Steemit itself was in read-only mode for a few hours earlier today. It was giving a message about "maintenance work". It didn't indicate whether this was planned maintenance or an error.

My guess is that, maybe, something went wrong with the blockchain, or the miners, or the witnesses or whatever, and that affected all the sites that run on Steem.

Steemit is now back up, but Steemd isn't, as you've noticed. I don't know any more.