June 4, 1993
getpgrp - get process group
.In unistd.h pid_t
getpgid pid_t pid
The process group of the current process is returned by
getpgrp. The process group of the process identified by pid is returned by
getpgid. If pid is zero,
getpgidreturns 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.
This system call is thus used by programs such as csh(1) to create process groups in implementing job control. The
tcsetpgrpcalls are used to get/set the process group of the control terminal.
getpgrpsystem call always succeeds. Upon successful completion, the
getpgidsystem call returns the process group of the specified process; otherwise, it returns a value of -1 and sets errno to indicate the error.
This version of
getpgrpdiffers from past Berkeley versions by not taking a pid_t pid argument. This incompatibility is required by -p1003.1-90.
From the -p1003.1-90 Rationale:
BSD 4.3 provides a
getpgrpsystem call 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 AT&T V
getpgrpsuffices, and the added complexity of the BSD 4.3
getpgrphas been omitted from POSIX.1. The old functionality is available from the
getpgidsystem call will succeed unless:
|there is no process whose process ID equals pid|
getpgrpsystem call is expected to conform to -p1003.1-90.
getpgrpsystem call appeared in BSD 4.0 . The
getpgidsystem call is derived from its usage in AT&T V.4 .