Determine printer status
lpstat -p -d
E.g:
me@pc ~ $ lpstat -p -d
printer Officejet_J6400 is idle. enabled since Fri 31 Aug 2012 10:22:16 BST
system default destination: Officejet_J6400
Set default printer
lpadmin -d <printer>
Where <printer>
is the printer name e.g. Officejet_J6400.