I was wondering what the letter T means on the following results.
$ ls -l /dev/mem crw-r----T 1 root kmem 1, 1 Jan 1 1970 /dev/mem
I have changed the permissions and now I don't know how restore that letter T.
Finally i figure out thanks to @SteveRobillard link.
To restore to original priviliges:
sudo chmod 640 /dev/mem sudo chmod +t /dev/mem
Smething with t permission is something that can only be moved or deleted by that object's owner, the directory owner, or the super-user.