setpgid, getpgid, setpgrp, getpgrp — set/get process group
#include <unistd.h>
int
setpgid( |
pid_t | pid, |
pid_t | pgid) ; |
pid_t
getpgid( |
pid_t | pid) ; |
int
setpgrp( |
void) ; |
pid_t
getpgrp( |
void) ; |
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 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 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.
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.
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
(), setpgrp
()).
pgid
is less
than 0 (setpgid
(),
setpgrp
()).
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
()).
For getpgid
():
pid
does not
match any process. For setpgid
(): pid
is not the current
process and not a child of the current process.
The functions setpgid
() and
getpgrp
() conform to
POSIX.1-2001. The function setpgrp
() is from 4.2BSD. The function
getpgid
() conforms to SVr4.
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.
getuid(2), setsid(2), tcgetpgrp(3), tcsetpgrp(3), termios(3), feature_test_macros(7)
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