title: Lines commented out in Linux configuration files
body: <p>I'm trying to find out why in Linux service configuration files almost all of the lines are commented out. I cannot find the answer.</p>
  
  <p>What is the valid configuration then? Is it hardcoded somewhere in the system and changes in config files (for example by uncommenting and changing the value) apply by overwriting the default configuration (in commented out lines)?</p>
  
  <p>What is a result of uncommenting of such lines? As far as I know it should do exactly nothing. Then why are they commented out?</p>
  
  <p>I know it may sound a bit silly but I really want to know why such mechanism was implemented, it's a bit unintuitive.</p>
  
  <p>This question applies to lots of services e.g. SSH service after installation.</p>