出错点：
(base) *@**demac ~ % ssh ubuntu@49.*.229.21 @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ @ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @ @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY! Someone could be eavesdropping on you right now (man-in-the-middle attack)! It is also possible that a host key has just been changed. The fingerprint for the ED25519 key sent by the remote host is SHA256:hFqsjmQ1EVzOSDmzTaTu7ysquakop/bsQoTLU6AyDMs. Please contact your system administrator. Add correct host key in /Users/*/.ssh/known_hosts to get rid of this message. Offending ECDSA key in /Users/*/.ssh/known_hosts:22 Host key for 49.*.229.21 has changed and you have requested strict checking. Host key verification failed.
解决方法：
删除know_hosts中的49.*.229.21这一行：
ssh-keygen -R 49.*.229.21
显示这个就代表成功了，它会自动在know_hosts.old中备份一份，不用管：
# Host 49.*.229.21 found: line 20 # Host 49.*.229.21 found: line 21 # Host 49.*.229.21 found: line 22 /Users/*/.ssh/known_hosts updated. Original contents retained as /Users/*/.ssh/known_hosts.old