On OS X 10.8 I deleted a user account which had Remote Login permissions. Now, in the Sharing tab of System Preferences, that user shows up as "Unknown User", and clicking the minus button won't remove it.
Found the solution here, hope this helps.
1) First remove all users that can be removed from GUI In System Preferences -> Sharing -> Remote login
2) Run the below command which shows the configuration of users who have remote login access
sudo dscl . -read /Groups/com.apple.access_ssh
AppleMetaNodeLocation: /Local/Default GeneratedUID: 2F60778C-0931-47A4-B656-DBE07ACD843F GroupMembers: **3D7C31B1-DEDE-4A5A-AAA8-CDD55645DC75** GroupMembership: youraccoutname PrimaryGroupID: 404 RealName: Remote Login ACL RecordName: com.apple.access_ssh RecordType: dsRecTypeStandard:Groups
3) remove the group GroupMembers that the user(Unknown User) is in
sudo dscl . delete /Groups/com.apple.access_ssh GroupMembers 3D7C31B1-DEDE-4A5A-AAA8-CDD55645DC75
4) Go to System preferences and see the result
Thank you! It worked. That command removed the entry from the Sys Prefs GUI, but running the dscl read command again still showed the old username. So I opened up Directory Utility and deleted it there, from the Group called Remote Login ACL.– ElliottSep 3, 2013 at 16:49
Expanding upon Kent's comment, if you prefer a graphical user interface:
In the Users & Groups pane of System Preferences, click Login Options.
If the Edit… button is greyed out, then click the lock to make changes.
Edit… > Open Directory Utility…
With Directory Utility
Click Directory Editor, then view Users in the /Local/Default node:
If you find debris that relates to the previously deleted user
You can authenticate and use Directory Utility to delete that debris.
If you find no such debris
There may be an issue with a configuration file …
Thanks. I did find "Unknown User" in the Directory Editor, but after deleting it and rebooting, the problem still shows in Sharing prefs.– ElliottJun 8, 2013 at 7:58
Please vote down this answer – sorry! Unknown User seems to be normal for some installations of OS X. It may be appropriate to recreate Unknown User to have it reappear in Directory Utility – then revisit the opening question with a different answer. Jun 8, 2013 at 9:47
@GrahamPerrin if you know it is wrong why don't you delete the answer?– mmmmmmJun 8, 2013 at 11:46
Leaving the answer could help to avoid others making the same mistake … Jun 8, 2013 at 18:03