Minimal steps for reproduction:
$ sudo apt install appstream
[..]
$ sudo apt -qq update
E: Failed to fetch
http://mirror.gsi.de/distrib/debian/dists/stretch/main/dep11/Components-amd64.yml
404 Not Found
E: Some index files failed to download. They have been ignored, or old ones
used instead.
This does not really look fatal, ie. it does not mention Packages files.
$ sudo apt dist-upgrade
Reading package lists... Done
Building dependency tree
Reading state information... Done
Calculating upgrade... Done
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
$ sudo apt purge appstream
[..]
$ sudo apt -qq update
18 packages can be upgraded. Run 'apt list --upgradable' to see them.
Kind regards,
Christopher
