The Vagrant base image is currently Stretch (Debian 9), which is [[https://wiki.debian.org/DebianReleases#Production_Releases|EOL in 2020-07-06]] (although the Debian LTS project supports it until 2022 summer). Wikimedia production and CI (which Vagrant is meant to be compatible with) are moving to Buster (Debian 10; {T247045}, {T252432}), MediaWiki-Vagrant should too.
See also:
* {T319167}
* {T245757}
* {T264991}
* {T247045}
* {T252432}
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It's preferable to just recreate your Vagrant boxes from scratch ([[https://devops.stackexchange.com/questions/653/what-is-the-definition-of-cattle-not-pets|cattle not pets]]) but if you really need to upgrade an existing Stretch-based box, here are the steps:
* dump DB with ##mysqldump --add-drop-database --databases `mysql -rNe 'show databases' | ack -v '^(mysql|information_schema|performance_schema)$'` > /vagrant/dump.sql##
* update Vagrant repo
* run `vagrant destroy -f; vagrant up`
* restore dump with `mysql < /vagrant/dump.sql`
* clear caches, e-g- by running `vagrant reload`
* regenerate all data wasn't stored in the DB:
** if the `cirrussearch` role is enabled, run `mwscript /vagrant/mediawiki/extensions/CirrusSearch/maintenance/ForceSearchIndex.php`