GETSID(2) BSD System Calls Manual GETSID(2)
getsid -- get process session
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.
Upon successful completion, the function getsid() returns the session ID
of the specified process; otherwise, it returns a value of -1 and sets
errno to indicate an error.
getsid() will succeed unless:
[EPERM] The current process and the process pid are not in the
[ESRCH] There is no process with a process ID equal to pid.
getpgid(2), getpgrp(2), setpgid(2), setsid(2), termios(4)
getsid() conforms to IEEE Std 1003.1-2008 (``POSIX.1'').
The getsid() function call is derived from its usage in AT&T System V
UNIX, and is mandated by X/Open Portability Guide Issue 4 (``XPG4'').
BSD March 30, 2013 BSD