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<HTML>
<!-- this file was generated by troffcvt and tc2html -->
<HEAD>
<TITLE>
distcc manual page
</TITLE>
</HEAD>
<BODY>
<H1>
distcc manual page<BR>
</H1>
<P>
<H2>
Table of Contents
</H2>
<!-- INSERT TOC HERE, MAYBE -->
<!-- TOC BEGIN -->
<UL>
<LI>
<A HREF=#TOC_1> NAME</A>
<LI>
<A HREF=#TOC_2> SYNOPSIS</A>
<LI>
<A HREF=#TOC_3> DESCRIPTION</A>
<LI>
<A HREF=#TOC_4> QUICKSTART</A>
<LI>
<A HREF=#TOC_5> QUICKSTART FOR DISTCC-PUMP MODE</A>
<LI>
<A HREF=#TOC_6> QUICKSTART FOR DISTCC-GSSAPI MODE</A>
<LI>
<A HREF=#TOC_7> HOW PLAIN (NON-PUMP) DISTCC WORKS</A>
<LI>
<A HREF=#TOC_8> HOW DISTCC-PUMP MODE WORKS</A>
<LI>
<A HREF=#TOC_9> RESTRICTIONS FOR PUMP MODE</A>
<LI>
<A HREF=#TOC_10> HOW DISTCC-GSSAPI MODE WORKS</A>
<LI>
<A HREF=#TOC_11> OPTION SUMMARY</A>
<LI>
<A HREF=#TOC_12> INSTALLING DISTCC</A>
<LI>
<A HREF=#TOC_13> MASQUERADING</A>
<LI>
<A HREF=#TOC_14> USING DISTCC WITH CCACHE</A>
<LI>
<A HREF=#TOC_15> HOST SPECIFICATIONS</A>
<LI>
<A HREF=#TOC_16> COMPRESSION</A>
<LI>
<A HREF=#TOC_17> SEARCH PATHS</A>
<LI>
<A HREF=#TOC_18> TIMEOUTS</A>
<LI>
<A HREF=#TOC_19> DIAGNOSTICS</A>
<LI>
<A HREF=#TOC_20> EXIT CODES</A>
<LI>
<A HREF=#TOC_21> FILES</A>
<LI>
<A HREF=#TOC_22> ENVIRONMENT VARIABLES</A>
<LI>
<A HREF=#TOC_23> CROSS COMPILING</A>
<LI>
<A HREF=#TOC_24> BUGS</A>
<LI>
<A HREF=#TOC_25> AUTHOR</A>
<LI>
<A HREF=#TOC_26> LICENCE</A>
<LI>
<A HREF=#TOC_27> SEE ALSO</A>
</UL>
<!-- TOC END -->
<BR>
<H2>
<A NAME=TOC_1>
NAME</A>
</H2>
distcc - distributed C/C++/ObjC compiler with distcc-pump extensions<BR>
<H2>
<A NAME=TOC_2>
SYNOPSIS</A>
</H2>
<B>distcc</B> <I> <compiler> [COMPILER OPTIONS]</I><BR>
<P>
<B>distcc</B> <I> [COMPILER OPTIONS]</I><BR>
<P>
<B><compiler></B> <I> [COMPILER OPTIONS]</I><BR>
<P>
<B>distcc</B> <I> [DISTCC OPTIONS]</I><BR>
<H2>
<A NAME=TOC_3>
DESCRIPTION</A>
</H2>
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.<BR>
<P>
This version incorporates plain distcc as well as an enhancement
called pump mode or distcc-pump.<BR>
<P>
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.<BR>
<P>
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 <B> distccd(1)</B>
daemon, C compiler and assembler as required.<BR>
<P>
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 <B> not</B> be listening for connections.<BR>
<P>
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.<BR>
<P>
distcc is intended to be used with GNU Make's <B> -j</B> 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 <B> -j</B> 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.<BR>
<P>
The <B> -j</B> setting, especially for large values of <B> -j,</B>
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 <B> --localslots_cpp</B>
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 <B> -j</B> 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.<BR>
<P>
In contrast, using pump mode and say 40 servers, a setting of
<B>-j80</B> or larger may be appropriate even for single-CPU clients.<BR>
<P>
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.<BR>
<H2>
<A NAME=TOC_4>
QUICKSTART</A>
</H2>
<BR>
<DL>
<DT>
1
</DT>
<DD>
For each machine, download distcc, unpack, and install.<BR>
</DD>
<DT>
2
</DT>
<DD>
On each of the servers, run <B> distccd --daemon</B> with <B>
--allow</B> options to restrict access.<BR>
</DD>
<DT>
3
</DT>
<DD>
Put the names of the servers in your environment:<BR>
</DD>
</DL>
<UL>
$ export DISTCC_HOSTS='localhost red green blue'<BR>
</UL>
<DL>
<DT>
4
</DT>
<DD>
Build!<BR>
</DD>
</DL>
<UL>
$ make -j8 CC=distcc<BR>
</UL>
<H2>
<A NAME=TOC_5>
QUICKSTART FOR DISTCC-PUMP MODE</A>
</H2>
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:<BR>
<UL>
$ export DISTCC_HOSTS='--randomize localhost red,cpp,lzo green,cpp,lzo
blue,cpp,lzo'<BR>
</UL>
The <B> --randomize</B> 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:<BR>
<UL>
$ pump make -j20 CC=distcc<BR>
</UL>
<H2>
<A NAME=TOC_6>
QUICKSTART FOR DISTCC-GSSAPI MODE</A>
</H2>
Proceed as per the <B> QUICKSTART</B> but in Step 3, specify that
the remote hosts are to mutually authenticate with the client:<BR>
<UL>
$ export DISTCC_HOSTS='--randomize localhost red,auth green,auth
blue,auth'<BR>
</UL>
If distccd runs under a specific principal name then execute the
following command prior to step 4:<BR>
<UL>
export DISTCC_PRINICIPAL=<name><BR>
</UL>
<H2>
<A NAME=TOC_7>
HOW PLAIN (NON-PUMP) DISTCC WORKS</A>
</H2>
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.<BR>
<P>
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.<BR>
<P>
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.<BR>
<P>
distcc examines its command line to determine which of these phases
are being invoked, and whether the job can be distributed.<BR>
<H2>
<A NAME=TOC_8>
HOW DISTCC-PUMP MODE WORKS</A>
</H2>
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.<BR>
<P>
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.<BR>
<P>
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 pump command starts the include
server so that throughout the build it can answer include queries
by distcc commands.<BR>
<P>
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).<BR>
<P>
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.<BR>
<P>
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.<BR>
<H2>
<A NAME=TOC_9>
RESTRICTIONS FOR PUMP MODE</A>
</H2>
<BR>
Using pump mode requires both client and servers to use release
3.0 or later of distcc and distccd (respectively).<BR>
<P>
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 <B>include_server(1)</B> man page.<BR>
<P>
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.<BR>
<P>
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.<BR>
<P>
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.<BR>
<P>
See the <B>include_server</B>(1) manual for more information on
symptoms and causes of violations of distcc-pump mode assumptions.<BR>
<H2>
<A NAME=TOC_10>
HOW DISTCC-GSSAPI MODE WORKS</A>
</H2>
<BR>
In this mode distcc will use the GSS-API framework to access the
currently configured security mechanism and perform mutual authentication
with the daemon.<BR>
<H2>
<A NAME=TOC_11>
OPTION SUMMARY</A>
</H2>
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.<BR>
<DL>
<DT>
<B>--help</B>
</DT>
<DD>
Displays summary instructions.<BR>
</DD>
</DL>
<P>
<DL>
<DT>
<B>--version</B>
</DT>
<DD>
Displays the distcc client version.<BR>
</DD>
</DL>
<P>
<DL>
<DT>
<B>--show-hosts</B>
</DT>
<DD>
Displays the host list that distcc would use. See the Host Specifications
section.<BR>
</DD>
</DL>
<P>
<DL>
<DT>
<B>--scan-includes</B>
</DT>
<DD>
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.<BR>
</DD>
</DL>
<UL>
The list output by <B>distcc --scan-includes</B> 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:<BR>
<DL>
<DT>
<BR>
</DT>
<DD>
<B>FILE</B> indicates a source file or header file that would
be sent to the distcc server host.<BR>
</DD>
<DT>
<BR>
</DT>
<DD>
<B>SYMLINK</B> indicates a symbolic link that would be sent to
the distcc server host.<BR>
</DD>
<DT>
<BR>
</DT>
<DD>
<B>DIRECTORY</B> 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.<BR>
</DD>
<DT>
<BR>
</DT>
<DD>
<B>SYSTEMDIR</B> 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.<BR>
</DD>
</DL>
</UL>
<DL>
<DT>
<B>-j</B>
</DT>
<DD>
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.<BR>
</DD>
</DL>
<P>
<DL>
<DT>
<B>--show-principal</B>
</DT>
<DD>
Displays the name of the distccd security principal extracted
from the environment. <B> This option is only available if distcc
was compiled with</B> <B> the --with-auth configure option.</B><BR>
</DD>
</DL>
<H2>
<A NAME=TOC_12>
INSTALLING DISTCC</A>
</H2>
There are three different ways to call distcc, to suit different
circumstances:<BR>
<UL>
<P>
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.<BR>
<P>
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.<BR>
<P>
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.<BR>
</UL>
<P>
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.<BR>
<H2>
<A NAME=TOC_13>
MASQUERADING</A>
</H2>
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.<BR>
<P>
For example:<BR>
<P>
<UL>
# mkdir /usr/lib/distcc/bin<BR>
# cd /usr/lib/distcc/bin<BR>
# ln -s ../../../bin/distcc gcc<BR>
# ln -s ../../../bin/distcc cc<BR>
# ln -s ../../../bin/distcc g++<BR>
# ln -s ../../../bin/distcc c++<BR>
</UL>
<P>
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.<BR>
<P>
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.<BR>
<P>
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.<BR>
<P>
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:<BR>
<P>
<UL>
#!/bin/sh<BR>
distcc /usr/bin/gcc "$@"<BR>
</UL>
<P>
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.<BR>
<H2>
<A NAME=TOC_14>
USING DISTCC WITH CCACHE</A>
</H2>
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.<BR>
<P>
The most reliable method is to set<BR>
<DL>
<DT>
<BR>
</DT>
<DD>
<B>CCACHE_PREFIX="distcc"</B><BR>
</DD>
</DL>
<P>
This tells ccache to run distcc as a wrapper around the real compiler.
ccache still uses the real compiler to detect compiler upgrades.<BR>
<P>
ccache can then be run using either a masquerade directory <I>
or</I> by setting<BR>
<DL>
<DT>
<BR>
</DT>
<DD>
<B>CC="ccache gcc"</B><BR>
</DD>
</DL>
<P>
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.<BR>
distcc's pump mode is not compatible with ccache.<BR>
<H2>
<A NAME=TOC_15>
HOST SPECIFICATIONS</A>
</H2>
A "host list" tells distcc which machines to use for
compilation. In order, distcc looks in the <B> $DISTCC_HOSTS</B>
environment variable, the user's <B> $DISTCC_DIR/hosts</B> file,
and the system-wide host file. If no host list can be found,
distcc emits a warning and compiles locally.<BR>
<P>
The host list is a simple whitespace separated list of host specifications.
The simplest and most common form is a host names, such as<BR>
<P>
<UL>
<B>localhost red green blue</B><BR>
</UL>
<P>
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 <I> --randomize</I>
below).<BR>
<P>
Placing <I> localhost</I> 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.<BR>
<P>
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 <I> --randomize</I> into the host list. This will
cause the host list to be randomized, which should improve performance
slightly for large build clusters.<BR>
<P>
There are two special host names <B> --localslots</B> and <B>
--localslots_cpp</B> which are useful for adjusting load on the
local machine. The <B> --localslots</B> host specifies how many
jobs that cannot be run remotely that can be run concurrently
on the local machine, while <B> --localslots_cpp</B> 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 machanism for measuring local
resource usage.<BR>
<P>
Finally there is the host entry<BR>
<P>
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 <B> -j</B> factor
may improve performance.<BR>
<P>
The syntax is<BR>
<P>
DISTCC_HOSTS = HOSTSPEC ...<BR>
HOSTSPEC = LOCAL_HOST | SSH_HOST | TCP_HOST | OLDSTYLE_TCP_HOST<BR>
| GLOBAL_OPTION<BR>
| ZEROCONF<BR>
LOCAL_HOST = localhost[/LIMIT]<BR>
| --localslots=<int><BR>
| --localslots_cpp=<int><BR>
SSH_HOST = [USER]@HOSTID[/LIMIT][:COMMAND][OPTIONS]<BR>
TCP_HOST = HOSTID[:PORT][/LIMIT][OPTIONS]<BR>
OLDSTYLE_TCP_HOST = HOSTID[/LIMIT][:PORT][OPTIONS]<BR>
HOSTID = HOSTNAME | IPV4 | IPV6<BR>
OPTIONS = ,OPTION[OPTIONS]<BR>
OPTION = lzo | cpp | auth<BR>
GLOBAL_OPTION = --randomize<BR>
ZEROCONF = +zeroconf<BR>
<P>
Here are some individual examples of the syntax:<BR>
<DL>
<DT>
<B>localhost</B>
</DT>
<DD>
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.)<BR>
</DD>
<DT>
<B>IPV6</B>
</DT>
<DD>
A literal IPv6 address enclosed in square brackets, such as <B>
[::1]</B><BR>
</DD>
<DT>
<B>IPV4</B>
</DT>
<DD>
A literal IPv4 address, such as <B> 10.0.0.1</B><BR>
</DD>
<DT>
<B>HOSTNAME</B>
</DT>
<DD>
A hostname to be looked up using the resolver.<BR>
</DD>
<DT>
<B>:PORT</B>
</DT>
<DD>
Connect to a specified decimal port number, rather than the default
of 3632.<BR>
</DD>
<DT>
<B>@HOSTID</B>
</DT>
<DD>
Connect to the host over SSH, rather than TCP. Options for the
SSH connection can be set in <B> ~/.ssh/config</B><BR>
</DD>
<DT>
<B>USER@</B>
</DT>
<DD>
Connect to the host over SSH as a specified username.<BR>
</DD>
<DT>
<B>:COMMAND</B>
</DT>
<DD>
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.<BR>
</DD>
<DT>
<B>/LIMIT</B>
</DT>
<DD>
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.<BR>
</DD>
<DT>
<B>,lzo</B>
</DT>
<DD>
Enables LZO compression for this TCP or SSH host.<BR>
</DD>
<DT>
<B>,cpp</B>
</DT>
<DD>
Enables distcc-pump mode for this host. Note: the build command
must be wrapped in the pump script in order to start the include
server.<BR>
</DD>
<DT>
<B>,auth</B>
</DT>
<DD>
Enables GSSAPI-based mutual authentication for this host.<BR>
</DD>
<DT>
<B>--randomize</B>
</DT>
<DD>
Randomize the order of the host list before execution.<BR>
</DD>
<DT>
<B>+zeroconf</B>
</DT>
<DD>
<B>This option is only available if distcc was compiled with Avahi
support enabled at configure time.</B> 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.<BR>
</DD>
</DL>
<P>
Here is an example demonstrating some possibilities:<BR>
<P>
<UL>
<B> localhost/2 @bigman/16:/opt/bin/distccd oldmachine:4200/1</B><BR>
<B> # cartman is down</B><BR>
<B> distant/3,lzo</B><BR>
</UL>
<P>
Comments are allowed in host specifications. Comments start with
a hash/pound sign (<B>#</B>) and run to the end of the line.<BR>
<P>
If a host in the list is not reachable distcc will emit a warning
and ignore that host for about one minute.<BR>
<H2>
<A NAME=TOC_16>
COMPRESSION</A>
</H2>
The <B> lzo</B> 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.<BR>
<P>
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.<BR>
<P>
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.<BR>
<P>
Pump mode requires the servers to have the lzo host option on.<BR>
<H2>
<A NAME=TOC_17>
SEARCH PATHS</A>
</H2>
<BR>
<P>
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:<BR>
<P>
<UL>
<B>distcc /usr/local/bin/gcc-3.1415 -c hello.c</B><BR>
</UL>
<P>
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.<BR>
<H2>
<A NAME=TOC_18>
TIMEOUTS</A>
</H2>
<BR>
<P>
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.<BR>
<P>
The timeouts are not configurable at present.<BR>
<H2>
<A NAME=TOC_19>
DIAGNOSTICS</A>
</H2>
Error messages or warnings from local or remote compilers are
passed through to diagnostic output on the client.<BR>
<P>
distcc can supply extensive debugging information when the verbose
option is used. This is controlled by the <B> DISTCC_VERBOSE</B>
environment variable on the client, and the <B> --verbose</B>
option on the server. For troubleshooting, examine both the client
and server error messages.<BR>
<H2>
<A NAME=TOC_20>
EXIT CODES</A>
</H2>
The exit code of distcc is normally that of the compiler: zero
for successful compilation and non-zero otherwise.<BR>
<P>
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.<BR>
<P>
If the compiler exits with a signal, distcc returns an exit code
of 128 plus the signal number.<BR>
<P>
distcc internal errors cause an exit code between 100 and 127.
In particular<BR>
<DL>
<DT>
100
</DT>
<DD>
General distcc failure.<BR>
</DD>
<DT>
101
</DT>
<DD>
Bad arguments.<BR>
</DD>
<DT>
102
</DT>
<DD>
Bind failed.<BR>
</DD>
<DT>
103
</DT>
<DD>
Connect failed.<BR>
</DD>
<DT>
104
</DT>
<DD>
Compiler crashed.<BR>
</DD>
<DT>
105
</DT>
<DD>
Out of memory.<BR>
</DD>
<DT>
106
</DT>
<DD>
Bad Host SPEC<BR>
</DD>
<DT>
107
</DT>
<DD>
I/O Error<BR>
</DD>
<DT>
108
</DT>
<DD>
Truncated.<BR>
</DD>
<DT>
109
</DT>
<DD>
Protocol Error.<BR>
</DD>
<DT>
110
</DT>
<DD>
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.<BR>
</DD>
<DT>
111
</DT>
<DD>
Recursive call to distcc.<BR>
</DD>
<DT>
112
</DT>
<DD>
Failed to discard privileges.<BR>
</DD>
<DT>
113
</DT>
<DD>
Network access denied.<BR>
</DD>
<DT>
114
</DT>
<DD>
In use by another process.<BR>
</DD>
<DT>
115
</DT>
<DD>
No such file.<BR>
</DD>
<DT>
116
</DT>
<DD>
No hosts defined and fallbacks disabled.<BR>
</DD>
<DT>
118
</DT>
<DD>
Timeout.<BR>
</DD>
<DT>
119
</DT>
<DD>
GSS-API - Catchall error code for GSS-API related errors.<BR>
</DD>
</DL>
<H2>
<A NAME=TOC_21>
FILES</A>
</H2>
If $DISTCC_HOSTS is not set, distcc reads a host list from either
<B>$DISTCC_DIR/hosts</B> or a system-wide configuration file set
at compile time. The file locations are shown in the output from
<B>distcc --help</B><BR>
<P>
distcc creates a number of temporary and lock files underneath
the temporary directory.<BR>
<H2>
<A NAME=TOC_22>
ENVIRONMENT VARIABLES</A>
</H2>
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.<BR>
<DL>
<DT>
<B>DISTCC_HOSTS</B>
</DT>
<DD>
Space-separated list of volunteer host specifications.<BR>
</DD>
<DT>
<B>DISTCC_VERBOSE</B>
</DT>
<DD>
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.<BR>
</DD>
<DT>
<B>DISTCC_LOG</B>
</DT>
<DD>
Log file to receive messages from distcc itself, rather than stderr.<BR>
</DD>
<DT>
<B>DISTCC_FALLBACK</B>
</DT>
<DD>
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.<BR>
</DD>
<DT>
<B>DISTCC_IO_TIMEOUT</B>
</DT>
<DD>
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.<BR>
</DD>
<DT>
<B>DISTCC_SAVE_TEMPS</B>
</DT>
<DD>
If set to 1, temporary files are not deleted after use. Good
for debugging, or if your disks are too empty.<BR>
</DD>
<DT>
<B>DISTCC_TCP_CORK</B>
</DT>
<DD>
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.<BR>
</DD>
<DT>
<B>DISTCC_SSH</B>
</DT>
<DD>
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.<BR>
</DD>
<DT>
<B>DISTCC_SKIP_LOCAL_RETRY</B>
</DT>
<DD>
If set, when a remote compile fails, distcc will no longer try
to recompile that file locally.<BR>
</DD>
<DT>
<B>DISTCC_DIR</B>
</DT>
<DD>
Per-user configuration directory to store lock files and state
files. By default <B> ~/.distcc/</B> is used.<BR>
</DD>
<DT>
<B>TMPDIR</B>
</DT>
<DD>
Directory for temporary files such as preprocessor output. By
default /tmp/ is used.<BR>
</DD>
<DT>
<B>UNCACHED_ERR_FD</B>
</DT>
<DD>
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.<BR>
</DD>
<DT>
<B>DISTCC_ENABLE_DISCREPANCY_EMAIL</B>
</DT>
<DD>
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.<BR>
</DD>
<DT>
<B>DISTCC_MAX_DISCREPANCY</B>
</DT>
<DD>
The maximum number of remote compilation failures allowed in pump
mode before distcc switches to plain distcc mode. By default set
to 1.<BR>
</DD>
<DT>
<B>DCC_EMAILLOG_WHOM_TO_BLAME</B>
</DT>
<DD>
The email address for discrepancy email; the default is "distcc-pump-errors".<BR>
</DD>
<DT>
<B>DISTCC_PRINCIPAL</B>
</DT>
<DD>
If set, specifies the name of the principal that distccd runs
under, and is used to authenticate the server to the client. <B>
This environment variable is only used if distcc was compiled
with</B> <B> the --with-auth configure option and the ,auth per
host option is specified.</B><BR>
</DD>
</DL>
<H2>
<A NAME=TOC_23>
CROSS COMPILING</A>
</H2>
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.<BR>
<P>
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 <B> distcc cc</B> will probably
not work, because that will normally invoke the volunteer's native
compiler.<BR>
<P>
Machines with the same CPU but different operating systems may
not necessarily generate compatible .o files.<BR>
<P>
Several different gcc configurations can be installed side-by-side
on any machine. If you build gcc from source, you should use
the <B> --program-suffix configuration</B> options to cause it
to be installed with a name that encodes the gcc version and the
target platform.<BR>
<P>
The recommended convention for the gcc name is <I> TARGET-gcc-VERSION</I>
such as <B> i686-linux-gcc-3.2</B> . GCC 3.3 will install itself
under this name, in addition to <I> TARGET-gcc</I> and, if it's
native, <I> gcc-VERSION</I> and <I> gcc</I> .<BR>
<P>
The compiler must be installed under the same name on the client
and on every volunteer machine.<BR>
<H2>
<A NAME=TOC_24>
BUGS</A>
</H2>
If you think you have found a distcc bug, please see the file
<I>reporting-bugs.txt</I> in the documentation directory for information
on how to report it.<BR>
<P>
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 <I>
Recursive Make Considered Harmful</I> by Peter Miller.) Makefile
bugs are the most common cause of trees failing to build under
distcc. Alternatives to Make such as <I> SCons</I> can give much
faster builds for some projects.<BR>
<P>
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.<BR>
<P>
gcc's <B> -MD</B> option can produce output in the wrong directory
if the source and object files are in different directories and
the <B> -MF</B> option is not used. There is no perfect solution
because of incompatible changes between gcc versions. Explicitly
specifying the dependency output file with <B> -MF</B> will fix
the problem.<BR>
<P>
TCP mode connections should only be used on trusted networks.<BR>
<P>
Including slow machines in the list of volunteer hosts can slow
the build down.<BR>
<P>
When distcc or ccache is used on NFS, the filesystem must be exported
with the <B> no_subtree_check</B> option to allow reliable renames
between directories.<BR>
<P>
The compiler can be invoked with a command line <B> gcc hello.c</B>
to both compile and link. distcc doesn't split this into separate
parts, but rather runs the whole thing locally.<BR>
<P>
distcc-pump mode reverts to plain distcc mode for source files
that contain includes with absolute paths (either directly or
in an included file).<BR>
<P>
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 <B> directory</B> 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.<BR>
<P>
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.<BR>
<P>
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.<BR>
<P>
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.<BR>
<P>
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 <B>include_server</B>(1().<BR>
Other known bugs may be documented on <I> http://code.google.com/p/distcc/</I><BR>
<H2>
<A NAME=TOC_25>
AUTHOR</A>
</H2>
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 <B>pump</B>(1) for the authors of pump mode.<BR>
<H2>
<A NAME=TOC_26>
LICENCE</A>
</H2>
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.<BR>
<H2>
<A NAME=TOC_27>
SEE ALSO</A>
</H2>
<B>distccd</B>(1), <B>pump</B>(1), <B>include_server</B>(1), <B>gcc</B>(1),
<B>make</B>(1), and <B>ccache</B>(1). <I> http://code.google.com/p/distcc/</I>
<I>http://ccache.samba.org/</I><BR>
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