getsid - get session ID
#include <unistd.h> pid_t getsid(pid_t pid));
getsid(0) returns the session ID of the calling process. getsid(p) returns the session ID of the process with process ID p.
On error, -1 will be returned. The only error which can happen is ESRCH, when no process with process ID p was found.
SVr4, which documents an additional EPERM error condition.