get session ID
Macro Requirements for glibc (see
_XOPEN_SOURCE >= 500
|| _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
|| /* Since glibc 2.12: */
_POSIX_C_SOURCE >= 200809L
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 success, a
session ID is returned. 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
calling process, and the implementation considers this an
No process with process ID p was found.
call is available on Linux since version 2.0.
Linux does not
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