No password prompt at sudo command
Solution 1:
Edit /etc/sudoers using sudo visudo, and remove the last line:
ALL ALL=(ALL) NOPASSWD:ALL
(By the way, please note that this line at the end of the file is not the preferred way to make sudo not prompt for a password, for those who want to do that.)
Solution 2:
Use this command to find the source of the problem:
sudo grep -HRn NOPASSWD /etc/sudoers.d/
In my case:
/etc/sudoers.d/50_stack_sh:1:username ALL=(root) NOPASSWD:ALL
comment the line with # and close your terminal.