redhat man page for getsid

GETSID(2)						     Linux Programmer's Manual							 GETSID(2)

NAME
       getsid - get session ID

SYNOPSIS
       #include <unistd.h>

       pid_t getsid(pid_t pid);

DESCRIPTION
       getsid(0)  returns the session ID of the calling process.  getsid(p) returns the session ID of the process with process ID p.  (The session
       ID of a process is the process group ID of the session leader.)	On error, (pid_t) -1 will be returned, and errno is set appropriately.

ERRORS
       EPERM  A process with process ID p exists, but it is not in the same session as the current process, and the implementation considers  this
	      an error.

       ESRCH  No process with process ID p was found.

CONFORMING TO
       SVr4, POSIX 1003.1-2001.

NOTES
       Linux does not return EPERM.

       Linux has this system call since Linux 1.3.44.  There is libc support since libc 5.2.19.

       To get the prototype under glibc, define both _XOPEN_SOURCE and _XOPEN_SOURCE_EXTENDED, or use "#define _XOPEN_SOURCE n" for some integer n
       larger than or equal to 500.

SEE ALSO
       getpgid(2), setsid(2)

Linux 2.5.0							    2001-12-17								 GETSID(2)