Why process leader can not call setsid() Post: 29525

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setsid

SETSID(2)						     Linux Programmer's Manual							 SETSID(2)

NAME

       setsid - creates a session and sets the process group ID

SYNOPSIS

       #include <unistd.h>

       pid_t setsid(void);

DESCRIPTION

       setsid() creates a new session if the calling process is not a process group leader.  The calling process is the leader of the new session,
       the process group leader of the new process group, and has no controlling tty.  The process group ID and session ID of the calling  process
       are set to the PID of the calling process.  The calling process will be the only process in this new process group and in this new session.

RETURN VALUE

       On  success,  the  (new) session ID of the calling process is returned.	On error, (pid_t) -1 is returned, and errno is set to indicate the
       error.

ERRORS

       EPERM  The process group ID of any process equals the PID of the calling process.  Thus, in  particular,  setsid()  fails  if  the  calling
	      process is already a process group leader.

CONFORMING TO

       SVr4, POSIX.1-2001.

NOTES

       A child created via fork(2) inherits its parent's session ID.  The session ID is preserved across an execve(2).

       A  process  group  leader is a process with process group ID equal to its PID.  In order to be sure that setsid() will succeed, fork(2) and
       _exit(2), and have the child do setsid().

SEE ALSO

       getsid(2), setpgid(2), setpgrp(2), tcgetsid(3), credentials(7)

COLOPHON

       This page is part of release 3.44 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/.

Linux								    2008-12-03								 SETSID(2)