Comment 46 for bug 26338

=== Summary ===
I've just reviewed the duplicates, and marked a few others as duplicates. The problem seems to be that the graphical users-admin tool has some SEVERE bugs that make a system unusable and insecure. It makes several unintended changes to /etc/group under various conditions, including:
  * stripping group membership from all/many accounts when adding a new user
  * allowing non-admin accounts to change the root password
  * deleting accounts other than the selected one (?)
Bug #64698 has a good statement of one manifestation.

Symptoms include:
  * User no longer in sudoers (because no longer in admin)
  * Network failures (because haldaemon is no longer in appropriate groups)
  * Sound failures (because user and haldaemon are no longer in audio)
  * USB and other devices no longer working (haldaemon again)
  * Gnome login problems (audio? hal? networking?)

Very likely this bug is causing a whole host of mysterious bugs that never got tracked back to /etc/group, because the symptoms are apparently unrelated.

One method to recover:
  * Reboot to "recovery" mode (a.k.a. single-user)
  * Edit /etc/group:
     * add the appropriate accounts to "admin" and "audio" (etc) again
     * add "haldaemon" to: cdrom, floppy, audio, plugdev, powerdev (maybe others, but that's what I found)

I am attaching my reconstructed /etc/group, to help people recover. I _appear_ to have everything working again (sound, network, gnome login, sudo) though I may yet have missed something, or your system may have other bits. It's been slightly anonymized -- users "daffy", "bugs", "marvin" and "donald" are fictitious. Hope this helps.

Other possibilities including reinstalling hal and/or udev to reset those permissions. (sudo aptitude reinstall hal hal-device-manger).

Mind you, I'm deleting "users-admin" from my system for now.