Allow/Deny Users to Print

By default, all users are allowed to print.
1) This will allow only sergey to print:
lpadmin -p HPLaserJet6MP -u allow:monalisa.phy.vanderbilt.edu\!sergey
2) The following line will be added to /etc/lp/printers/HPLaserJet6MP/users.allow :
monalisa.phy.vanderbilt.edu!sergey
3) If the file
/etc/lp/printers/HPLaserJet6MP/users.allow
exists, then users.deny file is ignored.