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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);
DESCRIPTION
setpgid() 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 termi-
nal 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 implementing 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 control-
ling 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 fol-
lowed by a SIGCONT signal will be sent to each process in the newly-orphaned pro-
cess 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 performed 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 different 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 setp-
grp() 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 integer n larger
than or equal to 500.
SEE ALSO
getuid(2), setsid(2), tcgetpgrp(3), tcsetpgrp(3), termios(3), fea-
ture_test_macros(7)
Linux 2003-01-20 SETPGID(2)
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