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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) 						    BSD General Commands Manual 						   KILL(1)

kill -- terminate or signal a process SYNOPSIS
kill [-s signal_name] pid ... kill -l [exit_status] kill -signal_name pid ... kill -signal_number pid ... DESCRIPTION
The kill utility sends a signal to the processes specified by the pid operand(s). Only the super-user may send signals to other users' processes. The options are as follows: -s signal_name A symbolic signal name specifying the signal to be sent instead of the default TERM. -l [exit_status] If no operand is given, list the signal names; otherwise, write the signal name corresponding to exit_status. -signal_name A symbolic signal name specifying the signal to be sent instead of the default TERM. -signal_number A non-negative decimal integer, specifying the signal to be sent instead of the default TERM. The following pids have special meanings: -1 If superuser, broadcast the signal to all processes; otherwise broadcast to all processes belonging to the user. Some of the more commonly used signals: 1 HUP (hang up) 2 INT (interrupt) 3 QUIT (quit) 6 ABRT (abort) 9 KILL (non-catchable, non-ignorable kill) 14 ALRM (alarm clock) 15 TERM (software termination signal) Some shells may provide a builtin kill command which is similar or identical to this utility. Consult the builtin(1) manual page. SEE ALSO
builtin(1), csh(1), killall(1), ps(1), kill(2), sigaction(2) STANDARDS
The kill function is expected to be IEEE Std 1003.2 (``POSIX.2'') compatible. HISTORY
A kill command appeared in Version 6 AT&T UNIX. BUGS
A replacement for the command ``kill 0'' for csh(1) users should be provided. BSD
April 28, 1995 BSD

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