I'm running an Apache server on Ubuntu. When I restart it, it asks me for a pass phrase; here's what the dialog looks like:

Apache/2.2.16 mod_ssl/2.2.16 (Pass Phrase Dialog) Some of your private key files are encrypted for security reasons. In order to read them you have to provide the pass phrases.

Server 127.0.0.1:443 (RSA) Enter pass phrase:

I've already worked out how to remove the pass phrase from the key file in question, but I can't find any information anywhere on how to determine which key file Apache is complaining about in the above dialog. I have dozens of key files on the server in question, although I don't know which ones are in active use (all I did is 'locate .pem' and ignore the false positives). Does anyone know how to track down which pem file I need to remove the passphrase from?