I was going to report this as a separate bug but it seems to have the same symptoms, so I''ll add it here. The context is that the package "hal" cannot be installed anymore because adduser misbehaves. I extracted the relevant command from the postinst and ran it by hand several times in a row. Behold: bell:~# getent passwd hal bell:~# getent group hal bell:~# adduser --quiet --system --home /var/run/hal --gecos "Hardware abstraction layer" --group hal useradd: unknown group hal adduser: `/usr/sbin/useradd -d /var/run/hal -g hal -s /bin/false -u 108 hal'' returned error code 6. Aborting. Cleaning up. Removing user `hal''. userdel: user hal does not exist Removing group `hal''. groupdel: group hal does not exist bell:~# getent passwd hal bell:~# getent group hal hal:x:108: bell:~# adduser --quiet --system --home /var/run/hal --gecos "Hardware abstraction layer" --group hal chfn: Unknown user hal adduser: `/usr/bin/chfn -f Hardware abstraction layer hal'' returned error code 1. Aborting. Cleaning up. Removing user `hal''. userdel: user hal does not exist bell:~# getent passwd hal bell:~# getent group hal hal:x:108: bell:~# adduser --quiet --system --home /var/run/hal --gecos "Hardware abstraction layer" --group hal useradd: user hal exists adduser: `/usr/sbin/useradd -d /var/run/hal -g hal -s /bin/false -u 114 hal'' returned error code 9. Aborting. Cleaning up. Removing user `hal''. bell:~# getent passwd hal hal:x:112:108::/var/run/hal:/bin/false bell:~# getent group hal bell:~# adduser --quiet --system --home /var/run/hal --gecos "Hardware abstraction layer" --group hal useradd: unknown group hal adduser: `/usr/sbin/useradd -d /var/run/hal -g hal -s /bin/false -u 108 hal'' returned error code 6. Aborting. Cleaning up. Removing user `hal''. userdel: user hal does not exist Removing group `hal''. groupdel: group hal does not exist bell:~# getent passwd hal bell:~# getent group hal hal:x:108: So as you see, it doesn''t even behave deterministically.