NAME

       system - execute a shell command

SYNOPSIS

       #include <stdlib.h>

       int system(const char *command);

DESCRIPTION

       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.

RETURN VALUE

       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.

CONFORMING TO

       C89, C99, POSIX.1-2001.

NOTES

       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.

SEE ALSO

       sh(1), signal(2), wait(2), exec(3)

COLOPHON

       This page is part of release 3.54 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)