Provided by: distcc_3.3.3-1_amd64 bug

NAME

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

SYNOPSIS

       distcc <compiler> [COMPILER OPTIONS]

       distcc [COMPILER OPTIONS]

       <compiler> [COMPILER OPTIONS]

       distcc [DISTCC OPTIONS]

DESCRIPTION

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

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

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

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

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

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

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

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

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

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

QUICKSTART

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

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

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

       4      Build!
              $ make -j8 CC=distcc

QUICKSTART FOR DISTCC-PUMP MODE

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

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

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

              $ distcc-pump make -j20 CC=distcc

QUICKSTART FOR DISTCC-GSSAPI MODE

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

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

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

              export DISTCC_PRINICIPAL=<name>

HOW PLAIN (NON-PUMP) DISTCC WORKS

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

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

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

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

HOW DISTCC-PUMP MODE WORKS

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

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

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

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

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

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

RESTRICTIONS FOR PUMP MODE

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

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

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

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

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

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

HOW DISTCC-GSSAPI MODE WORKS

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

OPTION SUMMARY

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

       --help Displays summary instructions.

       --version
              Displays the distcc client version.

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

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

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

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

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

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

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

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

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

INSTALLING DISTCC

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

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

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

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

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

MASQUERADING

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

       For example:

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

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

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

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

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

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

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

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

USING DISTCC WITH CCACHE

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

       The most reliable method is to set

              CCACHE_PREFIX="distcc"

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

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

              CC="ccache gcc"

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

       distcc's pump mode is not compatible with ccache.

HOST SPECIFICATIONS

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

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

              localhost red green blue

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

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

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

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

       Finally there is the host entry

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

       The syntax is

         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 | auth[=AUTH_NAME]
         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]

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

       IPV4   A literal IPv4 address, such as 10.0.0.1

       HOSTNAME
              A hostname to be looked up using the resolver.

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

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

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

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

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

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

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

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

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

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

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

       Here is an example demonstrating some possibilities:

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

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

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

COMPRESSION

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

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

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

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

SEARCH PATHS

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

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

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

TIMEOUTS

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

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

DIAGNOSTICS

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

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

EXIT CODES

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

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

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

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

       100    General distcc failure.

       101    Bad arguments.

       102    Bind failed.

       103    Connect failed.

       104    Compiler crashed.

       105    Out of memory.

       106    Bad Host SPEC

       107    I/O Error

       108    Truncated.

       109    Protocol Error.

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

       111    Recursive call to distcc.

       112    Failed to discard privileges.

       113    Network access denied.

       114    In use by another process.

       115    No such file.

       116    No hosts defined and fallbacks disabled.

       118    Timeout.

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

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

FILES

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

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

ENVIRONMENT VARIABLES

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

       DISTCC_HOSTS
              Space-separated list of volunteer host specifications.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

CROSS COMPILING

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

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

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

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

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

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

BUGS

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

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

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

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

       TCP mode connections should only be used on trusted networks.

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

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

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

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

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

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

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

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

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

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

AUTHOR

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

LICENCE

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

SEE ALSO

       distccd(1),  distcc-pump(1),   include_server(1),   gcc(1),   make(1),   and    ccache(1).
       http://code.google.com/p/distcc/ https://ccache.dev/

                                           9 June 2008                                  distcc(1)