"sudo Account validation failure, is your account locked", can't login linux system error

[yingshaoxo]

After you install debian

Then, if you:

1. add this line to the bottom of the /etc/apt/sources.list:

deb http://ftp.de.debian.org/debian sid main 

2. run those commands:

sudo apt update
sudo apt install firefox

Then, you'll get error of "Account validation failure" when you use sudo

And you'll never be able to get into your linux system anymore.