A common question: Is really ESXi a Linux OS ?!

I saw many times people ask and speak about what is really the operation system of VMware ESXi?! Generally many of them called it as a Linux OS (customized by VMware). Many factors cause to conclusion this result like the following list:

1. Commonly extension files used and structure of root directory (/) and its sub-directories.
   
2. Existence of the tradition administrator account (root).
3. Managing via Shell or a remote SSH connection.
4. Log file path: (/var/log)
   
5. Common CLI like: ls, pwd, cd, cp, mv, more and ...

But technically I should say VMware ESXi is NOT a Linux OS!

First of all, we should review the Linux definition again carefully: Linux is an open-source Unix-based OS that is developed by Linus Torvalds (1991) that has many popular distributions like Ubuntu, Fedora and Debian (free distributions) and some other commercial/supported distribution such as SUSE and RedHat, and all of them have an important common characteristic: All of them are based on the Linux Kernel that ESXi doesn't have it at all, because as you know the VMware developed its own special OS kernel: VMkernel (VMM) the primary part in the ESXi architecture.

But really all of those mentioned OS characteristics are exist inside VMware ESXi  too, but not because you may think ESXi is a Linux system. All of them are possible because the ESXi consists of a BusyBox: a lightweight unix-like shell includes of many of Unix applications/utilities inside a software suite and some other management CLIs and Unix-like tools provided by the VMware.

However because the ESXi does not provide all aspects of the Unix-OS functionalities, we cannot say it's a Unix OS too. I emphasis we speak about the ESXi product, not its precedence the traditional ESX! because the ESX used RHEL in many functionalities, like the installation wizard.