Locking Down a Linux box

I want to spend the next week looking at some of the different utilities used to lock down a Linux box and make it harder for someone to hack into it.

PS command
PS stands for process status. This command lists the current running processes on a system appropriate for the privilege of the user using the command and also their characteristics, when used with certain options. Used to check and minimize security breaches, unwanted accesses, and idle processes. If pid arguments are specified then only those processes are listed, otherwise all processes with the same effective user id and controlling terminal are listed.

Older versions of the PS program will return an error if the dash (-) is used. hence sometimes ps -aux will be shown as ps aux.

OPTIONS

-a, --interactive
List all processes associated with terminals.
-t, --terminals|ttys=tty...
List processes with controlling terminals in the tty list.
-T, --tree|forest
Display the process tree hierarchy in the COMMAND field list.
-u|U, --users=user...
List processes with real user id names or numbers in the user list.
-v, --verbose
List verbose error messages for inaccessible processes.
-x, --hex
List numeric entries in hexadecimal notation.