freebsd man page for getsid

GETSID(2)						      BSD System Calls Manual							 GETSID(2)

NAME
     getsid -- get process session

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <unistd.h>

     pid_t
     getsid(pid_t pid);

DESCRIPTION
     The session ID of the process identified by pid is returned by getsid().  If pid is zero, getsid() returns the session ID of the current
     process.

RETURN VALUES
     Upon successful completion, the getsid() system call returns the session ID of the specified process; otherwise, it returns a value of -1 and
     sets errno to indicate an error.

ERRORS
     The getsid() system call will succeed unless:

     [ESRCH]		if there is no process with a process ID equal to pid.

     Note that an implementation may restrict this system call to processes within the same session ID as the calling process.

SEE ALSO
     getpgid(2), getpgrp(2), setpgid(2), setsid(2), termios(4)

HISTORY
     The getsid() system call appeared in FreeBSD 3.0.	The getsid() system call is derived from its usage in AT&T System V UNIX.

BSD
								  August 19, 1997							       BSD