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So, in studying for the LPI Certification, and doing some practice exams, I keep running into questions that I get wrong simply because I assume the HUP signal is equivalent to restarting a service/daemon. Obviously, I'm wrong, but can someone enlighten me as to why?

The Apache documentation states that HUP kill off the process' children, but not the parent, which sense, but is this behaviour mimicked in unix?

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up vote 5 down vote accepted

The usual effect of HUP on long-running daemons is to reload the configuration. Sometimes this is done by restarting completely, sometimes something more intelligent/fast/safe is done.

There is nothing mandatory about this behavior, it's not really what that signal was intended for originally. (The SIGHUP article on Wikipedia has a bit more details.)

Each daemon's writer is free to implement SIGHUP handling as he/she wishes. This includes ignoring the signal entirely.

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Thanks for the extra information! :) – Julian H. Lam Apr 3 '11 at 17:18

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