1. Follow points 2-4 https://wikitech.wikimedia.org/wiki/Help:Single_Node_MediaWiki (without hostname, just for internal use)
2. Try and run a maintenance script, or something else

Observed:

PHP Warning: DOMDocument::load(): I/O warning : failed to load external entity "/srv/mediawiki/languages/data/plurals.xml" in /srv/mediawiki/includes/cache/LocalisationCache.php on line 640
PHP Warning: DOMDocument::load(): I/O warning : failed to load external entity "/srv/mediawiki/languages/data/plurals-mediawiki.xml" in /srv/mediawiki/includes/cache/LocalisationCache.php on line 640

And rebuildLocalisationCache.php --force doesn't help.

nemobis@dumps-stats:/srv/mediawiki/languages$ ls -lh data/
total 28K
-rw-r--r-- 1 root root 3.7K Mar 6 17:12 plurals-mediawiki.xml
-rwxr-xr-x 1 root root 21K Mar 6 17:12 plurals.xml
nemobis@dumps-stats:/srv/mediawiki/languages$ sudo chmod 755 data/*
nemobis@dumps-stats:/srv/mediawiki/languages$ ls -lh data/
total 28K
-rwxr-xr-x 1 root root 3.7K Mar 6 17:12 plurals-mediawiki.xml
-rwxr-xr-x 1 root root 21K Mar 6 17:12 plurals.xml

And then everything works.

Expected: permissions are set correctly since the beginnin.

Version: unspecified
Severity: normal
See Also:
https://bugzilla.wikimedia.org/show_bug.cgi?id=60435
https://bugzilla.wikimedia.org/show_bug.cgi?id=56439
https://bugzilla.wikimedia.org/show_bug.cgi?id=72046