Section: User Commands (1)
Updated: 9 June 2008
include_server.py - conservative approximation of include dependencies for C/C++
include_server.py starts an include server process. This process answers
clients about what files to include in C/C++ compilations. The include_server.py
command itself terminates as soon as the include server has been spawned.
The INCLUDE_SERVER_PORT argument is the name of a socket used for all
communication between distcc clients and the include server. The pump(1)
command is responsible for creating the socket location, for passing it to this
script, and for passing it to all distcc clients via the environment variable
The protocol used by the include server uses distcc's RPC implementation. Each
distcc request consists of (1) the current directory and (2) the list of
arguments of the compilation command.
If the include server is able to process the request, then it answers the distcc
client by sending a list of filepaths. The filepaths are those of the
compressed source and header files found to be necessary for compilation through
include analysis. The list also comprises symbolic links and even dummy files
needed for the compilation server to construct an accurate replica of the parts of
the filesystem needed for compilation. In this way, a needed header file like
/path/foo.h is compressed, renamed, and stored in a temporary location, such as
/dev/shm/tmpiAvfGv.include_server-9368-1/path/foo.h.lzo. The distcc client will
pass these files on to a compilation server, where they will be uncompressed and
If the include server is not able to process the request, then it returns the
empty list to the distcc client.
There are two kinds of failures that relate to the include server. The include
server may fail to compute the includes or fail in other ways, see section
INCLUDE SERVER SYMPTOMS. Also, the compilation on the remove server may
fail due to inadequacy of the calculated include closure, but then succeed when
locally retried, see section DISTCC DISCREPANCY SYMPTOMS.
The following options are understood by include_server.py.
- -dPAT, --debug_pattern=PAT
Bit vector for turning on warnings and debugging
1 = warnings
2 = trace some functions
other powers of two: see include_server/basics.py.
- -e, --email
Send email to 'distcc-pump-errors' or if defined, the value of environment
variable DISTCC_EMAILLOG_WHOM_TO_BLAME, when include server gets in trouble.
The default is to not send email.
- --email_bound NUMBER
Maximal number of emails to send (in addition to a final email). Default: 3.
Do not send email. This is the default.
Issue warning message whenever a filename is resolved to a realpath that is
matched by RE, which is a regular expression in Python syntax. This is useful
for finding out where files included actually come from. Use RE="" to find them
all. Note: warnings must be enabled with at least -d1.
- --pid_file FILEPATH
The pid of the include server is written to file FILEPATH. This allows a script
such a pump to tear down the include server.
- -s, --statistics
Print information to stdout about include analysis.
Flush stat caches when the timestamp of any filepath in LIST changes or the
filepath comes in or out of existence. LIST is a colon separated string of
filepaths, possibly containing simple globs (as allowed by Python's glob
module). Print a warning whenever such a change happens (if warnings are
enabled). This option allows limited exceptions to distcc_pump's normal
assumption that source files are not modified during the build.
- -t, --time
Print elapsed, user, and system time to stderr.
Do preprocessing on the compilation server even if includes of absolute
filepaths are encountered. Normally the include-server will fall back on local
preprocessing if it detects any absolute includes. Thus, this flag is useful
for preventing such fallbacks when the absolute includes are a false alarm,
either because the absolute include is discarded during preprocessing or because
the absolutely included file exists on the compilation servers.
More precisely, with --unsafe_absolute_includes absolute includes are ignored
for the purposes of gathering the include closure. Using this option may lead
to incorrect results because (1) the header may actually be included on the
compilation server and it may not be the same as on the client, (2) the include
directives of the header are not further analyzed.
The option is useful for compiling code that has such hardcoded absolute
locations of header files inside conditional directives (e.g. "#ifdef") that
render the includes irrelevant. More precisely, these includes must be
eliminated during preprocessing for the actual configuration. Then the question
of existence of the header file is moot and the remote compilation is sound.
This is often the case if such includes are meant for unusual configurations
different from the actual configuration.
Do not force the creation of all directories used
in an include path. May improve performance for
some cases, but will break builds which use
include structures like "<foo/../file.h>" without
including other files in foo/.
- -v, --verify
Verify that files in CPP closure are contained in
closure calculated by include processor.
- -w, --write_include_closure
Write a .d_approx file which lists all the included files calculated by the
include server; with -x, additionally write the included files as calculated by
CPP to a .d_exact file.
- -x, --exact_analysis
Use CPP instead, do not omit system headers files.
INCLUDE SERVER SYMPTOMS AND ISSUES
The most likely messages and warnings to come from the include processor are
- Preprocessing locally. Include server not covering: Couldn't determine default system include directories
To determine the default system header directories, the include server runs the
compiler once for each language needed during its session. This message
indicates that the compiler specified to distcc is not present on the client.
- Preprocessing locally. Include server not covering: Bailing out because include server spent more than ...s user time handling request
In uncommon situations, the include server fails to analyze very complicated
macro expressions. The distcc client will use plain distcc mode.
- Warning: Filepath must be relative but isn't
The include server does not accept absolute filepaths, such as
/usr/include/stdio.h, in include directives, because there is no guarantee that
this header on the compilation server machine will be the same as that on the
client. The include server gives up analyzing the include closure. The distcc
client cannot use pump-mode.
To overcome this problem in a not always reliable way, set the environment
variable INCLUDE_SERVER_ARGS='--unsafe_absolute_includes' when invoking the pump
script to pass the --unsafe_absolute_includes option to the include server.
- Warning: Absolute filepath ... was IGNORED
The --unsafe_absolute_includes is in use. This situation happens under the same
circumstances as when "Filepath must be relative but isn't" is issued, but in
this case the include will provide an answer to the distcc client.
- Warning: Path '/PATH/FILE' changed/came into existence/no longer exists
These warnings are issued when using stat reset triggers. Because /PATH/FILE
changed, the include server clears its caches; the new version of the file (or
the lack of it) renders the include analysis invalid. This message can usually
be ignored; it does signify a somewhat precarious use of files by the build
system. It is recommended to fix the build system so that files are not
- Warning: For translation unit ..., lookup of file ... resolved to ... whose realpath is ...
This warning occurs with --path_observation_re when a new realpath matching
a source or header file is observed.
DISTCC DISCREPANCY SYMPTOMS
The interactions between the build system, distcc, and the include server is
somewhat complex. When a distcc commands receives a failing compilation from the
remote server it retries the compilation locally. This section discusses the
causes of discrepancies between remote and local compilation. These are flagged
by the demotion message:
__________Warning: ... pump-mode compilation(s) failed on server,
but succeeded locally.
__________Distcc-pump was demoted to plain mode.
See the Distcc Discrepancy Symptoms section in the include_server(1) man
The pump script issues this message at the end of the build. This means that for
at least one distcc invocation a local compilation succeeded after the remote
compilation failed. Each distcc invocation for which such a discrepancy occurred
in turn also issues a message such as:
Warning: remote compilation of '...' failed,
retried locally and got a different result.
The demotion makes subsequent distcc invocations use plain distcc mode. Thus
preprocessing will take place on the local machine for the remainder of the
build. This technique prevents very slow builds where all compilations end up
on the local machine after failing remotely.
Of course, if the local compilations fails after the remote failures, then the
distcc invocation exits with the non-zero status of the local compilation. The
error messages printed are also those of the local compilation.
The fallback behavior for distcc-pump mode to local compilation can be disabled
by setting the environment variable DISTCC_FALLBACK to 0, which makes the distcc
command fail as soon as the remote compilation has failed. This setting is very
useful for debugging why the remote compilation went wrong, because now the
output from the server will be printed.
Next we discuss the possible causes of discrepancies.
- The user changed a source or header file during the build.
This yields inconsistent results of course.
- A source or header file changed during the build.
The build system rewrites a file. For Linux kernel 2.6, this happens
for 'include/linux/compile.h' and 'include/asm/asm-offsets.h'. This condition is
fixed by letting the include server know that it must reset its caches when a
stat of any of the files changes. Practically, this is done by gathering the
files in a colon-separated list and then setting the INCLUDE_SERVER_ARGS
environment variable when invoking the pump script, so that it passes
option; for example,
- A header file is potentially included, but does not exist, and is then later included.
This occurs when some header foo.h includes another header file trick.h, but the
trick.h file has not yet been generated and the inclusion is actually ignored
because of preprocessing directives. The include server will probe for the
existence of trick.h, because it overapproximates all possible ways directives
actually evaluate. The file trick.h is determined not to exist. If it is later
generated, and then really included, then the include server will falsely
believe that the file still does not exist. The solution to this problem is to
make the build system generate trick.h before the first time any header file
is included that makes a syntactic reference to trick.h
- The include server was started with --unsafe_absolute_includes.
This is a problem if there are header files locally that do not exist remotely
and that are actually used. Such includes are often protected by conditional
directives that evaluate so that are actually used on only specific and often
uncommon platforms. If you are not compiling for such a platform, then it may be
correct to use --unsafe_absolute_include.
- The include server has calculated the wrong includes.
We do not know of such a situation.
The exit code of include_server.py is usually 0. That the include server has
been started properly is communicated through the existence of the pid_file.
The email address to use for include server automated emails. The default
is 'distcc-pump-errors' (which is an email address that probably will not
exist in your domain).
Additionally, the invocation of the compiler may use additional environment
If you think you have found a distcc bug, please see the file
in the documentation directory for information on how to report it.
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.
Other known bugs may be documented on
The include server was written by Nils Klarlund, with assistance from Fergus
Henderson, Manos Renieris, and Craig Silverstein. Please report bugs to
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
(1), and gcc