# Pastebin 1fMNYoYE
root@f7c70c4c5c17:/var/lib/postgresql/data# touch a-file
root@f7c70c4c5c17:/var/lib/postgresql/data# cd /var/lib/postgresql13/data
root@f7c70c4c5c17:/var/lib/postgresql13/data# ln /var/lib/postgresql/data/a-file .
ln: failed to create hard link './a-file' => '/var/lib/postgresql/data/a-file': Invalid cross-device link
root@f7c70c4c5c17:/var/lib/postgresql13/data#