• 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 non-zero 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, then the macros described in
  wait(2)
  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 3.19 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/.

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