I had the same situation here, it turns out it was a stuck useradd process -
destroying it got useradd working again, something like this:
killall -9 userdel
rm -f /etc/*lock
In my case the stuck useradd was caused by a bug in my own script, but
for the others, if it was caused by the package manager then I guess there
might be a package out there with a bug in it's call to useradd.
I had the same situation here, it turns out it was a stuck useradd process -
destroying it got useradd working again, something like this:
killall -9 userdel
rm -f /etc/*lock
In my case the stuck useradd was caused by a bug in my own script, but
for the others, if it was caused by the package manager then I guess there
might be a package out there with a bug in it's call to useradd.