Add guide for disabling SSH password login - #932
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New host page covering how to switch a machine to SSH key only login on Ubuntu Server 22.04 and 24.04, with the steps ordered so the reader proves their key works before turning passwords off. Covers two things that commonly trip people up: a stock Ubuntu install has password login on because the setting ships commented out and sshd defaults to yes, and a drop in under /etc/ssh/sshd_config.d/ overrides the main config file. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
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Summary
New host guide for switching a machine to SSH key only login on Ubuntu Server 22.04 and 24.04.
host/disable-ssh-password-login.mdxhost/verification-stages.mdxSix steps, each one explanation, then the command, then the output to expect. The order matters: the reader proves key login works from a second terminal before turning passwords off, so a broken key cannot lock them out. A recovery section at the end covers getting back in over IPMI, iDRAC, iLO, or a directly attached monitor and keyboard.
Two things it deliberately covers, because both are easy to miss:
/etc/ssh/sshd_config.d/overrides the main config.sshd_configstarts withInclude /etc/ssh/sshd_config.d/*.confand OpenSSH keeps the first value it finds, so editingsshd_configalone can have no effect. Documented in the Ubuntu Server OpenSSH guide.Notes on the commands
ssh -o PreferredAuthentications=publickey, not-o PasswordAuthentication=no. The latter leaveskbdinteractiveauthentication yeson the client, so sshd can still prompt for a password and the check would pass without the key being used.sudo sshd -truns before every restart, so a bad config cannot take sshd down.systemctl restart ssh.serviceis correct on both releases. Ubuntu 24.04 socket activates sshd and 22.04 does not, but that does not change this command.Test plan
docs.jsonparsesssh-keygenandssh-copy-idoutput blocks taken from real output, not paraphrasedPreferredAuthentications=publickeyverified against the ssh client withssh -G