Learn difference between su and sudo. By learning difference you will be able to judge which one is best suited for your requirement of access management.
Learn everything about logrotate utility in Linux. This post explains what is logrotate, why to use it and its configuration steps.
Learn how to restart Apache webserver in Linux from command line. Know log file locations to look for troubleshooting during restart process.
Learn how to install SSL certificate on Apache webserver running on Linux machine. Steps includes installation, configuration and verification.
Step to generate CSR file. CSR file is a request file which is then submitted to vendor for getting SSL certificate for webserver.
Learn to restore nagios configuration backup. If you messed up nagios configuration, you can restore last known good config using these steps.