getsid(2) -- Linux man page
NAMEgetsid - get session ID
DESCRIPTIONgetsid(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.
- 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.
- No process with process ID p was found.
CONFORMING TOSVr4, POSIX 1003.1-2001.
NOTESLinux does not return EPERM.
Linux has this system call since Linux 1.3.44. There is libc support since libc 5.2.19.
SEE ALSOgetpgid(2), setsid(2)