I'm referring to this question. What is the 'passphrase-file' mentioned in here? Please clarify.
closed as off topic by cjm, uther, jasonwryan, Shadur, manatwork Jan 23 at 18:05
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The SSL certificate file has been encrypted, and the apache2 server must be supplied with a correct passphrase (password) as startup so it can decrypt the certificate and run in SSL mode. The "passphrase file" is just a shell script (program) which prints that passphrase to standard output. When apache2 starts it asks for the passphrase, reading the text from standard input. Because the configuration is set to run that script at that moment, the input to apache2 is the script output - so apache2 gets the passphrase it needs without a human having to intervene and type it. I hope this explains it sufficently!