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.\"     @(#)getpgrp.2	8.1 (Berkeley) 6/4/93
.\" $FreeBSD: releng/12.2/lib/libc/sys/getpgrp.2 314436 2017-02-28 23:42:47Z imp $
.\"
.Dd June 4, 1993
.Dt GETPGRP 2
.Os
.Sh NAME
.Nm getpgrp
.Nd get process group
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In unistd.h
.Ft pid_t
.Fn getpgrp void
.Ft pid_t
.Fn getpgid "pid_t pid"
.Sh DESCRIPTION
The process group of the current process is returned by
.Fn getpgrp .
The process group of the process identified by
.Fa pid
is returned by
.Fn getpgid .
If
.Fa pid
is zero,
.Fn getpgid
returns the process group of the current process.
.Pp
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.
.Pp
This system call is thus used by programs such as
.Xr csh 1
to create
process groups
in implementing job control.
The
.Fn tcgetpgrp
and
.Fn tcsetpgrp
calls
are used to get/set the process group of the control terminal.
.Sh RETURN VALUES
The
.Fn getpgrp
system call always succeeds.
Upon successful completion, the
.Fn getpgid
system call returns the process group of the specified process;
otherwise, it returns a value of \-1 and sets
.Va errno
to indicate the error.
.Sh COMPATIBILITY
This version of
.Fn getpgrp
differs from past Berkeley versions by not taking a
.Fa "pid_t pid"
argument.
This incompatibility is required by
.St -p1003.1-90 .
.Pp
From the
.St -p1003.1-90
Rationale:
.Pp
.Bx 4.3
provides a
.Fn 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 V
.Fn getpgrp
suffices, and the added complexity of the
.Bx 4.3
.Fn getpgrp
has been omitted from POSIX.1.
The old functionality is available from the
.Fn getpgid
system call.
.Sh ERRORS
The
.Fn getpgid
system call
will succeed unless:
.Bl -tag -width Er
.It Bq Er ESRCH
there is no process whose process ID equals
.Fa pid
.El
.Sh SEE ALSO
.Xr getsid 2 ,
.Xr setpgid 2 ,
.Xr termios 4
.Sh STANDARDS
The
.Fn getpgrp
system call is expected to conform to
.St -p1003.1-90 .
.Sh HISTORY
The
.Fn getpgrp
system call appeared in
.Bx 4.0 .
The
.Fn getpgid
system call is derived from its usage in
.At V.4 .