byobu/experimental/byobu-classroom

#!/bin/sh -e
#
#    byobu-classroom - set up a byobu-classroom shared screen session,
#                      with one writer and many guest readers
#
#    Copyright (C) 2011 Canonical Ltd.
#
#    Authors: Dustin Kirkland <kirkland@byobu.org>
#
#    This program is free software: you can redistribute it and/or modify
#    it under the terms of the GNU General Public License as published by
#    the Free Software Foundation, version 3 of the License.
#
#    This program is distributed in the hope that it will be useful,
#    but WITHOUT ANY WARRANTY; without even the implied warranty of
#    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#    GNU General Public License for more details.
#
#    You should have received a copy of the GNU General Public License
#    along with this program.  If not, see <http://www.gnu.org/licenses/>.


PKG="byobu"

. "/usr/lib/$PKG/include/shutil"

usage() {
	echo
	echo "Usage: $0 [HOSTUSER [GUESTUSER]]"
	echo
	echo "If HOSTUSER is unspecified, \$SUDO_USER [$SUDO_USER] is used."
	echo "If GUESTUSER is unspecified, 'guest' is used."
	echo
}

[ -n "${1}" ] && HOSTUSER="${1}" || HOSTUSER="$SUDO_USER"
[ -n "${2}" ] && GUESTUSER="${2}" || GUESTUSER="guest"

# Ensure that our host user exists
while ! id "$HOSTUSER" >/dev/null 2>&1; do
	error "Host user does not exist"
	id "$HOSTUSER"
	usage
	exit 1
done

# Ensure that there is not already a guest user
while id "$GUESTUSER" >/dev/null 2>&1; do
	echo
	info "To operate in classroom mode, we must create the [$GUESTUSER] user."
	info "There is already a [$GUESTUSER] user on this system."
	echo
	echo "Do you want to permanently delete the [$GUESTUSER] user now?  [y/N]: "
	c=$(head -n1)
	case "$c" in
		y|Y)
			deluser --force --remove-home "$GUESTUSER"
			info "[$GUESTUSER] user deleted"
		;;
		*)
			error "[$GUESTUSER] user still exists"
			id "$GUESTUSER"
		;;
	esac
done

# Ensure that our new guest exists
while ! id "$GUESTUSER" >/dev/null 2>&1; do
	echo
	info "To operate in classroom mode, we must create the [$GUESTUSER] user."
	echo
	echo "Do you want to create the [$GUESTUSER] user now?  [y/N]: "
	c=$(head -n1)
	case "$c" in
		y|Y)
			# Hardcode password to "guest"
			cryptpw="ubXWbZ4Ffn.mg"
			useradd -m -s /bin/bash -p "$cryptpw" "$GUESTUSER"
			touch "/home/$GUESTUSER/.screenrc"
			chown -R root:root /home/$GUESTUSER
			info "Guest user created"
		;;
		*)
			error "[$GUESTUSER] user does not exist"
			id "$GUESTUSER"
		;;
	esac
done

# Ensure the correct permissions on screen binary
screen=$(which screen)
while [ $(stat -c%a "$screen") != "6755" ]; do
	echo
	ls -alF "$screen"
	info "To operate in classroom mode, $screen must have 6755 permissions."
	printf "Do you want to set this now?  [y/N]: "
	c=$(head -n1)
	case "$c" in
		y|Y)
			dpkg-statoverride --add root root 6755 "$screen"
			info "Updated $screen"
			echo
			info "To revert this later, run:"
			info "  sudo dpkg-statoverride --remove $screen"
		;;
		*)
			error "Incorrect permissions on $screen"
			ls -alF "$screen"
		;;
	esac
done

# Ensure correct permissions on screen's run directory
service screen-cleanup start

# Ensure that SSH configuration is correct
while [ $(grep -c "#byobu-classrom" /etc/ssh/sshd_config) != "4" ]; do
	echo
	info "To operate in classroom mode, SSH must:"
	info " a) have password authentication enabled"
	info " b) disable TCP Forwarding"
	info " c) force the guest user's login command"
	echo
	printf "Do you want to set these now?  [y/N]: "
	c=$(head -n1)
	case "$c" in
		y|Y)
			$BYOBU_SED_INLINE -e '/#byobu-classroom/d' /etc/ssh/sshd_config || true
			echo "
PasswordAuthentication yes				#byobu-classroom
AllowTcpForwarding no					#byobu-classroom
Match User $GUESTUSER					#byobu-classroom
  ForceCommand exec screen -x $HOSTUSER/byobu-classroom	#byobu-classroom
" >> /etc/ssh/sshd_config
			echo
			info "To revert this later, run:"
			info "  sudo sed -i -e '/#byobu-classroom/d' /etc/ssh/sshd_config"
		;;
		*)
			error "Incorrect sshd configuration"
		;;
	esac
done
service ssh restart


# Launch the session detached
su -l $HOSTUSER -c 'byobu -c /usr/share/byobu/profiles/classroom -d -m -S byobu-classroom -t shell bash'

info "Byobu classroom setup successfully!"
echo
info "Please tell your guests to:"
info "  ssh -C $GUESTUSER@$(hostname)"
info "with password=guest"
echo
info "As the host, you should connect with:"
info "  ssh -C $HOSTUSER@$(hostname)"
info "to control the session"
echo


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