Display disk space consumed by Mastodon.

Use tootctl utility that can be executed from the command-line interface.

mastodon@mastodon:~/live$ RAILS_ENV=production ./bin/tootctl media usage
Attachments:	2.09 GB (516 KB local)
Custom emoji:	58.9 MB (9.58 KB local)
Preview cards:	165 MB
Avatars:	1.28 GB (74.9 KB local)
Headers:	2.86 GB (357 KB local)
Backups:	0 Bytes
Imports:	0 Bytes
Settings:	0 Bytes