Removing user `Debian-gdm' ... Warning: group `Debian-gdm' has no more members. userdel: user Debian-gdm is currently used by process 2019 /usr/sbin/deluser: `/usr/sbin/userdel Debian-gdm' returned error code 8. Exiting. Could not remove Debian-gdm user. /usr/sbin/delgroup: `Debian-gdm' still has `Debian-gdm' as their primary group! Could not remove Debian-gdm group. Presumably, the daemon wasn't stopped prior to removal, so the user is still being used and cannot be removed by postrm.