SETPGID(2) Linux Programmer's Manual SETPGID(2)NAME
setpgid, getpgid, setpgrp, getpgrp - set/get process group
SYNOPSIS
#include <unistd.h>
int setpgid(pid_t pid, pid_t pgid);
pid_t getpgid(pid_t pid);
int setpgrp(void);
pid_t getpgrp(void);
DESCRIPTIONsetpgid() sets the process group ID of the process specified by pid to
pgid. If pid is zero, the process ID of the current process is used.
If pgid is zero, the process ID of the process specified by pid is
used. If setpgid() is used to move a process from one process group to
another (as is done by some shells when creating pipelines), both
process groups must be part of the same session. In this case, the
pgid specifies an existing process group to be joined and the session
ID of that group must match the session ID of the joining process.
getpgid() returns the process group ID of the process specified by pid.
If pid is zero, the process ID of the current process is used.
The call setpgrp() is equivalent to setpgid(0,0).
Similarly, getpgrp() is equivalent to getpgid(0). Each process group
is a member of a session and each process is a member of the session of
which its process group is a member.
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. These calls are thus
used by programs such as csh(1) to create process groups in implement‐
ing job control. The TIOCGPGRP and TIOCSPGRP calls described in
termios(3) are used to get/set the process group of the control termi‐
nal.
If a session has a controlling terminal, CLOCAL is not set and a hangup
occurs, then the session leader is sent a SIGHUP. If the session
leader exits, the SIGHUP signal will be sent to each process in the
foreground process group of the controlling terminal.
If the exit of the process causes a process group to become orphaned,
and if any member of the newly-orphaned process group is stopped, then
a SIGHUP signal followed by a SIGCONT signal will be sent to each
process in the newly-orphaned process group.
RETURN VALUE
On success, setpgid() and setpgrp() return zero. On error, -1 is
returned, and errno is set appropriately.
getpgid() returns a process group on success. On error, -1 is
returned, and errno is set appropriately.
getpgrp() always returns the current process group.
ERRORS
EACCES An attempt was made to change the process group ID of one of the
children of the calling process and the child had already per‐
formed an execve() (setpgid(), setpgrp()).
EINVAL pgid is less than 0 (setpgid(), setpgrp()).
EPERM An attempt was made to move a process into a process group in a
different session, or to change the process group ID of one of
the children of the calling process and the child was in a dif‐
ferent session, or to change the process group ID of a session
leader (setpgid(), setpgrp()).
ESRCH For getpgid(): pid does not match any process. For setpgid():
pid is not the current process and not a child of the current
process.
CONFORMING TO
The functions setpgid() and getpgrp() conform to POSIX.1-2001. The
function setpgrp() is from 4.2BSD. The function getpgid() conforms to
SVr4.
NOTES
A child created via fork(2) inherits its parent's process group ID.
The process group ID is preserved across an execve(2).
POSIX took setpgid() from the BSD function setpgrp(). Also System V
has a function with the same name, but it is identical to setsid(2).
To get the prototypes under glibc, define both _XOPEN_SOURCE and
_XOPEN_SOURCE_EXTENDED, or use "#define _XOPEN_SOURCE n" for some inte‐
ger n larger than or equal to 500.
SEE ALSOgetuid(2), setsid(2), tcgetpgrp(3), tcsetpgrp(3), termios(3), fea‐
ture_test_macros(7)Linux 2003-01-20 SETPGID(2)
