Comment 24 for bug 406397

Tim, I'm sorry that you're experiencing the issue. I believe that squid may have always had this issue and we only stirred it up by updating squid.

There is a really scary workaround available which is to create a program that exhausts the pid-space until tracked pid exists again, and then upstart will be able to re-attach and kill it...

http://heh.fi/tmp/workaround-upstart-snafu

I do think that we may need something a little less perfect than a full rewrite of the ptrace tracker that we could possibly backport to lucid. There seems to be a missing command that would allow an administrator to tell upstart to just forget about an instance.