Ubuntu Manpage: borg - deduplicating and encrypting backup tool

Provided by: borgbackup2_2.0.0b14-3build1_amd64

NAME

       borg - deduplicating and encrypting backup tool

SYNOPSIS

       borg [common options] <command> [options] [arguments]

DESCRIPTION

       BorgBackup  (short:  Borg)  is  a  deduplicating backup program.  Optionally, it supports compression and
       authenticated encryption.

       The main goal of Borg is to provide an efficient and secure way to back data up.  The data  deduplication
       technique  used  makes  Borg suitable for daily backups since only changes are stored.  The authenticated
       encryption technique makes it suitable for backups to targets not fully trusted.

       Borg stores a set of files in an archive. A repository  is  a  collection  of  archives.  The  format  of
       repositories  is  Borg-specific. Borg does not distinguish archives from each other in any way other than
       their name, it does not matter when or where archives were created (e.g. different hosts).

EXAMPLES

   A step-by-step example
       1. Before a backup can be made, a repository has to be initialized:

             $ borg -r /path/to/repo repo-create --encryption=repokey-aes-ocb

       2. Back up the ~/src and ~/Documents directories into an archive called docs:

             $ borg -r /path/to/repo create docs ~/src ~/Documents

       3. The next day create a new archive using the same archive name:

             $ borg -r /path/to/repo create --stats docs ~/src ~/Documents

          This backup will be a lot quicker and a lot smaller since only new, never before seen data is  stored.
          The  --stats  option  causes  Borg  to  output  statistics about the newly created archive such as the
          deduplicated size (the amount of unique data not shared with other archives):

             Repository: /path/to/repo
             Archive name: docs
             Archive fingerprint: bcd1b53f9b4991b7afc2b339f851b7ffe3c6d030688936fe4552eccc1877718d
             Time (start): Sat, 2022-06-25 20:21:43
             Time (end):   Sat, 2022-06-25 20:21:43
             Duration: 0.07 seconds
             Utilization of max. archive size: 0%
             Number of files: 699
             Original size: 31.14 MB
             Deduplicated size: 502 B

       4. List all archives in the repository:

             $ borg -r /path/to/repo repo-list
             docs                                 Sat, 2022-06-25 20:21:14 [b80e24d2...b179f298]
             docs                                 Sat, 2022-06-25 20:21:43 [bcd1b53f...1877718d]

       5. List the contents of the first archive:

             $ borg -r /path/to/repo list aid:b80e24d2
             drwxr-xr-x user   group          0 Mon, 2016-02-15 18:22:30 home/user/Documents
             -rw-r--r-- user   group       7961 Mon, 2016-02-15 18:22:30 home/user/Documents/Important.doc
             ...

       6. Restore the first archive by extracting the files relative to the current directory:

             $ borg -r /path/to/repo extract aid:b80e24d2

       7. Delete the first archive (please note that this does not free repo disk space):

             $ borg -r /path/to/repo delete aid:b80e24d2

          Be careful if you use an archive NAME (and not an archive ID), that  might  match  multiple  archives!
          Always first use with --dry-run and --list!

       8. Recover disk space by compacting the segment files in the repo:

             $ borg -r /path/to/repo compact -v

       NOTE:
          Borg  is  quiet by default (it defaults to WARNING log level).  You can use options like --progress or
          --list to get specific reports during command execution.  You can also add the  -v  (or  --verbose  or
          --info) option to adjust the log level to INFO to get other informational messages.

NOTES

Positional Arguments and Options: Order matters
Borg only supports taking options (-s and --progress in the example) to the left or right of all
positional arguments (repo::archive and path in the example), but not in between them:

borg create -s --progress archive path # good and preferred
borg create archive path -s --progress # also works
borg create -s archive path --progress # works, but ugly
borg create archive -s --progress path # BAD

This is due to a problem in the argparse module: <https://bugs.python.org/issue15112>

Repository URLs
Local filesystem (or locally mounted network filesystem):

/path/to/repo - filesystem path to repo directory, absolute path

path/to/repo - filesystem path to repo directory, relative path

Also, stuff like ~/path/to/repo or ~other/path/to/repo works (this is expanded by your shell).

Note: you may also prepend a file:// to a filesystem path to get URL style.

Remote repositories accessed via ssh <user@host> :

ssh://user@host:port//abs/path/to/repo - absolute path

ssh://user@host:port/rel/path/to/repo - path relative to current directory

Remote repositories accessed via sftp:

sftp://user@host:port//abs/path/to/repo - absolute path

sftp://user@host:port/rel/path/to/repo - path relative to current directory

For ssh and sftp URLs, the user@ and :port parts are optional.

Remote repositories accessed via rclone:

rclone:remote:path - see the rclone docs for more details about remote:path.

If you frequently need the same repo URL, it is a good idea to set the BORG_REPO environment variable to
set a default for the repo URL:

export BORG_REPO='ssh://user@host:port/rel/path/to/repo'

Then just leave away the --repo option if you want to use the default - it will be read from BORG_REPO
then.

Repository Locations / Archive names
Many commands need to know the repository location, give it via -r / --repo or use the BORG_REPO
environment variable.

Commands needing one or two archive names usually get them as positional argument.

Commands working with an arbitrary amount of archives, usually take -a ARCH_GLOB.

Archive names must not contain the / (slash) character. For simplicity, maybe also avoid blanks or other
characters that have special meaning on the shell or in a filesystem (borg mount will use the archive
name as directory name).

Logging
Borg writes all log output to stderr by default. But please note that something showing up on stderr does
not indicate an error condition just because it is on stderr. Please check the log levels of the messages
and the return code of borg for determining error, warning or success conditions.

If you want to capture the log output to a file, just redirect it:

borg create repo::archive myfiles 2>> logfile

Custom logging configurations can be implemented via BORG_LOGGING_CONF.

The log level of the builtin logging configuration defaults to WARNING. This is because we want Borg to
be mostly silent and only output warnings, errors and critical messages, unless output has been requested
by supplying an option that implies output (e.g. --list or --progress).

Log levels: DEBUG < INFO < WARNING < ERROR < CRITICAL

Use --debug to set DEBUG log level - to get debug, info, warning, error and critical level output.

Use --info (or -v or --verbose) to set INFO log level - to get info, warning, error and critical level
output.

Use --warning (default) to set WARNING log level - to get warning, error and critical level output.

Use --error to set ERROR log level - to get error and critical level output.

Use --critical to set CRITICAL log level - to get critical level output.

While you can set misc. log levels, do not expect that every command will give different output on
different log levels - it's just a possibility.

WARNING:
Options --critical and --error are provided for completeness, their usage is not recommended as you
might miss important information.

Return codes
Borg can exit with the following return codes (rc):
┌─────────────┬───────────────────────────────────────┐
│ Return code │ Meaning │
├─────────────┼───────────────────────────────────────┤
│ 0 │ success (logged as INFO) │
├─────────────┼───────────────────────────────────────┤
│ 1 │ generic warning (operation reached │
│ │ its normal end, but there were │
│ │ warnings -- you should check the log, │
│ │ logged as WARNING) │
├─────────────┼───────────────────────────────────────┤
│ 2 │ generic error (like a fatal error, a │
│ │ local or remote exception, the │
│ │ operation did not reach its normal │
│ │ end, logged as ERROR) │
├─────────────┼───────────────────────────────────────┤
│ 3..99 │ specific error (enabled by │
│ │ BORG_EXIT_CODES=modern) │
├─────────────┼───────────────────────────────────────┤
│ 100..127 │ specific warning (enabled by │
│ │ BORG_EXIT_CODES=modern) │
├─────────────┼───────────────────────────────────────┤
│ 128+N │ killed by signal N (e.g. 137 == kill │
│ │ -9) │
└─────────────┴───────────────────────────────────────┘

If you use --show-rc, the return code is also logged at the indicated level as the last log entry.

The modern exit codes (return codes, "rc") are documented there: msgid

Environment Variables
Borg uses some environment variables for automation:

General:

BORG_REPO
When set, use the value to give the default repository location. Use this so you do not
need to type --repo /path/to/my/repo all the time.

BORG_OTHER_REPO
Similar to BORG_REPO, but gives the default for --other-repo.

BORG_PASSPHRASE
When set, use the value to answer the passphrase question for encrypted repositories. It
is used when a passphrase is needed to access an encrypted repo as well as when a new
passphrase should be initially set when initializing an encrypted repo. See also
BORG_NEW_PASSPHRASE.

BORG_PASSCOMMAND
When set, use the standard output of the command (trailing newlines are stripped) to answer
the passphrase question for encrypted repositories. It is used when a passphrase is needed
to access an encrypted repo as well as when a new passphrase should be initially set when
initializing an encrypted repo. Note that the command is executed without a shell. So
variables, like $HOME will work, but ~ won't. If BORG_PASSPHRASE is also set, it takes
precedence. See also BORG_NEW_PASSPHRASE.

BORG_PASSPHRASE_FD
When set, specifies a file descriptor to read a passphrase from. Programs starting borg may
choose to open an anonymous pipe and use it to pass a passphrase. This is safer than
passing via BORG_PASSPHRASE, because on some systems (e.g. Linux) environment can be
examined by other processes. If BORG_PASSPHRASE or BORG_PASSCOMMAND are also set, they
take precedence.

BORG_NEW_PASSPHRASE
When set, use the value to answer the passphrase question when a new passphrase is asked
for. This variable is checked first. If it is not set, BORG_PASSPHRASE and
BORG_PASSCOMMAND will also be checked. Main usecase for this is to automate fully borg
change-passphrase.

BORG_DISPLAY_PASSPHRASE
When set, use the value to answer the "display the passphrase for verification" question
when defining a new passphrase for encrypted repositories.

BORG_EXIT_CODES
When set to "modern", the borg process will return more specific exit codes (rc). When set
to "legacy", the borg process will return rc 2 for all errors, 1 for all warnings, 0 for
success. Default is "modern".

BORG_HOST_ID
Borg usually computes a host id from the FQDN plus the results of uuid.getnode() (which
usually returns a unique id based on the MAC address of the network interface. Except if
that MAC happens to be all-zero - in that case it returns a random value, which is not what
we want (because it kills automatic stale lock removal). So, if you have a all-zero MAC
address or other reasons to control better externally the host id, just set this
environment variable to a unique value. If all your FQDNs are unique, you can just use the
FQDN. If not, use <fqdn@uniqueid> .

BORG_LOCK_WAIT
You can set the default value for the --lock-wait option with this, so you do not need to
give it as a commandline option.

BORG_LOGGING_CONF
When set, use the given filename as INI
<https://docs.python.org/3/library/logging.config.html#configuration-file-format> -style
logging configuration. A basic example conf can be found at docs/misc/logging.conf.

BORG_RSH
When set, use this command instead of ssh. This can be used to specify ssh options, such as
a custom identity file ssh -i /path/to/private/key. See man ssh for other options. Using
the --rsh CMD commandline option overrides the environment variable.

BORG_REMOTE_PATH
When set, use the given path as borg executable on the remote (defaults to "borg" if
unset). Using --remote-path PATH commandline option overrides the environment variable.

BORG_FILES_CACHE_SUFFIX
When set to a value at least one character long, instructs borg to use a specifically named
(based on the suffix) alternative files cache. This can be used to avoid loading and saving
cache entries for backup sources other than the current sources.

BORG_FILES_CACHE_TTL
When set to a numeric value, this determines the maximum "time to live" for the files cache
entries (default: 2). The files cache is used to determine quickly whether a file is
unchanged.

BORG_USE_CHUNKS_ARCHIVE
When set to no (default: yes), the chunks.archive.d folder will not be used. This reduces
disk space usage but slows down cache resyncs.

BORG_SHOW_SYSINFO
When set to no (default: yes), system information (like OS, Python version, ...) in
exceptions is not shown. Please only use for good reasons as it makes issues harder to
analyze.

BORG_FUSE_IMPL
Choose the lowlevel FUSE implementation borg shall use for borg mount. This is a
comma-separated list of implementation names, they are tried in the given order, e.g.:

• pyfuse3,llfuse: default, first try to load pyfuse3, then try to load llfuse.

• llfuse,pyfuse3: first try to load llfuse, then try to load pyfuse3.

• pyfuse3: only try to load pyfuse3

• llfuse: only try to load llfuse

• none: do not try to load an implementation

BORG_SELFTEST
This can be used to influence borg's builtin self-tests. The default is to execute the
tests at the beginning of each borg command invocation.

BORG_SELFTEST=disabled can be used to switch off the tests and rather save some time.
Disabling is not recommended for normal borg users, but large scale borg storage providers
can use this to optimize production servers after at least doing a one-time test borg (with
selftests not disabled) when installing or upgrading machines / OS / borg.

BORG_WORKAROUNDS
A list of comma separated strings that trigger workarounds in borg, e.g. to work around
bugs in other software.

Currently known strings are:

basesyncfile
Use the more simple BaseSyncFile code to avoid issues with sync_file_range. You
might need this to run borg on WSL (Windows Subsystem for Linux) or in
systemd.nspawn containers on some architectures (e.g. ARM). Using this does not
affect data safety, but might result in a more bursty write to disk behaviour (not
continuously streaming to disk).

retry_erofs
Retry opening a file without O_NOATIME if opening a file with O_NOATIME caused
EROFS. You will need this to make archives from volume shadow copies in WSL1
(Windows Subsystem for Linux 1).

authenticated_no_key
Work around a lost passphrase or key for an authenticated mode repository (these are
only authenticated, but not encrypted). If the key is missing in the repository
config, add key = anything there.

This workaround is only for emergencies and only to extract data from an affected
repository (read-only access):

BORG_WORKAROUNDS=authenticated_no_key borg extract repo::archive

After you have extracted all data you need, you MUST delete the repository:

BORG_WORKAROUNDS=authenticated_no_key borg delete repo

Now you can init a fresh repo. Make sure you do not use the workaround any more.

Output formatting:

BORG_LIST_FORMAT
Giving the default value for borg repo-list --format=X.

BORG_RLIST_FORMAT
Giving the default value for borg repo-list --format=X.

BORG_PRUNE_FORMAT
Giving the default value for borg prune --format=X.

Some automatic "answerers" (if set, they automatically answer confirmation questions):

BORG_UNKNOWN_UNENCRYPTED_REPO_ACCESS_IS_OK=no (or =yes)
For "Warning: Attempting to access a previously unknown unencrypted repository"

BORG_RELOCATED_REPO_ACCESS_IS_OK=no (or =yes)
For "Warning: The repository at location ... was previously located at ..."

BORG_CHECK_I_KNOW_WHAT_I_AM_DOING=NO (or =YES)
For "This is a potentially dangerous function..." (check --repair)

BORG_DELETE_I_KNOW_WHAT_I_AM_DOING=NO (or =YES)
For "You requested to DELETE the repository completely including all archives it contains:"

Note: answers are case sensitive. setting an invalid answer value might either give the default
answer or ask you interactively, depending on whether retries are allowed (they by default are
allowed). So please test your scripts interactively before making them a non-interactive script.

Directories and files:

BORG_BASE_DIR
Defaults to $HOME or ~$USER or ~ (in that order). If you want to move all borg-specific
folders to a custom path at once, all you need to do is to modify BORG_BASE_DIR: the other
paths for cache, config etc. will adapt accordingly (assuming you didn't set them to a
different custom value).

BORG_CACHE_DIR
Defaults to $BORG_BASE_DIR/.cache/borg. If BORG_BASE_DIR is not explicitly set while XDG
env var <https://specifications.freedesktop.org/basedir-spec/0.6/ar01s03.html>
XDG_CACHE_HOME is set, then $XDG_CACHE_HOME/borg is being used instead. This directory
contains the local cache and might need a lot of space for dealing with big repositories.
Make sure you're aware of the associated security aspects of the cache location:
cache_security

BORG_CONFIG_DIR
Defaults to $BORG_BASE_DIR/.config/borg. If BORG_BASE_DIR is not explicitly set while XDG
env var <https://specifications.freedesktop.org/basedir-spec/0.6/ar01s03.html>
XDG_CONFIG_HOME is set, then $XDG_CONFIG_HOME/borg is being used instead. This directory
contains all borg configuration directories, see the FAQ for a security advisory about the
data in this directory: home_config_borg

BORG_DATA_DIR
Defaults to $BORG_BASE_DIR/.local/share/borg. If BORG_BASE_DIR is not explicitly set while
XDG env var <https://specifications.freedesktop.org/basedir-spec/0.6/ar01s03.html>
XDG_DATA_HOME is set, then $XDG_DATA_HOME/borg is being used instead. This directory
contains all borg data directories, see the FAQ for a security advisory about the data in
this directory: home_data_borg

BORG_RUNTIME_DIR
Defaults to $BORG_BASE_DIR/.cache/borg. If BORG_BASE_DIR is not explicitly set while XDG
env var <https://specifications.freedesktop.org/basedir-spec/0.6/ar01s03.html>
XDG_RUNTIME_DIR is set, then $XDG_RUNTIME_DIR/borg is being used instead. This directory
contains borg runtime files, like e.g. the socket file.

BORG_SECURITY_DIR
Defaults to $BORG_DATA_DIR/security. This directory contains security relevant data.

BORG_KEYS_DIR
Defaults to $BORG_CONFIG_DIR/keys. This directory contains keys for encrypted
repositories.

BORG_KEY_FILE
When set, use the given path as repository key file. Please note that this is only for
rather special applications that externally fully manage the key files:

• this setting only applies to the keyfile modes (not to the repokey modes).

• using a full, absolute path to the key file is recommended.

• all directories in the given path must exist.

• this setting forces borg to use the key file at the given location.

• the key file must either exist (for most commands) or will be created (borg repo-create).

• you need to give a different path for different repositories.

• you need to point to the correct key file matching the repository the command will
operate on.

TMPDIR This is where temporary files are stored (might need a lot of temporary space for some
operations), see tempfile
<https://docs.python.org/3/library/tempfile.html#tempfile.gettempdir>
for details.

Building:

BORG_OPENSSL_PREFIX
Adds given OpenSSL header file directory to the default locations (setup.py).

BORG_LIBACL_PREFIX
Adds given prefix directory to the default locations. If an 'include/acl/libacl.h' is found
Borg will be linked against the system libacl instead of a bundled implementation.
(setup.py)

BORG_LIBLZ4_PREFIX
Adds given prefix directory to the default locations. If a 'include/lz4.h' is found Borg
will be linked against the system liblz4 instead of a bundled implementation. (setup.py)

BORG_LIBZSTD_PREFIX
Adds given prefix directory to the default locations. If a 'include/zstd.h' is found Borg
will be linked against the system libzstd instead of a bundled implementation. (setup.py)

Please note:

• Be very careful when using the "yes" sayers, the warnings with prompt exist for your / your data's
security/safety.

• Also be very careful when putting your passphrase into a script, make sure it has appropriate file
permissions (e.g. mode 600, root:root).

File systems
We recommend using a reliable, scalable journaling filesystem for the repository, e.g. zfs, btrfs, ext4,
apfs.

Borg now uses the borgstore package to implement the key/value store it uses for the repository.

It currently uses the file: Store (posixfs backend) either with a local directory or via ssh and a remote
borg serve agent using borgstore on the remote side.

This means that it will store each chunk into a separate filesystem file (for more details, see the
borgstore project).

This has some pros and cons (compared to legacy borg 1.x's segment files):

Pros:

• Simplicity and better maintainability of the borg code.

• Sometimes faster, less I/O, better scalability: e.g. borg compact can just remove unused chunks by
deleting a single file and does not need to read and re-write segment files to free space.

• In future, easier to adapt to other kinds of storage: borgstore's backends are quite simple to
implement. sftp: and rclone: backends already exist, others might be easy to add.

• Parallel repository access with less locking is easier to implement.

Cons:

• The repository filesystem will have to deal with a big amount of files (there are provisions in
borgstore against having too many files in a single directory by using a nested directory structure).

• Bigger fs space usage overhead (will depend on allocation block size - modern filesystems like zfs are
rather clever here using a variable block size).

• Sometimes slower, due to less sequential / more random access operations.

Units
To display quantities, Borg takes care of respecting the usual conventions of scale. Disk sizes are
displayed in decimal <https://en.wikipedia.org/wiki/Decimal> , using powers of ten (so kB means 1000
bytes). For memory usage, binary prefixes <https://en.wikipedia.org/wiki/Binary_prefix>
are used, and are indicated using the IEC binary prefixes
<https://en.wikipedia.org/wiki/IEC_80000-13#Prefixes_for_binary_multiples> , using powers of two (so KiB
means 1024 bytes).

Date and Time
We format date and time conforming to ISO-8601, that is: YYYY-MM-DD and HH:MM:SS (24h clock).

For more information about that, see: <https://xkcd.com/1179/>

Unless otherwise noted, we display local date and time. Internally, we store and process date and time
as UTC. TIMESPAN

Some options accept a TIMESPAN parameter, which can be given as a number of days (e.g. 7d) or months
(e.g. 12m).

Resource Usage
Borg might use a lot of resources depending on the size of the data set it is dealing with.

If one uses Borg in a client/server way (with a ssh: repository), the resource usage occurs in part on
the client and in another part on the server.

If one uses Borg as a single process (with a filesystem repo), all the resource usage occurs in that one
process, so just add up client + server to get the approximate resource usage.

CPU client:

• borg create: does chunking, hashing, compression, crypto (high CPU usage)

• chunks cache sync: quite heavy on CPU, doing lots of hashtable operations.

• borg extract: crypto, decompression (medium to high CPU usage)

• borg check: similar to extract, but depends on options given.

• borg prune / borg delete archive: low to medium CPU usage

• borg delete repo: done on the server

It won't go beyond 100% of 1 core as the code is currently single-threaded. Especially higher
zlib and lzma compression levels use significant amounts of CPU cycles. Crypto might be cheap on
the CPU (if hardware accelerated) or expensive (if not).

CPU server:
It usually doesn't need much CPU, it just deals with the key/value store (repository) and uses the
repository index for that.

borg check: the repository check computes the checksums of all chunks (medium CPU usage) borg
delete repo: low CPU usage

CPU (only for client/server operation):
When using borg in a client/server way with a <ssh:-type> repo, the ssh processes used for the
transport layer will need some CPU on the client and on the server due to the crypto they are
doing - esp. if you are pumping big amounts of data.

Memory (RAM) client:
The chunks index and the files index are read into memory for performance reasons. Might need big
amounts of memory (see below). Compression, esp. lzma compression with high levels might need
substantial amounts of memory.

Memory (RAM) server:
The server process will load the repository index into memory. Might need considerable amounts of
memory, but less than on the client (see below).

Chunks index (client only):
Proportional to the amount of data chunks in your repo. Lots of chunks in your repo imply a big
chunks index. It is possible to tweak the chunker params (see create options).

Files index (client only):
Proportional to the amount of files in your last backups. Can be switched off (see create
options), but next backup might be much slower if you do. The speed benefit of using the files
cache is proportional to file size.

Repository index (server only):
Proportional to the amount of data chunks in your repo. Lots of chunks in your repo imply a big
repository index. It is possible to tweak the chunker params (see create options) to influence
the amount of chunks being created.

Temporary files (client):
Reading data and metadata from a FUSE mounted repository will consume up to the size of all
deduplicated, small chunks in the repository. Big chunks won't be locally cached.

Temporary files (server):
A non-trivial amount of data will be stored on the remote temp directory for each client that
connects to it. For some remotes, this can fill the default temporary directory at /tmp. This can
be remediated by ensuring the $TMPDIR, $TEMP, or $TMP environment variable is properly set for the
sshd process. For some OSes, this can be done just by setting the correct value in the .bashrc
(or equivalent login config file for other shells), however in other cases it may be necessary to
first enable PermitUserEnvironment yes in your sshd_config file, then add
environment="TMPDIR=/my/big/tmpdir" at the start of the public key to be used in the
authorized_hosts file.

Cache files (client only):
Contains the chunks index and files index (plus a collection of single- archive chunk indexes
which might need huge amounts of disk space, depending on archive count and size - see FAQ about
how to reduce).

Network (only for client/server operation):
If your repository is remote, all deduplicated (and optionally compressed/ encrypted) data of
course has to go over the connection (ssh:// repo url). If you use a locally mounted network
filesystem, additionally some copy operations used for transaction support also go over the
connection. If you back up multiple sources to one target repository, additional traffic happens
for cache resynchronization.

Support for file metadata
Besides regular file and directory structures, Borg can preserve

• symlinks (stored as symlink, the symlink is not followed)

• special files:

• character and block device files (restored via mknod)

• FIFOs ("named pipes")

• special file contents can be backed up in --read-special mode. By default the metadata to create
them with mknod(2), mkfifo(2) etc. is stored.

• hardlinked regular files, devices, symlinks, FIFOs (considering all items in the same archive)

• timestamps in nanosecond precision: mtime, atime, ctime

• other timestamps: birthtime (on platforms supporting it)

• permissions:

• IDs of owning user and owning group

• names of owning user and owning group (if the IDs can be resolved)

• Unix Mode/Permissions (u/g/o permissions, suid, sgid, sticky)

On some platforms additional features are supported:
┌────────────────────────┬──────────┬───────────┬───────────┐
│ Platform │ ACLs [5] │ xattr [6] │ Flags [7] │
├────────────────────────┼──────────┼───────────┼───────────┤
│ Linux │ Yes │ Yes │ Yes [1] │
├────────────────────────┼──────────┼───────────┼───────────┤
│ macOS │ Yes │ Yes │ Yes (all) │
├────────────────────────┼──────────┼───────────┼───────────┤
│ FreeBSD │ Yes │ Yes │ Yes (all) │
├────────────────────────┼──────────┼───────────┼───────────┤
│ OpenBSD │ n/a │ n/a │ Yes (all) │
├────────────────────────┼──────────┼───────────┼───────────┤
│ NetBSD │ n/a │ No [2] │ Yes (all) │
├────────────────────────┼──────────┼───────────┼───────────┤
│ Solaris and │ No [3] │ No [3] │ n/a │
│ derivatives │ │ │ │
├────────────────────────┼──────────┼───────────┼───────────┤
│ Windows (cygwin) │ No [4] │ No │ No │
└────────────────────────┴──────────┴───────────┴───────────┘

Other Unix-like operating systems may work as well, but have not been tested at all.

Note that most of the platform-dependent features also depend on the file system. For example, ntfs-3g
on Linux isn't able to convey NTFS ACLs.

[1] Only "nodump", "immutable", "compressed" and "append" are supported. Feature request #618 for more
flags.

[2] Feature request #1332

[3] Feature request #1337

[4] Cygwin tries to map NTFS ACLs to permissions with varying degrees of success.

[5] The native access control list mechanism of the OS. This normally limits access to non-native ACLs.
For example, NTFS ACLs aren't completely accessible on Linux with ntfs-3g.

[6] extended attributes; key-value pairs attached to a file, mainly used by the OS. This includes
resource forks on Mac OS X.

[7] aka BSD flags. The Linux set of flags [1] is portable across platforms. The BSDs define additional
flags.

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