Free operating system for various platforms that can be built and configured by the user or users to best suit their system needs.

Chart includes detailed information on:
- logging in & out
- user & group manipulation
- LINUX shells & command line
- the file system
- I/O redirection
- wildcards & the VI editor
- permissions & ownership
- shell & user variables
- FTP (File Transfer Protocol)
- archiving files & directories
- login shell scripts
- job control & processes
- command summary