1、远程ssh连接ubuntu失败？
The remote system refused the connection.
原因分析：sshd启动失败
systemd[1]: Starting OpenBSD Secure Shell server...
sshd[19621]: Could not load host key: /etc/ssh/ssh_host_ed25519_key
sshd[19621]: Missing privilege separation directory: /var/run/sshd
systemd[1]: ssh.service: failed with result "exit-code".
systemd[1]: Failed to start OpenBSD Secure Shell server.
systemd[1]: ssh.service: Unit entered failed state.
systemd[1]: ssh.service: Failed with result 'exit-code'
解决方法：
ssh-keygen -A
mkdir -p /var/run/sshd
systemctl restart sshd