Comment 11 for bug 424462

The problem is that apt-mirror is not handling SIGINT, SIGHUP, or SIGTERM correctly thereby leaving a stale lock file around and does not actually check for a running process before reporting that one is already running. It should trap these and clean up before exiting or at the very least report something such as "apt-mirror is dead, but lockfile /path/to/lockfile/apt-mirror.lock exists: exiting" instead of just reporting that the process is already running.

You will not see this behavior if the process completes normally.