get session ID
Standard C library (libc, -lc)
getsid() returns the session ID of the process with process ID pid. If pid is 0, getsid() returns the session ID of the calling process.
On success, a session ID is returned. On error, (pid_t) -1 is returned, and errno is set to indicate the error.
Linux does not return EPERM.
POSIX.1-2008.
POSIX.1-2001, SVr4. Linux 2.0.
See credentials(7) for a description of sessions and session IDs.