This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.
#include <unistd.h> pid_t getsid(pid_t pid);
The getsid() function shall obtain the process group ID of the process that is the session leader of the process specified by pid. If pid is (pid_t)0, it specifies the calling process.
Upon successful completion, getsid() shall return the process group ID of the session leader of the specified process. Otherwise, it shall return -1 and set errno to indicate the error.
The getsid() function shall fail if:
The process specified by pid is not in the same session as the calling process, and the implementation does not allow access to the process group ID of the session leader of that process from the calling process.
There is no process with a process ID equal to pid.
The following sections are informative.
exec, fork(), getpid(), getpgid(), setpgid(), setsid()
The Base Definitions volume of POSIX.1-2017, <unistd.h>
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .
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getpgid(3p), setpgrp(3p), setsid(3p), unistd.h(0p).