GETPGRP(2)

NAME
getpgid, getpgrp - get process group

LIBRARY
libc

SYNOPSIS
#include <unistd.h>
pid_t
getpgid(pid_t pid);
pid_t
getpgrp(void);

DESCRIPTION
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.

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 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 terminal.

RETURN VALUES
The getpgrp() call always succeeds. Upon successful completion, the getpgid() call returns the process group of the specified process; otherwise, it returns a value of -1 and sets errno to indicate the error.

ERRORS
getpgid() will succeed unless:

[ESRCH]
    There is no process whose process ID equals pid.

SEE ALSO
getsid(2), setpgid(2), termios(4)

HISTORY
The getpgrp() function call appeared in 4.0BSD. The getpgid() function call is derived from its usage in System V Release 4.

STANDARDS
The getpgrp() function call is expected to conform to p1003.1-90.

COMPATIBILITY
This version of getpgrp() differs 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:

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 AT&T 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() function.