Re: [PLUG] idle curiosity - ghost process

["Paul L. Snyder" <plsnyder@drexel.edu>]

On January 30, 2009 , "Matt Mossholder" <matt@mossholder.com>  wrote:

>----- "Bill East" <wm.east@gmail.com> wrote:
>
>To answer the idle curiosity part, yes, you can send input to the
processes, without
>bringing it back into the foreground (using fg as others have suggested).
>
>Off the top of my head, one way to do it would be to send data to
/proc/<pid>/fd/0.
>That sends data to file descriptor 0 of the process, which happens to be
"standard
>input".

Very cool idea!  Sadly, it doesn't look like it works.  Since the grep
process is
forked from the shell, it uses the same pseudoterminal as the shell.  When
it was
backgrounded, it would have suspended when it tried to read from its stdin.
So, /proc/<pid/>/fd/0 is a symlink to some pty, /dev/pts/<num>, and if you
check the
fd symlinks for both the shell and the forked process, they are the same. 
If you
direct data to it, it goes to the process that current has that pty open,
which is
the parent shell, and the text will show up unfiltered in the shell's stdout.

Paul


___________________________________________________________________________
Philadelphia Linux Users Group         --        http://www.phillylinux.org
Announcements - http://lists.phillylinux.org/mailman/listinfo/plug-announce
General Discussion  --   http://lists.phillylinux.org/mailman/listinfo/plug