Koen.pt

SSH shell wrapper to provide custom prompt

Or: How do you turn off login banner for non-interactive ssh?

I figured out two methods to accomplish this task;

1. Using command in .authorized_keys

In ~/.ssh/authorized_keys you add the following before a specific key

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command="/usr/local/bin/shell-wrapper" ssh-rsa AAAAB3NzaC1yc2...JZK1E8H60=

And in /usr/local/bin/shell-wrapper

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#!/bin/sh

# If there is a command given, it executes it with the users shell 
# if no command given it outputs the contents of BANNER and starts
# the user's shell.

BANNER=/etc/issue.net

if [ -n "$SSH_ORIGINAL_COMMAND" ] ; then
  $SHELL -c "$SSH_ORIGINAL_COMMAND"
else
  cat $BANNER
  $SHELL
fi

Downside of this method is that you have to set this for every rsa-key in the .authorized_keys file

2. Changing the users shell

Set shell for user (change USERNAME to your user):

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usermod --shell /usr/local/bin/shell-wrapper USERNAME

Create /usr/local/bin/shell-wrapper with the following content:

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#!/bin/sh

# If there are no arguments given, it outputs the contents of
# BANNER and starts the specified shell. When there are 
# arguments given it executes that with the specified shell

BANNER=/etc/issue.net
SHELL=/bin/sh

if [ $# -eq 0 ]; then
  cat $BANNER
  $SHELL
else
  shift
  $SHELL -c "$@"
fi