How will I enable dual side printing in the linux ,the option is nowhere to be seem ..

Might help if you provided details. What "the linux" are you using?? Version/distro?? What kind of printer? Attached how? Running CUPS, or printing directly to it via socket? From what program are you printing??

Many HP printers are supported by HPLIP, and the option can be found when you run the hp-setup program. Some office multifunction copiers (Ricoh, Xerox, etc.), have Linux drivers that support it easily.

If you tried to look it up on Google, you'd find many solutions:
http://www.linuxfoundation.org/colla...sdocumentation

from that page:
Read the man page for lpoptions. And if you searched on this site:
http://www.linuxquestions.org/questi...1320-a-393678/

You'd have found a solution there as well.

That will be a function of the printer device driver, assuming the printer is capable of duplexing. It's specific to the printer.

Yes the printer supports duplexing and I am using RHEL5 & the printer is a remote HP printer connected to a windows machine.

I am trying with cups but failing again and again

Ok...again, what KIND of HP printer? What are you doing? HOW is it failing?? Just saying "it's not working", doesn't give anyone any idea on how to help you.

Again, HPLIP will often support options like duplexing, if you ran the HP-SETUP program as I said in my first post. The lpoptions command is also used to do it via CUPS. But you don't say what you've done/tried or how it's failing. And if you're using RHEL, the best thing for you to do is call RedHat support, since you're paying for it with your RHEL subscription