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getsid — get process session
Standard C Library (libc, -lc)
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 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.
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.
getpgid(2), getpgrp(2), setpgid(2), setsid(2), termios(4)
The getsid() system call appeared in FreeBSD 3.0. The getsid() system
call is derived from its usage in AT&T System V UNIX.