Finally I was able to fix my problem with not being able to see or use any pictures in mastodon (neither mine nor other peoples).
My problem was that I use a soft link for /home/mastodon/live/public/system where all the media files are and point it to a hard drive.
With systemd's sandboxing `ReadWritePaths=/home/mastodon/live` was not enough and thus sidekiq couldn't write the files there.
For now I disabled sandboxing, but I need to figure out how to do it properly.
@jeena You could do a bind mount (`mount -o bind /source/path /target/path`) - that should work with sandboxing
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