linux su authentication failed
After Ubuntu is installed, the root user is locked by default and is not allowed to log in. , su to root is not allowed, you can log in to root by changing root's password.
su Switching to root does not work, so I use manual method to change the password.
sudo passwd root password for ubuntu18:当前用户的密码 Enter new UNIX password：这个是root的密码 Retype new UNIX password：重复root的密码
After that, you can enter su to log in to the root user.
su: Switch to a certain user mode, and when prompted to enter a password, the password is the password of the account after switching, and the usage is "su account name". If no account is added later, the system defaults to the root account, and the password is also the password of the super account. no time limit.
sudo: Temporarily switch to super user mode to perform super user privileges. When prompted for a password, the password is the password of the current user, not the password of the super account. However, there is a time limit. Ubuntu defaults to a 15-minute session.
Recommended: linux system tutorial
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