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Marcus Downing
Asked: 2015-12-16 05:39:12 +0800 CST

SSH banner: asking for confirmation

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It's standard practice to put a banner on SSH login notifying the user that a system belongs to somebody, "you may be subject to prosecution" etc. However, this banner scrolls past harmlessly.

Is there any way of requiring the user answer the question, "Do you accept? y/N" before they can proceed?

(This question isn't about the legal or practical value of having the banner or the confirmation step, just whether it's technically possible)

ssh

1 Answers

  1. Based on serverliving.com's comment, I solved this by writing a file /etc/profile.d/confirm.sh saying:

    #!/bin/bash

if [ -n "$SSH_CLIENT" ] || [ -n "$SSH_TTY" ]; then
        while true; do
                read -p "Do you accept the terms and conditions? [y/N] " yn
                case $yn in
                        [Yy]* ) break ;;
                        [Nn]* ) exit 1 ;;
                esac
        done
fi

    This fires on any SSH session, but not on non-SSH sessions. The major downside is that it doesn't fire on non-interactive shells that ignore profile, for example:

    $ ssh somehostname ls

    The exact wording of the prompt is up to you of course, and the message only makes sense following a copy of the terms being agreed to.

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