NAME
setpgid, getpgid, setpgrp, getpgrp - set/get process group
SYNOPSIS
#include <unistd.h>
I int setpgid(pid_t pid , pid_t pgid );
I pid_t getpgid(pid_t pid );
int setpgrp(void);
pid_t getpgrp(void);
DESCRIPTION
R setpgid ()
sets the process group ID of the process specified by
pid
to
R 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
R 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.
R getpgid ()
returns the process group ID of the process specified by
R pid .
If
pid
is zero, the process ID of the current process is used.
The call
R setpgrp ()
is equivalent to
R setpgid(0,0) .
Similarly,
R getpgrp ()
is equivalent to
R 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 implementing job control.
The
TIOCGPGRP
and
TIOCSPGRP
calls described in
termios(3)
are used to get/set the process group of the control terminal.
If a session has a controlling terminal,
CLOCAL
is not set and a hangup
occurs, then the session leader is sent a
R 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,
R setpgid ()
and
R setpgrp ()
return zero.
On error, -1 is returned, and
errno
is set appropriately.
R getpgid ()
returns a process group on success.
On error, -1 is returned, and
errno
is set appropriately.
R 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(2)
(setpgid(),
R setpgrp ()).
EINVAL
pgid
is less than 0
(setpgid(),
R 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(),
R setpgrp ()).
ESRCH
For
R getpgid ():
pid
does not match any process.
For
R setpgid ():
pid
is not the current process and not a child of the current process.
CONFORMING TO
The functions
R setpgid ()
and
R getpgrp ()
conform to POSIX.1-2001.
The function
R setpgrp ()
is from 4.2BSD.
The function
R 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
R setpgid ()
from the BSD function
R 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
ČLÁNKY DO MAILU