text: /* 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
   */
  //config:config SETSID
  //config:	bool "setsid (3.6 kb)"
  //config:	default y
  //config:	help
  //config:	setsid runs a program in a new session
  
  //applet:IF_SETSID(APPLET(setsid, BB_DIR_USR_BIN, BB_SUID_DROP))
  
  //kbuild:lib-$(CONFIG_SETSID) += setsid.o
  
  //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;
  
  	/* +: stop on first non-opt */
  	opt = getopt32(argv, "^+" "c" "\0" "-1"/* at least one arg */);
  	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);
  }
  