Install Icinga 2 monitoring instance with web-interface. Beware, it is a lengthly article, but the whole process is quite simple, so you should get grasp of it after first execution.
MariaDB unixODBC driver is not available in the Debian package repository at this moment, but you can build and configure it on your own. It requires some additional work, but in the end it is really worth the time.
Enable HTTP/2 in HTTP mode on HAProxy 1.8 and temporarily fix the bad request problem in the nginx backend using fastcgi/uwsgi.
Install recent HAProxy version to take advantage of the new fancy features.
Generate private key for an SSL certificate and verify its consistency.
You can still connect to the Microsoft SQL Server 2014 as a member of the sysadmin server role using single-user mode when you are locked out of the database.
Query APT configuration to inspect specific options or create universal Debian utilities.
It is very useful to know how to distinguish between different GnuPG public key files.
There is a large number of different ways to verify IPv4 address inside a shell script, but many of these are complicated or incomplete. I will describe a simple and verbose way to check IPv4 address using