release/src/router/busybox/miscutils/setsid.c

   1 /* vi: set sw=4 ts=4: */
   2 /*
   3  * setsid.c -- execute a command in a new session
   4  * Rick Sladkey <jrs@world.std.com>
   5  * In the public domain.
   6  *
   7  * 1999-02-22 Arkadiusz Mickiewicz <misiek@pld.ORG.PL>
   8  * - added Native Language Support
   9  *
  10  * 2001-01-18 John Fremlin <vii@penguinpowered.com>
  11  * - fork in case we are process group leader
  12  *
  13  * 2004-11-12 Paul Fox
  14  * - busyboxed
  15  */
  16
  17 //usage:#define setsid_trivial_usage
  18 //usage:       "[-c] PROG ARGS"
  19 //usage:#define setsid_full_usage "\n\n"
  20 //usage:       "Run PROG in a new session. PROG will have no controlling terminal\n"
  21 //usage:       "and will not be affected by keyboard signals (^C etc).\n"
  22 //usage:     "\n        -c      Set controlling terminal to stdin"
  23
  24 #include "libbb.h"
  25
  26 int setsid_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
  27 int setsid_main(int argc UNUSED_PARAM, char **argv)
  28 {
  29         unsigned opt;
  30
  31         opt_complementary = "-1"; /* at least one arg */
  32         opt = getopt32(argv, "+c"); /* +: stop on first non-opt */
  33         argv += optind;
  34
  35         /* setsid() is allowed only when we are not a process group leader.
  36          * Otherwise our PID serves as PGID of some existing process group
  37          * and cannot be used as PGID of a new process group.
  38          *
  39          * Example: setsid() below fails when run alone in interactive shell:
  40          *  $ setsid PROG
  41          * because shell's child (setsid) is put in a new process group.
  42          * But doesn't fail if shell is not interactive
  43          * (and therefore doesn't create process groups for pipes),
  44          * or if setsid is not the first process in the process group:
  45          *  $ true | setsid PROG
  46          * or if setsid is executed in backquotes (`setsid PROG`)...
  47          */
  48         if (setsid() < 0) {
  49                 pid_t pid = fork_or_rexec(argv);
  50                 if (pid != 0) {
  51                         /* parent */
  52                         /* TODO:
  53                          * we can waitpid(pid, &status, 0) and then even
  54                          * emulate exitcode, making the behavior consistent
  55                          * in both forked and non forked cases.
  56                          * However, the code is larger and upstream
  57                          * does not do such trick.
  58                          */
  59                         return EXIT_SUCCESS;
  60                 }
  61
  62                 /* child */
  63                 /* now there should be no error: */
  64                 setsid();
  65         }
  66
  67         if (opt) {
  68                 /* -c: set (with stealing) controlling tty */
  69                 ioctl(0, TIOCSCTTY, 1);
  70         }
  71
  72         BB_EXECVP_or_die(argv);
  73 }