1. 修改 root 密码

sudo passwd root

2. 以其他账户登录，通过 sudo nano 修改 /etc/ssh/sshd_config :

xxx@ubuntu14:~$ su - root
Password:
root@ubuntu14:~# vi /etc/ssh/sshd_config

3. 注释掉 #PermitRootLogin without-password，添加 PermitRootLogin ye

# Authentication:
LoginGraceTime 120
#PermitRootLogin without-password
PermitRootLogin yes
StrictModes yes

4. 重启 ssh  服务

root@ubuntu14:~# sudo service ssh restart
ssh stop/waiting
ssh start/running, process 1499
root@ubuntu14:~#