Comment 38 for bug 432964

i'm using ubuntu12.10 and i had the same bug that affects a lot of users (can't install or update any paquet that uses addgroup, adduser)
i tried "sudo rm /etc/{passwd,group,shadow}.lock" =>the same bug
then "fuser /etc/group" =>nothing
then "fuser /etc/passwd" => there was "cupsd" and "colord-sane"
then, i stopped only "colord-sane" by "killall colord-sane" because i didn't find it on " sudo gnome-system-monitor" =>but, the same bug
so, i tried again "sudo rm /etc/{passwd,group,shadow}.lock" to delete the new log files ('group.lock' and 'shadow.lock')
then "fuser /etc/passwd" =>nothing (even "cupsd")

so, i tried to create a new user and new group and every thing was Ok (no bug) also, i'm now able to install paquets that use add{user,group} :-)

I'm not sure if "colord-sane" was the problem, but i found many bug reports about it and also this: http://iso.qa.ubuntu.com/qatracker/reports/bugs/1026520
also, some other things i thought that may caused this problem :
-open guest sessions many times and sometimes i tried to "sudo *" command but i'm not sure because after i fixed the problem, i tried opening guest session 3 times but every thing is ok even after trying "sudo *" command on guest session
-opening root session for a long time (3 mounth). but can this be the problem (virus, permissions,...)?
-issues with the hardware of my graphic card nVidia (no software/driver issuses even i'm using nouveau driver from the daily build) that causes some problems with 3D apps and some color problems. but, the bug wasn't due to this hardware issues as i think