ultrix man page for setsid

setsid(2)							System Calls Manual							 setsid(2)

Name
       setsid - POSIX create session and set process group ID

Syntax
       #include <sys/types.h>
       pid_t
       setsid()

Description
       The  system call creates a new session, if the calling process is not a process group leader.  The calling process is the session leader of
       the new session, the process group leader of the new process group, and does not have a controlling terminal.  The process group ID of  the
       calling process is set equal to the process ID of the calling process.

Return Values
       Upon successful completion, the system call returns the value of the process group ID of the calling process.  If the system call fails, -1
       is returned, and the global variable errno indicates the reason.

Diagnostics
       The system call fails and a new session is not created if the following occurs:

       [EPERM]	      The calling process is already a process group leader.

		      The process group ID of a process other than the calling process matches the process ID of the calling process.

See Also
       getpgrp(2), setpgid(3)

																	 setsid(2)