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.
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: 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 (4)
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.