xenial (2) setsid.2.gz

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 (i.e., its session ID is made the same as its process ID).  The  calling
       process  also  becomes  the process group leader of a new process group in the session (i.e., its process
       group ID is made the same as its process ID).

       The calling process will be the only process in the new process group and in the new  session.   The  new
       session has no controlling terminal.

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

       POSIX.1-2001, POSIX.1-2008, SVr4.

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 whose process group ID equals its PID.  Disallowing a  process  group
       leader  from calling setsid() prevents the possibility that a process group leader places itself in a new
       session while other processes in the process group remain in the original session; such a scenario  would
       break  the  strict two-level hierarchy of sessions and process groups.  In order to be sure that setsid()
       will succeed, fork(2) and _exit(2), and have the child do setsid().

SEE ALSO

       setsid(1), getsid(2), setpgid(2), setpgrp(2), tcgetsid(3), credentials(7)

COLOPHON

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