Ubuntu Manpage: distcc - distributed C/C++/ObjC compiler with distcc-pump extensions

Provided by: distcc_3.4+really3.4-4build3_amd64

NAME

       distcc - distributed C/C++/ObjC compiler with distcc-pump extensions

SYNOPSIS

       distcc <compiler> [COMPILER OPTIONS]

       distcc [COMPILER OPTIONS]

       <compiler> [COMPILER OPTIONS]

       distcc [DISTCC OPTIONS]

DESCRIPTION

distcc distributes compilation of C code across several machines on a network. distcc should always
generate the same results as a local compile, it is simple to install and use, and it is often much
faster than a local compile.

This version incorporates plain distcc as well as an enhancement called pump mode or distcc-pump.

For each job, distcc in plain mode sends the complete preprocessed source code and compiler arguments
across the network from the client to a compilation server. In pump mode, distcc sends the source code
and recursively included header files (excluding those from the default system header directories), so
that both preprocessing and compilation can take place on the compilation servers. This speeds up the
delivery of compilations by up to an order of magnitude over plain distcc.

Compilation is driven by a client machine, which is typically the developer's workstation or laptop. The
distcc client runs on this machine, as does make, the preprocessor (if distcc's pump mode is not used),
the linker, and other stages of the build process. Any number of volunteer machines act as compilation
servers and help the client to build the program, by running the distccd(1) daemon, C compiler and
assembler as required.

distcc can run across either TCP sockets (on port 3632 by default), or through a tunnel command such as
ssh(1). For TCP connections the volunteers must run the distccd(1) daemon either directly or from inetd.
For SSH connections distccd must be installed but should not be listening for connections.

TCP connections should only be used on secure networks because there is no user authentication or
protection of source or object code. SSH connections are slower.

distcc is intended to be used with GNU Make's -j option, which runs several compiler processes
concurrently. distcc spreads the jobs across both local and remote CPUs. Because distcc is able to
distribute most of the work across the network, a higher concurrency level can be used than for local
builds. As a rule of thumb, the -j value should be set to about twice the total number of available
server CPUs but subject to client limitations. This setting allows for maximal interleaving of tasks
being blocked waiting for disk or network IO. Note that distcc can also work with other build control
tools, such as SCons, where similar concurrency settings must be adjusted.

The -j setting, especially for large values of -j, must take into account the CPU load on the client.
Additional measures may be needed to curtail the client load. For example, concurrent linking should be
severely curtailed using auxiliary locks. The effect of other build activity, such as Java compilation
when building mixed code, should be considered. The --localslots_cpp parameter is by default set to 8.
This limits the number of concurrent processes that do preprocessing in plain distcc (non-pump) mode.
Therefore, larger -j values than 8 may be used without overloading a single-CPU client due to
preprocessing. Such large values may speed up parts of the build that do not involve C compilations, but
they may not be useful to distcc efficiency in plain mode.

In contrast, using pump mode and say 40 servers, a setting of -j80 or larger may be appropriate even for
single-CPU clients.

It is strongly recommended that you install the same compiler version on all machines participating in a
build. Incompatible compilers may cause mysterious compile or link failures.

QUICKSTART

       1      For each machine, download distcc, unpack, and install.

       2      On each of the servers, run distccd --daemon with --allow options to restrict access.

       3      Put the names of the servers in your environment:
              $ export DISTCC_HOSTS='localhost red green blue'

       4      Build!
              $ make -j8 CC=distcc

QUICKSTART FOR DISTCC-PUMP MODE

       Proceed as above, but in Step 3, specify that the remote hosts are to carry the burden  of  preprocessing
       and that the files sent over the network should be compressed:

              $ export DISTCC_HOSTS='--randomize localhost red,cpp,lzo green,cpp,lzo blue,cpp,lzo'

       The --randomize option enforces a uniform usage of compile servers.  While you will get some benefit from
       distcc's  pump  mode with only a few servers, you get increasing benefit with more server CPUs (up to the
       hundreds!).  Wrap your build inside the pump command, here assuming 10 servers:

              $ distcc-pump make -j20 CC=distcc

QUICKSTART FOR DISTCC-GSSAPI MODE

       Proceed as per the QUICKSTART but in Step 3, specify that the remote hosts are to  mutually  authenticate
       with the client:

              $ export DISTCC_HOSTS='--randomize localhost red,auth green,auth blue,auth'

       If distccd runs under a specific principal name then execute the following command prior to step 4:

              export DISTCC_PRINICIPAL=<name>

HOW PLAIN (NON-PUMP) DISTCC WORKS

       distcc  only  ever  runs  the  compiler and assembler remotely.  With plain distcc, the preprocessor must
       always run locally because it needs to access various header files on the local machine which may not  be
       present,  or  may not be the same, on the volunteer.  The linker similarly needs to examine libraries and
       object files, and so must run locally.

       The compiler and assembler take only a single input file (the preprocessed source) and produce  a  single
       output  (the  object  file).   distcc  ships these two files across the network and can therefore run the
       compiler/assembler remotely.

       Fortunately, for most programs running the preprocessor is relatively cheap, and  the  linker  is  called
       relatively infrequent, so most of the work can be distributed.

       distcc  examines  its  command line to determine which of these phases are being invoked, and whether the
       job can be distributed.

HOW DISTCC-PUMP MODE WORKS

In pump mode, distcc runs the preprocessor remotely too. To do so, the preprocessor must have access to
all the files that it would have accessed if had been running locally. In pump mode, therefore, distcc
gathers all of the recursively included headers, except the ones that are default system headers, and
sends them along with the source file to the compilation server.

In distcc-pump mode, the server unpacks the set of all source files in a temporary directory, which
contains a directory tree that mirrors the part of the file system that is relevant to preprocessing,
including symbolic links.

The compiler is then run from the path in the temporary directory that corresponds to the current working
directory on the client. To find and transmit the many hundreds of files that are often part of a single
compilation, pump mode uses an incremental include analysis algorithm. The include server is a Python
program that implements this algorithm. The distcc-pump command starts the include server so that
throughout the build it can answer include queries by distcc commands.

The include server uses static analysis of the macro language to deal with conditional compilation and
computed includes. It uses the property that when a given header file has already been analyzed for
includes, it is not necessary to do so again if all the include options (-I's) are unchanged (along with
other conditions).

For large builds, header files are included, on average, hundreds of times each. With distcc-pump mode
each such file is analyzed only a few times, perhaps just once, instead of being preprocessed hundreds of
times. Also, each source or header file is now compressed only once, because the include server memoizes
the compressed files. As a result, the time used for preparing compilations may drop by up to an order
of magnitude over the preprocessing of plain distcc.

Because distcc in pump mode is able to push out files up to about ten times faster, build speed may
increase 3X or more for large builds compared to plain distcc mode.

RESTRICTIONS FOR PUMP MODE

Using pump mode requires both client and servers to use release 3.0 or later of distcc and distccd
(respectively).

The incremental include analysis of distc-pump mode rests on the fundamental assumption that source and
header files do not change during the build process. A few complex build systems, such as that for Linux
kernel 2.6, do not quite satisfy this requirement. To overcome such issues, and other corner cases such
as absolute filepaths in includes, see the include_server(1) man page.

Another important assumption is that the include configuration of all machines must be identical. Thus
the headers under the default system path must be the same on all servers and all clients. If a standard
GNU compiler installation is used, then this requirement applies to all libraries whose header files are
installed under /usr/include or /usr/local/include/. Note that installing software packages often lead
to additional headers files being placed in subdirectories of either.

If this assumption does not hold, then it is possible to break builds with distcc-pump mode, or worse, to
get wrong results without warning. Presently this condition is not verified, and it is on our TODO list
to address this issue.

An easy way to guarantee that the include configurations are identical is to use a cross-compiler that
defines a default system search path restricted to directories of the compiler installation.

See the include_server(1) manual for more information on symptoms and causes of violations of distcc-pump
mode assumptions.

HOW DISTCC-GSSAPI MODE WORKS

       In  this mode distcc will use the GSS-API framework to access the currently configured security mechanism
       and perform mutual authentication with the daemon.

OPTION SUMMARY

Most options passed to distcc are interpreted as compiler options. The following options are understood
by distcc itself. If any of these options are specified, distcc will not invoke the compiler.

--help Displays summary instructions.

--version
Displays the distcc client version.

--show-hosts
Displays the host list that distcc would use. See the Host Specifications section.

--scan-includes
Displays the list of files that distcc would send to the remote machine, as computed by the
include server. This is a conservative (over-)approximation of the files that would be read by
the C compiler. This option only works in pump mode. See the "How Distcc-pump Mode Works"
section for details on how this is computed.

The list output by distcc --scan-includes will contain one entry per line. Each line contains a
category followed by a path. The category is one of FILE, SYMLINK, DIRECTORY, or SYSTEMDIR:

FILE indicates a source file or header file that would be sent to the distcc server host.

SYMLINK indicates a symbolic link that would be sent to the distcc server host.

DIRECTORY indicates a directory that may be needed in order to compile the source file.
For example, a directory "foo" may be needed because of an include of the form #include
"foo/../bar.h". Such directories would be created on the distcc server host.

SYSTEMDIR indicates a system include directory, i.e. a directory which is on the compiler's
default include path, such as "/usr/include"; such directories are assumed to be present on
the distcc server host, and so would not be sent to the distcc server host.

-j Displays distcc's concurrency level, as calculated from the host list; it is the maximum number of
outstanding jobs issued by this client to all servers. By default this will be four times the
number of hosts in the host list, unless the /LIMIT option was used in the host list. See the
Host Specifications section.

--show-principal
Displays the name of the distccd security principal extracted from the environment. This option
is only available if distcc was compiled with the --with-auth configure option.

INSTALLING DISTCC

There are three different ways to call distcc, to suit different circumstances:

distcc can be installed under the name of the real compiler, to intercept calls to it and run them
remotely. This "masqueraded" compiler has the widest compatibility with existing source trees,
and is convenient when you want to use distcc for all compilation. The fact that distcc is being
used is transparent to the makefiles.

distcc can be prepended to compiler command lines, such as "distcc cc -c hello.c" or CC="distcc
gcc". This is convenient when you want to use distcc for only some compilations or to try it out,
but can cause trouble with some makefiles or versions of libtool that assume $CC does not contain
a space.

Finally, distcc can be used directly as a compiler. "cc" is always used as the name of the real
compiler in this "implicit" mode. This can be convenient for interactive use when "explicit" mode
does not work but is not really recommended for new use.

Remember that you should not use two methods for calling distcc at the same time. If you are using a
masquerade directory, don't change CC and/or CXX, just put the directory early on your PATH. If you're
not using a masquerade directory, you'll need to either change CC and/or CXX, or modify the makefile(s)
to call distcc explicitly.

MASQUERADING

The basic idea is to create a "masquerade directory" which contains links from the name of the real
compiler to the distcc binary. This directory is inserted early on the PATH, so that calls to the
compiler are intercepted and distcc is run instead. distcc then removes itself from the PATH to find the
real compiler.

For example:

# mkdir /usr/lib/distcc/bin
# cd /usr/lib/distcc/bin
# ln -s ../../../bin/distcc gcc
# ln -s ../../../bin/distcc cc
# ln -s ../../../bin/distcc g++
# ln -s ../../../bin/distcc c++

Then, to use distcc, a user just needs to put the directory /usr/lib/distcc/bin early in the PATH, and
have set a host list in DISTCC_HOSTS or a file. distcc will handle the rest.

To automatically discover compilers and create masquerade links run the provided update-distcc-symlinks
script.

Note that this masquerade directory must occur on the PATH earlier than the directory that contains the
actual compilers of the same names, and that any auxiliary programs that these compilers call (such as as
or ld) must also be found on the PATH in a directory after the masquerade directory since distcc calls
out to the real compiler with a PATH value that has all directory up to and including the masquerade
directory trimmed off.

It is possible to get a "recursion error" in masquerade mode, which means that distcc is somehow finding
itself again, not the real compiler. This can indicate that you have two masquerade directories on the
PATH, possibly because of having two distcc installations in different locations. It can also indicate
that you're trying to mix "masqueraded" and "explicit" operation.

Recursion errors can be avoided by using shell scripts instead of links. For example, in
/usr/lib/distcc/bin create a file cc which contains:

#!/bin/sh
distcc /usr/bin/gcc "$@"

In this way, we are not dependent on distcc having to locate the real gcc by investigating the PATH
variable. Instead, the compiler location is explicitly provided.

USING DISTCC WITH CCACHE

       ccache is a program that speeds software builds by  caching  the  results  of  compilations.   ccache  is
       normally  called  before distcc, so that results are retrieved from a normal cache.  Some experimentation
       may be required for idiosyncratic makefiles to make everything work together.

       The most reliable method is to set

              CCACHE_PREFIX="distcc"

       This tells ccache to run distcc as a wrapper around the  real  compiler.   ccache  still  uses  the  real
       compiler to detect compiler upgrades.

       ccache  can then be run using either a masquerade directory or by setting

              CC="ccache gcc"

       As  of  version  2.2,  ccache does not cache compilation from preprocessed source and so will never get a
       cache hit if it is run from distccd or distcc.  It must be run only on the client side and before  distcc
       to be any use.

       distcc's pump mode is not compatible with ccache.

HOST SPECIFICATIONS

A "host list" tells distcc which machines to use for compilation. In order, distcc looks in the
$DISTCC_HOSTS environment variable, the user's $DISTCC_DIR/hosts file, and the system-wide host file. If
no host list can be found, distcc emits a warning and compiles locally.

The host list is a simple whitespace separated list of host specifications. The simplest and most common
form is a host names, such as

localhost red green blue

distcc prefers hosts towards the start of the list, so machines should be listed in descending order of
speed. In particular, when only a single compilation can be run (such as from a configure script), the
first machine listed is used (but see --randomize below).

Placing localhost at the right point in the list is important to getting good performance. Because
overhead for running jobs locally is low, localhost should normally be first. However, it is important
that the client have enough cycles free to run the local jobs and the distcc client. If the client is
slower than the volunteers, or if there are many volunteers, then the client should be put later in the
list or not at all. As a general rule, if the aggregate CPU speed of the client is less than one fifth
of the total, then the client should be left out of the list.

If you have a large shared build cluster and a single shared hosts file, the above rules would cause the
first few machines in the hosts file to be tried first even though they are likely to be busier than
machines later in the list. To avoid this, place the keyword --randomize into the host list. This will
cause the host list to be randomized, which should improve performance slightly for large build clusters.

There are two special host names --localslots and --localslots_cpp which are useful for adjusting load on
the local machine. The --localslots host specifies how many jobs that cannot be run remotely that can be
run concurrently on the local machine, while --localslots_cpp controls how many preprocessors will run in
parallel on the local machine. Tuning these values can improve performance. Linking on large projects
can take large amounts of memory. Running parallel linkers, which cannot be executed remotely, may
force the machine to swap, which reduces performance over just running the jobs in sequence without
swapping. Getting the number of parallel preprocessors just right allows you to use larger parallel
factors with make, since the local machine now has some mechanism for measuring local resource usage.

Finally there is the host entry

Performance depends on the details of the source and makefiles used for the project, and the machine and
network speeds. Experimenting with different settings for the host list and -j factor may improve
performance.

The syntax is

Here are some individual examples of the syntax:

localhost
The literal word "localhost" is interpreted specially to cause compilations to be directly
executed, rather than passed to a daemon on the local machine. If you do want to connect to a
daemon on the local machine for testing, then give the machine's IP address or real hostname.
(This will be slower.)

IPV6 A literal IPv6 address enclosed in square brackets, such as [::1]

IPV4 A literal IPv4 address, such as 10.0.0.1

HOSTNAME
A hostname to be looked up using the resolver.

:PORT Connect to a specified decimal port number, rather than the default of 3632.

@HOSTID
Connect to the host over SSH, rather than TCP. Options for the SSH connection can be set in
~/.ssh/config

USER@ Connect to the host over SSH as a specified username.

:COMMAND
Connect over SSH, and use a specified path to find the distccd server. This is normally only
needed if for some reason you can't install distccd into a directory on the default PATH for SSH
connections. Use this if you get errors like "distccd: command not found" in SSH mode.

/LIMIT A decimal limit can be added to any host specification to restrict the number of jobs that this
client will send to the machine. The limit defaults to four per host (two for localhost), but may
be further restricted by the server. You should only need to increase this for servers with more
than two processors.

,lzo Enables LZO compression for this TCP or SSH host.

,cpp Enables distcc-pump mode for this host. Note: the build command must be wrapped in the distcc-
pump script in order to start the include server.

,auth Enables GSSAPI-based mutual authentication for this host.

AUTH_NAME
The "canonical" name to use for the service principal name instead of HOSTNAME (or its
corresponding fqdn). This option is useful in case of accessing an authenticated server via ssh
port forwarding, in which case the HOSTNAME is 127.0.0.1.

--randomize
Randomize the order of the host list before execution.

+zeroconf
This option is only available if distcc was compiled with Avahi support enabled at configure time.
When this special entry is present in the hosts list, distcc will use Avahi Zeroconf DNS Service
Discovery (DNS-SD) to locate any available distccd servers on the local network. This avoids the
need to explicitly list the host names or IP addresses of the distcc server machines. The distccd
servers must have been started with the "--zeroconf" option to distccd. An important caveat is
that in the current implementation, pump mode (",cpp") and compression (",lzo") will never be used
for hosts located via zeroconf.

Here is an example demonstrating some possibilities:

localhost/2 @bigman/16:/opt/bin/distccd oldmachine:4200/1
# cartman is down
distant/3,lzo

Comments are allowed in host specifications. Comments start with a hash/pound sign (#) and run to the
end of the line.

If a host in the list is not reachable distcc will emit a warning and ignore that host for about one
minute.

COMPRESSION

       The lzo host option  specifies  that  LZO  compression  should  be  used  for  data  transfer,  including
       preprocessed  source,  object  code  and  error  messages.  Compression is usually economical on networks
       slower than 100Mbps, but results may vary depending on the network, processors and source tree.

       Enabling compression makes the distcc client and server use more CPU time, but less network traffic.  The
       added CPU time is insignificant for pump mode.  The compression ratio is typically 4:1 for source and 2:1
       for object code.

       Using compression requires both client and server to use at least  release  2.9  of  distcc.   No  server
       configuration is required: the server always responds with compressed replies to compressed requests.

       Pump mode requires the servers to have the lzo host option on.

SEARCH PATHS

       If  the  compiler  name  is an absolute path, it is passed verbatim to the server and the compiler is run
       from that directory.  For example:

              distcc /usr/local/bin/gcc-3.1415 -c hello.c

       If the compiler name is not absolute, or not fully qualified, distccd's PATH is searched.  When distcc is
       run from a masquerade directory, only the base name of the compiler is used.  The client's PATH  is  used
       only to run the preprocessor and has no effect on the server's path.

TIMEOUTS

       Both  the  distcc  client  and  server  impose  timeouts on transfer of data across the network.  This is
       intended to detect hosts which are down or unreachable, and to prevent compiles hanging indefinitely if a
       server is disconnected while in use.  If a client-side timeout expires, the job will be re-run locally.

       The transfer timeout is not configurable at present. The timeout that detects stale  distributed  job  is
       configurable via DISTCC_IO_TIMEOUT environment variable.

DIAGNOSTICS

       Error  messages or warnings from local or remote compilers are passed through to diagnostic output on the
       client.

       distcc can supply extensive debugging information when the verbose option is used.  This is controlled by
       the DISTCC_VERBOSE environment variable on the client, and the  --verbose  option  on  the  server.   For
       troubleshooting, examine both the client and server error messages.

EXIT CODES

The exit code of distcc is normally that of the compiler: zero for successful compilation and non-zero
otherwise.

distcc distinguishes between "genuine" errors such as a syntax error in the source, and "accidental"
errors such as a networking problem connecting to a volunteer. In the case of accidental errors, distcc
will retry the compilation locally unless the DISTCC_FALLBACK option has been disabled.

If the compiler exits with a signal, distcc returns an exit code of 128 plus the signal number.

distcc internal errors cause an exit code between 100 and 127. In particular

100 General distcc failure.

101 Bad arguments.

102 Bind failed.

103 Connect failed.

104 Compiler crashed.

105 Out of memory.

106 Bad Host SPEC

107 I/O Error

108 Truncated.

109 Protocol Error.

110 The given compiler was not found on the remote host. Check that $CC is set appropriately and that
it's installed in a directory on the search path for distccd.

111 Recursive call to distcc.

112 Failed to discard privileges.

113 Network access denied.

114 In use by another process.

115 No such file.

116 No hosts defined and fallbacks disabled.

118 Timeout.

119 GSS-API - Catchall error code for GSS-API related errors.

120 Called for preprocessing, which needs to be done locally.

FILES

       If $DISTCC_HOSTS is not set, distcc reads a host list from  either  $DISTCC_DIR/hosts  or  a  system-wide
       configuration file set at compile time.  The file locations are shown in the output from distcc --help

       distcc creates a number of temporary and lock files underneath the temporary directory.

ENVIRONMENT VARIABLES

distcc's behaviour is controlled by a number of environment variables. For most cases nothing need be
set if the host list is stored in a file.

DISTCC_HOSTS
Space-separated list of volunteer host specifications.

DISTCC_VERBOSE
If set to 1, distcc produces explanatory messages on the standard error stream or in the log file.
This can be helpful in debugging problems. Bug reports should include verbose output.

DISTCC_LOG
Log file to receive messages from distcc itself, rather than stderr.

DISTCC_FALLBACK
By default distcc will compile locally if it fails to distribute a job to the intended machine, or
if no host list can be found. If this variable is set to 0 then fallbacks are disabled and those
compilations will simply fail. Note that this does not affect jobs which must always be local
such as linking.

DISTCC_NO_CROSS_REWRITE
By default distcc will rewrite calls gcc to use fully qualified names (like x86_64-linux-gnu-gcc),
and clang to use the -target option. Setting this turns that off.

DISTCC_BACKOFF_PERIOD
Specifies how long (in seconds) distcc will avoid trying to use a particular compilation server
after that server yields a compile failure. By default set to 60 seconds. To disable the backoff
behavior altogether, set this to 0.

DISTCC_IO_TIMEOUT
Specifies how long (in seconds) distcc will wait before deciding a distributed job has timed out.
If a distributed job is expected to takes a long time, consider increasing this value so the job
does not time out and fallback to a local compile. By default set to 300 seconds.

DISTCC_PAUSE_TIME_MSEC
Specifies how long (in milliseconds) distcc will pause when all compilation servers are in use.
By default set to 1000 milliseconds (1 second). Setting this to a smaller value (e.g. 10
milliconds) may improve throughput for some configurations, at the expense of increased CPU load
on the distcc client machine.

DISTCC_SAVE_TEMPS
If set to 1, temporary files are not deleted after use. Good for debugging, or if your disks are
too empty.

DISTCC_TCP_CORK
If set to 0, disable use of "TCP corks", even if they're present on this system. Using corks
normally helps pack requests into fewer packets and aids performance. This should normally be
left enabled.

DISTCC_SSH
Specifies the command used for opening SSH connections. Defaults to "ssh" but may be set to a
different connection command such as "lsh" or "tsocks-ssh" that accepts a similar command line.
The command is not split into words and is not executed through the shell.

DISTCC_SKIP_LOCAL_RETRY
If set, when a remote compile fails, distcc will no longer try to recompile that file locally.

DISTCC_DIR
Per-user configuration directory to store lock files and state files. By default ~/.distcc/ is
used.

TMPDIR Directory for temporary files such as preprocessor output. By default /tmp/ is used.

UNCACHED_ERR_FD
If set and if DISTCC_LOG is not set, distcc errors are written to the file descriptor identified
by this variable. This variable is intended mainly for automatic use by ccache, which sets it to
avoid caching transient errors such as network problems.

DISTCC_ENABLE_DISCREPANCY_EMAIL
If set, distcc sends an email when a compilation failed remotely, but succeeded locally. Built-in
heuristics prevent some such discrepancy email from being sent if the problem is that a local file
changed between the failing remote compilation and the succeeding local compilation.

DISTCC_MAX_DISCREPANCY
The maximum number of remote compilation failures allowed in pump mode before distcc switches to
plain distcc mode. By default set to 1.

DCC_EMAILLOG_WHOM_TO_BLAME
The email address for discrepancy email; the default is "distcc-pump-errors".

DISTCC_PRINCIPAL
If set, specifies the name of the principal that distccd runs under, and is used to authenticate
the server to the client. This environment variable is only used if distcc was compiled with the
--with-auth configure option and the ,auth per host option is specified.

CROSS COMPILING

       Cross  compilation  means building programs to run on a machine with a different processor, architecture,
       or operating system to where they were compiled.  distcc supports cross compilation, including  teams  of
       mixed-architecture machines, although some changes to the compilation commands may be required.

       The  compilation  command  passed  to  distcc  must  be one that will execute properly on every volunteer
       machine to produce an object file of the appropriate type.  If the machines  have  different  processors,
       then  simply  using  distcc  cc will probably not work, because that will normally invoke the volunteer's
       native compiler.

       Machines with the same CPU but different operating systems may not  necessarily  generate  compatible  .o
       files.

       Several different gcc configurations can be installed side-by-side on any machine.  If you build gcc from
       source, you should use the --program-suffix configuration options to cause it to be installed with a name
       that encodes the gcc version and the target platform.

       The  recommended  convention for the gcc name is TARGET-gcc-VERSION such as i686-linux-gcc-3.2 .  GCC 3.3
       will install itself under this name, in addition to TARGET-gcc and, if it's native, gcc-VERSION and gcc .

       The compiler must be installed under the same name on the client and on every volunteer machine.

BUGS

If you think you have found a distcc bug, please see the file reporting-bugs.txt in the documentation
directory for information on how to report it.

Some makefiles have missing or extra dependencies that cause incorrect or slow parallel builds.
Recursive make is inefficient and can leave processors unnecessarily idle for long periods. (See
Recursive Make Considered Harmful by Peter Miller.) Makefile bugs are the most common cause of trees
failing to build under distcc. Alternatives to Make such as SCons can give much faster builds for some
projects.

Using different versions of gcc can cause confusing build problems because the header files and binary
interfaces have changed over time, and some distributors have included incompatible patches without
changing the version number. distcc does not protect against using incompatible versions. Compiler
errors about link problems or declarations in system header files are usually due to mismatched or
incorrectly installed compilers.

gcc's -MD option can produce output in the wrong directory if the source and object files are in
different directories and the -MF option is not used. There is no perfect solution because of
incompatible changes between gcc versions. Explicitly specifying the dependency output file with -MF
will fix the problem.

TCP mode connections should only be used on trusted networks.

Including slow machines in the list of volunteer hosts can slow the build down.

When distcc or ccache is used on NFS, the filesystem must be exported with the no_subtree_check option to
allow reliable renames between directories.

The compiler can be invoked with a command line gcc hello.c to both compile and link. distcc doesn't
split this into separate parts, but rather runs the whole thing locally.

distcc-pump mode reverts to plain distcc mode for source files that contain includes with absolute paths
(either directly or in an included file).

Due to limitations in gcc, gdb may not be able to automatically find the source files for programs built
using distcc in some circumstances. The gdb directory command can be used. For distcc's plain (non-
pump) mode, this is fixed in gcc 3.4 and later. For pump mode, the fix in gcc 3.4 does not suffice;
we've worked around the gcc limitation by rewriting the object files that gcc produces, but this is only
done for ELF object files, but not for other object file formats.

The .o files produced by discc in pump mode will be different from those produced locally: for non-ELF
files, the debug information will specify compile directories of the server. The code itself should be
identical.

For the ELF-format, distcc rewrites the .o files to correct compile directory path information. While
the resulting .o files are not bytewise identical to what would have been produced by compiling on the
local client (due to different padding, etc), they should be functionally identical.

In distcc-pump mode, the include server is unable to handle certain very complicated computed includes as
found in parts of the Boost library. The include server will time out and distcc will revert to plain
mode.

In distcc-pump mode, certain assumptions are made that source and header files do not change during the
build. See discussion in section DISTCC DISCREPANCY SYMPTOMS of include_server(1().

Other known bugs may be documented on http://code.google.com/p/distcc/

AUTHOR

       distcc was written by Martin Pool <mbp@sourcefrog.net>, with the co-operation of many scholars  including
       Wayne Davison, Frerich Raabe, Dimitri Papadopoulos and others noted in the NEWS file.  Please report bugs
       to <distcc@lists.samba.org>.  See distcc-pump(1) for the authors of pump mode.

LICENCE

       You  are  free to use distcc.  distcc (including this manual) may be copied, modified or distributed only
       under the terms of the GNU General Public Licence version 2 or later.  distcc comes  with  absolutely  no
       warrany.  A copy of the GPL is included in the file COPYING.