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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 control‐
        ling 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.
        The session ID of the calling process.

ERRORS

        On error, -1 is returned, and errno is set.  The only error  which  can
        happen  is EPERM.  It is returned when the process group ID of any pro‐
        cess equals the PID of the calling process.  Thus, in particular,  set     
        sid() fails if the calling process is already a process group leader.
        SVr4, POSIX.1-2001.

NOTES

        A child created via fork(2) inherits its parent’s session ID.  The ses‐
        sion 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().
        setpgid(2), setpgrp(2), tcgetsid(3)