Where are the environmental variables (eg. $DISPLAY) stored?
 

Eg.

david:/etc# echo $DISPLAY
:0.0
david:/etc# echo $TERM
xterm

In which file can these environmental variables' assignment be found?

Thanks !

type 'env' or 'printenv' .

I think enviornment variables are stored in kernel space memory.
you can also set these.
setenv, $HOME=/blah , $whatever=$?

In either your .bash_profile or your .bashrc files. You generally have generic files in your /etc/skel directory, and every user has them in thier user directory. They're hidden files, as that's what the '.' in front of the name does, but you can see them with 'ls -A'

cat /home/username/.bash_profile should show some of your path (the $PATH part is based on your startup files in /etc), but there might be additional settings in /home/username/.bashrc