distcc(1)distcc(1)NAMEdistcc - distributed C/C++/ObjC compiler with distcc-pump extensions
SYNOPSISdistcc <compiler> [COMPILER OPTIONS]
distcc [COMPILER OPTIONS]
<compiler> [COMPILER OPTIONS]
distcc [DISTCC OPTIONS]
DESCRIPTIONdistcc 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 vol‐
unteers must run the distccd(1) daemon either directly or from inetd.
For SSH connections distccd must be installed but should not be listen‐
ing 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 typically 25% slower because of processor overhead for
encryption, although this can vary greatly depending on CPUs, network
and the program being built.
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 distrib‐
ute 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 inter‐
leaving 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 16.
This limits the number of concurrent processes that do preprocessing in
plain distcc (non-pump) mode. Therefore, larger -j values than 16 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 net‐
work 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
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 simi‐
larly needs to examine libraries and object files, and so must run
locally.
The compiler and assembler take only a single input file (the prepro‐
cessed source) and produce a single output (the object file). distcc
ships these two files across the network and can therefore run the com‐
piler/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 prop‐
erty 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 com‐
pared 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 funda‐
mental 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.
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 conserva‐
tive (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 com‐
puted.
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.
INSTALLING DISTCC
There are three different ways to call distcc, to suit different cir‐
cumstances:
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.
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 com‐
piler. This can indicate that you have two masquerade directories on
the PATH, possibly because of having two distcc installations in dif‐
ferent locations. It can also indicate that you're trying to mix "mas‐
queraded" 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 con‐
tains:
#!/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 set‐
ting
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 specifica‐
tions. 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 get‐
ting 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 --random‐
ize into the host list. This will cause the host list to be random‐
ized, which should improve performance slightly for large build clus‐
ters.
There are two special host names --localslots and --localslots_cpp
which are useful for adjusting load on the local machine. The --local‐
slots host specifies how many jobs that cannot be run remotely that can
be run concurrently on the local machine, while --localslots_cpp con‐
trols 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 can‐
not 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 machanism 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 perfor‐
mance.
The syntax is
DISTCC_HOSTS = HOSTSPEC ...
HOSTSPEC = LOCAL_HOST | SSH_HOST | TCP_HOST | OLDSTYLE_TCP_HOST
| GLOBAL_OPTION
| ZEROCONF
LOCAL_HOST = localhost[/LIMIT]
| --localslots=<int>
| --localslots_cpp=<int>
SSH_HOST = [USER]@HOSTID[/LIMIT][:COMMAND][OPTIONS]
TCP_HOST = HOSTID[:PORT][/LIMIT][OPTIONS]
OLDSTYLE_TCP_HOST = HOSTID[/LIMIT][:PORT][OPTIONS]
HOSTID = HOSTNAME | IPV4 | IPV6
OPTIONS = ,OPTION[OPTIONS]
OPTION = lzo | cpp
GLOBAL_OPTION = --randomize
ZEROCONF = +zeroconf
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: com‐
mand 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 local‐
host), but may be further restricted by the server. You should
only need to increase this for servers with more than two pro‐
cessors.
,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.
--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 explic‐
itly 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 timeouts are not configurable at present.
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 suc‐
cessful 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 con‐
necting 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 par‐
ticular
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.
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 tem‐
porary 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 stan‐
dard 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_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 com‐
mand such as "lsh" or "tsocks-ssh" that accepts a similar com‐
mand line. The command is not split into words and is not exe‐
cuted through the shell.
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 vari‐
able 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.
DCC_EMAILLOG_WHOM_TO_BLAME
The email address for discrepancy email; the default is "distcc-
pump-errors".
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 sim‐
ply 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 nec‐
essarily 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 --pro‐
gram-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 report‐
ing-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 chang‐
ing the version number. distcc does not protect against using incom‐
patible 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 byte‐
wise identical to what would have been produced by compiling on the
local client (due to different padding, etc), they should be function‐
ally 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/
AUTHORdistcc was written by Martin Pool <mbp@sourcefrog.net>, with the co-
operation of many scholars including Wayne Davison, Frerich Raabe, Dim‐
itri 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.
SEE ALSOdistccd(1), distcc-pump(1), include_server(1), gcc(1), make(1), and
ccache(1). http://code.google.com/p/distcc/ http://ccache.samba.org/
9 June 2008 distcc(1)
