Blocking ctrl-c to os.popen() or os.system()

[Erik Max Francis]

Sandeep Gupta wrote:

> I am executing a command from python via os.popen().  While the
> command is executing, if I type ctrl-c, the command receives the
> interrupt.  I would like to block the ctrl-c from the command and I've
> tried the following:
> 
> 1)Using python's signal module to ignore SIGINT.  This causes python
> to ignore SIGINT, but a ctrl-c that is typed during the popen() call
> still goes to the command.
> 
> 2)Adding "< /dev/null" to the os.popen() call.  This doesn't help.
> 
> 3)Using popen2() and immediately closing the stdin file.  This also
> doesn't work.
> 
> Any suggestions would be greatly appreciated!

The problem here (which other responders failed to identify) is that
it's the spawned program that's getting the INT signal, not the Python
program launching it.  Signals are really independent of stdin/stdout,
so that's why your redirection and file closing isn't helping.

Unfortunately, I don't think there's any pretty solution to your
problem.  What you probably need to do is write a wrapper program that
intercepts the INT signal and ignores it (presuming that's what you
actually want to do).  This would be similar to the nohup program (which
does something analogous, but for the HUP signal).

You can write a little script to do it, with bash, ksh, zsh, or
varieties.  In zsh it would look like:

	#!/bin/zsh -f

	function TRAPINT () { }

	"$@"

The other shells have similar mechanisms, I believe involving a trap
builtin.

Unfortunately you're probably going to be forced to use a wrapper script
for portability, since with os.popen (or os.system) you're not
guaranteed which shell is going to get run, so you can't do the trapping
inline.

Note that this won't stop other signals, such as TERM, and that nothing
can stop KILL.

-- 
 Erik Max Francis / max at alcyone.com / http://www.alcyone.com/max/
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