1 .\" Copyright (c) 1993 by Thomas Koenig (ig25@rz.uni-karlsruhe.de)
2 .\" and Copyright (c) 2014 by Michael Kerrisk <mtk.manpages@gmail.com>
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10 .\" manual under the conditions for verbatim copying, provided that the
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26 .\" Modified Sat Jul 24 17:51:15 1993 by Rik Faith (faith@cs.unc.edu)
27 .\" Modified 11 May 1998 by Joseph S. Myers (jsm28@cam.ac.uk)
28 .\" Modified 14 May 2001, 23 Sep 2001 by aeb
31 .TH SYSTEM 3 2014-06-13 "" "Linux Programmer's Manual"
33 system \- execute a shell command
36 .B #include <stdlib.h>
38 .BI "int system(const char *" "command" );
45 to create a child process that executes the shell command specified in
51 execl("/bin/sh", "sh", "-c", command, (char *) 0);
54 returns after the command has been completed.
56 During execution of the command,
62 will be ignored, in the process that calls
64 (these signals will be handled according to their defaults inside
65 the child process that executes
72 returns a status indicating whether a shell is available on the system
76 is one of the following:
80 is NULL, then a nonzero value if a shell is available,
81 or 0 if no shell is available.
83 If a child process could not be created,
84 or its status could not be retrieved,
85 the return value is \-1.
87 If a shell could not be executed in the child process,
88 then the return value is as though the child shell terminated by calling
92 If all system calls succeed,
93 then the return value is the termination status of the child shell
96 (The termination status of a shell is the termination status of
97 the last command it executes.)
99 In the last two cases,
100 the return value is a "wait status" that can be examined using
101 the macros described in
109 does not affect the wait status of any other children.
111 .SS Multithreading (see pthreads(7))
114 function is thread-safe.
116 C89, C99, POSIX.1-2001.
119 provides simplicity and convenience:
120 it handles all of the details of calling
125 as well as the necessary manipulations of signals;
127 the shell performs the usual substitutions and I/O redirections for
132 additional system calls are required to create the process that
133 runs the shell and to execute the shell.
137 feature test macro is defined
141 then the macros described in
143 .RB ( WEXITSTATUS (),
144 etc.) are made available when including
153 This may make programs that call it
154 from a loop uninterruptible, unless they take care themselves
155 to check the exit status of the child.
161 int ret = system("foo");
163 if (WIFSIGNALED(ret) &&
164 (WTERMSIG(ret) == SIGINT || WTERMSIG(ret) == SIGQUIT))
171 from a program with set-user-ID or set-group-ID privileges,
172 because strange values for some environment variables
173 might be used to subvert system integrity.
176 family of functions instead, but not
181 will not, in fact, work properly from programs with set-user-ID or
182 set-group-ID privileges on systems on which
184 is bash version 2, since bash 2 drops privileges on startup.
185 (Debian uses a modified bash which does not do this when invoked as
188 In versions of glibc before 2.1.3, the check for the availability of
190 was not actually performed if
192 was NULL; instead it was always assumed to be available, and
194 always returned 1 in this case.
195 Since glibc 2.1.3, this check is performed because, even though
196 POSIX.1-2001 requires a conforming implementation to provide
197 a shell, that shell may not be available or executable if
198 the calling program has previously called
200 (which is not specified by POSIX.1-2001).
202 It is possible for the shell command to terminate with a status of 127,
205 return value that is indistinguishable from the case
206 where a shell could not be executed in the child process.
216 This page is part of release 3.78 of the Linux
219 A description of the project,
220 information about reporting bugs,
221 and the latest version of this page,
223 \%http://www.kernel.org/doc/man\-pages/.