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distcc(1)                                                            distcc(1)




NAME

       distcc - distributed C/C++/ObjC compiler


SYNOPSIS

       distcc <compiler> [COMPILER OPTIONS]

       distcc [COMPILER OPTIONS]

       <compiler> [COMPILER 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,  is simple to install and use, and is often much faster than a
       local compile.

       distcc sends the complete preprocessed source code and  compiler  argu-
       ments  across  the network for each job, so the machines do not need to
       share a filesystem, have the same headers or  libraries  installed,  or
       have synchronized clocks.

       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, the linker, and other stages
       of the build process.  Any number  of  "volunteer"  machines  help  the
       client  to  build the program, by running the distccd(1) daemon, C com-
       piler 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.  The -j value should normally be set  to
       about twice the total number of available CPUs, to allow for some tasks
       being blocked waiting for disk or network IO.   distcc  can  also  work
       with other build control tools such as SCons.

       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 optionally 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


HOW IT WORKS

       distcc only ever runs the compiler and assembler  remotely.   The  pre-
       processor  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  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.


OPTION SUMMARY

       Most options passed to distcc are interpreted as compiler options.  Two
       options are understood by distcc itself:

       --help Displays summary instructions.

       --version
              Displays the distcc client version.


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.


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.


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.

       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.

       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
         LOCAL_HOST = localhost[/LIMIT]
         SSH_HOST = [USER]@HOSTID[/LIMIT][:COMMAND][OPTIONS]
         TCP_HOST = HOSTID[:PORT][/LIMIT][OPTIONS]
         OLDSTYLE_TCP_HOST = HOSTID[/LIMIT][:PORT][OPTIONS]
         HOSTID = HOSTNAME | IPV4
         OPTIONS = ,OPTION[OPTIONS]
         OPTION = lzo

       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.)

       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.

       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 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.


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.

       105    Out of memory.

       110    Compiler not found.

       111    Recursive call to distcc.

       116    No hosts defined and fallbacks disabled.

       (Others are listed in exitcode.h.)


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 /var/tmp/distcc.{UID}/ is used.

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


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.

       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.  This should be fixed in gcc
       3.4.

       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.

       Other known bugs may be documented on http://distcc.samba.org/


AUTHOR

       distcc  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>.


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 ALSO

       distccd(1),   ccache(1),   gcc(1),   make(1)   http://distcc.samba.org/
       http://ccache.samba.org/



                                 28 July 2004                        distcc(1)

Mac OS X 10.7 - Generated Fri Nov 4 06:15:37 CDT 2011
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