参考文档：
Ubuntu下postgresql出现Authentication failure（认证失败）的解决方法
zonglin@zonglin-virtual-machine:~/Desktop$ su
Password:
su: Authentication failure
zonglin@zonglin-virtual-machine:~/Desktop$ sudo passwd root
New password:
BAD PASSWORD: The password is shorter than 8 characters
Retype new password:
passwd: password updated successfully
zonglin@zonglin-virtual-machine:~/Desktop$ su root
Password:
su: Authentication failure
zonglin@zonglin-virtual-machine:~/Desktop$ su
Password:
root@zonglin-virtual-machine:/home/zonglin/Desktop# ls
root@zonglin-virtual-machine:/home/zonglin/Desktop#
root@zonglin-virtual-machine:/home/zonglin/Desktop#
root@zonglin-virtual-machine:/home/zonglin/Desktop#
使用 sudo passwd root 修改root 密码
使用 su 切换用户
标签：virtual,Desktop,machine,failure,Authentication,zonglin,su,root From： https://www.cnblogs.com/liuzonglin/p/17201971.html