Procedure for checking System
Check the environment.
...]# set
Show logged in users and what they are doing.
...]# w
Report process status -- make sure all needed processes are running (ex: apache, mysql, ssh).
...]# ps -auxf
Display used/free system memory.
...]# free -m
Display used/free disk memory.
...]# df -h
Display network interface information -- make sure your interfaces are up and running.
...]# ifconfig
Show network connections -- check the ports your system is listening on and the programs behind those ports.
...]# netstat -ape
View logged activity.
...]# less /var/log/secure
View logged activity.
...]# less /var/log/messages
Show listing of last logged in users.
...]# last
Show log of login activity by user name.
...]# lastlog
List loaded modules.
...]# lsmod