Re: su command...

[Alfred M. Szmidt]

   > Please, how can I execute the following idea: $ su gimp &
   > but really in bacground?

   I can not figure out what you want to do, but you might try=20
   this :

   if [[ $(grep gimp /etc/passwd | cut -d':' -f1) == "gimp" ]]; then su - gimp; 
else su -; export DISPLAY=:0.0; gimp &; logout; fi;

   In the hope that this may help.

I think you are overengineering the solution, the OP just wanted to
execute gimp as root, and spawn it to background.

The following would do the trick: su -c gimp &

Also, your solution will not work on anything that uses LDAP, NIS, ...