i am not able to modify $DISPLAY using setenv
 

i am not able to modify $DISPLAY using setenv
what could be the possible cause
do i need any permissions

It's better that you specify the command you type - where, in bash? And paste the error you get. DISPLAY is an environment variable and any specific user can change variables related to its own environment

What do you mean by "can't modify". Do you get an error, or does it appear to work. 'setenv' is for csh type shells, whereas bash uses 'export'. Either way, the environment variable you set will only be valid in the current terminal. If you want to change it globally, you will have to put it in a startup script (.profile, .login etc depending on your shell).

Can you post the output you get from trying setenv? And a bit more context would be useful.