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/.