xdm 1:1.0.5-2 (i386 binary) in ubuntu gutsy

 xdm manages a collection of X servers, which may be on the local host or
 remote machines. It provides services similar to those provided by init,
 getty, and login on character-based terminals: prompting for login name and
 password, authenticating the user, and running a session. xdm supports XDMCP
 (X Display Manager Control Protocol) and can also be used to run a chooser
 process which presents the user with a menu of possible hosts that offer
 XDMCP display management.
 .
 If the sessreg package is installed, xdm can use the sessreg utility to
 register login sessions to the system utmp file; this, however, is not
 necessary for xdm to function.
 .
 xdm requires the C preprocessor (cpp) to process its configuration files.