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)
5 .\" Permission is granted to make and distribute verbatim copies of this
6 .\" manual provided the copyright notice and this permission notice are
7 .\" preserved on all copies.
9 .\" Permission is granted to copy and distribute modified versions of this
10 .\" manual under the conditions for verbatim copying, provided that the
11 .\" entire resulting derived work is distributed under the terms of a
12 .\" permission notice identical to this one.
14 .\" Since the Linux kernel and libraries are constantly changing, this
15 .\" manual page may be incorrect or out-of-date. The author(s) assume no
16 .\" responsibility for errors or omissions, or for damages resulting from
17 .\" the use of the information contained herein. The author(s) may not
18 .\" have taken the same level of care in the production of this manual,
19 .\" which is licensed free of charge, as they might when working
22 .\" Formatted or processed versions of this manual, if unaccompanied by
23 .\" the source, must acknowledge the copyright and authors of this work.
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 2021-03-22 "" "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
53 execl("/bin/sh", "sh", "\-c", command, (char *) NULL);
58 returns after the command has been completed.
60 During execution of the command,
66 will be ignored, in the process that calls
68 (These signals will be handled according to their defaults inside
69 the child process that executes
76 returns a status indicating whether a shell is available on the system.
80 is one of the following:
84 is NULL, then a nonzero value if a shell is available,
85 or 0 if no shell is available.
87 If a child process could not be created,
88 or its status could not be retrieved,
89 the return value is \-1 and
91 is set to indicate the error.
93 If a shell could not be executed in the child process,
94 then the return value is as though the child shell terminated by calling
98 If all system calls succeed,
99 then the return value is the termination status of the child shell
102 (The termination status of a shell is the termination status of
103 the last command it executes.)
105 In the last two cases,
106 the return value is a "wait status" that can be examined using
107 the macros described in
115 does not affect the wait status of any other children.
118 can fail with any of the same errors as
121 For an explanation of the terms used in this section, see
129 Interface Attribute Value
132 T} Thread safety MT-Safe
138 POSIX.1-2001, POSIX.1-2008, C89, C99.
141 provides simplicity and convenience:
142 it handles all of the details of calling
147 as well as the necessary manipulations of signals;
149 the shell performs the usual substitutions and I/O redirections for
154 additional system calls are required to create the process that
155 runs the shell and to execute the shell.
159 feature test macro is defined
163 then the macros described in
165 .RB ( WEXITSTATUS (),
166 etc.) are made available when including
175 This may make programs that call it
176 from a loop uninterruptible, unless they take care themselves
177 to check the exit status of the child.
183 int ret = system("foo");
185 if (WIFSIGNALED(ret) &&
186 (WTERMSIG(ret) == SIGINT || WTERMSIG(ret) == SIGQUIT))
192 According to POSIX.1, it is unspecified whether handlers registered using
193 .BR pthread_atfork (3)
194 are called during the execution of
196 In the glibc implementation, such handlers are not called.
198 In versions of glibc before 2.1.3, the check for the availability of
200 was not actually performed if
202 was NULL; instead it was always assumed to be available, and
204 always returned 1 in this case.
205 Since glibc 2.1.3, this check is performed because, even though
206 POSIX.1-2001 requires a conforming implementation to provide
207 a shell, that shell may not be available or executable if
208 the calling program has previously called
210 (which is not specified by POSIX.1-2001).
212 It is possible for the shell command to terminate with a status of 127,
215 return value that is indistinguishable from the case
216 where a shell could not be executed in the child process.
221 from a privileged program
222 (a set-user-ID or set-group-ID program, or a program with capabilities)
223 because strange values for some environment variables
224 might be used to subvert system integrity.
227 could be manipulated so that an arbitrary program
228 is executed with privilege.
231 family of functions instead, but not
237 environment variable to search for an executable).
240 will not, in fact, work properly from programs with set-user-ID or
241 set-group-ID privileges on systems on which
243 is bash version 2: as a security measure, bash 2 drops privileges on startup.
244 (Debian uses a different shell,
246 which does not do this when invoked as
249 Any user input that is employed as part of
253 sanitized, to ensure that unexpected shell commands or command options
255 Such risks are especially grave when using
257 from a privileged program.
259 .\" [BUG 211029](https://bugzilla.kernel.org/show_bug.cgi?id=211029)
260 .\" [Glibc bug](https://sourceware.org/bugzilla/show_bug.cgi?id=27143)
261 .\" [POSIX bug](https://www.austingroupbugs.net/view.php?id=1440)
262 If the command name starts with a hyphen,
264 interprets the command name as an option,
265 and the behavior is undefined.
270 To work around this problem,
271 prepend the command with a space as in the following call:
275 system(" \-unfortunate\-command\-name");