make-dfsg/make.1

.TH MAKE 1 "28 February 2016" "GNU" "User Commands"
.SH NAME
make \- GNU make utility to maintain groups of programs
.SH SYNOPSIS
.B make
[\fIOPTION\fR]... [\fITARGET\fR]...
.SH DESCRIPTION
.LP
The
.I 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
.BR 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
.B make
with any programming language whose compiler can be run with a shell command.
In fact,
.B 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.
.LP
To prepare to use
.BR make ,
you must write a file called the
.I 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.
.LP
Once a suitable makefile exists, each time you change some source files,
this simple shell command:
.sp 1
.RS
.B make
.RE
.sp 1
suffices to perform all necessary recompilations.
The
.B 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.
.LP
.B make
executes commands in the
.I makefile
to update one or more target
.IR names ,
where
.I name
is typically a program.
If no
.B \-f
option is present,
.B make
will look for the makefiles
.IR GNUmakefile ,
.IR makefile ,
and
.IR Makefile ,
in that order.
.LP
Normally you should call your makefile either
.I makefile
or
.IR Makefile .
(We recommend
.I Makefile
because it appears prominently near the beginning of a directory
listing, right near other important files such as
.IR  README .)
The first name checked,
.IR GNUmakefile ,
is not recommended for most makefiles.  You should use this name if you have a
makefile that is specific to GNU
.BR make ,
and will not be understood by other versions of
.BR make .
If
.I makefile
is '\-', the standard input is read.
.LP
.B 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.
.SH OPTIONS
.sp 1
.TP 0.5i
\fB\-b\fR, \fB\-m\fR
These options are ignored for compatibility with other versions of
.BR make .
.TP 0.5i
\fB\-B\fR, \fB\-\-always\-make\fR
Unconditionally make all targets.
.TP 0.5i
\fB\-C\fR \fIdir\fR, \fB\-\-directory\fR=\fIdir\fR
Change to directory
.I dir
before reading the makefiles or doing anything else.
If multiple
.B \-C
options are specified, each is interpreted relative to the
previous one:
.BR "\-C " /
.BR "\-C " etc
is equivalent to
.BR "\-C " /etc.
This is typically used with recursive invocations of
.BR make .
.TP 0.5i
.B \-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
.B make
decides what to do.
.TP 0.5i
.BI \-\-debug "[=FLAGS]"
Print debugging information in addition to normal processing.
If the
.I FLAGS
are omitted, then the behavior is the same as if
.B \-d
was specified.
.I FLAGS
may be
.I a
for all debugging output (same as using
.BR \-d ),
.I b
for basic debugging,
.I v
for more verbose basic debugging,
.I i
for showing implicit rules,
.I j
for details on invocation of commands, and
.I m
for debugging while remaking makefiles.  Use
.I n
to disable all previous debugging flags.
.TP 0.5i
\fB\-e\fR, \fB\-\-environment\-overrides\fR
Give variables taken from the environment precedence
over variables from makefiles.
.TP 0.5i
\fB\-f\fR \fIfile\fR, \fB\-\-file\fR=\fIfile\fR, \fB\-\-makefile\fR=\fIFILE\fR
Use
.I file
as a makefile.
.TP 0.5i
\fB\-i\fR, \fB\-\-ignore\-errors\fR
Ignore all errors in commands executed to remake files.
.TP 0.5i
\fB\-I\fR \fIdir\fR, \fB\-\-include\-dir\fR=\fIdir\fR
Specifies a directory
.I dir
to search for included makefiles.
If several
.B \-I
options are used to specify several directories, the directories are
searched in the order specified.
Unlike the arguments to other flags of
.BR make ,
directories given with
.B \-I
flags may come directly after the flag:
.BI \-I dir
is allowed, as well as
.B \-I
.IR dir .
This syntax is allowed for compatibility with the C
preprocessor's
.B \-I
flag.
.TP 0.5i
\fB\-j\fR [\fIjobs\fR], \fB\-\-jobs\fR[=\fIjobs\fR]
Specifies the number of
.I jobs
(commands) to run simultaneously.
If there is more than one
.B \-j
option, the last one is effective.
If the
.B \-j
option is given without an argument,
.BR make
will not limit the number of jobs that can run simultaneously. When
.BR make
invokes a
.BR sub-make,
all instances of make will coordinate to run the specified number of
jobs at a time; see the section
.B PARALLEL MAKE AND THE JOBSERVER
for details.
.TP 0.5i
\fB\--jobserver-fds\fR [\fIR,W\fR]
Internal option
.BR make
uses to pass the jobserver pipe read and write file descriptor numbers
to
.BR sub-makes;
see the section
.B PARALLEL MAKE AND THE JOBSERVER
for details
.TP 0.5i
\fB\-k\fR, \fB\-\-keep\-going\fR
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.
.TP 0.5i
\fB\-l\fR [\fIload\fR], \fB\-\-load\-average\fR[=\fIload\fR]
Specifies that no new jobs (commands) should be started if there are
others jobs running and the load average is at least
.I load
(a floating-point number).
With no argument, removes a previous load limit.
.TP 0.5i
\fB\-L\fR, \fB\-\-check\-symlink\-times\fR
Use the latest mtime between symlinks and target.
.TP 0.5i
\fB\-n\fR, \fB\-\-just\-print\fR, \fB\-\-dry\-run\fR, \fB\-\-recon\fR
Print the commands that would be executed, but do not execute them (except in
certain circumstances).
.TP 0.5i
\fB\-o\fR \fIfile\fR, \fB\-\-old\-file\fR=\fIfile\fR, \fB\-\-assume\-old\fR=\fIfile\fR
Do not remake the file
.I file
even if it is older than its dependencies, and do not remake anything
on account of changes in
.IR file .
Essentially the file is treated as very old and its rules are ignored.
.TP 0.5i
\fB\-O\fR[\fItype\fR], \fB\-\-output\-sync\fR[=\fItype\fR]
When running multiple jobs in parallel with \fB-j\fR, ensure the output of
each job is collected together rather than interspersed with output from
other jobs.  If
.I type
is not specified or is
.B target
the output from the entire recipe for each target is grouped together.  If
.I type
is
.B line
the output from each command line within a recipe is grouped together.
If
.I type
is
.B recurse
output from an entire recursive make is grouped together.  If
.I type
is
.B none
output synchronization is disabled.
.TP 0.5i
\fB\-p\fR, \fB\-\-print\-data\-base\fR
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
.B \-v
switch (see below).
To print the data base without trying to remake any files, use
.IR "make \-p \-f/dev/null" .
.TP 0.5i
\fB\-q\fR, \fB\-\-question\fR
``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.
.TP 0.5i
\fB\-r\fR, \fB\-\-no\-builtin\-rules\fR
Eliminate use of the built\-in implicit rules.
Also clear out the default list of suffixes for suffix rules.
.TP 0.5i
\fB\-R\fR, \fB\-\-no\-builtin\-variables\fR
Don't define any built\-in variables.
.TP 0.5i
\fB\-s\fR, \fB\-\-silent\fR, \fB\-\-quiet\fR
Silent operation; do not print the commands as they are executed.
.TP 0.5i
\fB\-S\fR, \fB\-\-no\-keep\-going\fR, \fB\-\-stop\fR
Cancel the effect of the
.B \-k
option.
This is never necessary except in a recursive
.B make
where
.B \-k
might be inherited from the top-level
.B make
via MAKEFLAGS or if you set
.B \-k
in MAKEFLAGS in your environment.
.TP 0.5i
\fB\-t\fR, \fB\-\-touch\fR
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
.BR make .
.TP 0.5i
.B \-\-trace
Information about the disposition of each target is printed (why the target is
being rebuilt and what commands are run to rebuild it).
.TP 0.5i
\fB\-v\fR, \fB\-\-version\fR
Print the version of the
.B make
program plus a copyright, a list of authors and a notice that there
is no warranty.
.TP 0.5i
\fB\-w\fR, \fB\-\-print\-directory\fR
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
.B make
commands.
.TP 0.5i
.B \-\-no\-print\-directory
Turn off
.BR \-w ,
even if it was turned on implicitly.
.TP 0.5i
\fB\-W\fR \fIfile\fR, \fB\-\-what\-if\fR=\fIfile\fR, \fB\-\-new\-file\fR=\fIfile\fR, \fB\-\-assume\-new\fR=\fIfile\fR
Pretend that the target
.I file
has just been modified.
When used with the
.B \-n
flag, this shows you what would happen if you were to modify that file.
Without
.BR \-n ,
it is almost the same as running a
.I touch
command on the given file before running
.BR make ,
except that the modification time is changed only in the imagination of
.BR make .
.TP 0.5i
.B \-\-warn\-undefined\-variables
Warn when an undefined variable is referenced.
.SH "EXIT STATUS"
GNU
.B 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
.B \-q
flag was used and
.B make
determines that a target needs to be rebuilt.  A status of two will be
returned if any errors were encountered.
.SH "SEE ALSO"
The full documentation for
.B make
is maintained as a Texinfo manual.  If the
.B info
and
.B make
programs are properly installed at your site, the command
.IP
.B info make
.PP
should give you access to the complete manual. Additionally, the
manual is also available online at
.IR https://www.gnu.org/software/make/manual/html_node/index.html
.SH "PARALLEL MAKE AND THE JOBSERVER"
Using the
.I -j
option, the user can instruct
.BR make
to execute tasks in parallel. By specifying a numeric argument to
.I -j
the user may specify an upper limit of the number of parallel tasks to
be run.
.PP
When the build environment is such that a top level
.BR make
invokes
.BR sub-makes
(for instance, a style in which each sub-directory contains its own
.I Makefile
), no individual instance of
.BR 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
.BR make
instances running. While solutions like having the top level
.BR 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.
.PP
This pipe is created by the top-level
.BR make
process, and passed on to all the
.BR sub-makes.
The top level
.BR make process writes
.B N-1
one-byte tokens into the pipe (The top level
.BR make
is assumed to reserve one token for itself). Whenever any of the
.BR make
processes (including the top-level
.BR 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
.BR make
process writes a token back to the pipe (and thus, if the tokens had
been exhausted, unblocking the first
.BR make
process that was waiting to read a token).  Since only
.B N-1
tokens were written into the pipe, no more than
.B N
tasks can be running at any given time.
.PP
If the job to be run is not a
.BR sub-make
then
.BR make
will close the jobserver pipe file descriptors before invoking the
commands, so that the command can not interfere with the
.I jobserver,
and the command does not find any unusual file descriptors.
.SH BUGS
See the chapter ``Problems and Bugs'' in
.IR "The GNU Make Manual" .
.SH 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.
.SH "COPYRIGHT"
Copyright \(co 1992-1993, 1996-2016 Free Software Foundation, Inc.
This file is part of
.IR "GNU make" .
.LP
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.
.LP
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.
.LP
You should have received a copy of the GNU General Public License along with
this program.  If not, see
.IR http://www.gnu.org/licenses/ .