GETPGRP(2) BSD System Calls Manual GETPGRP(2)
getpgrp, getpgid -- get process group
The process group of the current process is returned by getpgrp(). The
process group of the pid process is returned by getpgid(). If pid is
zero, getpgid() returns the process group of the current process.
Process groups are used for distribution of signals, and by terminals to
arbitrate requests for their input: processes that have the same process
group as the terminal are foreground and may read, while others will
block with a signal if they attempt to read.
These calls are thus used by programs such as csh(1) to create process
groups in implementing job control. The tcgetpgrp() and tcsetpgrp()
calls are used to get/set the process group of the control terminal.
getpgrp() always succeeds, however getpgid() will succeed unless:
[EPERM] The current process and the process pid are not in the
[ESRCH] There is no process with a process ID equal to pid.
The getpgrp() and getpgid() functions conform to IEEE Std 1003.1-2008
A getpgrp() function call that took a pid_t pid argument appeared in
4.0BSD. This version, without an argument, is derived from its usage in
System V Release 4, and first appeared in NetBSD 0.9.
The getpgid() function call is derived from its usage in System V Release
4, and first appeared in NetBSD 1.2A.
BSD March 31, 2013 BSD