Removing A User From GDM

Maybe you just read-up on using rsnapshot for remote backups and have a horrible useless user listed in GDM, or maybe Google brought you here, either way:

Edit /etc/gdm/gdm.schemas and find the exclude section:

greeter/Exclude
s
bin,root,daemon,adm,lp,sync,shutdown,halt,mail,news,uucp,operator,nobody,nobody4,noaccess,postgres,pvm,rpm,nfsnobody,pcap

Add the user you want ignored:

greeter/Exclude
s
bin,root,daemon,adm,lp,sync,shutdown,halt,mail,news,uucp,operator,nobody,nobody4,noaccess,postgres,pvm,rpm,nfsnobody,pcap,rbackup

Note the addition of rbackup at the end, or, in your case whatever the username you want to remove.