SYSTEM(3) Linux Programmer's Manual SYSTEM(3)
system - execute a shell command
int system(const char *string);
system() executes a command specified in string by calling /bin/sh -c string, 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 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 exe-
cuted, the exit status will be that of a command that does exit(127).
If the value of string 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.
ANSI C, POSIX.2, BSD 4.3
As mentioned, system() ignores SIGINT and SIGQUIT. This may make programs that call it
from a loop uninterruptable, unless they take care themselves to check the exit status of
the child. E.g.
int ret = system("foo");
if (WIFSIGNALED(ret) &&
(WTERMSIG(ret) == SIGINT || WTERMSIG(ret) == SIGQUIT))
Do not use system() from a program with suid or sgid 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 suid or sgid 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.)
The check for the availability of /bin/sh is not actually performed; it is always assumed
to be available. ISO C specifies the check, but POSIX.2 specifies that the return shall
always be non-zero, since a system without the shell is not conforming, and it is this
that is implemented.
It is possible for the shell command to return 127, so that code is not a sure indication
that the execve() call failed.
sh(1), signal(2), wait(2), exec(3)