I personally don't want to write out a long detailed diatribe on unix commands, Which can be better taught by another source, Call it laziness, call it genius, call it whatever you like.
This will be your 'Homework' if you are behind the rest of everyone else
--Read and understand the importance of system variables
--Learn some security related native commands such as chown, setgacl etc.
--If there is any area of Unix that you feel weak in, Learn it.
I will give a quick rundown on some rlogin, /shadow and ssh conf file incantations you must know if you plan to do anything
+ + - Give access to everyone.
Ciphers
Specifies the ciphers allowed for protocol version 2. Multiple
ciphers must be comma-separated. The supported ciphers are
``3des-cbc'', ``aes128-cbc'', ``aes192-cbc'', ``aes256-cbc'',
``aes128-ctr'', ``aes192-ctr'', ``aes256-ctr'', ``arcfour128'',
``arcfour256'', ``arcfour'', ``blowfish-cbc'', and
``cast128-cbc''. The default is:
AllowGroups
This keyword can be followed by a list of group name patterns,
separated by spaces. If specified, login is allowed only for
users whose primary group or supplementary group list matches one
of the patterns. Only group names are valid; a numerical group
ID is not recognized. By default, login is allowed for all
groups. The allow/deny directives are processed in the following
order: DenyUsers, AllowUsers, DenyGroups, and finally
AllowGroups.
Banner Useful for funtime with Cyrillic letters
UseDNS Specifies whether sshd(8) should look up the remote host name and
check that the resolved host name for the remote IP address maps
back to the very same IP address. The default is ``yes''.
Zephyr-The-Zeph