getsid - Man Page

get session ID


#include <unistd.h>

pid_t getsid(pid_t pid);

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):


    _XOPEN_SOURCE >= 500
        || /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200809L


getsid(0) returns the session ID of the calling process. getsid() returns the session ID of the process with process ID pid. If pid is 0, getsid() returns the session ID of the calling process.

Return Value

On success, a session ID is returned. On error, (pid_t) -1 is returned, and errno is set to indicate the error.



A process with process ID pid 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 pid was found.


This system call is available on Linux since version 2.0.

Conforming to

POSIX.1-2001, POSIX.1-2008, SVr4.


Linux does not return EPERM.

See credentials(7) for a description of sessions and session IDs.

See Also

getpgid(2), setsid(2), credentials(7)


This page is part of release 5.13 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at

Referenced By

credentials(7), mksh(1), procenv(1), ps(1), sd_pid_get_owner_uid(3), setsid(2), syscalls(2), system_data_types(7), tcgetsid(3), utmp(5).

2021-03-22 Linux Programmer's Manual