Get session id
pid_t getsid(pid_t pid);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
_XOPEN_SOURCE >= 500 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
|| /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200809L
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 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 error.
No process with process ID p was found.
This system call is available on Linux since version 2.0.
Linux does not return EPERM.
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