman/backuppc-users/

You can subscribe to these lists by visiting:

http://lists.sourceforge.net/lists/listinfo/backuppc-announce
http://lists.sourceforge.net/lists/listinfo/backuppc-users
http://lists.sourceforge.net/lists/listinfo/backuppc-devel

The backuppc-announce list is moderated and is used only for important announcements (eg: new
versions). It is low traffic. You only need to subscribe to one of backuppc-announce and backuppc-
users: backuppc-users also receives any messages on backuppc-announce.

The backuppc-devel list is only for developers who are working on BackupPC. Do not post questions or
support requests there. But detailed technical discussions should happen on this list.

To post a message to the backuppc-users list, send an email to

backuppc-users@lists.sourceforge.net

Do not send subscription requests to this address!

Other Programs of Interest
If you want to mirror linux or unix files or directories to a remote server you should use rsync,
<http://rsync.samba.org>. BackupPC uses rsync as a transport mechanism; if you are already an rsync
user you can think of BackupPC as adding efficient storage (compression and pooling) and a convenient
user interface to rsync.

Two popular open source packages that do tape backup are Amanda (<http://www.amanda.org>) and Bacula
(<http://www.bacula.org>). These packages can be used as complete solutions, or also as back ends to
BackupPC to backup the BackupPC server data to tape.

Avery Pennarun's bup (<https://github.com/bup/bup>) uses the git packfile format to do efficient
incrementals and deduplication. Various programs and scripts use rsync to provide hardlinked
backups. See, for example, Mike Rubel's site (<http://www.mikerubel.org/computers/rsync_snapshots>),
JW Schultz's dirvish (<http://www.dirvish.org/>), Ben Escoto's rdiff-backup
(<http://www.nongnu.org/rdiff-backup>), and John Bowman's rlbackup
(<http://www.math.ualberta.ca/imaging/rlbackup>).

BackupPC provides many additional features, such as compressed storage, deduplicating any matching
files (rather than just files with the same name), and storing special files without root privileges.
But these other programs provide simple, effective and fast solutions and are definitely worthy of
consideration.

Road map
The new features planned for future releases of BackupPC are on the Wiki at
<https://github.com/backuppc/backuppc/wiki>.

Comments and suggestions are welcome.

You can help
BackupPC is free. I work on BackupPC because I enjoy doing it and I like to contribute to the open source
community.

BackupPC already has more than enough features for my own needs. The main compensation for continuing to
work on BackupPC is knowing that more and more people find it useful. So feedback is certainly
appreciated, both positive and negative.

Also, everyone is encouraged to contribute patches, bug reports, feature and design suggestions, new
code, Wiki additions (you can do those directly) and documentation corrections or improvements.
Answering questions on the mailing list is a big help too.

Installing BackupPC

Requirements
BackupPC requires:

• A linux, solaris, or unix based server with a substantial amount of free disk space (see the next
section for what that means). The CPU and disk performance on this server will determine how many
simultaneous backups you can run. You should be able to run 4-8 simultaneous backups on a moderately
configured server.

It is also recommended you consider either an LVM or RAID setup so that you can expand the file
system as necessary.

• Perl version 5.8.0 or later. If you don't have perl, please see <http://www.cpan.org>.

• The perl modules BackupPC::XS (version >= 0.50) is required, and several others, File::Listing,
Archive::Zip, XML::RSS, JSON::XS, Net::FTP, Net::FTP::RetrHandle, Net::FTP::AutoReconnect are
recommended.

Try "perldoc BackupPC::XS" and "perldoc Archive::Zip" to see if you have these modules. If not,
fetch them from <http://www.cpan.org> and see the instructions below for how to build and install
them.

The CGI Perl module is required for the http/cgi user interface. CGI was a core module, but from
version 5.22 Perl no longer ships with it.

• If you are using rsync to backup linux/unix machines you should have rsync on each client machine.
Version 3+ is strongly recommended, but earlier versions will work too. See <http://rsync.samba.org>.
Use "rsync --version" to check your version.

For BackupPC to use Rsync you will also need to install rsync-bpc on the server.

• If you are using smb to backup WinXX machines you need smbclient and nmblookup from the samba
package. You will also need nmblookup if you are backing up linux/unix DHCP machines. See
<http://www.samba.org>.

See <http://www.samba.org> for source and binaries. It's pretty easy to fetch and compile samba, and
just grab smbclient and nmblookup, without doing the installation. Alternatively,
<http://www.samba.org> has binary distributions for most platforms.

• If you are using tar to backup linux/unix machines, those machines should have version 1.13.20 or
higher recommended. Use "tar --version" to check your version. Various GNU mirrors have the newest
versions of tar; see <http://www.gnu.org/software/tar/>.

• The Apache web server, see <http://www.apache.org>, preferably built with mod_perl support.

• If rrdtool is installed on the BackupPC server, graphs of the pool usage will be maintained and
displayed. To enable the graphs, point $Conf{RrdToolPath} to the rrdtool executable.

What type of storage space do I need?
Starting with 4.0.0, BackupPC no longer uses hardlinks for storage of deduplicated files. However,
hardlinks are still used temporarily in a few places for doing atomic renames, with a fallback doing a
file copy if the hardlink fails, and files are moved (renamed) across various paths that turn into
expensive file copies if they span multiple file systems.

So ideally BackupPC's data store (__TOPDIR__) is a single file system that supports hardlinks. It is ok
to use a single symbolic link at the top-level directory (__TOPDIR__) to point the entire data store
somewhere else). You can of course use any kind of RAID system or logical volume manager that combines
the capacity of multiple disks into a single, larger, file system. Such approaches have the advantage
that the file system can be expanded without having to copy it.

Any standard linux or unix file system supports hardlinks. NFS mounted file systems work too (provided
the underlying file system supports hardlinks). But windows based FAT and NTFS file systems will not
work.

In BackupPC 3.x, hardlinks are fundamental to deduplication, so a startup check is done ensure that the
file system can support hardlinks, since this is a common area of configuration problems in v3. In 4.x,
that check is only done if the pool still contains v3 backups and pool files.

How much disk space do I need?
Here's one real example (circa 2002) for an environment that is backing up 65 laptops with compression
off. Each full backup averages 3.2GB. Each incremental backup averages about 0.2GB. Storing one full
backup and two incremental backups per laptop is around 240GB of raw data. But because of the pooling of
identical files, only 87GB is used. This is without compression.

Another example, with compression on: backing up 95 laptops, where each backup averages 3.6GB and each
incremental averages about 0.3GB. Keeping three weekly full backups, and six incrementals is around
1200GB of raw data. Because of pooling and compression, only 150GB is needed.

Here's a rule of thumb. Add up the disk usage of all the machines you want to backup (210GB in the first
example above). This is a rough minimum space estimate that should allow a couple of full backups and at
least half a dozen incremental backups per machine. If compression is on you can reduce the storage
requirements by maybe 30-40%. Add some margin in case you add more machines or decide to keep more old
backups.

Your actual mileage will depend upon the types of clients, operating systems and applications you have.
The more uniform the clients and applications the bigger the benefit from pooling common files.

In addition to total disk space, you should make sure you have plenty of inodes on your BackupPC data
partition. Some users have reported running out of inodes on their BackupPC data partition. So even if
you have plenty of disk space, BackupPC will report failures when the inodes are exhausted. This is a
particular problem with ext2/ext3 file systems that have a fixed number of inodes when the file system is
built. Use "df -i" to see your inode usage.

Step 1: Getting BackupPC
Many linux distributions now include BackupPC, so installing BackupPC via your package manager is the
best approach.

For example, for Debian, supported by Ludovic Drolez, can be found at
<http://packages.debian.org/backuppc> and is included in the current stable Debian release. On Debian,
BackupPC can be installed with the command:

apt-get install backuppc

You should also install rsync-bpc; the BackupPC package might include it already, but if not:

apt-get install rsync-bpc

If those commands work, you can skip to Step 3.

Alternatively, manually fetching and installing BackupPC is easy. Start by downloading the latest
version from

https://github.com/backuppc/backuppc/releases

Step 2: Installing the distribution
Note: most information in this step is only relevant if you build and install BackupPC yourself. If you
use a package provided by a distribution, the package management system should take of installing any
needed dependencies.

First off, there are several perl modules you should install. The first one, BackupPC::XS, is required.
The others are optional but highly recommended. Use either your linux package manager, or the cpan
command, or follow the instructions in the README files to install these packages:

BackupPC::XS
Significant portions of BackupPC are implemented in C code contained in this module. You can run
"perldoc BackupPC::XS" to see if this module is installed. You need to have version >= 0.50.
BackupPC::XS is available from:

https://github.com/backuppc/backuppc-xs/releases

and also CPAN.

Archive::Zip
To support restore via Zip archives you will need to install Archive::Zip, also from
<http://www.cpan.org>. You can run "perldoc Archive::Zip" to see if this module is installed.

XML::RSS
To support the RSS feature you will need to install XML::RSS, also from <http://www.cpan.org>. There
is not need to install this module if you don't plan on using RSS. You can run "perldoc XML::RSS" to
see if this module is installed.

JSON::XS
To support the JSON formatted metrics you will need to install JSON::XS, also from
<http://www.cpan.org>. There is not need to install this module if you don't plan on using JSON
formatted metrics. You can run "perldoc JSON::XS" to see if this module is installed.

CGI The CGI Perl module is required for the http/cgi user interface. CGI was a core module, but from
version 5.22 Perl no longer ships with it so you'll need to install it if you are using a recent
version of perl.

SCGI
The SCGI Perl module is required to use the S/CGI protocol for the http/cgi user interface.

File::Listing, Net::FTP, Net::FTP::RetrHandle, Net::FTP::AutoReconnect
To use ftp with BackupPC you will need four libraries, but actually need to install only
File::Listing from <http://www.cpan.org>. You can run "perldoc File::Listing" to see if this module
is installed. Net::FTP is a standard module. Net::FTP::RetrHandle and Net::FTP::AutoReconnect
included in BackupPC distribution.

To build and install these packages you should use the cpan command. At the prompt, type

install BackupPC::XS

Alternatively, if you want to install these manually, you can fetch the tarball from
<http://www.cpan.org> and then run these commands:

tar zxvf BackupPC-XS-0.50.tar.gz
cd BackupPC-XS-0.50
perl Makefile.PL
make
make test
make install

The same sequence of commands can be used for each module.

Next, you should install rsync_bpc if you want to use rsync to backup clients (which is the recommended
approach for all client types). If you don't use your package manager, fetch the release from:

https://github.com/backuppc/rsync-bpc/releases

Then run these commands (updating the version number as appropriate):

tar zxf rsync-bpc-3.0.9.5.tar.gz
cd rsync-bpc-3.0.9.5
./configure
make
make install

Now let's move onto BackupPC itself. After fetching BackupPC-4.4.0.tar.gz, run these commands as root:

tar zxf BackupPC-4.4.0.tar.gz
cd BackupPC-4.4.0
perl configure.pl

The configure.pl script also accepts command-line options if you wish to run it in a non-interactive
manner. It has self-contained documentation for all the command-line options, which you can read with
perldoc:

perldoc configure.pl

Starting with BackupPC 3.0.0, the configure.pl script by default complies with the file system hierarchy
(FHS) conventions. The major difference compared to earlier versions is that by default configuration
files will be stored in /etc/BackupPC rather than below the data directory, __TOPDIR__/conf, and the log
files will be stored in /var/log/BackupPC rather than below the data directory, __TOPDIR__/log.

Note that distributions may choose to use different locations for BackupPC files than these defaults.

If you are upgrading from an earlier version the configure.pl script will keep the configuration files
and log files in their original location.

When you run configure.pl you will be prompted for the full paths of various executables, and you will be
prompted for the following information.

BackupPC User
It is best if BackupPC runs as a special user, eg backuppc, that has limited privileges. It is
preferred that backuppc belongs to a system administrator group so that sysadmin members can browse
BackupPC files, edit the configuration files and so on. Although configurable, the default settings
leave group read permission on pool files, so make sure the BackupPC user's group is chosen
restrictively.

On this installation, this is __BACKUPPCUSER__.

For security purposes you might choose to configure the BackupPC user with the shell set to
/bin/false. Since you might need to run some BackupPC programs as the BackupPC user for testing
purposes, you can use the -s option to su to explicitly run a shell, eg:

su -s /bin/bash __BACKUPPCUSER__

Depending upon your configuration you might also need the -l option.

If the -s option is not available on your operating system, you can specify the -m option to use your
login shell as invoked shell:

su -m __BACKUPPCUSER__

Data Directory
You need to decide where to put the data directory, below which all the BackupPC data is stored.
This needs to be a big file system.

On this installation, this is __TOPDIR__.

Install Directory
You should decide where the BackupPC scripts, libraries and documentation should be installed, eg:
/usr/local/BackupPC.

On this installation, this is __INSTALLDIR__.

CGI bin Directory
You should decide where the BackupPC CGI script resides. This will usually be below Apache's cgi-bin
directory.

It is also possible to use a different directory and use Apache's ``<Directory>'' directive to
specify that location. See the Apache HTTP Server documentation for additional information.

On this installation, this is __CGIDIR__.

Apache image Directory
A directory where BackupPC's images are stored so that Apache can serve them. You should ensure this
directory is readable by Apache and create a symlink to this directory from the BackupPC CGI bin
Directory.

Config and Log Directories
In this installation the configuration and log directories are located in the following locations:

__CONFDIR__/config.pl main config file
__CONFDIR__/hosts hosts file
__CONFDIR__/pc/HOST.pl per-pc config file
__LOGDIR__/BackupPC log files, pid, status

The configure.pl script doesn't prompt for these locations but they can be set for new installations
using command-line options.

Step 3: Setting up config.pl
After running configure.pl, browse through the config file, __CONFDIR__/config.pl, and make sure all the
default settings are correct. In particular, you will need to decide whether to use smb, tar,or rsync or
ftp transport (or whether to set it on a per-PC basis) and set the relevant parameters for that transport
method. See the section "Step 5: Client Setup" for more details.

Step 4: Setting up the hosts file
The file __CONFDIR__/hosts contains the list of clients to backup. BackupPC reads this file in three
cases:

• Upon startup.

• When BackupPC is sent a HUP (-1) signal. Assuming you installed the init.d script, you can also do
this with "/etc/init.d/backuppc reload".

• When the modification time of the hosts file changes. BackupPC checks the modification time once
during each regular wakeup.

Whenever you change the hosts file (to add or remove a host) you can either do a kill -HUP BackupPC_pid
or simply wait until the next regular wakeup period.

Each line in the hosts file contains three fields, separated by whitespace:

Host name
This is typically the hostname or NetBios name of the client machine and should be in lowercase. The
hostname can contain spaces (escape with a backslash), but it is not recommended.

Please read the section "How BackupPC Finds Hosts".

In certain cases you might want several distinct clients to refer to the same physical machine. For
example, you might have a database you want to backup, and you want to bracket the backup of the
database with shutdown/restart using $Conf{DumpPreUserCmd} and $Conf{DumpPostUserCmd}. But you also
want to backup the rest of the machine while the database is still running. In the case you can
specify two different clients in the host file, using any mnemonic name (eg: myhost_mysql and
myhost), and use $Conf{ClientNameAlias} in myhost_mysql's config.pl to specify the real hostname of
the machine.

DHCP flag
Starting with v2.0.0 the way hosts are discovered has changed and now in most cases you should
specify 0 for the DHCP flag, even if the host has a dynamically assigned IP address. Please read the
section "How BackupPC Finds Hosts" to understand whether you need to set the DHCP flag.

You only need to set DHCP to 1 if your client machine doesn't respond to the NetBios multicast
request:

nmblookup myHost

but does respond to a request directed to its IP address:

nmblookup -A W.X.Y.Z

If you do set DHCP to 1 on any client you will need to specify the range of DHCP addresses to search
is specified in $Conf{DHCPAddressRanges}.

Note also that the $Conf{ClientNameAlias} feature does not work for clients with DHCP set to 1.

User name
This should be the unix login/email name of the user who "owns" or uses this machine. This is the
user who will be sent email about this machine, and this user will have permission to
stop/start/browse/restore backups for this host. Leave this blank if no specific person should
receive email or be allowed to stop/start/browse/restore backups for this host. Administrators will
still have full permissions.

More users
Additional usernames, separated by commas and with no whitespace, can be specified. These users will
also have full permission in the CGI interface to stop/start/browse/restore backups for this host.
These users will not be sent email about this host.

The first non-comment line of the hosts file is special: it contains the names of the columns and should
not be edited.

Here's a simple example of a hosts file:

host dhcp user moreUsers
farside 0 craig jim,dave
larson 1 gary andy

Step 5: Client Setup
Four methods for getting backup data from a client are supported: smb, tar, rsync and ftp. Smb or rsync
are the preferred methods for WinXX clients and rsync or tar are the preferred methods for
linux/unix/MacOSX clients.

The transfer method is set using the $Conf{XferMethod} configuration setting. If you have a mixed
environment (ie: you will use smb for some clients and tar for others), you will need to pick the most
common choice for $Conf{XferMethod} for the main config.pl file, and then override it in the per-PC
config file for those hosts that will use the other method. (Or you could run two completely separate
instances of BackupPC, with different data directories, one for WinXX and the other for linux/unix, but
then common files between the different machine types will duplicated.)

Here are some brief client setup notes:

WinXX
One setup for WinXX clients is to set $Conf{XferMethod} to "smb". Actually, rsyncd is the better
method for WinXX if you are prepared to run rsync/cygwin on your WinXX client.

If you want to use rsyncd for WinXX clients you can find a pre-packaged exe installer on
<https://github.com/backuppc/cygwin-rsyncd/releases>. The package is called cygwin-rsync. It
contains rsync.exe, template setup files and the minimal set of cygwin libraries for everything to
run. The README file contains instructions for running rsync as a service, so it starts
automatically every time you boot your machine. If you use rsync to backup WinXX machines, be sure
to set $Conf{ClientCharset} correctly (eg: 'cp1252') so that the WinXX filename encoding is correctly
converted to utf8.

Otherwise, to use SMB, you can either create shares for the data you want to backup or your can use
the existing C$ share. To create a new share, open "My Computer", right click on the drive (eg: C),
and select "Sharing..." (or select "Properties" and select the "Sharing" tab). In this dialog box you
can enable sharing, select the share name and permissions.

All Windows NT based OS (NT, 2000, XP Pro), are configured by default to share the entire C drive as
C$. This is a special share used for various administration functions, one of which is to grant
access to backup operators. All you need to do is create a new domain user, specifically for backup.
Then add the new backup user to the built in "Backup Operators" group. You now have backup capability
for any directory on any computer in the domain in one easy step. This avoids using administrator
accounts and only grants permission to do exactly what you want for the given user, i.e.: backup.
Also, for additional security, you may wish to deny the ability for this user to logon to computers
in the default domain policy.

The relevant configuration settings are $Conf{SmbShareName}, $Conf{SmbShareUserName},
$Conf{SmbSharePasswd}, $Conf{SmbClientPath}, $Conf{SmbClientFullCmd}, $Conf{SmbClientIncrCmd} and
$Conf{SmbClientRestoreCmd}.

BackupPC needs to know the smb share username and password for a client machine that uses smb. The
username is specified in $Conf{SmbShareUserName}. There are four ways to tell BackupPC the smb share
password:

• As an environment variable BPC_SMB_PASSWD set before BackupPC starts. If you start BackupPC
manually the BPC_SMB_PASSWD variable must be set manually first. For backward compatibility for
v1.5.0 and prior, the environment variable PASSWD can be used if BPC_SMB_PASSWD is not set.
Warning: on some systems it is possible to see environment variables of running processes.

• Alternatively the BPC_SMB_PASSWD setting can be included in /etc/init.d/backuppc, in which case
you must make sure this file is not world (other) readable.

• As a configuration variable $Conf{SmbSharePasswd} in __CONFDIR__/config.pl. If you put the
password here you must make sure this file is not world (other) readable.

• As a configuration variable $Conf{SmbSharePasswd} in the per-PC configuration file
(__CONFDIR__/pc/$host.pl or __TOPDIR__/pc/$host/config.pl in non-FHS versions of BackupPC). You
will have to use this option if the smb share password is different for each host. If you put the
password here you must make sure this file is not world (other) readable.

Placement and protection of the smb share password is a significant security issue, so please double-
check the file and directory permissions. In a future version there might be support for encryption
of this password, but a private key will still have to be stored in a protected place. Suggestions
are welcome.

As an alternative to setting $Conf{XferMethod} to "smb" (using smbclient) for WinXX clients, you can
use an smb network filesystem (eg: ksmbfs or similar) on your linux/unix server to mount the share,
and then set $Conf{XferMethod} to "tar" (use tar on the network mounted file system).

Also, to make sure that filenames with special characters are correctly transferred by smbclient you
should make sure that the smb.conf file has (for samba 3.x):

[global]
unix charset = UTF8

UTF8 is the default setting, so if the parameter is missing then it is ok. With this setting
$Conf{ClientCharset} should be empty, since smbclient has already converted the filenames to utf8.

Linux/Unix
The preferred setup for linux/unix clients is to set $Conf{XferMethod} to "rsync", "rsyncd" or "tar".

You can use either rsync, smb, or tar for linux/unix machines. Smb requires that the Samba server
(smbd) be run to provide the shares. Since the smb protocol can't represent special files like
symbolic links and fifos, tar and rsync are the better transport methods for linux/unix machines.
(In fact, by default samba makes symbolic links look like the file or directory that they point to,
so you could get an infinite loop if a symbolic link points to the current or parent directory. If
you really need to use Samba shares for linux/unix backups you should turn off the "follow symlinks"
samba config setting. See the smb.conf manual page.)

Important note: many linux systems use sparse files for /var/log/lastlog, and have large special
files below /proc and /run. Make sure you exclude those directories and files when you configure
your client.

The requirements for each Xfer Method are:

rsync
To use rsync, you need rsync-bpc installed on the BackupPC server.

On the client, you should have at least rsync 3.x. Rsync is run on the remote client via ssh.

The relevant configuration settings are $Conf{RsyncClientPath}, $Conf{RsyncSshArgs},
$Conf{RsyncShareName}, $Conf{RsyncArgs}, $Conf{RsyncArgsExtra}, $Conf{RsyncFullArgsExtra}, and
$Conf{RsyncRestoreArgs}.

rsyncd
To use rsync, you need rsync-bpc installed on the BackupPC server.

On the client, you should have at least rsync 3.x. In this case the rsync daemon should be
running on the client machine and BackupPC connects directly to it.

The relevant configuration settings are $Conf{RsyncBackupPCPath}, $Conf{RsyncdClientPort},
$Conf{RsyncdUserName}, $Conf{RsyncdPasswd}, $Conf{RsyncShareName}, $Conf{RsyncArgs},
$Conf{RsyncArgsExtra}, and $Conf{RsyncRestoreArgs}. $Conf{RsyncShareName} is the name of an rsync
module (ie: the thing in square brackets in rsyncd's conf file -- see rsyncd.conf), not a file
system path.

Be aware that rsyncd will remove the leading '/' from path names in symbolic links if you specify
"use chroot = no" in the rsynd.conf file. See the rsyncd.conf manual page for more information.

tar You must have GNU tar on the client machine. Use "tar --version" or "gtar --version" to verify.
The version should be at least 1.13.20. Tar is run on the client machine via rsh or ssh.

The relevant configuration settings are $Conf{TarClientPath}, $Conf{TarShareName},
$Conf{TarClientCmd}, $Conf{TarFullArgs}, $Conf{TarIncrArgs}, and $Conf{TarClientRestoreCmd}.

ftp FTP Xfer Method is supported in V4 but not recommended since it only handles minimal metadata, it
doesn't support hardlinks or special files, and can only restore regular files (not symbolic
links etc).

You need to be running an ftp server on the client machine. The relevant configuration settings
are $Conf{FtpShareName}, $Conf{FtpUserName}, $Conf{FtpPasswd}, $Conf{FtpBlockSize},
$Conf{FtpPort}, $Conf{FtpTimeout}, and $Conf{FtpFollowSymlinks}.

You need to set $Conf{ClientCharset} to the client's charset so that filenames are correctly
converted to utf8. Use "locale charmap" on the client to see its charset. Note, however, that
modern versions of smbclient and rsync handle this conversion automatically, so in most cases you
won't need to set $Conf{ClientCharset}.

For linux/unix machines you should not backup "/proc". This directory contains a variety of files
that look like regular files but they are special files that don't need to be backed up (eg:
/proc/kcore is a regular file that contains physical memory). See $Conf{BackupFilesExclude}. It is
safe to backup /dev since it contains mostly character-special and block-special files, which are
correctly handed by BackupPC (eg: backing up /dev/hda5 just saves the block-special file information,
not the contents of the disk). Similarly, on many linux systems, /var/log/lastlog is a sparse file,
with a very large apparent size, so you should exclude that too.

Alternatively, rather than backup all the file systems as a single share ("/"), it is easier to
restore a single file system if you backup each file system separately. To do this you should list
each file system mount point in $Conf{TarShareName} or $Conf{RsyncShareName}, and add the
--one-file-system option to $Conf{TarClientCmd} or $Conf{RsyncArgs}. In this case there is no need
to exclude /proc explicitly since it looks like a different file system.

Ssh allows BackupPC to run as a privileged user on the client (eg: root), since it needs sufficient
permissions to read all the backup files. Ssh is setup so that BackupPC on the server (an otherwise
low privileged user) can ssh as root on the client, without being prompted for a password. However,
directly enabled ssh root logins is not good practice. A better approach is the ssh as a regular
user, and then configure sudo to allow just rsync to be executed.

There are two common versions of ssh: v1 and v2. Here are some instructions for one way to setup ssh.
(Check which version of SSH you have by typing "ssh" or "man ssh".)

MacOSX
In general this should be similar to Linux/Unix machines. In versions 10.4 and later, the native
MacOSX tar works, and also supports resource forks. xtar is another option, and rsync works too
(although the MacOSX-supplied rsync has an extension for extended attributes that is not compatible
with standard rsync).

SSH Setup
SSH is a secure way to run tar or rsync on a backup client to extract the data. SSH provides strong
authentication and encryption of the network data.

Note that if you run rsyncd (rsync daemon), ssh is not used. In this case, rsyncd provides its own
authentication, but there is no encryption of network data. If you want encryption of network data
you can use ssh to create a tunnel, or use a program like stunnel.

Setup instructions for ssh can be found on the Wiki at <https://github.com/backuppc/backuppc/wiki>.

Clients that use DHCP
If a client machine uses DHCP BackupPC needs some way to find the IP address given the hostname. One
alternative is to set dhcp to 1 in the hosts file, and BackupPC will search a pool of IP addresses
looking for hosts. More efficiently, it is better to set dhcp = 0 and provide a mechanism for
BackupPC to find the IP address given the hostname.

For WinXX machines BackupPC uses the NetBios name server to determine the IP address given the
hostname. For unix machines you can run nmbd (the NetBios name server) from the Samba distribution
so that the machine responds to a NetBios name request. See the manual page and Samba documentation
for more information.

Alternatively, you can set $Conf{NmbLookupFindHostCmd} to any command that returns the IP address
given the hostname.

Please read the section "How BackupPC Finds Hosts" for more details.

Step 6: Running BackupPC
The installation contains an init.d backuppc script that can be copied to /etc/init.d so that BackupPC
can auto-start on boot. See init.d/README for further instructions.

BackupPC should be ready to start. If you installed the init.d script, then you should be able to run
BackupPC with:

/etc/init.d/backuppc start

(This script can also be invoked with "stop" to stop BackupPC and "reload" to tell BackupPC to reload
config.pl and the hosts file.)

Otherwise, just run

__INSTALLDIR__/bin/BackupPC -d

as user __BACKUPPCUSER__. The -d option tells BackupPC to run as a daemon (ie: it does an additional
fork).

Any immediate errors will be printed to stderr and BackupPC will quit. Otherwise, look in __LOGDIR__/LOG
and verify that BackupPC reports it has started and all is ok.

Step 7: Talking to BackupPC
You should verify that BackupPC is running by using BackupPC_serverMesg. This sends a message to
BackupPC via the unix (or TCP) socket and prints the response. Like all BackupPC programs,
BackupPC_serverMesg should be run as the BackupPC user (__BACKUPPCUSER__), so you should

su __BACKUPPCUSER__

before running BackupPC_serverMesg. If the BackupPC user is configured with /bin/false as the shell, you
can use the -s option to su to explicitly run a shell, eg:

su -s /bin/bash __BACKUPPCUSER__

Depending upon your configuration you might also need the -l option.

If the -s option is not available on your operating system, you can specify the -m option to use your
login shell as invoked shell:

su -m __BACKUPPCUSER__

You can request status information and start and stop backups using this interface. This socket interface
is mainly provided for the CGI interface (and some of the BackupPC subprograms use it too). But right
now we just want to make sure BackupPC is happy. Each of these commands should produce some status
output:

__INSTALLDIR__/bin/BackupPC_serverMesg status info
__INSTALLDIR__/bin/BackupPC_serverMesg status jobs
__INSTALLDIR__/bin/BackupPC_serverMesg status hosts

The output should be some hashes printed with Data::Dumper. If it looks cryptic and confusing, and
doesn't look like an error message, then all is ok.

The hosts status should produce a list of every host you have listed in __CONFDIR__/hosts as part of a
big cryptic output line.

You can also request that all hosts be queued:

__INSTALLDIR__/bin/BackupPC_serverMesg backup all

At this point you should make sure the CGI interface works since it will be much easier to see what is
going on. We'll get to that shortly.

Step 8: Checking email delivery
The script BackupPC_sendEmail sends status and error emails to the administrator and users. It is
usually run each night by BackupPC_nightly.

To verify that it can run sendmail and deliver email correctly you should ask it to send a test email to
you:

su __BACKUPPCUSER__
__INSTALLDIR__/bin/BackupPC_sendEmail -u MYNAME@MYDOMAIN.COM

BackupPC_sendEmail also takes a -c option that checks if BackupPC is running, and it sends an email to
$Conf{EMailAdminUserName} if it is not. That can be used as a keep-alive check by adding

__INSTALLDIR__/bin/BackupPC_sendEmail -c

to __BACKUPPCUSER__'s cron.

The -t option to BackupPC_sendEmail causes it to print the email message instead of invoking sendmail to
deliver the message.

Step 9: CGI interface
The CGI interface script, BackupPC_Admin, is a powerful and flexible way to see and control what BackupPC
is doing. It is written for an Apache server. If you don't have Apache, see <http://www.apache.org>.

There are three options for setting up the CGI interface:

SCGI
New to 4.x, SCGI uses the SCGI interface to Apache, which requires the mod_scgi.so module to be
installed and loaded by Apache. This allows Apache to run as any unprivileged user. The actual SCGI
server runs as the as the BackupPC user (__BACKUPPCUSER__), and handles the requests from Apache via
a TCP socket.

mod_perl
Mod_perl required the mod_perl module to be loaded by Apache. This allows BackupPC_Admin to be run
from inside Apache. Unlike SCGI, using mod_perl with BackupPC_Admin requires a dedicated Apache to
be run as the BackupPC user (__BACKUPPCUSER__). This is because BackupPC_Admin needs permission to
access various files in BackupPC's data directories.

standard
The standard mode, which is significantly slower than SCGI or mod_perl, is where Apache runs
BackupPC_Admin as a separate process for every request. This adds significant startup overhead for
every request, and also requires that BackupPC_Admin be run as setuid to the BackupPC user
(__BACKUPPCUSER__), if Apache isn't being run as that user. Setuid scripts are discouraged, so the
preference is to use SCGI or mod_perl.

Here are some specifics for each setup:

SCGI Setup
First you need to install mod_scgi. If you can't find a pre-built package, the source is available
at <http://python.ca/scgi>. The release has subdirectories for apache1 and apache2. Pick your
matching version (nowadays most likely apache2). You'll need apxs, the Apache Extension Tool,
installed to build from source. Once compiled, the module mod_scgi.so should be installed via the
Makefile.

To enable the SCGI server, set $Conf{SCGIServerPort} to an available non-privileged TCP port number,
eg: 10268. The matching port number has to appear in the Apache configuration file. Typical Apache
configuration entries will look like this:

LoadModule scgi_module modules/mod_scgi.so
SCGIMount /BackupPC_Admin 127.0.0.1:10268
<Location /BackupPC_Admin>
AuthUserFile /etc/httpd/conf/passwd
AuthType basic
AuthName "access"
require valid-user
</Location>

Or a typical Nginx configuration file:

server {
listen 80;
server_name yourBackupPCServerHost;

root /var/www/backuppc;

access_log /var/log/nginx/backuppc.access.log;
error_log /var/log/nginx/backuppc.error.log;

location /BackupPC_Admin {
auth_basic "BackupPC";
auth_basic_user_file conf.d/backuppc.users;

include scgi_params;
scgi_pass 127.0.0.1:10268;
scgi_param REMOTE_USER $remote_user;
scgi_param SCRIPT_NAME $document_uri;
}
}

This allows the SCGI interface to be accessed with a URL:

http://yourBackupPCServerHost/BackupPC_Admin

You can use a different path or name if you prefer a different URL. Unlike traditional CGI, there is
no need to specify a valid path to a CGI script.

Important security warning!! The SCGIServerPort must not be accessible by anyone untrusted. That
means you can't allow untrusted users access to the BackupPC server, and you should block the
SCGIServerPort TCP port on the BackupPC server. If you don't understand what that means, or can't
confirm you have configured SCGI securely, then don't enable SCGI - use one of the following two
methods!!

Mod_perl Setup
The advantage of the mod_perl setup is that no setuid script is needed (like in the standard method
below), and there is a significant performance advantage. Not only does all the perl code need to be
parsed just once, the config.pl and hosts files, plus the connection to the BackupPC server are
cached between requests. The typical speedup is around 10-15x.

To use mod_perl you need to run Apache as user __BACKUPPCUSER__. If you need to run multiple Apaches
for different services then you need to create multiple top-level Apache directories, each with their
own config file. You can make copies of /etc/init.d/httpd and use the -d option to httpd to point
each http to a different top-level directory. Or you can use the -f option to explicitly point to
the config file. Multiple Apache's will run on different Ports (eg: 80 is standard, 8080 is a
typical alternative port accessed via http://yourhost.com:8080).

Inside BackupPC's Apache http.conf file you should check the settings for ServerRoot, DocumentRoot,
User, Group, and Port. See <http://httpd.apache.org/docs/server-wide.html> for more details.

For mod_perl, BackupPC_Admin should not have setuid permission, so you should turn it off:

chmod u-s __CGIDIR__/BackupPC_Admin

To tell Apache to use mod_perl to execute BackupPC_Admin, add this to Apache's 1.x httpd.conf file:

<IfModule mod_perl.c>
PerlModule Apache::Registry
PerlTaintCheck On
<Location /cgi-bin/BackupPC/BackupPC_Admin> # <--- change path as needed
SetHandler perl-script
PerlHandler Apache::Registry
Options ExecCGI
PerlSendHeader On
</Location>
</IfModule>

Apache 2.0.44 with Perl 5.8.0 on RedHat 7.1, Don Silvia reports that this works (with tweaks from
Michael Tuzi):

LoadModule perl_module modules/mod_perl.so
PerlModule Apache2

<Directory /path/to/cgi/>
SetHandler perl-script
PerlResponseHandler ModPerl::Registry
PerlOptions +ParseHeaders
Options +ExecCGI
Order deny,allow
Deny from all
Allow from 192.168.0
AuthName "Backup Admin"
AuthType Basic
AuthUserFile /path/to/user_file
Require valid-user
</Directory>

There are other optimizations and options with mod_perl. For example, you can tell mod_perl to
preload various perl modules, which saves memory compared to loading separate copies in every Apache
process after they are forked. See Stas's definitive mod_perl guide at
<http://perl.apache.org/guide>.

Standard Setup
The CGI interface should have been installed by the configure.pl script in __CGIDIR__/BackupPC_Admin.
BackupPC_Admin should have been installed as setuid to the BackupPC user (__BACKUPPCUSER__), in
addition to user and group execute permission.

You should be very careful about permissions on BackupPC_Admin and the directory __CGIDIR__: it is
important that normal users cannot directly execute or change BackupPC_Admin, otherwise they can
access backup files for any PC. You might need to change the group ownership of BackupPC_Admin to a
group that Apache belongs to so that Apache can execute it (don't add "other" execute permission!).
The permissions should look like this:

ls -l __CGIDIR__/BackupPC_Admin
-swxr-x--- 1 __BACKUPPCUSER__ web 82406 Jun 17 22:58 __CGIDIR__/BackupPC_Admin

The setuid script won't work unless perl on your machine was installed with setuid emulation. This
is likely the problem if you get an error saying such as "Wrong user: my userid is 25, instead of
150", meaning the script is running as the httpd user, not the BackupPC user. This is because setuid
scripts are disabled by the kernel in most flavors of unix and linux.

To see if your perl has setuid emulation, see if there is a program called sperl5.8.0 (or sperl5.8.2
etc, based on your perl version) in the place where perl is installed. If you can't find this
program, then you have two options: rebuild and reinstall perl with the setuid emulation turned on
(answer "y" to the question "Do you want to do setuid/setgid emulation?" when you run perl's
configure script), or switch to the mod_perl alternative for the CGI script (which doesn't need
setuid to work).

BackupPC_Admin requires that users are authenticated by Apache. Specifically, it expects that Apache
sets the REMOTE_USER environment variable when it runs. There are several ways to do this. One way is
to create a .htaccess file in the cgi-bin directory that looks like:

AuthGroupFile /etc/httpd/conf/group # <--- change path as needed
AuthUserFile /etc/http/conf/passwd # <--- change path as needed
AuthType basic
AuthName "access"
require valid-user

You will also need "AllowOverride Indexes AuthConfig" in the Apache httpd.conf file to enable the
.htaccess file. Alternatively, everything can go in the Apache httpd.conf file inside a Location
directive. The list of users and password file above can be extracted from the NIS passwd file.

One alternative is to use LDAP. In Apache's http.conf add these lines:

LoadModule auth_ldap_module modules/auth_ldap.so
AddModule auth_ldap.c

# cgi-bin - auth via LDAP (for BackupPC)
<Location /cgi-bin/BackupPC/BackupPC_Admin> # <--- change path as needed
AuthType Basic
AuthName "BackupPC login"
# replace MYDOMAIN, PORT, ORG and CO as needed
AuthLDAPURL ldap://ldap.MYDOMAIN.com:PORT/o=ORG,c=CO?uid?sub?(objectClass=*)
require valid-user
</Location>

If you want to disable the user authentication you can set $Conf{CgiAdminUsers} to '*', which allows any
user to have full access to all hosts and backups. In this case the REMOTE_USER environment variable
does not have to be set by Apache.

Alternatively, you can force a particular username by getting Apache to set REMOTE_USER, eg, to hard code
the user to www you could add this to Apache's httpd.conf:

Finally, you should also edit the config.pl file and adjust, as necessary, the CGI-specific settings.
They're near the end of the config file. In particular, you should specify which users or groups have
administrator (privileged) access: see the config settings $Conf{CgiAdminUserGroup} and
$Conf{CgiAdminUsers}. Also, the configure.pl script placed various images into $Conf{CgiImageDir} that
BackupPC_Admin needs to serve up. You should make sure that $Conf{CgiImageDirURL} is the correct URL for
the image directory.

See the section "Fixing installation problems" for suggestions on debugging the Apache authentication
setup.

How BackupPC Finds Hosts
Starting with v2.0.0 the way hosts are discovered has changed. In most cases you should specify 0 for
the DHCP flag in the conf/hosts file, even if the host has a dynamically assigned IP address.

BackupPC (starting with v2.0.0) looks up hosts with DHCP = 0 in this manner:

• First DNS is used to lookup the IP address given the client's name using perl's gethostbyname()
function. This should succeed for machines that have fixed IP addresses that are known via DNS. You
can manually see whether a given host have a DNS entry according to perl's gethostbyname function
with this command:

perl -e 'print(gethostbyname("myhost") ? "ok\n" : "not found\n");'

• If gethostbyname() fails, BackupPC then attempts a NetBios multicast to find the host. Provided your
client machine is configured properly, it should respond to this NetBios multicast request.
Specifically, BackupPC runs a command of this form:

nmblookup myhost

If this fails you will see output like:

querying myhost on 10.10.255.255
name_query failed to find name myhost

If it is successful you will see output like:

querying myhost on 10.10.255.255
10.10.1.73 myhost<00>

Depending on your netmask you might need to specify the -B option to nmblookup. For example:

nmblookup -B 10.10.1.255 myhost

If necessary, experiment with the nmblookup command which will return the IP address of the client
given its name. Then update $Conf{NmbLookupFindHostCmd} with any necessary options to nmblookup.

For hosts that have the DHCP flag set to 1, these machines are discovered as follows:

• A DHCP address pool ($Conf{DHCPAddressRanges}) needs to be specified. BackupPC will check the
NetBIOS name of each machine in the range using a command of the form:

nmblookup -A W.X.Y.Z

where W.X.Y.Z is each candidate address from $Conf{DHCPAddressRanges}. Any host that has a valid
NetBIOS name returned by this command (ie: matching an entry in the hosts file) will be backed up.
You can modify the specific nmblookup command if necessary via $Conf{NmbLookupCmd}.

• You only need to use this DHCP feature if your client machine doesn't respond to the NetBios
multicast request:

nmblookup myHost

but does respond to a request directed to its IP address:

nmblookup -A W.X.Y.Z

Other installation topics
Removing a client
If there is a machine that no longer needs to be backed up (eg: a retired machine) you have two
choices. First, you can keep the backups accessible and browsable, but disable all new backups.
Alternatively, you can completely remove the client and all its backups.

To disable backups for a client $Conf{BackupsDisable} can be set to two different values in that
client's per-PC config.pl file:

1. Don't do any regular backups on this machine. Manually requested backups (via the CGI interface)
will still occur.

2. Don't do any backups on this machine. Manually requested backups (via the CGI interface) will be
ignored.

This will still allow the client's old backups to be browsable and restorable.

To completely remove a client and all its backups, you should remove its entry in the conf/hosts
file, and then delete the __TOPDIR__/pc/$host directory. Whenever you change the hosts file, you
should send BackupPC a HUP (-1) signal so that it re-reads the hosts file. If you don't do this,
BackupPC will automatically re-read the hosts file at the next regular wakeup.

Note that when you remove a client's backups you won't initially recover much disk space. That's
because the client's files are still in the pool. Overnight, when BackupPC_nightly next runs, all
the unused pool files will be deleted and this will recover the disk space used by the client's
backups.

Copying the pool
If the pool disk requirements grow you might need to copy the entire data directory to a new (bigger)
file system. Hopefully you are lucky enough to avoid this by having the data directory on a RAID
file system or LVM that allows the capacity to be grown in place by adding disks.

Backups prior to V4 make extensive use of hardlinks. So unless you have a virgin V4 installation,
your file system will contain large numbers of hardlinks. This makes it hard to copy.

Prior to V4 (or a V4 upgrade to a V3 installation), the backup data directories contain large numbers
of hardlinks. If you try to copy the pool the target directory will occupy a lot more space if the
hardlinks aren't re-established.

Unless you have a pure V4 installation, the best way to copy a pool file system, if possible, is by
copying the raw device at the block level (eg: using dd). Application level programs that understand
hardlinks include the GNU cp program with the -a option and rsync -H. However, the large number of
hardlinks in the pool will make the memory usage large and the copy very slow. Don't forget to stop
BackupPC while the copy runs.

If you have a pure V4 installation, copying the pool and PC backup directories should be quite easy.
Rsync 3.x should work well.

Fixing installation problems
If you find a solution to your problem that could help other users please add it to the Wiki at
<https://github.com/backuppc/backuppc/wiki>.

Restore functions

BackupPC supports several different methods for restoring files. The most convenient restore options are
provided via the CGI interface. Alternatively, backup files can be restored using manual commands.

CGI restore options
By selecting a host in the CGI interface, a list of all the backups for that machine will be displayed.
By selecting the backup number you can navigate the shares and directory tree for that backup.

BackupPC's CGI interface automatically fills incremental backups with the corresponding full backup,
which means each backup has a filled appearance. Therefore, there is no need to do multiple restores
from the incremental and full backups: BackupPC does all the hard work for you. You simply select the
files and directories you want from the correct backup vintage in one step.

You can download a single backup file at any time simply by selecting it. Your browser should prompt you
with the filename and ask you whether to open the file or save it to disk.

Alternatively, you can select one or more files or directories in the currently selected directory and
select "Restore selected files". (If you need to restore selected files and directories from several
different parent directories you will need to do that in multiple steps.)

If you select all the files in a directory, BackupPC will replace the list of files with the parent
directory. You will be presented with a screen that has three options:

Option 1: Direct Restore
With this option the selected files and directories are restored directly back onto the host, by
default in their original location. Any old files with the same name will be overwritten, so use
caution. You can optionally change the target hostname, target share name, and target path prefix
for the restore, allowing you to restore the files to a different location.

Once you select "Start Restore" you will be prompted one last time with a summary of the exact source
and target files and directories before you commit. When you give the final go ahead the restore
operation will be queued like a normal backup job, meaning that it will be deferred if there is a
backup currently running for that host. When the restore job is run, smbclient, tar, rsync or rsyncd
is used (depending upon $Conf{XferMethod}) to actually restore the files. Sorry, there is currently
no option to cancel a restore that has been started. Currently ftp restores are not fully
implemented.

A record of the restore request, including the result and list of files and directories, is kept. It
can be browsed from the host's home page. $Conf{RestoreInfoKeepCnt} specifies how many old restore
status files to keep.

Note that for direct restore to work, the $Conf{XferMethod} must be able to write to the client. For
example, that means an SMB share for smbclient needs to be writable, and the rsyncd module needs
"read only" set to "false". This creates additional security risks. If you only create read-only
SMB shares (which is a good idea), then the direct restore will fail. You can disable the direct
restore option by setting $Conf{SmbClientRestoreCmd}, $Conf{TarClientRestoreCmd} and
$Conf{RsyncRestoreArgs} to undef.

Option 2: Download Zip archive
With this option a zip file containing the selected files and directories is downloaded. The zip
file can then be unpacked or individual files extracted as necessary on the host machine. The
compression level can be specified. A value of 0 turns off compression.

When you select "Download Zip File" you should be prompted where to save the restore.zip file.

BackupPC does not consider downloading a zip file as an actual restore operation, so the details are
not saved for later browsing as in the first case. However, a mention that a zip file was downloaded
by a particular user, and a list of the files, does appear in BackupPC's log file.

Option 3: Download Tar archive
This is identical to the previous option, except a tar file is downloaded rather than a zip file (and
there is currently no compression option).

Command-line restore options
Apart from the CGI interface, BackupPC allows you to restore files and directories from the command line.
The following programs can be used:

BackupPC_zcat
For each filename argument it inflates (uncompresses) the file and writes it to stdout. To use
BackupPC_zcat you could give it the full filename, eg:

__INSTALLDIR__/bin/BackupPC_zcat __TOPDIR__/pc/host/5/fc/fcraig/fexample.txt > example.txt

It's your responsibility to make sure the file is really compressed: BackupPC_zcat doesn't check
which backup the requested file is from. BackupPC_zcat returns a nonzero status if it fails to
uncompress a file.

In V4, BackupPC_zcat can be invoked in several other ways:

BackupPC_zcat file...
BackupPC_zcat MD5_digest...
BackupPC_zcat $TopDir/pc/host/num/share/mangledPath...
BackupPC_zcat [-h host] [-n num] [-s share] clientPath...

For example, you can do this:

BackupPC_zcat d73955e08410dfc5ea8069b05d2f43b2

That digest can be pasted from the output of BackupPC_ls.

The last form uses unmangled paths, so you can do this:

BackupPC_zcat -h HOST -n 10 -s / /home/craig/file

You can also mix real paths with unmangled paths. Both of these versions work:

BackupPC_zcat /data/BackupPC/pc/HOST/10/fhome/fcraig/ffile
BackupPC_zcat /data/BackupPC/pc/HOST/10/home/craig/file

BackupPC_tarCreate
BackupPC_tarCreate creates a tar file for any files or directories in a particular backup. Merging
of incrementals is done automatically, so you don't need to worry about whether certain files appear
in the incremental or full backup.

The usage is:

BackupPC_tarCreate [options] files/directories...
Required options:
-h host host from which the tar archive is created
-n dumpNum dump number from which the tar archive is created
A negative number means relative to the end (eg -1
means the most recent dump, -2 2nd most recent etc).
-s shareName share name from which the tar archive is created;
can be "*" to mean all shares.

Other options:
-t print summary totals
-r pathRemove path prefix that will be replaced with pathAdd
-p pathAdd new path prefix
-b BLOCKS BLOCKS x 512 bytes per record (default 20; same as tar)
-w writeBufSz write buffer size (default 1048576 = 1MB)
-e charset charset for encoding filenames (default: value of
$Conf{ClientCharset} when backup was done)
-l just print a file listing; don't generate an archive
-L just print a detailed file listing; don't generate an archive

The command-line files and directories are relative to the specified shareName. The tar file is
written to stdout.

The -h, -n and -s options specify which dump is used to generate the tar archive. The -r and -p
options can be used to relocate the paths in the tar archive so extracted files can be placed in a
location different from their original location.

BackupPC_zipCreate
BackupPC_zipCreate creates a zip file for any files or directories in a particular backup. Merging
of incrementals is done automatically, so you don't need to worry about whether certain files appear
in the incremental or full backup.

The usage is:

BackupPC_zipCreate [options] files/directories...
Required options:
-h host host from which the zip archive is created
-n dumpNum dump number from which the tar archive is created
A negative number means relative to the end (eg -1
means the most recent dump, -2 2nd most recent etc).
-s shareName share name from which the zip archive is created

Other options:
-t print summary totals
-r pathRemove path prefix that will be replaced with pathAdd
-p pathAdd new path prefix
-c level compression level (default is 0, no compression)
-e charset charset for encoding filenames (default: utf8)

The command-line files and directories are relative to the specified shareName. The zip file is
written to stdout. The -h, -n and -s options specify which dump is used to generate the zip archive.
The -r and -p options can be used to relocate the paths in the zip archive so extracted files can be
placed in a location different from their original location.

BackupPC_ls
In V3, a full (or filled) backup tree contains all the files, albeit with "mangled" names, and the
file contents are compressed. Some users found it convenient to directly navigate a PC's backup tree
to check for files.

In V4 that is not possible, since only a single attrib file is stored per directory in the PC backup
tree, so the directory contents aren't visible without looking in the attrib file.

A new utility BackupPC_ls (like "ls") can be used to view PC backup trees. It shows file digests,
which can be pasted to BackupPC_zcat if you want to view the file contents. The arguments are
similar to BackupPC_zcat. The usage is:

BackupPC_ls [-iR] [-h host] [-n bkupNum] [-s shareName] dirs/files...

The -i option will show inodes (inode number and number of links). The -R option recurses into
directories.

If you don't specify -h, -n and -s, then you can specify the real file system path instead. For
example, the following three commands are equivalent:

BackupPC_ls -h HOST -n 10 -s cDrive /home/craig/file
BackupPC_ls /data/BackupPC/pc/HOST/10/fcDrive/fhome/fcraig/ffile
BackupPC_ls /data/BackupPC/pc/HOST/10/cDrive/home/craig/file

As you can see, the portion of the full path after the backup number can be either mangled or not.
Note that using the mangled form allows directory-name completion via the shell, since those
directories actually exist.

It would be great if someone would like to volunteer to add features to BackupPC_ls to make file and
directory completion work with unmangled names via the shell. In tcsh you can specify a completion
program to run - BackupPC_ls could be given special arguments to spit out the potential (unmangled)
completions. I'm not sure how bash does this.

Each of these programs reside in __INSTALLDIR__/bin.

Archive functions

BackupPC supports archiving to removable media. For users that require offsite backups, BackupPC can
create archives that stream to tape devices, or create files of specified sizes to fit onto cd or dvd
media.

Each archive type is specified by a BackupPC host with its XferMethod set to 'archive'. This allows for
multiple configurations at sites where there might be a combination of tape and cd/dvd backups being
made.

BackupPC provides a menu that allows one or more hosts to be archived. The most recent backup of each
host is archived using BackupPC_tarCreate, and the output is optionally compressed and split into fixed-
sized files (eg: 650MB).

The archive for each host is done by default using __INSTALLDIR__/bin/BackupPC_archiveHost. This script
can be copied and customized as needed.

Configuring an Archive Host
To create an Archive Host, add it to the hosts file just as any other host and call it a name that best
describes the type of archive, e.g. ArchiveDLT

To tell BackupPC that the Host is for Archives, create a config.pl file in the Archive Hosts's pc
directory, adding the following line:

$Conf{XferMethod} = 'archive';

To further customise the archive's parameters you can add the changed parameters in the host's config.pl
file. The parameters are explained in the config.pl file. Parameters may be fixed or the user can be
allowed to change them (eg: output device).

The per-host archive command is $Conf{ArchiveClientCmd}. By default this invokes

__INSTALLDIR__/bin/BackupPC_archiveHost

which you can copy and customize as necessary.

Starting an Archive
In the web interface, click on the Archive Host you wish to use. You will see a list of previous archives
and a summary on each. By clicking the "Start Archive" button you are presented with the list of hosts
and the approximate backup size (note this is raw size, not projected compressed size) Select the hosts
you wish to archive and press the "Archive Selected Hosts" button.

The next screen allows you to adjust the parameters for this archive run. Press the "Start the Archive"
to start archiving the selected hosts with the parameters displayed.

Starting an Archive from the command line
The script BackupPC_archiveStart can be used to start an archive from the command line (or cron etc).
The usage is:

BackupPC_archiveStart archiveHost userName hosts...

This creates an archive of the most recent backup of each of the specified hosts. The first two
arguments are the archive host and the username making the request.

Other Command Line Utilities

       These utilities are automatically run by BackupPC when needed.  You don't  need  to  manually  run  these
       utilities.

       BackupPC_attribPrint
           BackupPC_attribPrint prints the contents of an attrib file.  Usage:

                   BackupPC_attribPrint attribPath
                   BackupPC_attribPrint inodePath/inodeNum

       BackupPC_backupDelete
           BackupPC_backupDelete deletes an entire backup, or a directory path within a backup.  Usage:

               BackupPC_backupDelete -h host -n num [-p] [-l] [-r] [-s shareName [dirs...]]
               Options:
                  -h host         hostname
                  -n num          backup number to delete
                  -s shareName    don't delete the backup; delete just this share
                                  (or only dirs below this share if specified)
                  -p              don't print progress information
                  -l              don't remove XferLOG files
                  -r              do a ref count update (default: none)
               If a shareName is specified, just that share (or share/dirs) are deleted.
               The backup itself is not deleted, nor is the log file removed.

       BackupPC_backupDuplicate
           BackupPC_backupDuplicate  duplicates  the  last backup, which is used to create a filled backup copy,
           and also to convert a V3 backup to a new V4 starting point.  Usage:

               BackupPC_backupDuplicate -h host [-p]
               Options:
                  -h host         hostname
                  -p              don't print progress information

       BackupPC_fixupBackupSummary
           BackupPC_fixupBackupSummary is used to re-create the backups file for all the hosts if it is  damaged
           or deleted.  Usage:

               BackupPC_fixupBackupSummary [-l]
               Options:
                 -l    legacy mode: try to reconstruct backups from LOG
                       files for backups prior to BackupPC v3.0.

       BackupPC_fsck
           BackupPC_fsck  can  only be run manually, and only while BackupPC isn't running.  It updates the host
           reference counts, the overall pool reference counts and stats.  Usage:

               BackupPC_fsck [options]
               Options:
                  -f              force regeneration of per-host reference counts
                  -n              don't remove zero count pool files - print only
                  -s              recompute pool stats

       BackupPC_migrateV3toV4
           If you upgraded an existing 3.x installation, BackupPC 4.x is backward compatible with  3.x  backups:
           it  can  browse,  view and restore files.  However, the existing 3.x backups will still use hardlinks
           for storage, and until those 3.x backups eventually expire, hardlinks will  still  be  used  for  3.x
           backups.

           BackupPC_migrateV3toV4  is  an  optional  utility that can migrate existing 3.x backups to 4.x stoage
           format, eliminating hardlinks.  This allows you to eliminate the old V3 pool and  you  can  then  set
           $Conf{PoolV3Enabled} to 0.

               BackupPC_migrateV3toV4 -a [-m] [-p] [-v]
               BackupPC_migrateV3toV4 -h host [-n V3backupNum] [-m] [-p] [-v]
               Options:
                  -a              migrate all hosts and all backups
                  -h host         migrate just a specific host
                  -n V3backupNum  migrate specific host backup; does all V3 backups
                                  for that host if not specified
                  -m              don't migrate anything; just print what would be done
                  -p              don't print progress information
                  -v              verbose

           The  BackupPC  server  should  not be running when you run BackupPC_migrateV3toV4.  It will check and
           exit if the BackupPC server is running.

           If you want to test BackupPC_migrateV3toV4, a cautious approach is to make backup copies  of  the  V3
           backups,  allowing  you to restore them if there is any issue.  For example, if exampleHost has three
           3.x backups numbered 5, 6, 7, you can use cp -prl (preserving hardlinks) to make copies:

               cd /data/BackupPC/pc/exampleHost
               mv 5 5.orig ; cp -prl 5.orig 5
               mv 6 6.orig ; cp -prl 6.orig 6
               mv 7 7.orig ; cp -prl 7.orig 7
               cp backups backups.save

               BackupPC_migrateV3toV4 -h exampleHost -n 5
               BackupPC_migrateV3toV4 -h exampleHost -n 6
               BackupPC_migrateV3toV4 -h exampleHost -n 7

           If you want to put things back the way they were:

               rm -rf 5 ; mv 5.orig 5
               rm -rf 6 ; mv 6.orig 6
               rm -rf 7 ; mv 7.orig 7
               # copy the [567] lines from backups.save into backups;
               # only do "cp backups.save backups" if you are sure no
               # new backups have been done

           Two important things to note with BackupPC_migrateV3toV4.  First, V4 storage does use more filesystem
           inodes than V3 (that's the small cost of getting rid of hardlinks).  In particular, each directory in
           a backup tree uses two inodes in V4 (one for the directory, and one for the (empty) attrib file), and
           only one inode in V3 (one for the directory, and the attrib and all other files are hardlinked to the
           pool).  So before you run BackupPC_migrateV3toV4, make sure you have enough inodes in __TOPDIR__; use
           df -i to make sure you are under 45% inode usage.

           Secondly, if you run BackupPC_migrateV3toV4 on all your backups, the old V3  pool  should  be  empty,
           except  for  old-style  attrib  files,  which  should  all have only one link since no backups should
           reference them any longer.  Before you turn off the V3 pool by  setting  $Conf{PoolV3Enabled}  to  0,
           make  sure  BackupPC_nightly  has  run enough times (specifically, $Conf{PoolSizeNightlyUpdatePeriod}
           times) so that the V3 pool can be emptied.  You could do this manually, but  only  if  you  are  very
           careful to check that the remaining files only have one link.

       BackupPC_poolCntPrint
           BackupPC_poolCntPrint  is  used  to print reference count information, either per-backup, per-host or
           for the entire pool depending on the file path you use.

           If you provide a hex md5 digest, the entire pool count for that digest is printed.  Usage:

               BackupPC_poolCntPrint [poolCntFilePath|hexDigest]...

       BackupPC_refCountUpdate
           BackupPC_refCountUpdate is used to either update the per-backup and per-host reference counts, or the
           system-wide reference counts. It is used by BackupPC_dump,  BackupPC_nightly,  BackupPC_backupDelete,
           BackupPC_backupDuplicate and BackupPC_fsck.  Usage:

               BackupPC_refCountUpdate -h HOST [-c] [-f] [-F] [-o N] [-p] [-v]
                   With no other args, updates count db on backups with poolCntDelta files
                   and computers the host's total reference counts.  Also builds refCnt for
                   any >=4.0 backups without refCnts.
                     -f     - do an fsck on this HOST, which involves a rebuild of the
                              last two backup refCnts.  poolCntDelta files are ignored.
                              Also forces fsck if requested by needFsck flag files
                              in TopDir/pc/HOST/refCnt.  Equivalent to -o 2.
                     -F     - rebuild all the >=4.0 per-backup refCnt files for this
                              host.  Equivalent to -o 3.
                     -c     - compare current count db to new db before replacing
                     -o N   - override $Conf{RefCntFsck}.
                     -p     - don't show progress
                     -v     - verbose
                 Notes: in case there are legacy (ie: <=4.0.0alpha3) unapplied poolCntDelta
                 files in TopDir/pc/HOST/refCnt then the -f flag is turned on.

               BackupPC_refCountUpdate -m [-f] [-p] [-c] [-r N-M] [-s] [-v] [-P phase]
                     -m       Updates main count db, based on each HOST
                     -f     - do an fsck on all the hosts, ignoring poolCntDelta files,
                              and replacing each host's count db.  Will wait for backups
                              to finish if any are running.
                     -F     - rebuild all the >=4.0 per-backup refCnt files.
                     -p     - don't show progress
                     -c     - clean pool files
                     -r N-M - process a subset of the main count db, 0 <= N <= M <= 255
                     -s     - prints stats
                     -v     - verbose
                     -P phase Phase from 0..15 each time we run BackupPC_nightly.  Used
                              to compute exact pool size for portions of the pool based
                              on the phase and $Conf{PoolSizeNightlyUpdatePeriod}.

Other CGI Functions

Configuration and Host Editor
The CGI interface has a complete configuration and host editor. Only the administrator can edit the main
configuration settings and hosts. The edit links are in the left navigation bar.

When changes are made to any parameter a "Save" button appears at the top of the page. If you are
editing a text box you will need to click outside of the text box to make the Save button appear. If you
don't select Save then the changes won't be saved.

The host-specific configuration can be edited from the host summary page using the link in the left
navigation bar. The administrator can edit any of the host-specific configuration settings.

When editing the host-specific configuration, each parameter has an "override" setting that denotes the
value is host-specific, meaning that it overrides the setting in the main configuration. If you deselect
"override" then the setting is removed from the host-specific configuration, and the main configuration
file is displayed.

User's can edit their host-specific configuration if enabled via $Conf{CgiUserConfigEditEnable}. The
specific subset of configuration settings that a user can edit is specified with
$Conf{CgiUserConfigEdit}. It is recommended to make this list short as possible (you probably don't want
your users saving dozens of backups) and it is essential that they can't edit any of the Cmd
configuration settings, otherwise they can specify an arbitrary command that will be executed as the
BackupPC user.

Metrics
BackupPC supports a metrics endpoint that expose common information in a digest format. Allowed metrics
formats are "json" (default), "prometheus" and "rss". Format should be specified using "format" query
parameter, a URL similar to this will provide metrics information:

http://localhost/cgi-bin/BackupPC/BackupPC_Admin?action=metrics
http://localhost/cgi-bin/BackupPC/BackupPC_Admin?action=metrics?format=json
http://localhost/cgi-bin/BackupPC/BackupPC_Admin?action=metrics?format=prometheus
http://localhost/cgi-bin/BackupPC/BackupPC_Admin?action=metrics?format=rss

JSON format requires the JSON::XS module to be installed. RSS format requires the XML::RSS module to be
installed.

This feature is experimental. The information included will probably change.

RSS
The RSS feed has been merged in the metrics endpoint (see section above). Please use the metrics endpoint
to access the RSS feed, as the old endpoint will be deprecated.

BackupPC supports a very basic RSS feed. Provided you have the XML::RSS perl module installed, a URL
similar to this will provide RSS information:

http://localhost/cgi-bin/BackupPC/BackupPC_Admin?action=rss

This feature is experimental. The information included will probably change.

BackupPC Design

Some design issues
Pooling common files
To see if a file is already in the pool, an MD5 digest of the file contents is used. This can't
guarantee a file is identical: it just reduces the search to often a single file or handful of files.

Depending on the Xfer method and settings, a complete file comparison is done to verify if two files
are really the same.

Prior to V4, identical files on multiples backups are represented by hard links. Hardlinks are used
so that identical files all refer to the same physical file on the server's disk. Also, hard links
maintain reference counts so that BackupPC knows when to delete unused files from the pool.

In V4+, hardlinks are not used and reference counting is done at the application level. It is done
in a batch manner, which simplifies the implementation.

For the computer-science majors among you, you can think of the pooling system used by BackupPC as
just a chained hash table stored on a (big) file system.

The hashing function
In V4+, the file digest is the MD5 digest of the complete file. While MD5 collisions are now well
known, and can be easily constructed, in real use collisions will be extremely unlikely.

Prior to V4, just a portion of all but the smallest files was used for the digest. That decision was
made long ago when CPUs were a lot slower. For files less than 256K, the digest is the MD5 digest of
the file size and the full file. For files up to 1MB, the first and last 128K of the file, and for
over 1MB, the first and eighth 128K chunks are used, together with the file size.

Compression
BackupPC supports compression. It uses the deflate and inflate methods in the Compress::Zlib module,
which is based on the zlib compression library (see <http://www.gzip.org/zlib/>).

The $Conf{CompressLevel} setting specifies the compression level to use. Zero (0) means no
compression. Compression levels can be from 1 (least cpu time, slightly worse compression) to 9 (most
cpu time, slightly better compression). The recommended value is 3. Changing it to 5, for example,
will take maybe 20% more cpu time and will get another 2-3% additional compression. Diminishing
returns set in above 5. See the zlib documentation for more information about compression levels.

BackupPC implements compression with minimal CPU load. Rather than compressing every incoming backup
file and then trying to match it against the pool, BackupPC computes the MD5 digest based on the
uncompressed file, and matches against the candidate pool files by comparing each uncompressed pool
file against the incoming backup file. Since inflating a file takes roughly a factor of 10 less CPU
time than deflating there is a big saving in CPU time.

The combination of pooling common files and compression can yield a factor of 8 or more overall
saving in backup storage.

Note that you should not turn compression on and off are you have started running BackupPC. It will
result in double the storage needs, since all the files will be stored in both the compressed and
uncompressed pools.

BackupPC operation
BackupPC reads the configuration information from __CONFDIR__/config.pl. It then runs and manages all the
backup activity. It maintains queues of pending backup requests, user backup requests and administrative
commands. Based on the configuration various requests will be executed simultaneously.

As specified by $Conf{WakeupSchedule}, BackupPC wakes up periodically to queue backups on all the PCs.
This is a four step process:

1. For each host and DHCP address backup requests are queued on the background command queue.

2. For each PC, BackupPC_dump is forked. Several of these may be run in parallel, based on the
configuration. First a ping is done to see if the machine is alive. If this is a DHCP address,
nmblookup is run to get the netbios name, which is used as the hostname. If DNS lookup fails,
$Conf{NmbLookupFindHostCmd} is run to find the IP address from the hostname. The file
__TOPDIR__/pc/$host/backups is read to decide whether a full or incremental backup needs to be run.
If no backup is scheduled, or the ping to $host fails, then BackupPC_dump exits.

The backup is done using the specified XferMethod. Either samba's smbclient or tar over ssh/rsh/nfs
piped into BackupPC_tarExtract, or rsync over ssh/rsh is run, or rsyncd is connected to, with the
incoming data extracted to __TOPDIR__/pc/$host/new. The XferMethod output is put into
__TOPDIR__/pc/$host/XferLOG.

The letter in the XferLOG file shows the type of object, similar to the first letter of the modes
displayed by ls -l:

d -> directory
l -> symbolic link
b -> block special file
c -> character special file
p -> pipe file (fifo)
nothing -> regular file

The words mean:

create
new for this backup (ie: directory or file not in pool)

pool
found a match in the pool

same
file is identical to previous backup (contents were checksummed and verified during full dump).

skip
file skipped in incremental because attributes are the same (only displayed if
$Conf{XferLogLevel} >= 2).

As BackupPC_tarExtract extracts the files from smbclient or tar, or as rsync or ftp runs, it checks
each file in the backup to see if it is identical to an existing file from any previous backup of any
PC. It does this without needed to write the file to disk. If the file matches an existing file, a
hardlink is created to the existing file in the pool. If the file does not match any existing files,
the file is written to disk and inserted into the pool.

BackupPC_tarExtract and rsync can handle arbitrarily large files and multiple candidate matching
files without needing to write the file to disk in the case of a match. This significantly reduces
disk writes (and also reads, since the pool file comparison is done disk to memory, rather than disk
to disk).

Based on the configuration settings, BackupPC_dump checks each old backup to see if any should be
removed.

3. Once each night, BackupPC_nightly is run to complete some additional administrative tasks, such as
cleaning the pool. This involves removing any files in the pool that only have a single hard link
(meaning no backups are using that file).

If BackupPC_nightly takes too long to run, the settings $Conf{MaxBackupPCNightlyJobs} and
$Conf{BackupPCNightlyPeriod} can be used to run several BackupPC_nightly processes in parallel, and
to split its job over several nights.

BackupPC also listens for TCP connections on $Conf{ServerPort}, which is used by the CGI script
BackupPC_Admin for status reporting and user-initiated backup or backup cancel requests.

Storage layout
BackupPC resides in several directories:

__INSTALLDIR__
Perl scripts comprising BackupPC reside in __INSTALLDIR__/bin, libraries are in __INSTALLDIR__/lib
and documentation is in __INSTALLDIR__/doc.

__CGIDIR__
The CGI script BackupPC_Admin resides in this cgi binary directory.

__CONFDIR__
All the configuration information resides below __CONFDIR__. This directory contains:

The directory __CONFDIR__ contains:

config.pl
Configuration file. See "Configuration File" below for more details.

hosts
Hosts file, which lists all the PCs to backup.

pc The directory __CONFDIR__/pc contains per-client configuration files that override settings in
the main configuration file. Each file is named __CONFDIR__/pc/HOST.pl, where HOST is the
hostname.

In pre-FHS versions of BackupPC these files were located in __TOPDIR__/pc/HOST/config.pl.

__LOGDIR__
The directory __LOGDIR__ (__TOPDIR__/log on pre-FHS versions of BackupPC) contains:

LOG Current (today's) log file output from BackupPC.

LOG.0 or LOG.0.z
Yesterday's log file output. Log files are aged daily and compressed (if compression is
enabled), and old LOG files are deleted.

status.pl
A summary of BackupPC's status written periodically by BackupPC so that certain state information
can be maintained if BackupPC is restarted. Should not be edited.

UserEmailInfo.pl
A summary of what email was last sent to each user, and when the last email was sent. Should not
be edited.

__RUNDIR__
The directory __RUNDIR__ (__TOPDIR__/log on pre-FHS versions of BackupPC) contains:

BackupPC.pid
Contains BackupPC's process id.

BackupPC.sock
A unix domain socket for communicating to the BackupPC server.

__TOPDIR__
All of BackupPC's data (PC backup images, logs, configuration information) is stored below this
directory.

Below __TOPDIR__ are several directories:

__TOPDIR__/pool
All uncompressed files from PC backups are stored below __TOPDIR__/pool. Each file's name is
based on the MD5 hex digest of the file contents.

For V4+, the digest is the MD5 digest of the full file contents (the length is not used). For
V4+ the pool files are stored in a 2 level tree, using 7 bits from the top of the first two bytes
of the digest. So there are 128 directories are each level, numbered evenly in hex from 0x00,
0x02, to 0xfe.

For example, if a file has an MD5 digest of 123456789abcdef0123456789abcdef0, the uncompressed
file is stored in __TOPDIR__/pool/12/34/123456789abcdef0123456789abcdef0.

Duplicates digest are represented with one (or more) hex byte extensions. So three colliding
files would be stored as

__TOPDIR__/pool/12/34/123456789abcdef0123456789abcdef0
__TOPDIR__/pool/12/34/123456789abcdef0123456789abcdef000
__TOPDIR__/pool/12/34/123456789abcdef0123456789abcdef001

The rest of this section describes the old pool layout. Note that both V3 and V4 pools can exist
together, since they use different names for their directory trees.

As exampled earlier, prior to V4 the digest is computed as follows. For files less than 256K,
the file length and the entire file is used. For files up to 1MB, the file length and the first
and last 128K are used. Finally, for files longer than 1MB, the file length, and the first and
eighth 128K chunks for the file are used.

Both BackupPC_dump (actually, BackupPC_tarExtract or rsync_bpc) are responsible for checking
newly backed up files against the pool. For each file, the MD5 digest is used to generate a
filename in the pool directory.

If the file exists in the pool, the contents are compared. If there is no match, additional
files in the chain are checked (if any). (Actually, multiple candidate files are compared in
parallel.)

If $Conf{PoolV3Enabled} is set, then the V3 pool is checked if there are no matches in the V4
pool. If a V3 file matches, it is simply moved (renamed) the the V4 pool with it's new filename
based on the V4 digest. That still allows the V3 backups to be browsed etc, since those backups
are still based on hardlinks.

If the file contents exactly match, a reference count is incremented. Otherwise, the file is
added to the pool by using an atomic link operation, followed by unlinking the temporary file.

One other issue: zero length files are not pooled, since there are a lot of these files and on
most file systems it doesn't save any disk space to turn these files into hard links.

Prior to V4, each pool file is stored in a subdirectory X/Y/Z, where X, Y, Z are the first 3 hex
digits of the MD5 digest.

For example, if a file has an MD5 digest of 123456789abcdef0123456789abcdef0, the file is stored
in __TOPDIR__/pool/1/2/3/123456789abcdef0123456789abcdef0.

The MD5 digest might not be unique (especially since not all the file's contents are used for
files bigger than 256K). Different files that have the same MD5 digest are stored with a trailing
suffix "_n" where n is an incrementing number starting at 0. So, for example, if two additional
files were identical to the first, except the last byte was different, and assuming the file was
larger than 1MB (so the MD5 digests are the same but the files are actually different), the three
files would be stored as:

__TOPDIR__/pool/1/2/3/123456789abcdef0123456789abcdef0
__TOPDIR__/pool/1/2/3/123456789abcdef0123456789abcdef0_0
__TOPDIR__/pool/1/2/3/123456789abcdef0123456789abcdef0_1

__TOPDIR__/cpool
All compressed files from PC backups are stored below __TOPDIR__/cpool. Its layout is the same
as __TOPDIR__/pool, and the hashing function is the same (and, importantly, based on the
uncompressed file, not the compressed file).

__TOPDIR__/pc/$host
For each PC $host, all the backups for that PC are stored below the directory
__TOPDIR__/pc/$host. This directory contains the following files:

LOG Current log file for this PC from BackupPC_dump.

LOG.MMYYYY or LOG.MMYYYY.z
Last month's log file. Log files are aged monthly and compressed (if compression is
enabled), and old LOG files are deleted. In earlier versions of BackupPC these files used to
have a suffix of 0, 1, ....

XferERR or XferERR.z
Output from the transport program (ie: smbclient, tar, rsync or ftp) for the most recent
failed backup.

XferLOG or XferLOG.z
Output from the transport program (ie: smbclient, tar, rsync or ftp) for the current backup.

nnn (an integer)
Backups are in directories numbered sequentially starting at 0. Below each backup directory
are the inodes (in nnn/inode) and the reference counts for this backup are in nnn/refCnt.

refCnt
The host's reference count database is stored below the refCnt directory.

XferLOG.nnn or XferLOG.nnn.z
Output from the transport program (ie: smbclient, tar, rsync or ftp) corresponding to backup
number nnn.

RestoreInfo.nnn
Information about restore request #nnn including who, what, when, and why. This file is in
Data::Dumper format. (Note that the restore numbers are not related to the backup number.)

RestoreLOG.nnn.z
Output from smbclient, tar or rsync during restore #nnn. (Note that the restore numbers are
not related to the backup number.)

ArchiveInfo.nnn
Information about archive request #nnn including who, what, when, and why. This file is in
Data::Dumper format. (Note that the archive numbers are not related to the restore or backup
number.)

ArchiveLOG.nnn.z
Output from archive #nnn. (Note that the archive numbers are not related to the backup or
restore number.)

config.pl
Old location of optional configuration settings specific to this host. Settings in this file
override the main configuration file. In new versions of BackupPC the per-host configuration
files are stored in __CONFDIR__/pc/HOST.pl.

backups
A tab-delimited ascii table listing information about each successful backup, one per row.
The columns are:

num The backup number, an integer that starts at 0 and increments for each successive backup.
The corresponding backup is stored in the directory num (eg: if this field is 5, then the
backup is stored in __TOPDIR__/pc/$host/5).

type
Set to "full" or "incr" for full or incremental backup.

startTime
Start time of the backup in unix seconds.

endTime
Stop time of the backup in unix seconds.

nFiles
Number of files backed up (as reported by smbclient, tar, rsync or ftp).

size
Total file size backed up (as reported by smbclient, tar, rsync or ftp).

nFilesExist
Number of files that were already in the pool (as determined by BackupPC_dump).

sizeExist
Total size of files that were already in the pool (as determined by BackupPC_dump).

nFilesNew
Number of files that were not in the pool (as determined by BackupPC_dump).

sizeNew
Total size of files that were not in the pool (as determined by BackupPC_dump).

xferErrs
Number of errors or warnings from smbclient, tar, rsync or ftp.

xferBadFile
Number of errors from smbclient that were bad file errors (zero otherwise).

xferBadShare
Number of errors from smbclient that were bad share errors (zero otherwise).

tarErrs
Number of errors from BackupPC_tarExtract.

compress
The compression level used on this backup. Zero or empty means no compression.

sizeExistComp
Total compressed size of files that were already in the pool (as determined by
BackupPC_dump).

sizeNewComp
Total compressed size of files that were not in the pool (as determined by
BackupPC_dump).

noFill
Set if this backup has not been filled - it just includes the deltas from the next backup
necessary to reconstruct this backup.

fillFromNum
If this backup was filled (ie: noFill is 0) then this is the number of the backup that it
was filled from

mangle
Set if this backup has mangled filenames and attributes. Always true for backups in
v1.4.0 and above. False for all backups prior to v1.4.0.

xferMethod
Set to the value of $Conf{XferMethod} when this dump was done.

level
The level of this dump. A full dump is level 0. Currently incrementals are 1. In V4+
multi-level incrementals are no longer supported, so this is just a 0 or 1.

charset
The client charset when this backup was made.

version
The BackupPC version when this backup was made.

inodeLast
The last inode number used in this backup.

keep
If set this backup won't be deleted.

share2path
Saves the value of $Conf{ClientShareName2Path} via Data::Dumper (with some tabs, newlines
and % characters replaced with %xx) so that the actual client path for each share can be
displayed when browsing.

restores
A tab-delimited ascii table listing information about each requested restore, one per row.
The columns are:

num Restore number (matches the suffix of the RestoreInfo.nnn and RestoreLOG.nnn.z file),
unrelated to the backup number.

startTime
Start time of the restore in unix seconds.

endTime
End time of the restore in unix seconds.

result
Result (ok or failed).

errorMsg
Error message if restore failed.

nFiles
Number of files restored.

size
Size in bytes of the restored files.

tarCreateErrs
Number of errors from BackupPC_tarCreate during restore.

xferErrs
Number of errors from smbclient, tar, rsync or ftp during restore.

archives
A tab-delimited ascii table listing information about each requested archive, one per row.
The columns are:

num Archive number (matches the suffix of the ArchiveInfo.nnn and ArchiveLOG.nnn.z file),
unrelated to the backup or restore number.

startTime
Start time of the restore in unix seconds.

endTime
End time of the restore in unix seconds.

result
Result (ok or failed).

errorMsg
Error message if archive failed.

Compressed file format
The compressed file format is as generated by Compress::Zlib::deflate with one minor, but important,
tweak. Since Compress::Zlib::inflate fully inflates its argument in memory, it could take large amounts
of memory if it was inflating a highly compressed file. For example, a 200MB file of 0x0 bytes compresses
to around 200K bytes. If Compress::Zlib::inflate was called with this single 200K buffer, it would need
to allocate 200MB of memory to return the result.

BackupPC watches how efficiently a file is compressing. If a big file has very high compression (meaning
it will use too much memory when it is inflated), BackupPC calls the flush() method, which gracefully
completes the current compression. BackupPC then starts another deflate and simply appends the output
file. So the BackupPC compressed file format is one or more concatenated deflations/flushes. The
specific ratios that BackupPC uses is that if a 6MB chunk compresses to less than 64K then a flush will
be done.

Back to the example of the 200MB file of 0x0 bytes. Adding flushes every 6MB adds only 200 or so bytes
to the 200K output. So the storage cost of flushing is negligible.

To easily decompress a BackupPC compressed file, the script BackupPC_zcat can be found in
__INSTALLDIR__/bin. For each filename argument it inflates the file and writes it to stdout.

Rsync checksum caching
Rsync checksum caching is not implemented in V4. That's because a full backup with rsync in V4 uses
client-side whole-file checksums during a full backup, meaning that the server doesn't need to send
block-level digests on every full backup.

The rest of this section applies to V3.

An incremental backup with rsync compares attributes on the client with the last full backup. Any files
with identical attributes are skipped. In V3, a full backup with rsync sets the --ignore-times option,
which causes every file to be examined independent of attributes.

Each file is examined by generating block checksums (default 2K blocks) on the receiving side (that's the
BackupPC side), sending those checksums to the client, where the remote rsync matches those checksums
with the corresponding file. The matching blocks and new data is sent back, allowing the client file to
be reassembled. A checksum for the entire file is sent to as an extra check the the reconstructed file
is correct.

This results in significant disk IO and computation for BackupPC: every file in a full backup, or any
file with non-matching attributes in an incremental backup, needs to be uncompressed, block checksums
computed and sent. Then the receiving side reassembles the file and has to verify the whole-file
checksum. Even if the file is identical, prior to 2.1.0, BackupPC had to read and uncompress the file
twice, once to compute the block checksums and later to verify the whole-file checksum.

Filename mangling
Backup filenames are stored in "mangled" form. Each node of a path is preceded by "f" (mnemonic: file),
and special characters (\n, \r, % and /) are URI-encoded as "%xx", where xx is the ascii character's hex
value. So c:/craig/example.txt is now stored as fc/fcraig/fexample.txt.

This was done mainly so metadata could be stored alongside the backup files without name collisions. In
particular, the attributes for the files in a directory are stored in a file called "attrib", and
mangling avoids filename collisions (I discarded the idea of having a duplicate directory tree for every
backup just to store the attributes). Other metadata (eg: rsync checksums) could be stored in filenames
preceded by, eg, "c". There are two other benefits to mangling: the share name might contain "/" (eg:
"/home/craig" for tar transport), and I wanted that represented as a single level in the storage tree.

The CGI script undoes the mangling, so it is invisible to the user.

Special files
Linux/unix file systems support several special file types: symbolic links, character and block device
files, fifos (pipes) and unix-domain sockets. All except unix-domain sockets are supported by BackupPC
(there's no point in backing up or restoring unix-domain sockets since they only have meaning after a
process creates them). Symbolic links are stored as a plain file whose contents are the contents of the
link (not the file it points to). This file is compressed and pooled like any normal file. Character and
block device files are also stored as plain files, whose contents are two integers separated by a comma;
the numbers are the major and minor device number. These files are compressed and pooled like any normal
file. Fifo files are stored as empty plain files (which are not pooled since they have zero size). In all
cases, the original file type is stored in the attrib file so it can be correctly restored.

Hardlinks are supported. In V4, file metadata include an inode number and a link count. Any file with
more than one link points at the inode information stored below the backup directory in the inode
directory. That directory contains a tree of up to 16K attrib files based on bits 10-23 of the inode
number. In particular, the directory name uses bits 17-23, and the attrib filename includes bits 10-16.
The key (index) in the attrib file is the hex inode number. The original file metadata's link count
might not be accurate; it's more a flag (>1) for when to look up the inode information. The correct link
count is stored in the inode.

In V3, hardlinks are stored in a similar manner to symlinks. When GNU tar first encounters a file with
more than one link (ie: hardlinks) it dumps it as a regular file. When it sees the second and subsequent
hardlinks to the same file, it dumps just the hardlink information. BackupPC correctly recognizes these
hardlinks and stores them just like symlinks: a regular text file whose contents is the path of the file
linked to. The CGI script will download the original file when you click on a hardlink.

Also, BackupPC_tarCreate has enough magic to re-create the hardlinks dynamically based on whether or not
the original file and hardlinks are both included in the tar file. For example, imagine a/b/x is a
hardlink to a/c/y. If you use BackupPC_tarCreate to restore directory a, then the tar file will include
a/b/x as the original file and a/c/y will be a hardlink to a/b/x. If, instead you restore a/c, then the
tar file will include a/c/y as the original file, not a hardlink.

Attribute file format
V4 attrib files
The attribute file format is new in V4. Every backup directory contains an attrib file, which is
zero length and its name includes the MD5 pool digest, eg:

attrib_33fe8f9ae2f5cedbea63b9d3ea767ac0

The digest is used to look up the contents in the V4 cpool, eg:

__TOPDIR__/cpool/32/fe/33fe8f9ae2f5cedbea63b9d3ea767ac0

For inode attrib files, bits 17-23 (XX in hex) of the inode number are used for the directory name,
and the attrib filename includes bits 10-16 (YY in hex), so relative to the backup directory:

inode/XX/attribYY_33fe8f9ae2f5cedbea63b9d3ea767ac0

An empty attrib file has the name "attrib_0" (or "attribYY_0" for inodes).

The attrib file starts with a magic number, followed by the concatenation of the following
information for each file (all integers are stored in perl's pack "w" format (variable length base
128)):

• Filename length, followed by the filename

• Count of extended attributes

• The unix file type, mtime, mode, uid, gid, size, inode number, compress, number of links

• MD5 digest length, followed by the digest contents

• Each extended attribute (length of xattr name, length of xattr value, name, value)

V3 attrib files
The unix attributes for the contents of a directory (all the files and directories in that directory)
are stored in a file called attrib. There is a single attrib file for each directory in a backup.
For example, if c:/craig contains a single file c:/craig/example.txt, that file would be stored as
fc/fcraig/fexample.txt and there would be an attribute file in fc/fcraig/attrib (and also fc/attrib
and ./attrib). The file fc/fcraig/attrib would contain a single entry containing the attributes for
fc/fcraig/fexample.txt.

The attrib file starts with a magic number, followed by the concatenation of the following
information for each file:

• Filename length in perl's pack "w" format (variable length base 128).

• Filename.

• The unix file type, mode, uid, gid and file size divided by 4GB and file size modulo 4GB (type
mode uid gid sizeDiv4GB sizeMod4GB), in perl's pack "w" format (variable length base 128).

• The unix mtime (unix seconds) in perl's pack "N" format (32 bit integer).

The attrib file is also compressed if compression is enabled. See the lib/BackupPC/Attrib.pm module
for full details.

Attribute files are pooled just like normal backup files. This saves space if all the files in a
directory have the same attributes across multiple backups, which is common.

Optimizations
BackupPC doesn't care about the access time of files in the pool since it saves attribute metadata
separate from the files. Since BackupPC mostly does reads from disk, maintaining the access time of
files generates a lot of unnecessary disk writes. So, provided BackupPC has a dedicated data disk, you
should consider mounting BackupPC's data directory with the noatime (or, with Linux kernels >=2.6.20,
relatime) attribute (see mount(1)).

Some Limitations
BackupPC isn't perfect (but it is getting better). Please see
<http://backuppc.sourceforge.net/faq/limitations.html> for a discussion of some of BackupPC's
limitations. (Note, this is old and we should move this to the Github Wiki.)

Security issues
Please see <http://backuppc.sourceforge.net/faq/security.html> for a discussion of some of various
security issues. (Note, this is old and we should move this to the Github Wiki.)

Configuration File

The BackupPC configuration file resides in __CONFDIR__/config.pl. Optional per-PC configuration files
reside in __CONFDIR__/pc/$host.pl (or __TOPDIR__/pc/$host/config.pl in non-FHS versions of BackupPC).
This file can be used to override settings just for a particular PC.

Modifying the main configuration file
The configuration file is a perl script that is executed by BackupPC, so you should be careful to
preserve the file syntax (punctuation, quotes etc) when you edit it. Specifically, preserving quotes
means you should never use undef for configuration parameters that expect string values. An empty string
('') should be used in this case. It is recommended that you use CVS, RCS or some other method of source
control for changing config.pl.

BackupPC reads or re-reads the main configuration file and the hosts file in three cases:

• Upon startup.

• When BackupPC is sent a HUP (-1) signal. Assuming you installed the init.d script, you can also do
this with "/etc/init.d/backuppc reload".

• When the modification time of config.pl file changes. BackupPC checks the modification time once
during each regular wakeup.

Whenever you change the configuration file you can either do a kill -HUP BackupPC_pid or simply wait
until the next regular wakeup period.

Each time the configuration file is re-read a message is reported in the LOG file, so you can tail it (or
view it via the CGI interface) to make sure your kill -HUP worked. Errors in parsing the configuration
file are also reported in the LOG file.

The optional per-PC configuration file (__CONFDIR__/pc/$host.pl or __TOPDIR__/pc/$host/config.pl in non-
FHS versions of BackupPC) is read whenever it is needed by BackupPC_dump, BackupPC_restore and others.

Configuration Parameters

       The configuration parameters are divided into five general  groups.   The  first  group  (general  server
       configuration) provides general configuration for BackupPC.  The next two groups describe what to backup,
       when to do it, and how long to keep it.  The fourth group are settings for email reminders, and the final
       group contains settings for the CGI interface.

       All  configuration  settings in the second through fifth groups can be overridden by the per-PC config.pl
       file.

   General server configuration
       $Conf{ServerHost} = '';
           Host name on which the BackupPC server is running.

       $Conf{ServerPort} = -1;
           TCP port number on which the BackupPC server listens for  and  accepts  connections.   Normally  this
           should  be  disabled  (set to -1).  The TCP port is only needed if apache runs on a different machine
           from BackupPC.  In that case, set this to any spare port number over 1024 (eg: 2359).  If you  enable
           the TCP port, make sure you set $Conf{ServerMesgSecret} too!

       $Conf{ServerMesgSecret} = '';
           Shared  secret to make the TCP port secure.  Set this to a hard to guess string if you enable the TCP
           port (ie: $Conf{ServerPort} > 0).

           To avoid possible attacks via the TCP socket interface, every client message is protected by  an  MD5
           digest. The MD5 digest includes four items:
             - a seed that is sent to the client when the connection opens
             - a sequence number that increments for each message
             - a shared secret that is stored in $Conf{ServerMesgSecret}
             - the message itself.

           The  message is sent in plain text preceded by the MD5 digest.  A snooper can see the plain-text seed
           sent by BackupPC and plain-text message from the client, but cannot  construct  a  valid  MD5  digest
           since  the secret $Conf{ServerMesgSecret} is unknown.  A replay attack is not possible since the seed
           changes on a per-connection and per-message basis.

       $Conf{MyPath} = '/bin';
           PATH setting for BackupPC.  An explicit value is necessary for taint mode.   Value  shouldn't  matter
           too  much  since  all  execs  use  explicit paths.  However, taint mode in perl will complain if this
           directory is world writable.

       $Conf{UmaskMode} = 027;
           Permission mask for directories and files created by BackupPC.  Default  value  prevents  any  access
           from group other, and prevents group write.

       $Conf{WakeupSchedule} = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22,
       23];
           Times  at which we wake up, check all the PCs, and schedule necessary backups.  Times are measured in
           hours since midnight local time.  Can be fractional if necessary (eg: 4.25 means 4:15am).

           If the hosts you are backing up are always connected to the network you might have only  one  or  two
           wakeups  each  night.  This will keep the backup activity after hours.  On the other hand, if you are
           backing up laptops that are only intermittently connected to  the  network  you  will  want  to  have
           frequent wakeups (eg: hourly) to maximize the chance that each laptop is backed up.

           Examples:

               $Conf{WakeupSchedule} = [22.5];         # once per day at 10:30 pm.
               $Conf{WakeupSchedule} = [2,4,6,8,10,12,14,16,18,20,22];  # every 2 hours

           The default value is every hour except midnight.

           The  first  entry  of  $Conf{WakeupSchedule}  is when BackupPC_nightly is run.  You might want to re-
           arrange the entries in $Conf{WakeupSchedule} (they don't have to be  ascending)  so  that  the  first
           entry is when you want BackupPC_nightly to run (eg: when you don't expect a lot of regular backups to
           run).

       $Conf{PoolV3Enabled} = 0;
           If  a  V3  pool  exists  (ie:  an  upgrade) set this to 1.  This causes the V3 pool to be checked for
           matches if there are no matches in the V4 pool.

           For new installations, this should be set to 0.

       $Conf{MaxBackups} = 4;
           Maximum number of simultaneous backups to run.  If there are no user backup requests then this is the
           maximum number of simultaneous backups.

       $Conf{MaxUserBackups} = 4;
           Additional number of simultaneous backups that  users  can  run.   As  many  as  $Conf{MaxBackups}  +
           $Conf{MaxUserBackups} requests can run at the same time.

       $Conf{MaxPendingCmds} = 15;
           Maximum  number  of pending link commands. New backups will only be started if there are no more than
           $Conf{MaxPendingCmds} plus $Conf{MaxBackups} number of pending  link  commands,  plus  running  jobs.
           This limit is to make sure BackupPC doesn't fall too far behind in running BackupPC_link commands.

       $Conf{CmdQueueNice} = 10;
           Nice level at which CmdQueue commands (eg: BackupPC_link and BackupPC_nightly) are run at.

       $Conf{MaxBackupPCNightlyJobs} = 2;
           How many BackupPC_nightly processes to run in parallel.

           Each night, at the first wakeup listed in $Conf{WakeupSchedule}, BackupPC_nightly is run.  Its job is
           to  remove  unneeded files in the pool, ie: files that only have one link.  To avoid race conditions,
           BackupPC_nightly and BackupPC_link cannot run at the same time.  Starting in v3.0.0, BackupPC_nightly
           can run concurrently with backups (BackupPC_dump).

           So  to  reduce  the  elapsed  time,  you  might  want  to  increase  this  setting  to  run   several
           BackupPC_nightly processes in parallel (eg: 4, or even 8).

       $Conf{BackupPCNightlyPeriod} = 1;
           How  many  days  (runs)  it  takes BackupPC_nightly to traverse the entire pool.  Normally this is 1,
           which means every night it runs, it does traverse the entire pool removing unused pool files.

           Other valid values are 2, 4, 8, 16.  This causes BackupPC_nightly to traverse 1/2, 1/4, 1/8 or 1/16th
           of the pool each night, meaning it takes 2, 4, 8 or 16 days to completely  traverse  the  pool.   The
           advantage  is  that each night the running time of BackupPC_nightly is reduced roughly in proportion,
           since the total job is split over multiple days.  The disadvantage is that  unused  pool  files  take
           longer to get deleted, which will slightly increase disk usage.

           Note  that  even  when $Conf{BackupPCNightlyPeriod} > 1, BackupPC_nightly still runs every night.  It
           just does less work each time it runs.

           Examples:

              $Conf{BackupPCNightlyPeriod} = 1;   # entire pool is checked every night

              $Conf{BackupPCNightlyPeriod} = 2;   # two days to complete pool check
                                                  # (different half each night)

              $Conf{BackupPCNightlyPeriod} = 4;   # four days to complete pool check
                                                  # (different quarter each night)

       $Conf{PoolSizeNightlyUpdatePeriod} = 16;
           The total size of the files in the new V4 pool is updated  every  night  when  BackupPC_nightly  runs
           BackupPC_refCountUpdate.   Instead of adding up the size of every pool file, it just updates the pool
           size total when files are added to or removed from the pool.

           To make sure these cumulative pool file sizes stay accurate, we recompute the  V4  pool  size  for  a
           portion of the pool each night from scratch, ie: by checking every file in that portion of the pool.

           $Conf{PoolSizeNightlyUpdatePeriod}  sets  how  many  nights it takes to completely update the V4 pool
           size.  It can be set to:
             0:  never do a full refresh; simply maintain the cumulative sizes
                 when files are added or deleted (fastest option)
             1:  recompute all  the V4 pool size every night (slowest option)
             2:  recompute 1/2  the V4 pool size every night
             4:  recompute 1/4  the V4 pool size every night
             8:  recompute 1/8  the V4 pool size every night
             16: recompute 1/16 the V4 pool size every night
                 (2nd fastest option; ensures the pool files sizes
                  stay accurate after a few day, in case the relative
                  upgrades miss a file)

       $Conf{PoolNightlyDigestCheckPercent} = 1;
           Integrity check the pool files by confirming the md5 digest of the contents matches their file  name.
           Because the pool is very large, only check a small random percentage of the pool files each night.

           This is check if there has been any server file system corruption.

           The  default  value  of  1%  means  approximately  30%  of the pool files will be checked each month,
           although the actual number will be a bit less since some files might be checked  more  than  once  in
           that time. If BackupPC_nightly takes too long, you could reduce this value.

       $Conf{RefCntFsck} = 1;
           Reference  counts  of  pool files are computed per backup by accumulating the relative changes.  That
           means, however, that any error will never be corrected.  To be more conservative, we  do  a  periodic
           full-redo  of  the  backup reference counts (called an "fsck").  $Conf{RefCntFsck} controls how often
           this is done:

             0: no additional fsck
             1: do an fsck on the last backup if it is from a full backup
             2: do an fsck on the last two backups always
             3: do a full fsck on all the backups

           $Conf{RefCntFsck} = 1 is the recommended setting.

       $Conf{MaxOldLogFiles} = 14;
           Maximum number of log files we keep around in log  directory.   These  files  are  aged  nightly.   A
           setting  of  14 means the log directory will contain about 2 weeks of old log files, in particular at
           most the files LOG, LOG.0, LOG.1, ... LOG.13  (except  today's  LOG,  these  files  will  have  a  .z
           extension if compression is on).

           If  you  decrease  this  number after BackupPC has been running for a while you will have to manually
           remove the older log files.

       $Conf{DfPath} = '';
           Full path to the df command.  Security caution: normal users should not allowed to write to this file
           or directory.

       $Conf{DfCmd} = '$dfPath $topDir';
           Command to run df.  The following variables are substituted at run-time:

             $dfPath      path to df ($Conf{DfPath})
             $topDir      top-level BackupPC data directory

           Note: all Cmds are executed directly without a shell, so the prog name needs to be a  full  path  and
           you can't include shell syntax like redirection and pipes; put that in a script if you need it.

       $Conf{DfInodeUsageCmd} = '$dfPath -i $topDir';
           Command to run df to get inode % usage.  The following variables are substituted at run-time:

             $dfPath      path to df ($Conf{DfPath})
             $topDir      top-level BackupPC data directory

           Note:  all  Cmds  are executed directly without a shell, so the prog name needs to be a full path and
           you can't include shell syntax like redirection and pipes; put that in a script if you need it.

       $Conf{SplitPath} = '';
       $Conf{ParPath} = '';
       $Conf{CatPath} = '';
       $Conf{GzipPath} = '';
       $Conf{Bzip2Path} = '';
           Full path to various commands for archiving

       $Conf{DfMaxUsagePct} = 95;
           Maximum threshold for disk utilization on the __TOPDIR__ filesystem.  If the output from $Conf{DfCmd}
           reports a percentage larger than this number then no new regularly scheduled  backups  will  be  run.
           However,  user  requested  backups  (which  are  usually  incremental and tend to be small) are still
           performed, independent of disk usage.  Also, currently running backups will not  be  terminated  when
           the disk usage exceeds this number.

       $Conf{DfMaxInodeUsagePct} = 95;
           Maximum  threshold  for  inode  utilization  on  the  __TOPDIR__  filesystem.   If  the  output  from
           $Conf{DfInodeUsageCmd} reports a percentage larger than this number then no new  regularly  scheduled
           backups  will  be run.  However, user requested backups (which are usually incremental and tend to be
           small) are still performed, independent of disk usage.  Also, currently running backups will  not  be
           terminated when the disk inode usage exceeds this number.

       $Conf{DHCPAddressRanges} = [];
           List of DHCP address ranges we search looking for PCs to backup.  This is an array of hashes for each
           class C address range.  This is only needed if hosts in the conf/hosts file have the dhcp flag set.

           Examples:

              # to specify 192.10.10.20 to 192.10.10.250 as the DHCP address pool
              $Conf{DHCPAddressRanges} = [
                  {
                      ipAddrBase => '192.10.10',
                      first => 20,
                      last  => 250,
                  },
              ];
              # to specify two pools (192.10.10.20-250 and 192.10.11.10-50)
              $Conf{DHCPAddressRanges} = [
                  {
                      ipAddrBase => '192.10.10',
                      first => 20,
                      last  => 250,
                  },
                  {
                      ipAddrBase => '192.10.11',
                      first => 10,
                      last  => 50,
                  },
              ];

       $Conf{BackupPCUser} = '';
           The BackupPC user.

       $Conf{TopDir} = '';
       $Conf{ConfDir} = '';
       $Conf{LogDir} = '';
       $Conf{RunDir} = '';
       $Conf{InstallDir} = '';
       $Conf{CgiDir} = '';
           Important installation directories:

             TopDir     - where all the backup data is stored
             ConfDir    - where the main config and hosts files resides
             LogDir     - where log files and other transient information resides
             RunDir     - where pid and sock files reside
             InstallDir - where the bin, lib and doc installation dirs reside.
                          Note: you cannot change this value since all the
                          perl scripts include this path.  You must reinstall
                          with configure.pl to change InstallDir.
             CgiDir     - Apache CGI directory for BackupPC_Admin

           Note:  it  is  STRONGLY  recommended  that  you  don't  change  the  values  here.   These are set at
           installation time and are here for reference and are used during upgrades.

           Instead of changing TopDir here it is recommended that you use a symbolic link to the  new  location,
           or mount the new BackupPC store at the existing $Conf{TopDir} setting.

       $Conf{BackupPCUserVerify} = 1;
           Whether  BackupPC  and  the  CGI  script  BackupPC_Admin  verify that they are really running as user
           $Conf{BackupPCUser}.   If  this  flag  is  set  and  the  effective  user  id  (euid)  differs   from
           $Conf{BackupPCUser} then both scripts exit with an error.  This catches cases where BackupPC might be
           accidentally started as root or the wrong user, or if the CGI script is not installed correctly.

       $Conf{HardLinkMax} = 31999;
           Maximum  number  of hardlinks supported by the $TopDir file system that BackupPC uses.  Most linux or
           unix file systems should support at least 32000 hardlinks per file, or 64000 in other  cases.   If  a
           pool  file already has this number of hardlinks, a new pool file is created so that new hardlinks can
           be accommodated.  This limit will only be hit if an identical file appears at least  this  number  of
           times across all the backups.

       $Conf{PerlModuleLoad} = undef;
           Advanced  option  for  asking  BackupPC to load additional perl modules.  Can be a list (arrayref) of
           module names to load at startup.

       $Conf{ServerInitdPath} = '';
       $Conf{ServerInitdStartCmd} = '';
           Path to init.d script and command to use that script to start the server from the CGI interface.  The
           following variables are substituted at run-time:

             $sshPath           path to ssh ($Conf{SshPath})
             $serverHost        same as $Conf{ServerHost}
             $serverInitdPath   path to init.d script ($Conf{ServerInitdPath})

           Example:

           $Conf{ServerInitdPath}     = '/etc/init.d/backuppc'; $Conf{ServerInitdStartCmd} = '$sshPath -q -x  -l
           root $serverHost'
                                      . ' $serverInitdPath start'
                                      . ' < /dev/null >& /dev/null';

           Note:  all  Cmds  are executed directly without a shell, so the prog name needs to be a full path and
           you can't include shell syntax like redirection and pipes; put that in a script if you need it.

   What to backup and when to do it
       $Conf{FullPeriod} = 6.97;
           Minimum period in days between full backups. A full dump will only be done if at least this much time
           has elapsed since the last full dump, and at least $Conf{IncrPeriod} days has elapsed since the  last
           successful dump.

           Typically  this  is  set slightly less than an integer number of days. The time taken for the backup,
           plus the granularity of $Conf{WakeupSchedule} will make the actual backup interval a bit longer.

       $Conf{IncrPeriod} = 0.97;
           Minimum period in days between incremental backups (a user requested incremental backup will be  done
           anytime on demand).

           Typically  this  is  set slightly less than an integer number of days. The time taken for the backup,
           plus the granularity of $Conf{WakeupSchedule} will make the actual backup interval a bit longer.

       $Conf{FillCycle} = 0;
           In V4+, full/incremental backups are decoupled from whether the stored backup is filled/unfilled.

           To mimic V3 behaviour, if $Conf{FillCycle} is set to zero then fill/unfilled will continue  to  match
           full/incremental:  full  backups  will  remained  filled,  and  incremental backups will be unfilled.
           (However, the most recent backup is always filled, whether it is full or incremental.)  This  is  the
           recommended  setting  to  keep  things  simple:  since  the  backup  expiry is actually done based on
           filled/unfilled (not full/incremental), keeping them synched makes it easier to understand the expiry
           settings.

           If you plan to do incremental-only backups (ie: set FullPeriod to  a  very  large  value),  then  you
           should  set  $Conf{FillCycle}  to  how  often you want a stored backup to be filled.  For example, if
           $Conf{FillCycle} is set to 7, then every 7th backup will be filled (whether or not the  corresponding
           backup was a full or not).

           There  are  two  reasons  you  will  want a non-zero $Conf{FillCycle} setting when you are only doing
           incrementals:

             - a filled backup is a starting point for merging deltas when you restore
               or view backups.  So having periodic filled backups makes it more
               efficient to view or restore older backups.

             - more importantly, in V4+, deleting backups is done based on Fill/Unfilled,
               not whether the original backup was full/incremental.  If there aren't any
               filled backups (other than the most recent), then the $Conf{FullKeepCnt}
               and related settings won't have any effect.

       $Conf{FullKeepCnt} = 1;
           Number of filled backups to keep.  Must be >= 1.

           The most recent backup (which is always filled) doesn't count when checking  $Conf{FullKeepCnt}.   So
           if  you  specify  $Conf{FullKeepCnt} = 1 then that means keep one full backup in addition to the most
           recent backup (which might be a filled incr or full).

           Note: Starting in V4+, deleting backups is done based on  Fill/Unfilled,  not  whether  the  original
           backup  was  full/incremental.  For  backward  compatibility,  these parameters continue to be called
           FullKeepCnt, rather than FilledKeepCnt.  If $Conf{FillCycle} is 0, then full backups continue  to  be
           filled,  so  the  terms are interchangeable.  For V3 backups, the expiry settings have their original
           meanings.

           In the steady state, each time a full backup completes successfully the oldest one  is  removed.   If
           this number is decreased, the extra old backups will be removed.

           Exponential backup expiry is also supported.  This allows you to specify:

             - num fulls to keep at intervals of 1 * $Conf{FillCycle}, followed by
             - num fulls to keep at intervals of 2 * $Conf{FillCycle},
             - num fulls to keep at intervals of 4 * $Conf{FillCycle},
             - num fulls to keep at intervals of 8 * $Conf{FillCycle},
             - num fulls to keep at intervals of 16 * $Conf{FillCycle},

           and  so  on.   This  works by deleting every other full as each expiry boundary is crossed.  Note: if
           $Conf{FillCycle} is 0, then $Conf{FullPeriod} is used instead in these calculations.

           Exponential expiry is specified using an array for $Conf{FullKeepCnt}:

             $Conf{FullKeepCnt} = [4, 2, 3];

           Entry #n specifies how many fulls to keep at an interval of 2^n * $Conf{FillCycle} (ie: 1, 2,  4,  8,
           16, 32, ...).

           The  example  above  specifies  keeping  4 of the most recent full backups (1 week interval) two full
           backups at 2 week intervals, and 3 full backups at 4 week intervals, eg:

              full 0 19 weeks old   \
              full 1 15 weeks old    >---  3 backups at 4 * $Conf{FillCycle}
              full 2 11 weeks old   /
              full 3  7 weeks old   \____  2 backups at 2 * $Conf{FillCycle}
              full 4  5 weeks old   /
              full 5  3 weeks old   \
              full 6  2 weeks old    \___  4 backups at 1 * $Conf{FillCycle}
              full 7  1 week old     /
              full 8  current       /

           On a given week the spacing might be less than shown as each backup ages through each expiry  period.
           For example, one week later, a new full is completed and the oldest is deleted, giving:

              full 0 16 weeks old   \
              full 1 12 weeks old    >---  3 backups at 4 * $Conf{FillCycle}
              full 2  8 weeks old   /
              full 3  6 weeks old   \____  2 backups at 2 * $Conf{FillCycle}
              full 4  4 weeks old   /
              full 5  3 weeks old   \
              full 6  2 weeks old    \___  4 backups at 1 * $Conf{FillCycle}
              full 7  1 week old     /
              full 8  current       /

           You  can  specify 0 as a count (except in the first entry), and the array can be as long as you wish.
           For example:

             $Conf{FullKeepCnt} = [4, 0, 4, 0, 0, 2];

           This will keep 10 full dumps, 4 most recent at 1 * $Conf{FillCycle}, followed by 4 at an interval  of
           4  *  $Conf{FillCycle}  (approx  1  month  apart), and then 2 at an interval of 32 * $Conf{FillCycle}
           (approx 7-8 months apart).

           Example: these two settings are equivalent and both keep just the four most recent full dumps:

              $Conf{FullKeepCnt} = 4;
              $Conf{FullKeepCnt} = [4];

       $Conf{FullKeepCntMin} = 1;
       $Conf{FullAgeMax} = 180;
           Very old full  backups  are  removed  after  $Conf{FullAgeMax}  days.   However,  we  keep  at  least
           $Conf{FullKeepCntMin} full backups no matter how old they are.

           Note  that  $Conf{FullAgeMax}  will  be  increased  to  $Conf{FullKeepCnt}  times $Conf{FillCycle} if
           $Conf{FullKeepCnt} specifies enough full backups to exceed $Conf{FullAgeMax}.

       $Conf{IncrKeepCnt} = 6;
           Number of incremental backups to keep.  Must be >= 1.

           Note: Starting in V4+, deleting backups is done based on  Fill/Unfilled,  not  whether  the  original
           backup  was  full/incremental.   For  historical  reasons  these  parameters  continue  to  be called
           IncrKeepCnt, rather than  UnfilledKeepCnt.   If  $Conf{FillCycle}  is  0,  then  incremental  backups
           continue  to be unfilled, so the terms are interchangeable.  For V3 backups, the expiry settings have
           their original meanings.

           In the steady state, each time an incr backup completes successfully the oldest one is  removed.   If
           this number is decreased, the extra old backups will be removed.

       $Conf{IncrKeepCntMin} = 1;
       $Conf{IncrAgeMax} = 30;
           Very  old  incremental  backups  are removed after $Conf{IncrAgeMax} days.  However, we keep at least
           $Conf{IncrKeepCntMin} incremental backups no matter how old they are.

       $Conf{BackupsDisable} = 0;
           Disable all full and incremental backups.  These settings are useful for a client that is  no  longer
           being backed up (eg: a retired machine), but you wish to keep the last backups available for browsing
           or restoring to other machines.

           There are three values for $Conf{BackupsDisable}:

             0    Backups are enabled.

             1    Don't do any regular backups on this client.  Manually
                  requested backups (via the CGI interface) will still occur.

             2    Don't do any backups on this client.  Manually requested
                  backups (via the CGI interface) will be ignored.

           In versions prior to 3.0 Backups were disabled by setting $Conf{FullPeriod} to -1 or -2.

       $Conf{RestoreInfoKeepCnt} = 10;
           Number  of  restore  logs  to keep.  BackupPC remembers information about each restore request.  This
           number per client will be kept around before the oldest ones are pruned.

           Note: files/dirs delivered via Zip or Tar downloads don't count as restores.  Only the first  restore
           option (where the files and dirs are written to the host) count as restores that are logged.

       $Conf{ArchiveInfoKeepCnt} = 10;
           Number  of  archive  logs  to keep.  BackupPC remembers information about each archive request.  This
           number per archive client will be kept around before the oldest ones are pruned.

       $Conf{BackupFilesOnly} = undef;
           List of directories or files to backup.  If this is defined, only these directories or files will  be
           backed up.

           For Smb, only one of $Conf{BackupFilesExclude} and $Conf{BackupFilesOnly} can be specified per share.
           If   both  are  set  for  a  particular  share,  then  $Conf{BackupFilesOnly}  takes  precedence  and
           $Conf{BackupFilesExclude} is ignored.

           This can be set to a string, an array of strings, or, in the case  of  multiple  shares,  a  hash  of
           strings  or  arrays.   A hash is used to give a list of directories or files to backup for each share
           (the share name is the key).  If this is set to just  a  string  or  array,  and  $Conf{SmbShareName}
           contains multiple share names, then the setting is assumed to apply all shares.

           If a hash is used, a special key "*" means it applies to all shares that don't have a specific entry.

           Examples:

              $Conf{BackupFilesOnly} = '/myFiles';
              $Conf{BackupFilesOnly} = ['/myFiles'];     # same as first example
              $Conf{BackupFilesOnly} = ['/myFiles', '/important'];
              $Conf{BackupFilesOnly} = {
                 'c' => ['/myFiles', '/important'],      # these are for 'c' share
                 'd' => ['/moreFiles', '/archive'],      # these are for 'd' share
              };
              $Conf{BackupFilesOnly} = {
                 'c' => ['/myFiles', '/important'],      # these are for 'c' share
                 '*' => ['/myFiles', '/important'],      # these are other shares
              };

       $Conf{BackupFilesExclude} = undef;
           List   of   directories   or   files   to   exclude   from   the   backup.   For  Smb,  only  one  of
           $Conf{BackupFilesExclude} and $Conf{BackupFilesOnly} can be specified per share.  If both are set for
           a particular share, then $Conf{BackupFilesOnly} takes  precedence  and  $Conf{BackupFilesExclude}  is
           ignored.

           This  can  be  set  to  a  string, an array of strings, or, in the case of multiple shares, a hash of
           strings or arrays.  A hash is used to give a list of directories or files to exclude for  each  share
           (the  share  name  is  the  key).   If this is set to just a string or array, and $Conf{SmbShareName}
           contains multiple share names, then the setting is assumed to apply to all shares.

           The exact behavior is determined  by  the  underlying  transport  program,  smbclient  or  tar.   For
           smbclient  the  exclude  file list is passed into the X option.  Simple shell wild-cards using "*" or
           "?" are allowed.

           For tar, if the exclude file contains a "/" it is assumed to be anchored at the start of the  string.
           Since  all  the  tar paths start with "./", BackupPC prepends a "." if the exclude file starts with a
           "/".  Note that GNU tar version >= 1.13.7 is required for the exclude option to work correctly.   For
           linux  or unix machines you should add "/proc" to $Conf{BackupFilesExclude} unless you have specified
           --one-file-system in $Conf{TarClientCmd} or --one-file-system in $Conf{RsyncArgs}.  Also, for tar, do
           not use a trailing "/" in the directory name: a trailing "/" causes the name to  not  match  and  the
           directory will not be excluded.

           Users  report  that  for  smbclient  you  should specify a directory followed by "/*", eg: "/proc/*",
           instead of just "/proc".

           FTP servers are traversed recursively so excluding directories will also exclude its  contents.   You
           can  use  the  wildcard  characters  "*"  and  "?" to define files for inclusion and exclusion.  Both
           attributes $Conf{BackupFilesOnly} and $Conf{BackupFilesExclude} can be defined for the same share.

           If a hash is used, a special key "*" means it applies to all shares that don't have a specific entry.

           Examples:

              $Conf{BackupFilesExclude} = '/temp';
              $Conf{BackupFilesExclude} = ['/temp'];     # same as first example
              $Conf{BackupFilesExclude} = ['/temp', '/winnt/tmp'];
              $Conf{BackupFilesExclude} = {
                 'c' => ['/temp', '/winnt/tmp'],         # these are for 'c' share
                 'd' => ['/junk', '/dont_back_this_up'], # these are for 'd' share
              };
              $Conf{BackupFilesExclude} = {
                 'c' => ['/temp', '/winnt/tmp'],         # these are for 'c' share
                 '*' => ['/junk', '/dont_back_this_up'], # these are for other shares
              };

       $Conf{BlackoutBadPingLimit} = 3;
       $Conf{BlackoutGoodCnt} = 7;
           PCs that are always or often on the network can be backed up after hours, to reduce PC,  network  and
           server load during working hours. For each PC a count of consecutive good pings is maintained. Once a
           PC  has  at  least  $Conf{BlackoutGoodCnt} consecutive good pings it is subject to "blackout" and not
           backed up during hours and days specified by $Conf{BlackoutPeriods}.

           To allow for periodic rebooting of a PC or other brief periods when a PC is not  on  the  network,  a
           number  of  consecutive  bad  pings is allowed before the good ping count is reset. This parameter is
           $Conf{BlackoutBadPingLimit}.

           Note that bad and good pings don't occur with the same interval.  If  a  machine  is  always  on  the
           network, it will only be pinged roughly once every $Conf{IncrPeriod} (eg: once per day). So a setting
           for  $Conf{BlackoutGoodCnt}  of  7  means  it  will take around 7 days for a machine to be subject to
           blackout. On the other hand, if a ping is failed, it will be  retried  roughly  every  time  BackupPC
           wakes  up,  eg,  every one or two hours. So a setting for $Conf{BlackoutBadPingLimit} of 3 means that
           the PC will lose its blackout status after 3-6 hours of unavailability.

           To disable the blackout feature set $Conf{BlackoutGoodCnt} to a negative value.  A value  of  0  will
           make  all  machines  subject  to blackout.  But if you don't want to do any backups during the day it
           would be easier to just set $Conf{WakeupSchedule} to a restricted schedule.

       $Conf{BlackoutPeriods} = [ ... ];
           One or more blackout periods can be specified.  If a client is subject to blackout  then  no  regular
           (non-manual)  backups  will  be  started  during any of these periods.  hourBegin and hourEnd specify
           hours from midnight and weekDays is a list of days of the week where 0 is Sunday, 1 is Monday etc.

           For example:

              $Conf{BlackoutPeriods} = [
                   {
                       hourBegin =>  7.0,
                       hourEnd   => 19.5,
                       weekDays  => [1, 2, 3, 4, 5],
                   },
              ];

           specifies one blackout period from 7:00am to 7:30pm local time on Mon-Fri.

           The blackout period can also span midnight by setting hourBegin > hourEnd, eg:

              $Conf{BlackoutPeriods} = [
                   {
                       hourBegin =>  7.0,
                       hourEnd   => 19.5,
                       weekDays  => [1, 2, 3, 4, 5],
                   },
                   {
                       hourBegin => 23,
                       hourEnd   =>  5,
                       weekDays  => [5, 6],
                   },
              ];

           This specifies one blackout period from 7:00am to 7:30pm local time on Mon-Fri, and a  second  period
           from 11pm to 5am on Friday and Saturday night.

       $Conf{BackupZeroFilesIsFatal} = 1;
           A backup of a share that has zero files is considered fatal. This is used to catch miscellaneous Xfer
           errors  that  result  in  no  files  being  backed  up.   If you have shares that might be empty (and
           therefore an empty backup is valid) you should set this flag to 0.

   How to backup a client
       $Conf{XferMethod} = 'smb';
           What transport method to use to backup each host.  If you have a mixed set of  WinXX  and  linux/unix
           hosts you will need to override this in the per-PC config.pl.

           The valid values are:

             - 'smb':     backup and restore via smbclient and the SMB protocol.
                          Easiest choice for WinXX.

             - 'rsync':   backup and restore via rsync (via rsh or ssh).
                          Best choice for linux/unix.  Good choice also for WinXX.

             - 'rsyncd':  backup and restore via rsync daemon on the client.
                          Best choice for linux/unix if you have rsyncd running on
                          the client.  Good choice also for WinXX.

             - 'tar':    backup and restore via tar, tar over ssh, rsh or nfs.
                         Good choice for linux/unix.

             - 'archive': host is a special archive host.  Backups are not done.
                          An archive host is used to archive other host's backups
                          to permanent media, such as tape, CDR or DVD.

       $Conf{XferLogLevel} = 1;
           Level  of  verbosity in Xfer log files.  0 means be quiet, 1 will give one line per file, 2 will also
           show skipped files on incrementals, higher values give more output.

       $Conf{ClientCharset} = '';
           Filename charset encoding on the client.  BackupPC uses utf8 on the server for filename encoding.  If
           this is empty, then utf8 is assumed and client filenames will not be modified.  If set to a different
           encoding then filenames will converted to/from utf8 automatically during backup and restore.

           If the filenames displayed in the browser (eg: accents or special characters) don't look  right  then
           it is likely you haven't set $Conf{ClientCharset} correctly.

           If  you  are using smbclient on a WinXX machine, smbclient will convert to the "unix charset" setting
           in smb.conf.  The default is utf8, in which case leave  $Conf{ClientCharset}  empty  since  smbclient
           does the right conversion.

           If  you  are using rsync on a WinXX machine then it does no conversion.  A typical WinXX encoding for
           latin1/western europe is 'cp1252', so in this case set $Conf{ClientCharset} to 'cp1252'.

           On  a  linux  or  unix  client,  run  "locale  charmap"   to   see   the   client's   charset.    Set
           $Conf{ClientCharset} to this value.  A typical value for english/US is 'ISO-8859-1'.

           Do   "perldoc   Encode::Supported"  to  see  the  list  of  possible  charset  values.   The  FAQ  at
           http://www.cl.cam.ac.uk/~mgk25/unicode.html              is              excellent,               and
           http://czyborra.com/charsets/iso8859.html provides more information on the iso-8859 charsets.

       $Conf{ClientCharsetLegacy} = 'iso-8859-1';
           Prior to 3.x no charset conversion was done by BackupPC.  Backups were stored in whatever charset the
           XferMethod provided - typically utf8 for smbclient and the client's locale settings for rsync and tar
           (eg:  cp1252  for  rsync  on  WinXX  and perhaps iso-8859-1 with rsync on linux).  This setting tells
           BackupPC the charset that was used to store filenames in old backups taken with BackupPC 2.x, so that
           non-ascii filenames in old backups can be viewed and restored.

       $Conf{ClientShareName2Path} = {};
           Optionally map the share name to a different path on the client when the xfer program  is  run.  This
           can  be  used  if  you  create a snapshot on the client, which has a different path to the real share
           name.  Or you could use simpler names for the share instead of a path (eg: root, home, usr)  and  map
           them to the real paths here.

           This  should  be a hash whose key is the share name used in $Conf{SmbShareName}, $Conf{TarShareName},
           $Conf{RsyncShareName}, $Conf{FtpShareName}, and the value is the string  path  name  on  the  client.
           When  a  backup  or restore is done, if there is no matching entry in $Conf{ClientShareName2Path}, or
           the entry is empty, then the share name is not modified (so the default behavior is unchanged).

           If you are using the rsyncd xfer method, then there is no need  to  use  this  configuration  setting
           (since rsyncd already supports mapping of share names to paths in the client's rsyncd.conf).

   Samba Configuration
       $Conf{SmbShareName} = 'C$';
           Name of the host share that is backed up when using SMB.  This can be a string or an array of strings
           if there are multiple shares per host.  Examples:

             $Conf{SmbShareName} = 'c';          # backup 'c' share
             $Conf{SmbShareName} = ['c', 'd'];   # backup 'c' and 'd' shares

           This setting only matters if $Conf{XferMethod} = 'smb'.

       $Conf{SmbShareUserName} = '';
           Smbclient share username.  This is passed to smbclient's -U argument.

           This setting only matters if $Conf{XferMethod} = 'smb'.

       $Conf{SmbSharePasswd} = '';
           Smbclient  share  password.   This is passed to smbclient via its PASSWD environment variable.  There
           are several ways you can tell BackupPC the smb share password.  In  each  case  you  should  be  very
           careful  about  security.   If you put the password here, make sure that this file is not readable by
           regular users!  See the "Setting up config.pl" section in the documentation for more information.

           This setting only matters if $Conf{XferMethod} = 'smb'.

       $Conf{SmbClientPath} = '';
           Full path for smbclient. Security caution: normal users should not allowed to write to this  file  or
           directory.

           smbclient  is  from  the Samba distribution. smbclient is used to actually extract the incremental or
           full dump of the share filesystem from the PC.

           This setting only matters if $Conf{XferMethod} = 'smb'.

       $Conf{SmbClientFullCmd} = ...
           Command to run smbclient for a full dump.  This setting only matters if $Conf{XferMethod} = 'smb'.

           The following variables are substituted at run-time:

              $smbClientPath   same as $Conf{SmbClientPath}
              $host            host to backup/restore
              $hostIP          host IP address
              $shareName       share name
              $userName        username
              $fileList        list of files to backup (based on exclude/include)
              $I_option        optional -I option to smbclient
              $X_option        exclude option (if $fileList is an exclude list)
              $timeStampFile   start time for incremental dump

           Note: all Cmds are executed directly without a shell, so the prog name needs to be a  full  path  and
           you can't include shell syntax like redirection and pipes; put that in a script if you need it.

       $Conf{SmbClientIncrCmd} = ...
           Command  to  run smbclient for an incremental dump.  This setting only matters if $Conf{XferMethod} =
           'smb'.

           Same variable substitutions are applied as $Conf{SmbClientFullCmd}.

           Note: all Cmds are executed directly without a shell, so the prog name needs to be a  full  path  and
           you can't include shell syntax like redirection and pipes; put that in a script if you need it.

       $Conf{SmbClientRestoreCmd} = ...
           Command to run smbclient for a restore.  This setting only matters if $Conf{XferMethod} = 'smb'.

           Same variable substitutions are applied as $Conf{SmbClientFullCmd}.

           If   your   smb   share   is   read-only   then   direct   restores   will   fail.   You  should  set
           $Conf{SmbClientRestoreCmd} to undef and the corresponding CGI restore option will be removed.

           Note: all Cmds are executed directly without a shell, so the prog name needs to be a  full  path  and
           you can't include shell syntax like redirection and pipes; put that in a script if you need it.

   Tar Configuration
       $Conf{TarShareName} = '/';
           Which  host  directories  to  backup  when  using tar transport.  This can be a string or an array of
           strings if there are multiple directories to backup per host.  Examples:

             $Conf{TarShareName} = '/';                    # backup everything
             $Conf{TarShareName} = '/home';                # only backup /home
             $Conf{TarShareName} = ['/home', '/src'];      # backup /home and /src

           The fact this parameter is called 'TarShareName' is for historical consistency with the Smb transport
           options.  You can use any valid directory on the client: there is no need for it to correspond to any
           Smb share or device mount point.

           Note also that you can also use $Conf{BackupFilesOnly} to specify a specific list of  directories  to
           backup.  It's more efficient to use this option instead of $Conf{TarShareName} since a new tar is run
           for each entry in $Conf{TarShareName}.

           On  the  other  hand,  if  you  add --one-file-system to $Conf{TarClientCmd} you can backup each file
           system separately, which makes restoring one bad file system easier.  In this case you would list all
           of the mount points here, since you can't get the same result with $Conf{BackupFilesOnly}:

               $Conf{TarShareName} = ['/', '/var', '/data', '/boot'];

           This setting only matters if $Conf{XferMethod} = 'tar'.

       $Conf{TarClientCmd} = '$sshPath -q -x -n -l root $host env LC_ALL=C $tarPath -c -v -f - -C $shareName+
       --totals';
           Command to run tar on the client.  GNU tar is required.  You will need to fill in the  correct  paths
           for ssh2 on the local host (server) and GNU tar on the client.  Security caution: normal users should
           not allowed to write to these executable files or directories.

           $Conf{TarClientCmd}  is  appended with with either $Conf{TarFullArgs} or $Conf{TarIncrArgs} to create
           the final command that is run.

           See the documentation for more information about setting up ssh2 keys.

           If you plan to use NFS then tar just runs locally and ssh2 is not needed.  For example, assuming  the
           client filesystem is mounted below /mnt/hostName, you could use something like:

              $Conf{TarClientCmd} = '$tarPath -c -v -f - -C /mnt/$host/$shareName'
                                  . ' --totals';

           In  the case of NFS or rsh you need to make sure BackupPC's privileges are sufficient to read all the
           files you want to backup.  Also, you will probably want to add "/proc" to $Conf{BackupFilesExclude}.

           The following variables are substituted at run-time:

             $host        hostname
             $hostIP      host's IP address
             $incrDate    newer-than date for incremental backups
             $shareName   share name to backup (ie: top-level directory path)
             $fileList    specific files to backup or exclude
             $tarPath     same as $Conf{TarClientPath}
             $sshPath     same as $Conf{SshPath}

           If a variable is followed by a "+" it is shell escaped.  This is necessary for the  command  part  of
           ssh or rsh, since it ends up getting passed through the shell.

           This setting only matters if $Conf{XferMethod} = 'tar'.

           Note:  all  Cmds  are executed directly without a shell, so the prog name needs to be a full path and
           you can't include shell syntax like redirection and pipes; put that in a script if you need it.

       $Conf{TarFullArgs} = '$fileList+';
           Extra tar  arguments  for  full  backups.   Several  variables  are  substituted  at  run-time.   See
           $Conf{TarClientCmd} for the list of variable substitutions.

           If  you  are running tar locally (ie: without rsh or ssh) then remove the "+" so that the argument is
           no longer shell escaped.

           This setting only matters if $Conf{XferMethod} = 'tar'.

       $Conf{TarIncrArgs} = '--newer=$incrDate+ $fileList+';
           Extra tar  arguments  for  incr  backups.   Several  variables  are  substituted  at  run-time.   See
           $Conf{TarClientCmd} for the list of variable substitutions.

           Note that GNU tar has several methods for specifying incremental backups, including:

             --newer-mtime $incrDate+
                    This causes a file to be included if the modification time is
                    later than $incrDate (meaning its contents might have changed).
                    But changes in the ownership or modes will not qualify the
                    file to be included in an incremental.

             --newer=$incrDate+
                    This causes the file to be included if any attribute of the
                    file is later than $incrDate, meaning either attributes or
                    the modification time.  This is the default method.  Do
                    not use --atime-preserve in $Conf{TarClientCmd} above,
                    otherwise resetting the atime (access time) counts as an
                    attribute change, meaning the file will always be included
                    in each new incremental dump.

           If  you  are running tar locally (ie: without rsh or ssh) then remove the "+" so that the argument is
           no longer shell escaped.

           This setting only matters if $Conf{XferMethod} = 'tar'.

       $Conf{TarClientRestoreCmd} = ...
           Full command to run tar for restore on the client.  GNU tar is required.  This can  be  the  same  as
           $Conf{TarClientCmd}, with tar's -c replaced by -x and ssh's -n removed.

           See $Conf{TarClientCmd} for full details.

           This setting only matters if $Conf{XferMethod} = "tar".

           If  you want to disable direct restores using tar, you should set $Conf{TarClientRestoreCmd} to undef
           and the corresponding CGI restore option will be removed.

           Note: all Cmds are executed directly without a shell, so the prog name needs to be a  full  path  and
           you can't include shell syntax like redirection and pipes; put that in a script if you need it.

       $Conf{TarClientPath} = '';
           Full  path  for tar on the client. Security caution: normal users should not allowed to write to this
           file or directory.

           This setting only matters if $Conf{XferMethod} = 'tar'.

   Rsync/Rsyncd Configuration
       $Conf{RsyncClientPath} = '';
           Path to rsync executable on the client.  If it is set,  it  is  passed  to  to  rsync_bpc  using  the
           --rsync-path option.  You can also add sudo, for example:

                 $Conf{RsyncClientPath} = 'sudo /usr/bin/rsync';

           For OSX laptop clients, you can use caffeinate to make sure the laptop stays awake during the backup,
           eg:

                 $Conf{RsyncClientPath} = '/usr/bin/sudo /usr/bin/caffeinate -ism /usr/bin/rsync';

           This setting only matters if $Conf{XferMethod} = 'rsync'.

       $Conf{RsyncBackupPCPath} = "";
           Full  path  to rsync_bpc on the server.  Rsync_bpc is the customized version of rsync that is used on
           the server for rsync and rsyncd transfers.

       $Conf{RsyncSshArgs} = ['-e', '$sshPath -l root'];
           Ssh arguments for rsync to run ssh to connect to the client.  Rather than  permit  root  ssh  on  the
           client,  it  is  more  secure  to  just  allow  ssh  via  a  low-privileged  user,  and  use  sudo in
           $Conf{RsyncClientPath}.

           The setting should only have two entries: "-e"  and  everything  else;  don't  add  additional  array
           elements.

           This setting only matters if $Conf{XferMethod} = 'rsync'.

       $Conf{RsyncShareName} = '/';
           Share  name  to backup.  For $Conf{XferMethod} = "rsync" this should be a file system path, eg '/' or
           '/home'.

           For $Conf{XferMethod} = "rsyncd" this should be the name of the module to backup (ie: the  name  from
           /etc/rsynd.conf).

           This  can  also  be  a  list  of  multiple  file  system  paths  or  modules.  For example, by adding
           --one-file-system to $Conf{RsyncArgs} you  can  backup  each  file  system  separately,  which  makes
           restoring one bad file system easier.  In this case you would list all of the mount points:

               $Conf{RsyncShareName} = ['/', '/var', '/data', '/boot'];

       $Conf{RsyncdClientPort} = 873;
           Rsync daemon port on the client, for $Conf{XferMethod} = "rsyncd".

       $Conf{RsyncdUserName} = '';
           Rsync  daemon  username  on  client, for $Conf{XferMethod} = "rsyncd".  The username and password are
           stored on the client in whatever file the "secrets file" parameter  in  rsyncd.conf  points  to  (eg:
           /etc/rsyncd.secrets).

       $Conf{RsyncdPasswd} = '';
           Rsync  daemon  username  on  client, for $Conf{XferMethod} = "rsyncd".  The username and password are
           stored on the client in whatever file the "secrets file" parameter  in  rsyncd.conf  points  to  (eg:
           /etc/rsyncd.secrets).

       $Conf{RsyncArgs} = [ ... ];
           Arguments  to  rsync  for  backup.  Do not edit the first set unless you have a good understanding of
           rsync options.

       $Conf{RsyncArgsExtra} = [];
           Additional arguments added to RsyncArgs.  This can be used in combination  with  $Conf{RsyncArgs}  to
           allow  customization  of  the  rsync  arguments on a part-client basis.  The standard arguments go in
           $Conf{RsyncArgs} and $Conf{RsyncArgsExtra} can be set on a per-client basis.

           Examples of additional arguments that should work are --exclude/--include, eg:

               $Conf{RsyncArgsExtra} = [
                     '--exclude', '/proc',
                     '--exclude', '*.tmp',
                     '--acls',
                     '--xattrs',
               ];

           Both $Conf{RsyncArgs} and $Conf{RsyncArgsExtra} are subject to the following variable substitutions:

                  $client       client name being backed up
                  $host         hostname (could be different from client name if
                                           $Conf{ClientNameAlias} is set)
                  $hostIP       IP address of host
                  $confDir      configuration directory path
                  $shareName    share name being backed up

           This allows settings of the form:

               $Conf{RsyncArgsExtra} = [
                       '--exclude-from=$confDir/pc/$host.exclude',
               ];

       $Conf{RsyncFullArgsExtra} = ['--checksum'];
           Additional arguments for a full rsync or rsyncd backup.

           The --checksum argument causes the client to send full-file checksum  for  every  file  (meaning  the
           client reads every file and computes the checksum, which is sent with the file list).  On the server,
           rsync_bpc  will skip any files that have a matching full-file checksum, and size, mtime and number of
           hardlinks.  Any file that has different attributes will be updating using the block rsync algorithm.

           In V3, full backups applied the block rsync algorithm to every file, which is a lot slower but a  bit
           more conservative.  To get that behavior, replace --checksum with --ignore-times.

       $Conf{RsyncIncrArgsExtra} = [];
           Additional arguments for an incremental rsync or rsyncd backup.

       $Conf{RsyncRestoreArgs} = [ ... ];
           Arguments  to  rsync for restore.  Do not edit the first set unless you have a thorough understanding
           of how File::RsyncP works.

           If you want to disable direct restores using rsync (eg: is the module is read-only), you  should  set
           $Conf{RsyncRestoreArgs} to undef and the corresponding CGI restore option will be removed.

           $Conf{RsyncRestoreArgs} is subject to the following variable substitutions:

                  $client       client name being backed up
                  $host         hostname (could be different from client name if
                                           $Conf{ClientNameAlias} is set)
                  $hostIP       IP address of host
                  $confDir      configuration directory path

           Note: $Conf{RsyncArgsExtra} doesn't apply to $Conf{RsyncRestoreArgs}.

       $Conf{RsyncRestoreArgsExtra} = [];
           Additional arguments for an rsync or rsyncd restore.

           This makes it easy to have per-client arguments.

   FTP Configuration
       $Conf{FtpShareName} = '';
           Which  host  directories  to  backup  when using FTP.  This can be a string or an array of strings if
           there are multiple shares per host.

           This value must be specified in one of two ways: either as a subdirectory of the 'share root' on  the
           server, or as the absolute path of the directory.

           In  the  following  example, if the directory /home/username is the root share of the ftp server with
           the given username, the following two values will back up the same directory:

              $Conf{FtpShareName} = 'www';                # www directory
              $Conf{FtpShareName} = '/home/username/www'; # same directory

           Path resolution is not supported; i.e.; you may not have an ftp share path defined as  '../otheruser'
           or '~/games'.

            Multiple shares may also be specified, as with other protocols:

              $Conf{FtpShareName} = [ 'www',
                                      'bin',
                                      'config' ];

           Note  also  that you can also use $Conf{BackupFilesOnly} to specify a specific list of directories to
           backup.  It's more efficient to use this option instead of $Conf{FtpShareName} since a new tar is run
           for each entry in $Conf{FtpShareName}.

           This setting only matters if $Conf{XferMethod} = 'ftp'.

       $Conf{FtpUserName} = '';
           FTP username.  This is used to log into the server.

           This setting is used only if $Conf{XferMethod} = 'ftp'.

       $Conf{FtpPasswd} = '';
           FTP user password.  This is used to log into the server.

           This setting is used only if $Conf{XferMethod} = 'ftp'.

       $Conf{FtpPassive} = 1;
           Whether passive mode is used.  The correct setting depends upon whether local  or  remote  ports  are
           accessible  from  the  other  machine,  which  is affected by any firewall or routers between the FTP
           server on the client and the BackupPC server.

           This setting is used only if $Conf{XferMethod} = 'ftp'.

       $Conf{FtpBlockSize} = 10240;
           Transfer block size. This sets the size of the amounts of data in each frame. While  undefined,  this
           value takes the default value.

           This setting is used only if $Conf{XferMethod} = 'ftp'.

       $Conf{FtpPort} = 21;
           The port of the ftp server.  If undefined, 21 is used.

           This setting is used only if $Conf{XferMethod} = 'ftp'.

       $Conf{FtpTimeout} = 120;
           Connection timeout for FTP.  When undefined, the default is 120 seconds.

           This setting is used only if $Conf{XferMethod} = 'ftp'.

       $Conf{FtpFollowSymlinks} = 0;
           Behaviour when BackupPC encounters symlinks on the FTP share.

           Symlinks  cannot  be  restored  via  FTP, so the desired behaviour will be different depending on the
           setup of the share. The default for this behavior is  1.   Directory  shares  with  more  complicated
           directory structures should consider other protocols.

   Archive Configuration
       $Conf{ArchiveDest} = '/tmp';
           Archive Destination

           The Destination of the archive e.g. /tmp for file archive or /dev/nst0 for device archive

       $Conf{ArchiveComp} = 'gzip';
           Archive Compression type

           The valid values are:

             - 'none':  No Compression

             - 'gzip':  Medium Compression. Recommended.

             - 'bzip2': High Compression but takes longer.

       $Conf{ArchivePar} = 0;
           Archive Parity Files

           The  amount  of  Parity data to generate, as a percentage of the archive size.  Uses the command line
           par2 (par2cmdline) available from http://parchive.sourceforge.net

           Only useful for file dumps.

           Set to 0 to disable this feature.

       $Conf{ArchiveSplit} = 0;
           Archive Size Split

           Only for file archives. Splits the output into the specified size * 1,000,000.  e.g.  to  split  into
           650,000,000 bytes, specify 650 below.

           If  the  value  is  0,  or if $Conf{ArchiveDest} is an existing file or device (e.g. a streaming tape
           drive), this feature is disabled.

       $Conf{ArchiveClientCmd} = ...
           Archive Command

           This is the command that is called to actually run the archive process for each host.  The  following
           variables are substituted at run-time:

             $Installdir    The installation directory of BackupPC
             $tarCreatePath The path to BackupPC_tarCreate
             $splitpath     The path to the split program
             $parpath       The path to the par2 program
             $host          The host to archive
             $backupnumber  The backup number of the host to archive
             $compression   The path to the compression program
             $compext       The extension assigned to the compression type
             $splitsize     The number of bytes to split archives into
             $archiveloc    The location to put the archive
             $parfile       The amount of parity data to create (percentage)

           Note:  all  Cmds  are executed directly without a shell, so the prog name needs to be a full path and
           you can't include shell syntax like redirection and pipes; put that in a script if you need it.

       $Conf{SshPath} = '';
           Full path for ssh. Security caution: normal users should  not  allowed  to  write  to  this  file  or
           directory.

       $Conf{NmbLookupPath} = '';
           Full  path  for nmblookup. Security caution: normal users should not allowed to write to this file or
           directory.

           nmblookup is from the Samba distribution. nmblookup is used to get the netbios  name,  necessary  for
           DHCP hosts.

       $Conf{NmbLookupCmd} = '$nmbLookupPath -A $host';
           NmbLookup  command.   Given  an  IP  address,  does  an  nmblookup on that IP address.  The following
           variables are substituted at run-time:

             $nmbLookupPath      path to nmblookup ($Conf{NmbLookupPath})
             $host               IP address

           This command is only used for DHCP hosts: given an IP address, this command should try  to  find  its
           NetBios name.

           Note:  all  Cmds  are executed directly without a shell, so the prog name needs to be a full path and
           you can't include shell syntax like redirection and pipes; put that in a script if you need it.

       $Conf{NmbLookupFindHostCmd} = '$nmbLookupPath $host';
           NmbLookup command.  Given a netbios name, finds  that  host  by  doing  a  NetBios  lookup.   Several
           variables are substituted at run-time:

             $nmbLookupPath      path to nmblookup ($Conf{NmbLookupPath})
             $host               NetBios name

           In  some  cases  you  might  need  to  change  the  broadcast  address, for example if nmblookup uses
           192.168.255.255 by default and you find that doesn't work,  try  192.168.1.255  (or  your  equivalent
           class C address) using the -B option:

              $Conf{NmbLookupFindHostCmd} = '$nmbLookupPath -B 192.168.1.255 $host';

           If  you  use  a WINS server and your machines don't respond to multicast NetBios requests you can use
           this (replace 1.2.3.4 with the IP address of your WINS server):

              $Conf{NmbLookupFindHostCmd} = '$nmbLookupPath -R -U 1.2.3.4 $host';

           This is preferred over multicast since it minimizes network traffic.

           Experiment manually for your site to see what form of nmblookup command works.

           Note: all Cmds are executed directly without a shell, so the prog name needs to be a  full  path  and
           you can't include shell syntax like redirection and pipes; put that in a script if you need it.

       $Conf{FixedIPNetBiosNameCheck} = 0;
           For  fixed  IP address hosts, BackupPC_dump can also verify the netbios name to ensure it matches the
           hostname.  An error is generated if they do not match.  Typically this flag is off.  But if  you  are
           going  to  transition  a  bunch of machines from fixed host addresses to DHCP, setting this flag is a
           great way to verify that the machines have their netbios name set correctly before turning on DHCP.

       $Conf{PingPath} = '';
           Full path to the ping command.  Security caution: normal users should not be allowed to write to this
           file or directory.

           If you want to disable ping checking, set this to some program that exits with 0 status, eg:

               $Conf{PingPath} = '/bin/echo';

       $Conf{Ping6Path} = '';
           Like PingPath, but for IPv6.  Security caution: normal users should not be allowed to write  to  this
           file  or  directory.   In  some  environments,  this  is  something like '/usr/bin/ping6'.  In modern
           environments, the regular ping command can handle both IPv4 and IPv6. In the latter case, just set it
           to $Conf{PingPath}

           If you want to disable ping checking for IPv6 hosts, set this to  some  program  that  exits  with  0
           status, eg:

               $Conf{Ping6Path} = '/bin/echo';

       $Conf{PingCmd} = '$pingPath -c 1 $host';
           Ping command.  The following variables are substituted at run-time:

             $pingPath      path to ping ($Conf{PingPath} or $Conf{Ping6Path})
                            depending on the address type of $host.
             $host          hostname

           Wade  Brown  reports  that  on  solaris  2.6 and 2.7 ping -s returns the wrong exit status (0 even on
           failure).  Replace with "ping $host 1", which gets the correct exit  status  but  we  don't  get  the
           round-trip time.

           Note:  all  Cmds  are executed directly without a shell, so the prog name needs to be a full path and
           you can't include shell syntax like redirection and pipes; put that in a script if you need it.

       $Conf{PingMaxMsec} = 20;
           Maximum round-trip ping time in milliseconds.  This threshold is set to avoid backing up PCs that are
           remotely connected through WAN or dialup connections.  The  output  from  ping  -s  (assuming  it  is
           supported  on your system) is used to check the round-trip packet time.  On your local LAN round-trip
           times should be much less than 20msec.  On most WAN or dialup connections the round-trip time will be
           typically more than 20msec.  Tune if necessary.

       $Conf{CompressLevel} = 3;
           Compression level to use on files.  0 means no compression.  Compression levels can be from 1  (least
           cpu  time,  slightly  worse  compression)  to  9  (most  cpu time, slightly better compression).  The
           recommended value is 3.  Changing to 5, for example, will take maybe 20% more cpu time and  will  get
           another  2-3%  additional  compression.  See  the  zlib  documentation  for  more  information  about
           compression levels.

           Changing compression on or off after backups have already been done will require both compressed  and
           uncompressed  pool  files  to  be stored.  This will increase the pool storage requirements, at least
           until all the old backups expire and are deleted.

           It is ok to change the compression value (from one non-zero value to another  non-zero  value)  after
           dumps are already done.  Since BackupPC matches pool files by comparing the uncompressed versions, it
           will still correctly match new incoming files against existing pool files.  The new compression level
           will take effect only for new files that are newly compressed and added to the pool.

           If  compression  was  off  and  you  are  enabling  compression  for  the  first time you can use the
           BackupPC_compressPool utility to compress the pool.  This avoids having the pool grow to  accommodate
           both compressed and uncompressed backups.  See the documentation for more information.

       $Conf{ClientTimeout} = 72000;
           Timeout  in  seconds  when  listening  for the transport program's (smbclient, tar etc) stdout. If no
           output is received during this time, then it is assumed that something has wedged  during  a  backup,
           and the backup is terminated.

           Note that stdout buffering combined with huge files being backed up could cause longish delays in the
           output  from  smbclient  that  BackupPC_dump  sees,  so in some cases you might want to increase this
           value.

           For rsync, this is passed onto rsync_bpc using the --timeout argument, which is based on any I/O,  so
           you could likely reduce this value.

       $Conf{MaxOldPerPCLogFiles} = 12;
           Maximum  number  of  log files we keep around in each PC's directory (ie: pc/$host).  These files are
           aged monthly.  A setting of 12 means there will be at most the files LOG, LOG.0, LOG.1, ... LOG.11 in
           the pc/$host directory (ie: about a year's worth).  (Except this month's LOG, these files will have a
           .z extension if compression is on).

           If you decrease this number after BackupPC has been running for a while you  will  have  to  manually
           remove the older log files.

       $Conf{DumpPreUserCmd} = undef;
       $Conf{DumpPostUserCmd} = undef;
       $Conf{DumpPreShareCmd} = undef;
       $Conf{DumpPostShareCmd} = undef;
       $Conf{RestorePreUserCmd} = undef;
       $Conf{RestorePostUserCmd} = undef;
       $Conf{ArchivePreUserCmd} = undef;
       $Conf{ArchivePostUserCmd} = undef;
           Optional commands to run before and after dumps and restores, and also before and after each share of
           a dump.

           Stdout  from  these commands will be written to the Xfer (or Restore) log file.  One example of using
           these commands would be to shut down and restart a database server, dump  a  database  to  files  for
           backup, or doing a snapshot of a share prior to a backup.  Example:

              $Conf{DumpPreUserCmd} = '$sshPath -q -x -l root $host /usr/bin/dumpMysql';

           The   following   variable   substitutions   are   made   at   run  time  for  $Conf{DumpPreUserCmd},
           $Conf{DumpPostUserCmd}, $Conf{DumpPreShareCmd} and $Conf{DumpPostShareCmd}:

                  $type         type of dump (incr or full)
                  $xferOK       1 if the dump succeeded, 0 if it didn't
                  $client       client name being backed up
                  $host         hostname (could be different from client name if
                                           $Conf{ClientNameAlias} is set)
                  $hostIP       IP address of host
                  $user         username from the hosts file
                  $moreUsers    list of additional users from the hosts file
                  $share        the first share name (or current share for
                                  $Conf{DumpPreShareCmd} and $Conf{DumpPostShareCmd})
                  $shares       list of all the share names
                  $XferMethod   value of $Conf{XferMethod} (eg: tar, rsync, smb)
                  $sshPath      value of $Conf{SshPath},
                  $cmdType      set to DumpPreUserCmd or DumpPostUserCmd

           The  following  variable  substitutions  are  made  at  run  time  for  $Conf{RestorePreUserCmd}  and
           $Conf{RestorePostUserCmd}:

                  $client       client name being backed up
                  $xferOK       1 if the restore succeeded, 0 if it didn't
                  $host         hostname (could be different from client name if
                                           $Conf{ClientNameAlias} is set)
                  $hostIP       IP address of host
                  $user         username from the hosts file
                  $moreUsers    list of additional users from the hosts file
                  $share        the first share name
                  $XferMethod   value of $Conf{XferMethod} (eg: tar, rsync, smb)
                  $sshPath      value of $Conf{SshPath},
                  $type         set to "restore"
                  $bkupSrcHost  hostname of the restore source
                  $bkupSrcShare share name of the restore source
                  $bkupSrcNum   backup number of the restore source
                  $pathHdrSrc   common starting path of restore source
                  $pathHdrDest  common starting path of destination
                  $fileList     list of files being restored
                  $cmdType      set to RestorePreUserCmd or RestorePostUserCmd

           The  following  variable  substitutions  are  made  at  run  time  for  $Conf{ArchivePreUserCmd}  and
           $Conf{ArchivePostUserCmd}:

                  $client       client name being backed up
                  $xferOK       1 if the archive succeeded, 0 if it didn't
                  $host         Name of the archive host
                  $user         username from the hosts file
                  $share        the first share name
                  $XferMethod   value of $Conf{XferMethod} (eg: tar, rsync, smb)
                  $HostList     list of hosts being archived
                  $BackupList   list of backup numbers for the hosts being archived
                  $archiveloc   location where the archive is sent to
                  $parfile      amount of parity data being generated (percentage)
                  $compression  compression program being used (eg: cat, gzip, bzip2)
                  $compext      extension used for compression type (eg: raw, gz, bz2)
                  $splitsize    size of the files that the archive creates
                  $sshPath      value of $Conf{SshPath},
                  $type         set to "archive"
                  $cmdType      set to ArchivePreUserCmd or ArchivePostUserCmd

           Note: all Cmds are executed directly without a shell, so the prog name needs to be a  full  path  and
           you can't include shell syntax like redirection and pipes; put that in a script if you need it.

       $Conf{UserCmdCheckStatus} = 0;
           Whether the exit status of each PreUserCmd and PostUserCmd is checked.

           If  set  and  the  Dump/Restore/Archive  Pre/Post  UserCmd  returns  a  non-zero exit status then the
           dump/restore/archive is aborted.  To maintain backward compatibility (where the exit status in  early
           versions was always ignored), this flag defaults to 0.

           If   this   flag   is   set   and   the  Dump/Restore/Archive  PreUserCmd  fails  then  the  matching
           Dump/Restore/Archive PostUserCmd is not executed.  If DumpPreShareCmd returns a non-exit status, then
           DumpPostShareCmd is not executed, but the DumpPostUserCmd is still  run  (since  DumpPreUserCmd  must
           have previously succeeded).

           An  example  of a DumpPreUserCmd that might fail is a script that snapshots or dumps a database which
           fails because of some database error.

       $Conf{ClientNameAlias} = undef;
           Override the client's hostname.  This allows multiple clients to all refer to the same physical host.
           This should only be set in the per-PC config file and is only used by BackupPC  at  the  last  moment
           prior  to  checking  the host is alive, and generating the command used to backup # that machine (ie:
           the value of $Conf{ClientNameAlias} is invisible everywhere else in BackupPC).  The setting can be  a
           hostname or IP address, eg:

                   $Conf{ClientNameAlias} = 'realHostName';
                   $Conf{ClientNameAlias} = '192.1.1.15';

           which will cause the relevant smb/tar/rsync backup/restore commands to be directed to realHostName or
           the IP address, not the client name.

           It  can  also  be  an  array, to allow checking (in order) of several host names or IP addresses that
           refer to the same host.  For example, if your client has a wired and wireless  connection  you  could
           set:

                   $Conf{ClientNameAlias} = ['hostname-lan', 'hostname-wifi'];

           If  hostname-lan  is alive, it will be used for the backup/restore.  If not, the next name (hostname-
           wifi) is tested.

           Note: this setting doesn't work for hosts with DHCP set to 1.

       $Conf{ClientComment} = undef;
           A user-settable comment string that is displayed in this  host's  status.   The  value  is  otherwise
           ignored by BackupPC.

   Email reminders, status and messages
       $Conf{SendmailPath} = '';
           Full  path  to  the  sendmail command.  Security caution: normal users should not allowed to write to
           this file or directory.

       $Conf{EMailNotifyMinDays} = 2.5;
           Minimum period between consecutive emails to a single user.  This tries to  keep  annoying  email  to
           users to a reasonable level.  Email checks are done nightly, so this number is effectively rounded up
           (ie: 2.5 means a user will never receive email more than once every 3 days).

       $Conf{EMailFromUserName} = '';
           Name  to  use  as the "from" name for email.  Depending upon your mail handler this is either a plain
           name (eg: "admin") or a fully-qualified name (eg: "admin@mydomain.com").

       $Conf{EMailAdminUserName} = '';
           Destination address to an administrative user who will receive a  nightly  email  with  warnings  and
           errors.   If  there  are  no warnings or errors then no email will be sent.  Depending upon your mail
           handler  this  is  either  a  plain   name   (eg:   "admin")   or   a   fully-qualified   name   (eg:
           "admin@mydomain.com").

       $Conf{EMailAdminSubject} = '';
           Subject for admin emails.  If empty, defaults to pre-4.2.2 values.

       $Conf{EMailUserDestDomain} = '';
           Destination  domain name for email sent to users.  By default this is empty, meaning email is sent to
           plain, unqualified addresses.  Otherwise, set it to the destination domain, eg:

              $Cong{EMailUserDestDomain} = '@mydomain.com';

           With this setting user email will be set to 'user@mydomain.com'.

       $Conf{EMailNoBackupEverSubj} = undef;
       $Conf{EMailNoBackupEverMesg} = undef;
           This subject and message is sent to a user if their PC has never been backed up.

           These values are language-dependent.  The default versions can be found in  the  language  file  (eg:
           lib/BackupPC/Lang/en.pm).  If you need to change the message, copy it here and edit it, eg:

             $Conf{EMailNoBackupEverMesg} = <<'EOF';
             To: $user$domain
             cc:
             Subject: $subj

             Dear $userName,

             This is a site-specific email message.
             EOF

       $Conf{EMailNotifyOldBackupDays} = 7.0;
           How  old  the most recent backup has to be before notifying user.  When there have been no backups in
           this number of days the user is sent an email.

       $Conf{EMailNoBackupRecentSubj} = undef;
       $Conf{EMailNoBackupRecentMesg} = undef;
           This subject and message is sent to a user if their PC has not recently been backed up (ie: more than
           $Conf{EMailNotifyOldBackupDays} days ago).

           These values are language-dependent.  The default versions can be found in  the  language  file  (eg:
           lib/BackupPC/Lang/en.pm).  If you need to change the message, copy it here and edit it, eg:

             $Conf{EMailNoBackupRecentMesg} = <<'EOF';
             To: $user$domain
             cc:
             Subject: $subj

             Dear $userName,

             This is a site-specific email message.
             EOF

       $Conf{EMailNotifyOldOutlookDays} = 5.0;
           How old the most recent backup of Outlook files has to be before notifying user.

       $Conf{EMailOutlookBackupSubj} = undef;
       $Conf{EMailOutlookBackupMesg} = undef;
           This  subject  and  message is sent to a user if their Outlook files have not recently been backed up
           (ie: more than $Conf{EMailNotifyOldOutlookDays} days ago).

           These values are language-dependent.  The default versions can be found in  the  language  file  (eg:
           lib/BackupPC/Lang/en.pm).  If you need to change the message, copy it here and edit it, eg:

             $Conf{EMailOutlookBackupMesg} = <<'EOF';
             To: $user$domain
             cc:
             Subject: $subj

             Dear $userName,

             This is a site-specific email message.
             EOF

       $Conf{EMailHeaders} = <<EOF;
           Additional email headers.  This sets to charset to utf8.

   CGI user interface configuration settings
       $Conf{CgiAdminUserGroup} = '';
       $Conf{CgiAdminUsers} = '';
           Normal  users can only access information specific to their host.  They can start/stop/browse/restore
           backups.

           Administrative users have full access to all hosts, plus overall status and log information.

           The administrative users are the union of the list of unix/linux  groups,  separated  by  spaces,  in
           $Conf{CgiAdminUserGroup}  and the list of users, separated by spaces, in $Conf{CgiAdminUsers}. If you
           don't want a list of groups or users set the corresponding configuration setting to undef or an empty
           string.

           If you want every user to have admin privileges (careful!), set $Conf{CgiAdminUsers} = '*'.

           Examples:

              $Conf{CgiAdminUserGroup} = 'admin wheel';
              $Conf{CgiAdminUsers}     = 'craig celia';
              --> administrative users are the union of groups admin and wheel, plus
                craig and celia.

              $Conf{CgiAdminUserGroup} = '';
              $Conf{CgiAdminUsers}     = 'craig celia';
              --> administrative users are only craig and celia'.

       $Conf{SCGIServerPort} = -1;
           TCP port number of the SCGI server.  A negative value disables the SCGI server.  Set to any available
           unprivileged TCP port number, eg: 10268.  Apache needs the mod_scgi module installed,  and  you  will
           need  to  set the same port number in the Apache configuration. Here are some typical settings you'll
           need in Apache's httpd.conf:

              LoadModule scgi_module modules/mod_scgi.so
              SCGIMount /BackupPC_Admin 127.0.0.1:10268
              <Location /BackupPC_Admin>
                  AuthUserFile /etc/httpd/conf/passwd
                  AuthType basic
                  AuthName "access"
                  require valid-user
              </Location>

           Important security warning!!  The SCGIServerPort must not be accessible by  anyone  untrusted.   That
           means  you  can't  allow  untrusted  users  access  to  the BackupPC server, and you should block the
           SCGIServerPort TCP port on the BackupPC server.  If you don't understand what that  means,  or  can't
           confirm you have configured SCGI securely, then don't enable it!!

       $Conf{CgiURL} = '';
           Full  URL of the BackupPC_Admin CGI script, or the configured path for SCGI.  Used for links in email
           messages.

       $Conf{RrdToolPath} = '';
           Full path to the rrdtool command.  If available, graphs of pool usage will be generated.   If  empty,
           then the graphs will be skipped.

           Security caution: normal users should not allowed to write to this file or directory.

       $Conf{Language} = 'en';
           Language  to  use.   See lib/BackupPC/Lang for the list of supported languages, which include English
           (en), French (fr), Spanish (es), German (de), Italian  (it),  Dutch  (nl),  Polish  (pl),  Portuguese
           Brazilian (pt_br) and Chinese (zh_CN).

           Currently  the  Language  setting applies to the CGI interface and email messages sent to users.  Log
           files and other text are still in English.

       $Conf{CgiUserHomePageCheck} = '';
       $Conf{CgiUserUrlCreate} = 'mailto:%s';
           User names that are rendered by the CGI interface can be turned into links into their  home  page  or
           other information about the user.  To set this up you need to create two sprintf() strings, that each
           contain a single '%s' that will be replaced by the user name.  The default is a mailto: link.

           $Conf{CgiUserHomePageCheck} should be an absolute file path that is used to check (via "-f") that the
           user has a valid home page.  Set this to undef or an empty string to turn off this check.

           $Conf{CgiUserUrlCreate}  should be a full URL that points to the user's home page.  Set this to undef
           or an empty string to turn off generation of URLs for usernames.

           Example:

              $Conf{CgiUserHomePageCheck} = '/var/www/html/users/%s.html';
              $Conf{CgiUserUrlCreate}     = 'http://myhost/users/%s.html';
              --> if /var/www/html/users/craig.html exists, then 'craig' will
                be rendered as a link to http://myhost/users/craig.html.

       $Conf{CgiDateFormatMMDD} = 2;
           Date display format for CGI interface.  A value of 1 uses US-style dates (MM/DD), a value of  2  uses
           full YYYY-MM-DD format, and zero for international dates (DD/MM).

       $Conf{CgiNavBarAdminAllHosts} = 1;
           If  set,  the complete list of hosts appears in the left navigation bar pull-down for administrators.
           Otherwise, just the hosts for which the user is listed in the host file (as either  the  user  or  in
           moreUsers) are displayed.

       $Conf{CgiSearchBoxEnable} = 1;
           Enable/disable the search box in the navigation bar.

       $Conf{CgiNavBarLinks} = [ ... ];
           Additional  navigation bar links.  These appear for both regular users and administrators.  This is a
           list of hashes giving the link (URL) and the text (name) for the link.  Specifying lname  instead  of
           name  uses  the  language  specific  string (ie: $Lang->{lname}) instead of just literally displaying
           name.

       $Conf{CgiStatusHilightColor} = { ...
           Highlight colors based on status that are used in the PC summary page.

       $Conf{CgiHeaders} = '<meta http-equiv="pragma" content="no-cache">';
           Additional CGI header text.

       $Conf{CgiImageDir} = '';
           Directory where images are stored.  This directory should be below Apache's DocumentRoot.  This value
           isn't used by BackupPC but is used by configure.pl when you upgrade BackupPC.

           Example:

               $Conf{CgiImageDir} = '/var/www/htdocs/BackupPC';

       $Conf{CgiExt2ContentType} = {};
           Additional mappings of  filename  extensions  to  Content-Type  for  individual  file  restore.   See
           $Ext2ContentType in BackupPC_Admin for the default setting.  You can add additional settings here, or
           override any default settings.  Example:

               $Conf{CgiExt2ContentType} = {
                           'pl'  => 'text/plain',
                    };

       $Conf{CgiImageDirURL} = '';
           URL (without the leading http://host) for BackupPC's image directory.  The CGI script uses this value
           to serve up image files.

           Example:

               $Conf{CgiImageDirURL} = '/BackupPC';

       $Conf{CgiCSSFile} = 'BackupPC_stnd.css';
           CSS  stylesheet  "skin"  for the CGI interface.  It is stored in the $Conf{CgiImageDir} directory and
           accessed via the $Conf{CgiImageDirURL} URL.

           For  BackupPC  v3  and  v2  the  prior  css  versions  are  available  as  BackupPC_retro_v3.css  and
           BackupPC_retro_v2.css

       $Conf{CgiUserDeleteBackupEnable} = 0;
           Whether  the  user  is  allowed  to  delete backups. If set to a positive value, the user will have a
           delete button for each backup on any host they  have  permission  to  access.   If  set  to  0,  only
           administrators  have  access  to  the backup delete feature.  If set to a negative value, even admins
           will not be able to use the delete feature.

       $Conf{CgiUserConfigEditEnable} = 1;
           Whether the user is allowed to edit their per-PC config.

       $Conf{CgiUserConfigEdit} = { ...
           Which per-host config variables a non-admin user is allowed to edit.  Admin users can edit  all  per-
           host config variables, even if disabled in this list.

           SECURITY WARNING: Do not let users edit any of the Cmd config variables!  That's because a user could
           set  a  Cmd  to  a shell script of their choice and it will be run as the BackupPC user.  That script
           could do all sorts of bad things.

Version Numbers

       BackupPC uses a X.Y.Z version numbering system.  The first digit is for major new  releases,  the  middle
       digit  is  for  significant  feature  releases  and  improvements (most of the releases have been in this
       category).

Author

       Craig Barratt  <cbarratt@users.sourceforge.net>

       See <https://backuppc.github.io/backuppc/BackupPC.html>.

Copyright

       Copyright (C) 2001-2020 Craig Barratt

Credits

Ryan Kucera contributed the directory navigation code and images for v1.5.0. He contributed the first
skeleton of BackupPC_restore. He also added a significant revision to the CGI interface, including CSS
tags, in v2.1.0, and designed the BackupPC logo.

Xavier Nicollet, with additions from Guillaume Filion, added the internationalization (i18n) support to
the CGI interface for v2.0.0. Xavier provided the French translation fr.pm, with additions from
Guillaume.

Guillaume Filion wrote BackupPC_zipCreate and added the CGI support for zip download, in addition to some
CGI cleanup, for v1.5.0. Guillaume continues to support fr.pm updates for each new version.

Josh Marshall implemented the Archive feature in v2.1.0.

Ludovic Drolez supports the BackupPC Debian package.

Javier Gonzalez provided the Spanish translation, es.pm for v2.0.0.

Manfred Herrmann provided the German translation, de.pm for v2.0.0. Manfred continues to support de.pm
updates for each new version, together with some help from Ralph Paßgang.

Lorenzo Cappelletti provided the Italian translation, it.pm for v2.1.0. Giuseppe Iuculano and Vittorio
Macchi updated it for 3.0.0.

Lieven Bridts provided the Dutch translation, nl.pm, for v2.1.0, with some tweaks from Guus Houtzager,
and updates for 3.0.0.

Reginaldo Ferreira provided the Portuguese Brazilian translation pt_br.pm for v2.2.0.

Rich Duzenbury provided the RSS feed option to the CGI interface.

Jono Woodhouse from CapeSoft Software (www.capesoft.com) provided a new CSS skin for 3.0.0 with several
layout improvements. Sean Cameron (also from CapeSoft) designed new and more compact file icons for
3.0.0.

Youlin Feng provided the Chinese translation for 3.1.0.

Karol 'Semper' Stelmaczonek provided the Polish translation for 3.1.0.

Jeremy Tietsort provided the host summary table sorting feature for 3.1.0.

Paul Mantz contributed the ftp Xfer method for 3.2.0.

Petr Pokorny provided the Czech translation for 3.2.1.

Rikiya Yamamoto provided the Japanese translation for 3.3.0.

Yakim provided the Ukrainian translation for 3.3.0.

Sergei Butakov provided the Russian translation for 3.3.0.

Alexander Moisseev provided the rrdtool graphing code in 4.0.0 and has provided many fixes and
improvements in 3.x and 4.x.

Many people have provided user support on the mail lists, reported bugs, made useful suggestions, and
helped with testing; see the ChangeLog and the mailing lists.

Your name could appear here in the next version!

License

       This  program  is  free  software:  you  can  redistribute it and/or modify it under the terms of the GNU
       General Public License as published by the Free Software Foundation, either version 3 of the License,  or
       (at your option) any later version.

       This  program  is  distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even
       the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General  Public
       License for more details.

       You  should  have received a copy of the GNU General Public License along with this program.  If not, see
       <http://www.gnu.org/licenses/>.

perl v5.38.2                                       2024-04-08                                        BACKUPPC(8)