Ubuntu Manpage: make - GNU make utility to maintain groups of programs

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.

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, 1996-2016 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/.