1 .\" Copyright (c) 1993 by Thomas Koenig (ig25@rz.uni-karlsruhe.de)
2 .\" and Copyright (c) 2014 by Michael Kerrisk <mtk.manpages@gmail.com>
4 .\" %%%LICENSE_START(VERBATIM)
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10 .\" manual under the conditions for verbatim copying, provided that the
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14 .\" Since the Linux kernel and libraries are constantly changing, this
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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 2014-05-10 "" "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 C89, C99, POSIX.1-2001.
114 provides simplicity and convenience:
115 it handles all of the details of calling
120 as well as the necessary manipulations of signals;
122 the shell performs the usual substitutions and I/O redirections for
127 additional system calls are required to create the process that
128 runs the shell and to execute the shell.
132 feature test macro is defined
136 then the macros described in
138 .RB ( WEXITSTATUS (),
139 etc.) are made available when including
148 This may make programs that call it
149 from a loop uninterruptible, unless they take care themselves
150 to check the exit status of the child.
156 int ret = system("foo");
158 if (WIFSIGNALED(ret) &&
159 (WTERMSIG(ret) == SIGINT || WTERMSIG(ret) == SIGQUIT))
166 from a program with set-user-ID or set-group-ID privileges,
167 because strange values for some environment variables
168 might be used to subvert system integrity.
171 family of functions instead, but not
176 will not, in fact, work properly from programs with set-user-ID or
177 set-group-ID privileges on systems on which
179 is bash version 2, since bash 2 drops privileges on startup.
180 (Debian uses a modified bash which does not do this when invoked as
183 In versions of glibc before 2.1.3, the check for the availability of
185 was not actually performed if
187 was NULL; instead it was always assumed to be available, and
189 always returned 1 in this case.
190 Since glibc 2.1.3, this check is performed because, even though
191 POSIX.1-2001 requires a conforming implementation to provide
192 a shell, that shell may not be available or executable if
193 the calling program has previously called
195 (which is not specified by POSIX.1-2001).
197 It is possible for the shell command to terminate with a status of 127,
200 return value that is indistinguishable from the case
201 where a shell could not be executed in the child process.
211 This page is part of release 3.67 of the Linux
214 A description of the project,
215 information about reporting bugs,
216 and the latest version of this page,
218 \%http://www.kernel.org/doc/man\-pages/.