I need help

hello, i am a newbie and i really need your help

i have an centos 6.5 and i wonder if i can create a list with random 4 letters :

gdjf
ornc
tyrn
jfdn
nofd
etc....


if it can be done , i will really apreciate your help ! THANKS !!!

ohhh...i forgot .... i want to use all letters....all posibilities.....