What does the ssh-keyscan command do?

Question

linux

I understand the principle of building an ssh connection using keys ... But I can't figure out why this command is needed, and what keys it pulls into the known hosts file. Maybe I'm confused with these private and public keys. Could you explain to me the practical need for this command. And the main question, what am I fixated on, why do hosts give this information? let public keys that are used as locks and have nothing to do with decryption ... but I think that the remote host should not give this information, but it happens that this is possible, what's the idea?
PS As I understand it, they are additionally hashed when added to known_hosts, is that true? What for?

Answer 1

Could you explain to me the practical need for this command
man ssh-keyscan
to check or create ssh_known_hosts
can collect keys from a large number of hosts very quickly
what is the idea
if the server is changed, then ssh will say that the king is not real