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