1SYSTEM(3) Linux Programmer's Manual SYSTEM(3)
2
6 system - execute a shell command
7
9 #include <stdlib.h>
10 int system(const char *command);
12
14 system() executes a command specified in command by calling /bin/sh -c
15 command, and returns after the command has been completed. During exe‐
16 cution of the command, SIGCHLD will be blocked, and SIGINT and SIGQUIT
17 will be ignored.
18
20 The value returned is -1 on error (e.g. fork(2) failed), and the
21 return status of the command otherwise. This latter return status is
22 in the format specified in wait(2). Thus, the exit code of the command
23 will be WEXITSTATUS(status). In case /bin/sh could not be executed,
24 the exit status will be that of a command that does exit(127).
25 If the value of command is NULL, system() returns non-zero if the shell
27 is available, and zero if not.
28 system() does not affect the wait status of any other children.
30
32 C89, C99, POSIX.1-2001.
33
35 If the _XOPEN_SOURCE feature test macro is defined, then the macros
36 described in wait(2) (WEXITSTATUS(), etc.) are made available when
37 including <stdlib.h>.
38 As mentioned, system() ignores SIGINT and SIGQUIT. This may make pro‐
40 grams that call it from a loop uninterruptible, unless they take care
41 themselves to check the exit status of the child. E.g.
42 while (something) {
44 int ret = system("foo");
45 if (WIFSIGNALED(ret) &&
47 (WTERMSIG(ret) == SIGINT || WTERMSIG(ret) == SIGQUIT))
48 break;
49 }
50 Do not use system() from a program with set-user-ID or set-group-ID
52 privileges, because strange values for some environment variables might
53 be used to subvert system integrity. Use the exec(3) family of func‐
54 tions instead, but not execlp(3) or execvp(3). system() will not, in
55 fact, work properly from programs with set-user-ID or set-group-ID
56 privileges on systems on which /bin/sh is bash version 2, since bash 2
57 drops privileges on startup. (Debian uses a modified bash which does
58 not do this when invoked as sh.)
59 In versions of glibc before 2.1.3, the check for the availability of
61 /bin/sh was not actually performed if command was NULL; instead it was
62 always assumed to be available, and system() always returned 1 in this
63 case. Since glibc 2.1.3, this check is performed because, even though
64 POSIX.1-2001 requires a conforming implementation to provide a shell,
65 that shell may not be available or executable if the calling program
66 has previously called chroot(2) (which is not specified by
67 POSIX.1-2001).
68 It is possible for the shell command to return 127, so that code is not
70 a sure indication that the execve(2) call failed.
71
73 sh(1), signal(2), wait(2), exec(3)
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76 This page is part of release 3.22 of the Linux man-pages project. A
77 description of the project, and information about reporting bugs, can
78 be found at http://www.kernel.org/doc/man-pages/.
79 2004-12-20 SYSTEM(3)