debian man page for getpgid

GETPGRP(2)						      BSD System Calls Manual							GETPGRP(2)

NAME
     getpgrp -- get process group

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <unistd.h>

     pid_t
     getpgrp(void);

     pid_t
     getpgid(pid_t pid);

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 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 terminal.

RETURN VALUES
     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 the error.

COMPATIBILITY
     This version of getpgrp() differs from past Berkeley versions by not taking a pid_t pid argument.	This incompatibility is required by
     ISO/IEC 9945-1:1990 (``POSIX.1'').

     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.

ERRORS
     The getpgid() system call will succeed unless:

     [ESRCH]		there is no process whose process ID equals pid

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

STANDARDS
     The getpgrp() system call is expected to conform to ISO/IEC 9945-1:1990 (``POSIX.1'').

HISTORY
     The getpgrp() system call appeared in 4.0BSD.  The getpgid() system call is derived from its usage in AT&T System V Release 4 UNIX.

BSD
								   June 4, 1993 							       BSD