Ubuntu – switch between two users in a single click

switch-userusers

I share my home computer with my wife, and we often switch between our two accounts.
I'm considering using Ubuntu on my next computer, and I'm evaluation different desktop environments (E.g. Gnome, Unity, or Xfce).
Fast user switching is a deal breaker for me on most of the desktop environments. In Unity it is best – you always have a menu with all users, and you can switch with a single click (assuming no passwords):

On Gnome and Xfce it's quite bad. I need to click on "Switch User", select the other user, and click "Login" – all involving tiny buttons on different positions of the screen.

Is there a way of switching users quickly – preferably with a single click and/or a hotkey? Is there anything that would work regardless of desktop environment?

I've found a similar question: Keyboard shortcut to switch user accounts – but it only goes as far as the display manager. I want to skip it and switch to the other user's session.

Best Answer

Not a single click, but I can give you a keyboard shortcut solution.

Go into the menu to set custom keyboard shortcuts

and add a new one with this command:

dm-tool switch-to-user suzi

Assuming suzi is your wife's username, and set a shortcut of your choice by clicking where is says "disabled" and then pressing the key combination you want to use (for example, super+alt+S if the user's initial is S). Set another shortcut to switch to your own account (with your own username in the command).

Summary: done, usable, current solution is acceptable only in a cooperative multi-user environment, can be improved.

I wrote a usable-proof-of-concept patch to lightdm that does the job.

It does what we need here!

See below for installation instructions.

Prerequisites

A system with at least two user accounts and users willing to allow quick switch between graphical sessions without retyping passwords.
Each user can use any desktop environment that fully uses lightdm, including using light-locker for session locking. Unity and XFCE should work.

Tested with XFCE.

How to use, how to see the changes

Try this before performing the changes:

have user A open a graphical session
have user B open another graphical session

Now from any of the two session you can do :

    dm-tool switch-to-user userA

    dm-tool switch-to-user userB

Effect of the changes

Without the change you will see a login prompt requiring to type a password.

With the change you will see an immediate switch without login prompt.

Here the switch is really quick. Much quicker than in Ubuntu 12.04 and even without flickering in some cases.

Practical use

For maximum benefit, I recommend to create a launcher icon somewhere in a dock/panel/wharf (whatever it is called in your particular desktop environment) that when clicked runs:

    dm-tool switch-to-user name-of-other-user

SECURITY WARNING

Applying the commands below replaces system's lightdm packages with modified versions that allow switching between any two users currently being logged in a graphical session. This weakens system security, for example user A logs in graphically, locks session, walks away, user B logs in. User B can unlock user A session and switch to it any time it is opened. And the other way round (swap A and B).

The changes cannot be applied without administrator access (sudo is assumed, especially for package install).

It works fine for us, but still, note that lightdm is an important package and this might break it or introduce other subtle bugs. Breaking it will break ability to use graphical login sessions for all users. You are fully responsible for the use of the commands below. You have been warned.

Permanence warning

Changes are near-permanent. They stay after rebooting. To revert them, install (using aptitude, synaptic or whatever) the regular lightdm* packages which will replace the changed ones.

Notice that any time Ubuntu updates lightdm packages, and the updates are installed, they will revert the changes. Administrator can apply them again.

Possible refinement (restore security)

This proof-of-concept could be refined by a clever use of e.g. Unix groups. lightdm would only allow the switch if current and target users are listed in any group with a conventional filename, like lightdm-quickswitch-anystringfoo. Such a change (possible along with others) could be eventually merged into some official solution.

Commands

I suggest to login on a text console (press Ctrl-Alt-F1 and login) to do the steps below. This allows to restart lightdm without losing the current shell.

Copy-paste the commands below in a bash shell and it will adjust lightdm to perform the changes.

(
set -euxv

echo Making sure system has necessary packages.

echo Installing packages will be done only once but might be long as it may fetch around 40Mbytes of data from the Internet.
sudo apt-get --assume-yes install devscripts

echo Enabling source packages in apt.
sudo sed -i '/^#\sdeb-src /s/^# *//' "/etc/apt/sources.list"
sudo apt-get update
sudo apt-get --assume-yes --no-install-recommends build-dep lightdm

THETEMPDIR=$( mktemp -d )
cd $THETEMPDIR

echo Getting package source

apt-get source lightdm
cd */

pwd

if [ -d .pc ]
then
quilt push -a || echo "Quilt returned an error code, we ignore it because we saw it was sometimes irrelevant."
quilt new allow_switch_between_logged_users_without_authentication
quilt add src/seat.c
fi

patch -p0 <<EOF
--- src/seat.c  2016-07-29 05:19:45.000000000 +0200
+++ src/seat.c  2016-08-15 19:37:11.693364683 +0200
@@ -1578,6 +1578,20 @@

     l_debug (seat, "Switching to user %s", username);

+    if (session)
+    {
+   l_debug (seat, "WIP quick switch: found inactive existing user session, switching to it: %s. For details, see https://askubuntu.com/questions/811953/switching-between-two-opened-x-sessions-without-reauthenticating", username);
+
+   session_unlock (session);
+   seat_set_active_session (seat, session);
+
+   l_debug (seat, "WIP quick switch to user complete: %s.  For details, see https://askubuntu.com/questions/811953/switching-between-two-opened-x-sessions-without-reauthenticating", username);
+   return TRUE;
+    }
+
+    l_debug (seat, "WIP quick switch: no session for user, switching to greeter: %s. For details, see https://askubuntu.com/questions/811953/switching-between-two-opened-x-sessions-without-reauthenticating", username);
+
+
     /* Attempt to authenticate them */
     session = create_user_session (seat, username, FALSE);
     g_signal_connect (session, SESSION_SIGNAL_AUTHENTICATION_COMPLETE, G_CALLBACK (switch_authentication_complete_cb), seat);
EOF

if [ -d .pc ]
then
quilt refresh
ls -al debian/patches/allow_switch_between_logged_users_without_authentication
cat debian/patches/allow_switch_between_logged_users_without_authentication
fi

echo Building modified packages.

dch -lquickswitch "Allow dm-tool switch-to-user username to switch without authentication if user session is already opened.  WARNING: this negates local security. For details, see https://askubuntu.com/questions/811953/switching-between-two-opened-x-sessions-without-reauthenticating"
head debian/changelog
time dpkg-buildpackage -rfakeroot -uc -b

echo Installing modified packages.

cd ..
PACKAGESTOINSTALL=$( for DEBNAME in *.deb ; do PACKAGENAME="$( echo "$DEBNAME" | cut -f 1 -d _ )" ; if dpkg -l $PACKAGENAME | grep -q ^ii ; then echo $DEBNAME ; fi ; done ) ; sudo dpkg --install ${PACKAGESTOINSTALL}
dpkg -l '*lightdm*'
)

Notice that the command below will close immediately all graphical sessions without a chance to save data, so all users should close applications properly and save needed data first.

If packages did install well, the change can be activated immediately with :

    sudo service lightdm restart

or by rebooting.

Feedback

Does it work for you? Can you think of a variant? Feedback welcome.