getpgrp(2) -- Linux man page
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 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.
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
(setpgid, setpgrp).
- 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).
- 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.
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 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)
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