Comment 1 for bug 1466125

First, the problem isn't specific to the rootfs being *currently* writable. The problem exists if the rootfs has *ever* been marked writable (and modified).

Second, as discussed elswhere in mail, it would be better to force a full update in this case, *not* refuse to update the system. The Ubuntu Phone model is that users should receive updates automatically and seamlessly; while users can fiddle with their filesystem, we probably /don't/ want to leave those users islanded on the currently-installed image version forever, but instead propose a full update, possibly with appropriate caveats. This will clobber any (unsupported) local modifications but at least won't leave them with an insecure and unsupportable device.