No password required to use sudo

1. Edit /etc/sudoers:

sudo vim /etc/sudoers

1. Add or modify the specified user configuration

username_   ALL=(ALL) NOPASSWD: ALL

Then the user (username) can use sudo without a password

If you want a user group to be able to sudo without a password:

%group_name  ALL=(ALL) NOPASSWD: ALL
# Don't forget the "%"  in front of the group name