permissions wrong in Ubuntu 12.04 v4 image
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In the Ubuntu 12.04 v4 small image, /etc/shadow and /sbin/unix_chkpwd are owned by group root, not group shadow, and /sbin/unix_chkpwd is not set-gid.
These problems prevent ecrypt-private-setup from using the user's login password since it can't verify the password with unix_chkpwd.
These files have the correct permissions in the Ubuntu 13.04 BETA small image, the only other one that I've checked.