osx man page for setsid

SETSID(2)						      BSD System Calls Manual							 SETSID(2)

NAME
     setsid -- create session and set process group ID

SYNOPSIS
     #include <unistd.h>

     pid_t
     setsid(void);

DESCRIPTION
     The setsid function creates a new session.  The calling process is the session leader of the new session, is the process group leader of a
     new process group and has no controlling terminal.  The calling process is the only process in either the session or the process group.

     Upon successful completion, the setsid function returns the value of the process group ID of the new process group, which is the same as the
     process ID of the calling process.

ERRORS
     If an error occurs, setsid returns -1 and the global variable errno is set to indicate the error, as follows:

     [EPERM]		The calling process is already a process group leader, or the process group ID of a process other than the calling process
			matches the process ID of the calling process.

LEGACY SYNOPSIS
     #include <sys/types.h>
     #include <unistd.h>

     The include file <sys/types.h> is necessary.

SEE ALSO
     setpgid(3), tcgetpgrp(3), tcsetpgrp(3), compat(5)

STANDARDS
     The setsid function is expected to be compliant with the IEEE Std 1003.1-1988 (``POSIX.1'') specification.

BSD
								   June 4, 1993 							       BSD