I edited the sudoers file like below:
myuser ALL=(ALL) NOPASSWD: ALL
newuser ALL=(ALL) NOPASSWD: ALL
There is no another line that contains "myuser" in sudoers file. But Linux asks password when I try sudo anything for once. It's like that only for myuser. myuser is the first user after installation. If I add a new user and give it sudo privilege as same, it can be root without password but myuser cannot.
The server runs on Azure by the way.