我們在遠程ssh鏈接ubuntn服務器的時候，會出現一下的一個問題
ssh: connect to host localhost port 22: Connection refused
之所以出現這個問題，是因為我們ubuntn系統默認是沒有安裝openssh-server的。
解決辦法就是安裝這個模塊
sudo apt-get install openssh-server
安裝完成后，我們再輸入下面的命令，就可以遠程登錄了
ssh ubuntu@xx.20.xxx.63
再執行完命令的時候，還會出現一個問題
➜ ~ ssh ubuntu@xx.20.xxx.63
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@ 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 ECDSA key sent by the remote host is
SHA256:mPfvt1SS+fncIH5f8DYiFtoII7eLtHdTJ1CbTRYx6oo.
Please contact your system administrator.
Add correct host key in /Users/用戶名/.ssh/known_hosts to get rid of this message.
Offending ECDSA key in /Users/用戶名/.ssh/known_hosts:6
ECDSA host key for xx.20.xxx.63 has changed and you have requested strict checking.
Host key verification failed.
原因：
因為服務器的ip發生變更了
第一次SSH連接時，會生成一個認證，儲存在客戶端（也就是用SSH連線其他電腦的那個，自己操作的那個）中的known_hosts，但是如果服務器驗證過了，認證資訊當然也會更改，服務器端與客戶端不同時，就會跳出錯誤啦。
解決辦法：
輸入命令：ssh-keygen -R +輸入服務器的IP
~ ssh-keygen -R xx.20.xxx.63
# Host xx.20.xxx.63 found: line 36
/Users/用戶名/.ssh/known_hosts updated.
或者
rm ~/.ssh/known_hosts
上面兩個命令執行其中一個之后，在繼續執行ssh ubuntu@xx.20.xxx.63
~ ssh ubuntu@172.20.110.63
The authenticity of host '172.20.110.63 (172.20.110.63)' can't be established.
ECDSA key fingerprint is SHA256:mPfvt1SS+fncIH5f8DYiFtoII7eLtHdTJ1CbTRYx6oo.
Are you sure you want to continue connecting (yes/no/[fingerprint])?
輸入yes
ubuntu@172.20.110.63's password: [輸入密碼]
Welcome to Ubuntu 18.04.6 LTS (GNU/Linux 5.4.0-107-generic x86_64)
* Documentation: https://help.ubuntu.com
* Management: https://landscape.canonical.com
* Support: https://ubuntu.com/advantage
26 updates can be applied immediately.
To see these additional updates run: apt list --upgradable
Your Hardware Enablement Stack (HWE) is supported until April 2023.
The programs included with the Ubuntu system are free software;
the exact distribution terms for each program are described in the
individual files in /usr/share/doc/*/copyright.
Ubuntu comes with ABSOLUTELY NO WARRANTY, to the extent permitted by
applicable law.
ubuntu@ubuntu-HP-Z4-G4-Workstation:~$ [進入服務器]