Linux and Unix

The UNIX brand has traditionally been applied to the family of multitasking, multi-user computer operating systems that derive from the original AT&T UNIX operating system. It was eventually standardized in a series of publications called Portable Operating System Interface (POSIX).
Linux, in its turn, is basically the name of the Kernel based on Unix, a complete rewrite from scratch. BSD projects are a bit different from Linux in that they are partial clones. They contain a mixture of real Unix freely licensed source code and some newly written clone code and other later code emerging as part of rewrites or as needed to support modern HW and modern POSIX specifications.
The main difference between all of those is how the kernel core and its services are running, how the kernel threads and process contexts are organized. Unix software is written to the POSIX API's and typically runs on all versions of Unix, Linux, and BSD.

13+ years of advanced hand-on experience

High-standard of experience deploying and configuring FreeBSD, Debian, Ubuntu, RedHat, SUSE as a server operating systems, public Internet facing servers management.
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Ansible, Puppet and Chef Linux environment management.