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
maintained 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
executable 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
beginning 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
anything else. If multiple -C options are specified, each is
interpreted 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
interesting 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
commands, 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
variables 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
arguments 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
specified 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
PARALLEL 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
dependencies, 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
synchronization 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
specified. 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 jobserver 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 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/.
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