| NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | CONFORMING TO | NOTES | SEE ALSO | COLOPHON | The Linux Programming Interface |
SYSTEM(3) Linux Programmer's Manual SYSTEM(3)
system - execute a shell command
#include <stdlib.h>
int system(const char *command);
system() executes a command specified in command by calling /bin/sh -c
command, and returns after the command has been completed. During execution
of the command, SIGCHLD will be blocked, and SIGINT and SIGQUIT will be
ignored.
The value returned is -1 on error (e.g. fork(2) failed), and the return
status of the command otherwise. This latter return status is in the format
specified in wait(2). Thus, the exit code of the command will be
WEXITSTATUS(status). In case /bin/sh could not be executed, the exit status
will be that of a command that does exit(127).
If the value of command is NULL, system() returns nonzero if the shell is
available, and zero if not.
system() does not affect the wait status of any other children.
C89, C99, POSIX.1-2001.
If the _XOPEN_SOURCE feature test macro is defined (before including any
header files), then the macros described in wait(2) (WEXITSTATUS(), etc.) are
made available when including <stdlib.h>.
As mentioned, system() ignores SIGINT and SIGQUIT. This may make programs
that call it from a loop uninterruptible, unless they take care themselves to
check the exit status of the child. E.g.
while (something) {
int ret = system("foo");
if (WIFSIGNALED(ret) &&
(WTERMSIG(ret) == SIGINT || WTERMSIG(ret) == SIGQUIT))
break;
}
Do not use system() from a program with set-user-ID or set-group-ID
privileges, because strange values for some environment variables might be
used to subvert system integrity. Use the exec(3) family of functions
instead, but not execlp(3) or execvp(3). system() will not, in fact, work
properly from programs with set-user-ID or set-group-ID privileges on systems
on which /bin/sh is bash version 2, since bash 2 drops privileges on startup.
(Debian uses a modified bash which does not do this when invoked as sh.)
In versions of glibc before 2.1.3, the check for the availability of /bin/sh
was not actually performed if command was NULL; instead it was always assumed
to be available, and system() always returned 1 in this case. Since glibc
2.1.3, this check is performed because, even though POSIX.1-2001 requires a
conforming implementation to provide a shell, that shell may not be available
or executable if the calling program has previously called chroot(2) (which is
not specified by POSIX.1-2001).
It is possible for the shell command to return 127, so that code is not a sure
indication that the execve(2) call failed.
sh(1), signal(2), wait(2), exec(3)
This page is part of release 3.32 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can be found
at http://www.kernel.org/doc/man-pages/.
2010-09-10 SYSTEM(3)
HTML rendering created 2010-12-03 by Michael Kerrisk, author of The Linux Programming Interface