make(1)



MAKE(1)                          User Commands                         MAKE(1)

NAME
       make - GNU make utility to maintain groups of programs

SYNOPSIS
       make [OPTION]... [TARGET]...

DESCRIPTION
       The  make  utility will determine automatically which pieces of a large
       program need to be recompiled, and  issue  the  commands  to  recompile
       them.   The  manual describes the GNU implementation of make, which was
       written by Richard Stallman and Roland McGrath, and is currently  main-
       tained  by  Paul  Smith.   Our examples show C programs, since they are
       very common, but you can use make with any programming  language  whose
       compiler can be run with a shell command.  In fact, make is not limited
       to programs.  You can use it to describe any task where some files must
       be updated automatically from others whenever the others change.

       To  prepare to use make, you must write a file called the makefile that
       describes the relationships among files in your program, and the states
       the  commands for updating each file.  In a program, typically the exe-
       cutable file is updated from object files, which are in  turn  made  by
       compiling source files.

       Once  a  suitable  makefile  exists,  each  time you change some source
       files, this simple shell command:

              make

       suffices to perform all necessary  recompilations.   The  make  program
       uses  the  makefile  description and the last-modification times of the
       files to decide which of the files need to be  updated.   For  each  of
       those files, it issues the commands recorded in the makefile.

       make  executes  commands  in  the makefile to update one or more target
       names, where name is typically a program.  If no -f option is  present,
       make  will  look for the makefiles GNUmakefile, makefile, and Makefile,
       in that order.

       Normally you should call your makefile  either  makefile  or  Makefile.
       (We  recommend  Makefile because it appears prominently near the begin-
       ning of a directory listing, right near other important files  such  as
       README.)   The  first name checked, GNUmakefile, is not recommended for
       most makefiles.  You should use this name if you have a  makefile  that
       is  specific  to GNU make, and will not be understood by other versions
       of make.  If makefile is '-', the standard input is read.

       make updates a target if it depends on  prerequisite  files  that  have
       been modified since the target was last modified, or if the target does
       not exist.

OPTIONS
       -b, -m
            These options are ignored for compatibility with other versions of
            make.

       -B, --always-make
            Unconditionally make all targets.

       -C dir, --directory=dir
            Change to directory dir before reading the makefiles or doing any-
            thing else.  If multiple -C options are specified, each is  inter-
            preted  relative to the previous one: -C / -C etc is equivalent to
            -C /etc.  This is typically used  with  recursive  invocations  of
            make.

       -d   Print debugging information in addition to normal processing.  The
            debugging information says which files are  being  considered  for
            remaking,  which  file-times  are  being  compared  and  with what
            results, which files actually need to be  remade,  which  implicit
            rules  are considered and which are applied---everything interest-
            ing about how make decides what to do.

       --debug[=FLAGS]
            Print debugging information in addition to normal processing.   If
            the  FLAGS are omitted, then the behavior is the same as if -d was
            specified.  FLAGS may be a for all debugging output (same as using
            -d),  b for basic debugging, v for more verbose basic debugging, i
            for showing implicit rules, j for details on  invocation  of  com-
            mands,  and  m  for  debugging while remaking makefiles.  Use n to
            disable all previous debugging flags.

       -e, --environment-overrides
            Give variables taken from the environment  precedence  over  vari-
            ables from makefiles.

       -f file, --file=file, --makefile=FILE
            Use file as a makefile.

       -i, --ignore-errors
            Ignore all errors in commands executed to remake files.

       -I dir, --include-dir=dir
            Specifies  a  directory  dir to search for included makefiles.  If
            several -I options are used to specify  several  directories,  the
            directories are searched in the order specified.  Unlike the argu-
            ments to other flags of make, directories given with -I flags  may
            come directly after the flag: -Idir is allowed, as well as -I dir.
            This syntax is allowed for compatibility with the C preprocessor's
            -I flag.

       -j [jobs], --jobs[=jobs]
            Specifies the number of jobs (commands) to run simultaneously.  If
            there is more than one -j option, the last one is  effective.   If
            the  -j  option  is given without an argument, make will not limit
            the number of jobs that can run simultaneously. When make  invokes
            a sub-make, all instances of make will coordinate to run the spec-
            ified number of jobs at a time; see the section PARALLEL MAKE  AND
            THE JOBSERVER for details.

       --jobserver-fds [R,W]
            Internal  option  make  uses  to  pass the jobserver pipe read and
            write file descriptor numbers to sub-makes; see the section PARAL-
            LEL MAKE AND THE JOBSERVER for details

       -k, --keep-going
            Continue  as  much  as  possible after an error.  While the target
            that failed, and those that depend on it, cannot  be  remade,  the
            other dependencies of these targets can be processed all the same.

       -l [load], --load-average[=load]
            Specifies  that  no new jobs (commands) should be started if there
            are others jobs running and the load average is at least  load  (a
            floating-point number).  With no argument, removes a previous load
            limit.

       -L, --check-symlink-times
            Use the latest mtime between symlinks and target.

       -n, --just-print, --dry-run, --recon
            Print the commands that would be executed, but do not execute them
            (except in certain circumstances).

       -o file, --old-file=file, --assume-old=file
            Do not remake the file file even if it is older than its dependen-
            cies, and do not remake anything on account of  changes  in  file.
            Essentially  the  file  is  treated  as very old and its rules are
            ignored.

       -O[type], --output-sync[=type]
            When running multiple jobs in parallel with -j, ensure the  output
            of  each  job  is collected together rather than interspersed with
            output from other jobs.  If type is not specified or is target the
            output from the entire recipe for each target is grouped together.
            If type is line the output from each command line within a  recipe
            is  grouped  together.   If  type is recurse output from an entire
            recursive make is grouped together.  If type is none  output  syn-
            chronization is disabled.

       -p, --print-data-base
            Print  the data base (rules and variable values) that results from
            reading the makefiles; then execute as usual or as otherwise spec-
            ified.   This  also prints the version information given by the -v
            switch (see below).  To print the  data  base  without  trying  to
            remake any files, use make -p -f/dev/null.

       -q, --question
            ``Question  mode''.   Do  not run any commands, or print anything;
            just return an exit status that is zero if the  specified  targets
            are already up to date, nonzero otherwise.

       -r, --no-builtin-rules
            Eliminate  use of the built-in implicit rules.  Also clear out the
            default list of suffixes for suffix rules.

       -R, --no-builtin-variables
            Don't define any built-in variables.

       -s, --silent, --quiet
            Silent operation; do not print the commands as they are executed.

       -S, --no-keep-going, --stop
            Cancel the effect of the  -k  option.   This  is  never  necessary
            except  in  a  recursive make where -k might be inherited from the
            top-level make via MAKEFLAGS or if you set -k in MAKEFLAGS in your
            environment.

       -t, --touch
            Touch  files  (mark  them up to date without really changing them)
            instead of running their commands.  This is used to  pretend  that
            the  commands  were  done,  in order to fool future invocations of
            make.

       --trace
            Information about the disposition of each target is  printed  (why
            the  target  is being rebuilt and what commands are run to rebuild
            it).

       -v, --version
            Print the version of the make program plus a copyright, a list  of
            authors and a notice that there is no warranty.

       -w, --print-directory
            Print  a message containing the working directory before and after
            other processing.  This may be useful  for  tracking  down  errors
            from complicated nests of recursive make commands.

       --no-print-directory
            Turn off -w, even if it was turned on implicitly.

       -W file, --what-if=file, --new-file=file, --assume-new=file
            Pretend  that  the  target file has just been modified.  When used
            with the -n flag, this shows you what would happen if you were  to
            modify  that file.  Without -n, it is almost the same as running a
            touch command on the given file before running make,  except  that
            the modification time is changed only in the imagination of make.

       --warn-undefined-variables
            Warn when an undefined variable is referenced.

EXIT STATUS
       GNU make exits with a status of zero if all makefiles were successfully
       parsed and no targets that were built failed.  A status of one will  be
       returned  if  the  -q  flag  was used and make determines that a target
       needs to be rebuilt.  A status of two will be returned  if  any  errors
       were encountered.

SEE ALSO
       The  full documentation for make is maintained as a Texinfo manual.  If
       the info and make programs are properly installed  at  your  site,  the
       command

              info make

       should give you access to the complete manual.

PARALLEL MAKE AND THE JOBSERVER
       Using  the  -j  option,  the user can instruct make to execute tasks in
       parallel. By specifying a numeric argument to -j the user  may  specify
       an upper limit of the number of parallel tasks to be run.

       When  the  build environment is such that a top level make invokes sub-
       makes (for instance, a style in which each sub-directory  contains  its
       own Makefile ), no individual instance of make knows how many tasks are
       running in parallel, so keeping the number of  tasks  under  the  upper
       limit  would  be  impossible without communication between all the make
       instances running. While solutions like having the top level make serve
       as  a  central  controller are feasible, or using other synchronization
       mechanisms like shared memory or sockets can be  created,  the  current
       implementation uses a simple shared pipe.

       This  pipe  is  created by the top-level make process, and passed on to
       all the sub-makes.  The top level makeprocesswrites N-1 one-byte tokens
       into  the  pipe (The top level make is assumed to reserve one token for
       itself). Whenever any of the make processes  (including  the  top-level
       make  )  needs to run a new task, it reads a byte from the shared pipe.
       If there are no tokens left, it must wait for a  token  to  be  written
       back to the pipe. Once the task is completed, the make process writes a
       token back to the pipe (and thus, if the  tokens  had  been  exhausted,
       unblocking  the  first  make process that was waiting to read a token).
       Since only N-1 tokens were written into the pipe, no more than N  tasks
       can be running at any given time.

       If  the  job  to be run is not a sub-make then make will close the job-
       server pipe file descriptors before invoking the commands, so that  the
       command  can not interfere with the jobserver, and the command does not
       find any unusual file descriptors.

BUGS
       See the chapter ``Problems and Bugs'' in The GNU Make Manual.

AUTHOR
       This manual page contributed by Dennis Morse  of  Stanford  University.
       Further updates contributed by Mike Frysinger.  It has been reworked by
       Roland McGrath.  Maintained by Paul Smith.

COPYRIGHT
       Copyright (C) 1992-1993, 1996-2014 Free Software Foundation, Inc.  This
       file is part of GNU make.

       GNU  Make  is  free  software; you can redistribute it and/or modify it
       under the terms of the GNU General Public License as published  by  the
       Free  Software Foundation; either version 3 of the License, or (at your
       option) any later version.

       GNU Make is distributed in the hope that it will be useful, but WITHOUT
       ANY  WARRANTY;  without even the implied warranty of MERCHANTABILITY or
       FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General  Public  License
       for more details.

       You should have received a copy of the GNU General Public License along
       with this program.  If not, see http://www.gnu.org/licenses/.

GNU                              03 March 2012                         MAKE(1)

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