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getpgrp - get process group
Standard C Library (libc, -lc)
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, getpgid() returns the process group of the current
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 tcgetpgrp() and
tcsetpgrp() calls are used to get/set the process group of the control
The getpgrp() system call always succeeds. Upon successful completion,
the getpgid() system call returns the process group of the specified
process; otherwise, it returns a value of -1 and sets errno to indicate
This version of getpgrp() differs from past Berkeley versions by not
taking a pid_t pid argument. This incompatibility is required by ISO/IEC
From the ISO/IEC 9945-1:1990 (“POSIX.1”) Rationale:
4.3BSD provides a getpgrp() system 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 System V UNIX getpgrp()
suffices, and the added complexity of the 4.3BSD getpgrp() has been
omitted from POSIX.1. The old functionality is available from the
getpgid() system call.
The getpgid() system call will succeed unless:
[ESRCH] there is no process whose process ID equals pid
getsid(2), setpgid(2), termios(4)
The getpgrp() system call is expected to conform to ISO/IEC 9945-1:1990
The getpgrp() system call appeared in 4.0BSD. The getpgid() system call
is derived from its usage in AT&T System V.4 UNIX.