Jeremy Davis's picture

Apologies to everyone. We will fix this and re-release a fixed build. In the meantime here is a workaround:

In a terminal set your new password:

NEW_PASS="your-new-admin-password"
then copy/paste this:
service mongodb stop
mongod --dbpath /var/lib/mongodb --noauth --fork --logpath /var/log/mongodb/mongodb.reset-admin.log --bind_ip 127.0.0.1
mongo admin --eval "db.changeUserPassword(\"admin\",\"$NEW_PASS\");" 
mongod --dbpath /var/lib/mongodb --shutdown
service mongodb start

[updated] to use the proper syntax for running mongo within a bash script (i.e. "--eval"); plus added "--bind_ip 127.0.0.1" when starting mongo with "--noauth" (so that mongo will only accept local connections while running with no authorisation required).