- Call the first target specified in the Makefile (usually named "all"):make- Call a specific target:make [target]- Call a specific target, executing 4 jobs at a time in parallel:make -J [target]- Use a specific Makefile:make --file [file]- Execute make from another directory:make --directory [directory]- Force making of a target, even if source files are unchanged:make --always-make [target]
make [OPTION]... [TARGET]...
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:
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.
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.
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
should give you access to the complete manual.
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.
See the chapter ``Problems and Bugs'' in The GNU Make Manual.
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 © 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/.