i was trying to change the permissions for my user account so i can have read/write access to all files so in another post someone recommended doing this:

~# chmod -R a+rwx /

and it changed the permissions ok but now when i try to su to root from my user account i get this:

~$ su
Password:
initgroups: Operation not permitted

"su -" does the same thing too

how can i fix this?

The advice was bad, you just trashed your system. Unfortunately it looks like you are going to have to reinstall.

really?

i can still log in to root and do things from there but thats a hassle.

When important system files have incorrect permissions set, things won't work. A lot of programs will not run as expected. Although it is possible to fix the permissions, it is a lot of hard work and it will almost certainly be faster to back up your files and reinstall.

In future if you need to modify files owned by root, you should 'su', change the files and then exit as soon as your are done. This both decreases the chance of accidentally deleting your entire harddisk, and increases security from hackers/malicious users of your system.

I would suggest a little background reading about Linux before you start executing unknown commands as root. As a user though you can happily play around without fear of damaging your system.

Good luck,
Mark.

The whole idea of having the root user and different levels of accessability is to prevent harm (accidental or otherwise) to the system. By modifying the entire system to give you write access as a normal user you're removing that protection. There's a very good reason things are set up as they are, so don't go messing!