I am Linux user with no knowledge on security , up to now i dont know that is my system was in attack or not . I havent felt anything wrong with my system . but every Computer user must have some knowledge on basic system security . so what are the basic things/methods i need to follow the check the security of system and to protect it .
You may be interested in a Linux hardening guide. There are copious amounts of articles online which cover how to secure your operating system. Here are a few:
I agree with Jeff, your post is much to vague to receive any kind of constructive information. Are you a system administrator or are you trying to secure a personal Linux machine? Is this a server or a workstation?