A dot in the linux username causes: "Username is not in the sudoers file. This incident will be reported."

Question

I have a correctly working Debian server. All existing users who have been granted sudo rights can utilize sudo without any problems. However, a new user with a username that has a dot in it sees "Username is not in the sudoers file. This incident will be reported" when attempting to sudo.

I don't see any steps that were missed for this user. Here are my steps:

Create a privileged user with a dot in the username. I use this little script to add developer user accounts.

#!/bin/bash
uu=$1
useradd -m -G sudo,webdev -s /bin/bash $uu
passwd $uu
cd /home/$uu/
mkdir .ssh/
touch .ssh/authorized_keys
chmod 600 .ssh/authorized_keys
chmod 700 .ssh/
chown -R $uu:$uu .ssh/
ls -la .ssh/
cat $uu.pub > /home/$uu/.ssh/authorized_keys
echo "finished"

Check that user is in the sudo group:

getent group sudo

This already exists in /etc/sudoers

# Allow members of group sudo to execute any command
%sudo   ALL=(ALL:ALL) ALL

Next I made /etc/sudoers.d/user.name (and set permissions to 640):

nano /etc/sudoers.d/user.name
user.name ALL=(ALL) NOPASSWD: ALL

To test, log in with the user account and try to sudo. I get the above error.

One way I was able to resolve this was by adding this user to a different group that has sudo rights.

Either I am missing something, or the dot in the username is causing a problem that is not experienced with the other usernames.

Answer 1

The solution was given in a comment by muru.

sudo will read each file in /etc/sudoers.d, skipping file names that end in ‘~’ or contain a ‘.’ character ...

• Including other files from within sudoers

As roaima pointed out in another comment:

The dot in the username doesn't cause the issue. It's because you chose to put the sudo configuration in a file whose name contains a dot.

That was exactly the issue. And the solution, which I veriifed, was just:

sudo mv /etc/sudoers.d/user.name /etc/sudoers.d/username