Ask HN: How do you manage emergency contacts as freelance dev?

As a software freelancer running some (small-ish) websites/apps etc. for clients, it's sometimes hard to give clients guarantees of response times for critical bugs or outages - since you work on your own, and need some holiday as well.

Since most of these things happen very sporadically and can often be solved (temporarily) by clearing some disk space, rebooting a server etc., I wondered how other freelancers handle these kind of situations. I.e. do you have an emergency contacts in a network (requires you to directly hand over all your server login details) or something better?