A lot of systems administrators will use SED for string substitution, when they should try using PERL. When doing string substitutions with SED the string substitutions write to a seperate file, then the file is copied over the target file. This second file that is created utilizes Disk I/O, another issue you can run into are file permissions if your umask doesn’t match the permissions of the target file. With PERL you do not have any of these issues since its effects are directly onto the target file with no usage of secondary files therefore not Disk I/O.
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Sometimes you need to edit a new or existing file while looking at a separate file using VI. This can be very useful and a powerful time saver. Fortunately you can do this using some simple commands.
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Reverse DNS is the process of using DNS to translate IP addresses to hostnames. Reverse DNS is the opposite of Forward DNS, which is used to translate hostnames to IP addresses.
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For all those who don’t like to remember the details I have included my quick reference to IPv4. Its not full fledged but can offer some pointing in the right direction. IPv4 is the fourth iteration of the Internet Protocol (IP) and is the most widely deployed. If you want some ugly history details you can always refer to IETF RFC (791). Otherwise just know IPv4 is a data oriented protocol to be used on packet switched internetworks such as ethernet.
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