ubuntu服务器只给了公钥，需要修改ubuntu用户为root用户
sudo passwd root
sudo vi /etc/ssh/sshd_config
将PermitRootLogin这一项改为yes
sudo service ssh restart一波操作后结果
ssh: permission denied (publickey)
ssh出现permission denied (publickey)问题:
修改/etc/ssh/sshd-config文件.
将其中的PermitRootLogin no修改为yes
PubkeyAuthentication yes修改为no
AuthorizedKeysFile .ssh/authorized_keys前面加上#屏蔽掉，
PasswordAuthentication no修改为yes就可以了。
vi /etc/ssh/sshd-config (详细说说sshd-config的配置解释)
Subsystem sftp /usr/libexec/openssh/sftp-server
Port 22
Protocol 2
PermitRootLogin no
PubkeyAuthentication yes
AuthorizedKeysFile .ssh/authorized_keys
CACertificateFile /etc/ssh/ca/ca.cert
PasswordAuthentication no
PermitEmptyPasswords no
PrintMotd no
ChallengeResponseAuthentication no
UseDNS no
ClientAliveInterval 60OK
