Detecting a stale pid file in a Unix environment

Question

What is the standard, cross-platform way to detect stale pid file in a Unix environment? Say I would like to kill an old instance of my application, but I certainly don\'t want

Answer 1

File times at /proc/ date back to at least 1991; see p. 243. And, although mtime can be faked (e.g. via touch -m --date=<needed_date> <target_file>), for a userland app there is no way to do so on its own /proc/ entry.