Deleted password for my user on VPS, but still asks for password (locked out)?

Question

I just bought a VPS plan with my hosting provider. I did all the necessary measurements for security and disabled root ssh login, created a custom myuser in the sudoer group etc.. so far so good. But it annoyed me to always type the password for myuser on every ssh login, so I deleted it with

sudo passwd –d myuser

Now apparently this was a mistake, since I'm now still asked about the password on every ssh login, but obviously there is no password? I'm a bit confused. Either way, if I type my old password it won't let me login and if I type no password it won't either. Is there a way to save my VPS still or did I officially lock myself out?

And since this hit me a bit unexpectedly, what the hell is going on? Why does ubuntu ask for a password when there is none?

Answer 1

Ok figured it out.

Obviously passwd -d myuser doesn't work.

So I had to reinstall my VPS operating system since it seemed that I'm really locked out. I only found out after the fact that usually providers will offer a web terminal that would potentially allow login even if ssh is screwed up. In any case, try this first if you have valuable data on your VPS, and reset password with sudo passwd myuser!

To setup passwordless authentication I had to change /etc/ssh/sshd_config to disallow password authentication and allow pubkey authentication:

PasswordAuthentication no
PubkeyAuthentication yes

What's important here is that the /etc/ssh/sshd_config file usually includes all files in /etc/ssh/ssh_config.d/*.conf* and if any file pre-sets the above keys your change will be ignored. So make sure that none of the included files preset these values or change them in the includes directly.

Now to make pubkey based authentication possible I had to put the client machine's pubkey into the myclient user's ~/.ssh/authorized_keys file:

mkdir -p /home/myuser/.ssh
chmod 700 /home/myuser/.ssh
vim /home/myuser/.ssh/authorized_keys

and paste (pubkey probably resides in your client machine's ~/.ssh/serverkeyfile.pub)

Make sure access permissions are right.

chmod 600 /home/myuser/.ssh/authorized_keys
chown -R myuser:myuser /home/myuser/.ssh

And restart ssh daemon:

sudo systemctl restart sshd

(Note: You could also perform the above steps automatically using ssh-copy-id -i ~/.ssh/serverkeyfile.pub myuser@host)

Try login to your machine now it should work.