How to hide users from the login screen?

I have recently added several new users, that I need for qmail. Now they appear in the box in the login screen and clutter it, and I have to scroll to find my user. How can I hide those users from the login box?

From ubuntu gruszczy

• Hacky but you can modify the user's level so they don't show in the list:

  sudo usermod -u 999 <username>
  

  The only other way I know is to hide the list completely:

  sudo -u gdm gconftool-2 --type bool --set /apps/gdm/simple-greeter/disable_user_list 'true'
  

  João Pinto : There is no such thing as "user's level", it's user's ids .
  From Oli

• Edit the file /etc/gdm/gdm.schema find the section that currently looks like this:

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

  And to exclude a user called qmail for example add qmail to the default list so the section looks like this.

    <schema>
      <key>greeter/Exclude</key>
      <signature>s</signature>
      <default>qmail, bin,root,daemon,adm,lp,sync,shutdown,halt,mail,news,uucp,operator,nobody,nobody4,noaccess,postgres,pvm,rpm,nfsnobody,pcap</default>
    </schema>
  

  That will stop user qmail appearing in the gdm greeter. There used to be a nice GUI tool to do this but is has not been in Ubuntu for the last few releases.

  The other alternative is to set the UID of the user to under 1000. Those are considered to be system accounts which are excluded in the GDM greeter too.

  Source Lab : afaik, the GUI tool doesn't work any more, due to the fact that GDM switched from plane textfiles for its config to Gconf schemas.

  Richard Holloway : Thanks for the information Source Lab. I have noticed over the last few releases several GUI tools have been lost for similar reasons.

  Gilles : Actually, I don't think you should modify `/etc/gdm/gdm.schema`. Instead, add the two lines `[greeter]` `Exclude=nobody,qmail-foo,qmail-bar` to `/etc/gdm/custom.conf`. (Apart from `nobody`, the names in the default list won't show up anyway because their uid is <1000.)

  txwikinger : Usually you should use uids under 1000 for this.

  Richard Holloway : +1 Thanks Gilles. That is very useful to know.

  gruszczy : gdm.schemas worked perfect. Thanks a lot :-)
  From Richard Holloway

• I don't know whether appending Exclude=foobar in /etc/gdm/gdm.conf works, have you tried it?

  From Umang