What is unix system security

Can someone please discuss the Unix system security? Just need a short summarization of what it is, tried searching google but am having no such luck, please help as soon as possible.

The UNIX server I deal with uses the CHMOD system. I'm not sure if that's universal.

Files and folders can be set for Users, Groups and Owners. Each of them can be set for Read, Write or Execute. They are combined into a three digit number based on 4 for read, 2 for write, 1 for execute.

The following example would produce a CHMOD value of 755

User: r-w-x = 4 + 2 + 1 = 7
Group: r-x = 4 + 0 + 1 = 5
Owner: r-x = 4 + 0 + 1 = 5

unix operating system security depend itself because it is open source operating system .it may easily available on www.vtu.us you may refer this .

UNIX system security alludes to the method for securing a UNIX OS. A protected situation is accomplished not just by the design ideas of these Operating systems, additionally through cautious client and authoritative practices. Also, you may refer AskPCExperts for more information.