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GETPGRP(2) System Calls Manual GETPGRP(2)

getpgrp, getpgidget process group

#include <unistd.h>

pid_t
getpgrp(void);

pid_t
getpgid(pid_t pid);

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:

[]
The current process and the process pid are not in the same session.
[]
There is no process with a process ID equal to pid.

setpgid(2), termios(4)

This version of getpgrp() differs from past Berkeley versions by not taking a pid_t pid argument. This incompatibility is required by IEEE Std 1003.1-1988 (“POSIX.1”).

From the IEEE Std 1003.1-1988 (“POSIX.1”) Rationale:

4.3BSD provides a getpgrp() function that returns the process group ID for a specified process. Although this function is used to support job control, all known job-control shells always specify the calling process with this function. Thus, the simpler System V getpgrp() suffices, and the added complexity of the 4.3BSD getpgrp() has been omitted from POSIX.1.

The getpgrp() function conforms to IEEE Std 1003.1-1988 (“POSIX.1”). The getpgid() function call is derived from its usage in System V Release 4, and first appeared in NetBSD 1.2A.

The getpgrp() function call appeared in 4.0BSD.

July 21, 2007 OpenBSD-5.1