Comment 2 for bug 113283

apt-setup-verify already checks for whether the Release file exists. This suggests that the mirror is half-present but kind of broken.

Christian: I'm not exactly convinced by using the Launchpad mirror prober here. Static lists are no good (they change after release), and the Launchpad mirror prober is kind of heavyweight to query in every single installation. Why is just checking for the Release file not sufficient?