can any one tell me how to know the password from /etc/passwd file and /etc/shadow

/etc/shadow, encrypted password you can not view

tell me how to install the .tar.bz2 files in RHEL6 and also the media player codecs when im not a registered with RHN

Rather asking all these you can search in google or manpage. For mplayer just refer their website

It is essential security step to encrypt all user passwords in the system.

When you log into system, you enter a string to login program. Then there is "salt" string added to the string you entered, and the result is encrypted with some algorithm. If the result matches the one in /etc/shadow (or /etc/passwd), you are successfully logged in.

Therefore, if you want to 'crack' encrypted password from /etc/shadow or /etc/passwd, you have to try every combination of letters in password which could be possibly used.

You can use programs like John The Rippers to approach this.

However, I discourage you from stealing any passwords from computers other than yours.

//edit: Take a look at ways of installing programs in Linux.

Skyer

how to plot xgraph?

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You uncompress the file, and read the installation instructions that come with it, read them from the website where you downloaded it, or reference whatever information source the program has. Each program will tell you how to install it.
You don't. If you want the benefits of RHEL, then you pay for it. Otherwise, you don't get them.

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You read the documentation on xgraph, and follow it:
http://www.xgraph.org/

And do not hijack someone elses thread..open your own thread for your own question.

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Worst thread ever. Lousy title, questionable questions, and a hijacking. Must be a Monday. (No... it's Wednesday.)

@dinesh_singh: for starters, please read the LQ Rules.

You can't reverse a (good) cryptographic digest. That's the point. You can try to brute force it. If your users have selected strong passwords, you will need a massive amount of time, CPU power, disk space, or all three. Failing that, plan on living to be around 5,000 years old (barring unexpected advances in computing before that time, which could certainly happen) in order to get what you want.

If you're not paying for RHEL, then use CentOS, Scientific Linux or some other derivative. Or use a non-RHEL, like Debian. If you had taken a few seconds to search the forums, you'd find that some form of this question is asked about once every day or two.

As yesterday was a public holiday here, it does really feel like a Monday