The getpgid() function shall return the process group ID of
the process whose process ID is equal to pid. If
pid is equal to 0, getpgid() shall return the process
group ID of the calling process.
Upon successful completion, getpgid() shall return a process
group ID. Otherwise, it shall return (pid_t)-1 and
set errno to indicate the error.
The getpgid() function shall fail if:
The process whose process ID is equal to pid is not in the same
session as the calling process, and the implementation
does not allow access to the process group ID of that process from
the calling process.
There is no process with a process ID equal to pid.
The getpgid() function may fail if:
The value of the pid argument is invalid.
The following sections are informative.
exec() , fork() , getpgrp() , getpid() , getsid()
, setpgid() , setsid() , the Base Definitions volume of
IEEE Std 1003.1-2001, <unistd.h>
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 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