Differences between current version and predecessor to the previous major change of ProcessGroup.
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| Newer page: | version 11 | Last edited on Tuesday, September 4, 2007 6:09:44 pm | by BenStaz | |
| Older page: | version 6 | Last edited on Tuesday, January 2, 2007 10:11:03 pm | by LawrenceDoliveiro | Revert |
@@ -1,11 +1,39 @@
-Process groups are used for distribution of signals, and by terminals to arbitrate requests for their input and output: 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.
+A Process group is a collection of related processes. One important feature is that it is possible to send a signal to every process in the group. Typically when the shell creates a process to run an application, the process is placed into a new process
+group. As that application forks new processes, the processes are all members of the process group.
Process groups are used for distribution of signals, and by terminals to arbitrate requests for their input and output:
+
+!Foreground Process Groups
+
+* A foreground
process has read and write access to
the terminal.
+* Every process in the
foreground receives [SIGINT] [SIGQUIT]
and [SIGTSTP] signals.
+* Usually consists of the processes forked by the shell and all the processes they fork.
+
+!Background Process Groups
+
+* A background process does not have
read access to the terminal.
+* If
a background process attempts
to read from its controlling terminal its process group will be sent a [SIGTTIN]
.
+
+!Example
+
+Notice that cat, sort and uniq all have the same PGID
(Process Group ID
).
+<verbatim>
+staz@tokra:~/log$ cat results | sort | uniq & ps -jf
+[1] 1239
+UID PID PPID PGID SID C STIME TTY TIME CMD
+staz 1237 28341 1237 28341 0 17:55 pts/6 00:00:00 cat results
+staz 1238 28341 1237 28341 0 17:55 pts/6 00:00:00 sort
+staz 1239 28341 1237 28341 0 17:55 pts/6 00:00:00 uniq
+</verbatim>
+
+
The [TIOCGPGRP] and [TIOCSPGRP] calls described in termios(4) are used to get/set the process group of the control terminal.
If a ProcessGroup has a ControllingTerminal, [CLOCAL] is not set and a hangup occurs, then the ProcessGroup is sent a [SIGHUP].
If a ProcessGroup Leader exits, all children processes are sent a [SIGHUP]
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.
+
+
!! See Also
* ProcessRelationships
