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 speci
fied by pid. If pid is zero, the process ID of the cur
rent process is used.
In the Linux DLL 4.4.1 library, setpgrp simply calls
setpgid(0,0).
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: Pro
cesses 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(4) are used to get/set the pro
cess 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
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
EINVAL pgid is less than 0.
EPERM Various permission violations.
ESRCH pid does not match any process.
CONFORMING TO
The functions setpgid and getpgrp conform to POSIX.1. The
function setpgrp is from BSD 4.2. The function getpgid
conforms to SVr4.
NOTES
POSIX took setpgid from the BSD function setpgrp. Also
SysV has a function with the same name, but it is identi
cal to setsid(2).
SEE ALSO
getuid(2), setsid(2), tcsetpgrp(3), termios(4)
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