Linux man pages : getpgid (2)
SETPGID(2) Linux Programmer's Manual SETPGID(2)
setpgid, getpgid, setpgrp, getpgrp - set/get process group
int setpgid(pid_t pid, pid_t pgid);
pid_t getpgid(pid_t pid);
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 pro-
cess 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.
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 pro-
cess 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 implement-
ing job control. The TIOCGPGRP and TIOCSPGRP calls described in
termios(3) are used to get/set the process group of the control termi-
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 pro-
cess 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.
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 per-
formed 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 dif-
ferent session, or to change the process group ID of a session
leader (setpgid, setpgrp).
ESRCH pid does not match any process.
The functions setpgid and getpgrp conform to POSIX.1. The function
setpgrp is from BSD 4.2. The function getpgid conforms to SVr4.
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 inte-
ger n larger than or equal to 500.
getuid(2), setsid(2), tcsetpgrp(3), termios(3)
Linux 1999-09-02 SETPGID(2)