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Killing an Xterm while leaving subprocess alive...

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Old 10-21-2005
Killing an Xterm while leaving subprocess alive...

I'm not quite understanding what I'm doing (happens often). This pseudocode works:


function kill_parent {
when i_want_to ; do
sleep 2
kill -TERM $PPID

kill_parent &
ssh remote_host sh <<-EOF
notify_kill_parent # let the bg function know it's ok to kill parent
run_command # something x-based

Now, if I start my script in an xterm:
xterm -e run_my_script
It works as expected! The xterm pops up, ssh queries me for a password, the command runs and displays, and, seconds later, the xterm is killed. This is what I want to have happen. But I'm not sure why the remote shell and my application (run_command, above) still stick around. I've been pretty sloppy with stdin/stdout so I'm surprised they don't disappear when I kill the parent (xterm).

I'm happy it works, but I'm worried about a bug creeping in later- for example, since I'm not handling stdout, am I in danger of filling a buffer that is going to make the app hang? Or something like this.

I'm looking for insight into what happens when xterm calls ssh which calls a shell which calls a command. Xterm dies but the command does not. Why?

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KILL(1) 						      General Commands Manual							   KILL(1)

kill - terminate a process with extreme prejudice SYNOPSIS
kill [ -sig ] processid ... kill -l DESCRIPTION
Kill sends the TERM (terminate, 15) signal to the specified processes. If a signal name or number preceded by `-' is given as first argu- ment, that signal is sent instead of terminate (see sigvec(2)). The signal names are listed by `kill -l', and are as given in /usr/include/signal.h, stripped of the common SIG prefix. The terminate signal will kill processes that do not catch the signal; `kill -9 ...' is a sure kill, as the KILL (9) signal cannot be caught. By convention, if process number 0 is specified, all members in the process group (i.e. processes resulting from the current login) are signaled (but beware: this works only if you use sh(1); not if you use csh(1).) Negative process numbers also have special meanings; see kill(2) for details. The killed processes must belong to the current user unless he is the super-user. The process number of an asynchronous process started with `&' is reported by the shell. Process numbers can also be found by using ps(1). Kill is a built-in to csh(1); it allows job specifiers of the form ``%...'' as arguments so process id's are not as often used as kill arguments. See csh(1) for details. SEE ALSO
csh(1), ps(1), kill(2), sigvec(2) BUGS
A replacement for ``kill 0'' for csh(1) users should be provided. 4th Berkeley Distribution April 20, 1986 KILL(1)

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