source: MondoRescue/branches/3.3/mindi-busybox/miscutils/setsid.c@ 3865

/* vi: set sw=4 ts=4: */
/*
 * setsid.c -- execute a command in a new session
 * Rick Sladkey <jrs@world.std.com>
 * In the public domain.
 *
 * 1999-02-22 Arkadiusz Mickiewicz <misiek@pld.ORG.PL>
 * - added Native Language Support
 *
 * 2001-01-18 John Fremlin <vii@penguinpowered.com>
 * - fork in case we are process group leader
 *
 * 2004-11-12 Paul Fox
 * - busyboxed
 */

//usage:#define setsid_trivial_usage
//usage:       "[-c] PROG ARGS"
//usage:#define setsid_full_usage "\n\n"
//usage:       "Run PROG in a new session. PROG will have no controlling terminal\n"
//usage:       "and will not be affected by keyboard signals (^C etc).\n"
//usage:     "\n    -c  Set controlling terminal to stdin"

#include "libbb.h"

int setsid_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int setsid_main(int argc UNUSED_PARAM, char **argv)
{
    unsigned opt;

    opt_complementary = "-1"; /* at least one arg */
    opt = getopt32(argv, "+c"); /* +: stop on first non-opt */
    argv += optind;

    /* setsid() is allowed only when we are not a process group leader.
     * Otherwise our PID serves as PGID of some existing process group
     * and cannot be used as PGID of a new process group.
     *
     * Example: setsid() below fails when run alone in interactive shell:
     *  $ setsid PROG
     * because shell's child (setsid) is put in a new process group.
     * But doesn't fail if shell is not interactive
     * (and therefore doesn't create process groups for pipes),
     * or if setsid is not the first process in the process group:
     *  $ true | setsid PROG
     * or if setsid is executed in backquotes (`setsid PROG`)...
     */
    if (setsid() < 0) {
        pid_t pid = fork_or_rexec(argv);
        if (pid != 0) {
            /* parent */
            /* TODO:
             * we can waitpid(pid, &status, 0) and then even
             * emulate exitcode, making the behavior consistent
             * in both forked and non forked cases.
             * However, the code is larger and upstream
             * does not do such trick.
             */
            return EXIT_SUCCESS;
        }

        /* child */
        /* now there should be no error: */
        setsid();
    }

    if (opt) {
        /* -c: set (with stealing) controlling tty */
        ioctl(0, TIOCSCTTY, 1);
    }

    BB_EXECVP_or_die(argv);
}