$ cd ~/.ssh
$ ssh-keygen -o
    Enter file in which to save the key (/root/.ssh/id_rsa): 
    Enter passphrase (empty for no passphrase): 
    Enter same passphrase again: 
    Your identification has been saved in /root/.ssh/id_rsa.
    Your public key has been saved in /root/.ssh/id_rsa.pub.
    The key fingerprint is:
    SHA256:ofYUUApFdLQf0u5+mlA1xnBrOLp/R9ZWhUobAs root@ecs--0005
    The key's randomart image is:
    
    上面一路回车即可

$ ls
    authorized_keys  id_rsa  id_rsa.pub

$ cat ~/.ssh/id_rsa.pub 
   ssh-rsa AAAAB3NzaC1yc2EAAAADABAjKFWVLKgOyYW2gtJ18rK5p8vGxg+vCekwcsZfIYTKDrvBtRlvQWglkzO4zttBNWgurecgV
   asM1qbhBbZUKSOYbS5vHrcLEIY6rWFgEhLu043jE2Cjy/H1pht2m7uOCGPUEOHcJ3+6PtBbghJ4AFtuFn4KLVojfMxdxNTSp/bk/
   075xbff02By........

   上面的字符串就是公钥