Re: lightdm or gdm?

[Robert Ancell]

Hi all,

Where we are today:
- GDM is undergoing a security check to be included in main [1].
- We've got GNOME Shell onto the 17.10 image, running under LightDM.
- We've attempted to get the GNOME Shell lock screen running with LightDM
and using GNOME Shell as a LightDM Greeter. Which this still seems
possible, it's not easy to patch GNOME Shell as the GDM code is hard to
decouple.
- Other tasks have left not much time to work on GNOME Shell / LightDM
integration.

When we started investigating LightDM with GNOME Shell we wanted to
re-assess after about a month and see if it was still worth continuing
with. That time is now.

Given the workload we have and the risks in modifying GNOME the decision is
to use GDM for 17.10 and thus 18.04 LTS.

Where this leaves LightDM:
- We continue to support LightDM for the supported Ubuntu releases.
- We will support LightDM for use in the other flavours, though this is
likely to be limited to bug fixes from the Ubuntu desktop team.
- Others are still welcome to contribute to LightDM.

Thanks,
--Robert

[1] https://bugs.launchpad.net/bugs/1686393

On Thu, Apr 20, 2017 at 2:32 AM Sebastien Bacher  wrote:

> Hey there,
>
> That's a topic that was mentioned during the meeting yesterday and
> something we need to decide on early in the cycle since there is going
> to be work needed on that front to have a fully working session.
>
> I'm doing a small summary of what I think are the pro (+) and con (-) of
> each
>
> * lightdm
>
> + well tested in Ubuntu
> + we have people in the team knowing the codebase
> + shared with other flavors/greeters selection
> + guest session
> - divergence from upstream
> - we are the maintainers so it's more work for us
> - gnome-shell uses gdm for its lockscreen so work is needed to make it
> work with lightdm
>
> * gdm
>
> + that's the GNOME solution, works today with wayland & gnome-shell
> - we started lightdm because we found the gdm codebase not easy to work
> on, that might still be true
> - ?keeps an active session from the greeter even after logging which
> uses resources? (it was mentioned on IRC, to be confirmed, is that
> needed due to the lockscreen?)
> - no guest session, we need to work on that or decide to drop the
> feature from Ubuntu
>
>
> I talked a bit with Robert yesterday who said he could make lightdm use
> the gdm greeter (he has some work started on that a few cycles ago)
> which means it could be used as GNOME lockscreen instead of gdm. He's
> probably the best placed to comment on the work and pro/con of the
> solutions though so I'm going to let him go into the details when he
> replies.
>
> Cheers,
> Sebastien Bacher
>
>
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Re: lightdm or gdm?

[Daniel van Vugt]

(I know the question wasn't directly relevant to this thread but it's 
worth clearing up...)


Mir /was/ going to support remote desktops eventually. Just as Gnome 
Shell on Wayland will (if not already) support them. The functionality 
might not be complete yet, but that's just because it's still too new 
and nobody has done the work yet.


Regardless, you always have the option of running other desktop 
environments with Ubuntu.


If some feature like remote desktop support is broken or missing in 
Ubuntu 17.10/18.04, please log a bug...


- Daniel


On 01/05/17 13:35, Khurshid Alam wrote:

Hi,

On Thu, Apr 27, 2017 at 10:30 PM, Oliver Grawert  wrote:

thats not a gdm thing ... vnc and any remote desktop feature wont run
under any of the new display server technologies (be it wayland or mir
...). a lightdm running under wayland wouldnt be able to provide that
feature either.


Yes I know. But I was testing under x with 17.04. For me,
X+lightdm+shell+mutter works, but X+gdm+shell+mutter doesn't.


I know Ubuntu will choose wayland as default session in 17.10/18.04. By
then if my vnc session doesn't work I will have to shift to another
desktop environment.






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Re: lightdm or gdm?

[Oliver Grawert]

hi,
Am Donnerstag, den 27.04.2017, 21:52 +0500 schrieb Khurshid Alam:
> 
> I just tried gdm Ubuntu-Gnome 17.04. I couldn't make it work with any
> x11 vnc server like x11vnc. So it is safe to assume with gdm+wayland
> these vnc servers will become obsolete.
> 
thats not a gdm thing ... vnc and any remote desktop feature wont run
under any of the new display server technologies (be it wayland or mir
...).
a lightdm running under wayland wouldnt be able to provide that feature
either.

ciao
oli

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Re: lightdm or gdm?

[Khurshid Alam]

Hi,

On Wed, Apr 19, 2017 at 8:02 PM, Sebastien Bacher  
wrote:

* lightdm

+ well tested in Ubuntu
+ we have people in the team knowing the codebase
+ shared with other flavors/greeters selection
+ guest session
- divergence from upstream
- we are the maintainers so it's more work for us
- gnome-shell uses gdm for its lockscreen so work is needed to make it
work with lightdm



I am all for lightdm. Lightdm has a very nice feature like remote login.

I just tried gdm Ubuntu-Gnome 17.04. I couldn't make it work with any 
x11 vnc server like x11vnc. So it is safe to assume with gdm+wayland 
these vnc servers will become obsolete.



About lock-screen. Antergos uses lightdm + light-locker with 
gnome-shell and it works well.



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Re: lightdm or gdm?

[Bryan Quigley]

On Fri, Apr 21, 2017 at 6:03 PM, Jeremy Bicha  wrote:
> On Fri, Apr 21, 2017 at 4:56 PM, Bryan Quigley
>  wrote:
>> One of my concerns for a gdm change is are we ready to reorg our VTs?
>
> GDM could default to VT7 if we really wanted to, but why should it
> except for tradition?
>
> I think it's easier for users to start counting at 1 rather than 7.
> And it also matches how most other distros work now. (Debian switched
> gdm3 to vt1 before Ubuntu did.)
>
> lightdm could default to VT1 too.

I completely agree we can switch this up and improve things. Based on
how Gdm3 does VTs (possibly random VT) we *have* to consider
rethinking it at least a bit.

I've got some ideas on how we could make it easier for the average
user.  I've seen users accidentally press Ctrl-Alt-number and have no
idea what happened - or how to get back.  (Most times it was
Ctrl-Alt-1 (then 4, then 3) so actually gdm3 would improve that a
bit!)

It looks like we start ttys on demand. We only start the tty1 getty
automatically (for boot) and the others actually start when you go to
them.  Neat!

My big ask is that we have a consistent Ctrl-Alt-XX (let's say F12)
combination that is for where users will always get the same thing
they can use if things go wrong (or can be instructed over the
phone/etc).  That is true today with Ctrl-Alt-F1 - it always has a
getty on it. This can just be a standard getty login or we can make it
more of a recovery menu kind of thing (happy to spec it out/make a
demo if their is interest).

>
>> Is their a process I can kill from a user session to break the lock?
>
> loginctl list-sessions
> # Find the session you are using. If the session is named '2', run
> loginctl unlock-session 2
>
> That works with gdm3, but it didn't seem to work when I tried with
> unity-greeter on lightdm.

With that and Robert's post it looks like they behave in quite similar ways.

Thanks!
Bryan

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Re: lightdm or gdm?

[C de-Avillez]

On Sat, 22 Apr 2017 20:21:36 -0500
C de-Avillez  wrote:



> On point for LightDM that I think should be stressed: we can
> select DEs on the login pane.

A few minutes after my email jbicha pointed to me that gdm3 *does*
allow one to select an installed DE. I stand corrected.
> 
> Perhaps I am an exception, but I usually have at least two DEs
> installed; right now, I have three: KDE, Unity, and Gnome. Neither
> gdm3 nor sdm allow me to select which of the three DEs I want to
> start the session under, but instead default to the last one selected.
> 
> On the other hand, a common drawback on all three DMs is the inability
> to consider left-handed persons (where, usually, the primary
> mouse|touchpad button is the right one). That sucks for all three.

Interestingly, gdm3 accepts left and right clicks as selectors
everywhere on the first page, but *not* on the gear box (where you
select a DE).



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Re: lightdm or gdm?

[C de-Avillez]

On Thu, 20 Apr 2017 15:13:40 +0200
Sebastien Bacher  wrote:

> Hey,
> 
> Le 20/04/2017 à 14:56, Tim a écrit :
> > What technical reasons remain ? So far as I can tell its really only
> > the tests?   
> 
> Robert made the list in his replies, not sure how configuration
> systems/logging/remote login/etc compared and how useful they are but
> we have several flavors relying on lightdm and having their own
> greeters, it would be nice to be able to keep supporting those
> communities and share that piece of infrastructure between Ubuntu
> variants (it's not likely that we invest work on several codebases so
> if we switch to gdm we are likely going to stop working on lightdm)

On point for LightDM that I think should be stressed: we can select DEs
on the login pane.

Perhaps I am an exception, but I usually have at least two DEs
installed; right now, I have three: KDE, Unity, and Gnome. Neither gdm3
nor sdm allow me to select which of the three DEs I want to start the
session under, but instead default to the last one selected.

On the other hand, a common drawback on all three DMs is the inability
to consider left-handed persons (where, usually, the primary
mouse|touchpad button is the right one). That sucks for all three.

Cheers,

..C..


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Re: lightdm or gdm?

[Tim]

On 22/04/17 08:03, Jeremy Bicha wrote:

Is their a process I can kill from a user session to break the lock?

loginctl list-sessions
# Find the session you are using. If the session is named '2', run
loginctl unlock-session 2
that will only work if you are logged in as the user that owns the 
session, otherwise you will be required to authenticate. So short of the 
user leaving an open tty, is not really any form of a bypass.
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Re: lightdm or gdm?

[Jeremy Bicha]

On Fri, Apr 21, 2017 at 4:56 PM, Bryan Quigley
 wrote:
> One of my concerns for a gdm change is are we ready to reorg our VTs?

GDM could default to VT7 if we really wanted to, but why should it
except for tradition?

I think it's easier for users to start counting at 1 rather than 7.
And it also matches how most other distros work now. (Debian switched
gdm3 to vt1 before Ubuntu did.)

lightdm could default to VT1 too.

> Is their a process I can kill from a user session to break the lock?

loginctl list-sessions
# Find the session you are using. If the session is named '2', run
loginctl unlock-session 2

That works with gdm3, but it didn't seem to work when I tried with
unity-greeter on lightdm.

Thanks,
Jeremy Bicha

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Re: lightdm or gdm?

[Robert Ancell]

On Sat, Apr 22, 2017 at 8:56 AM Bryan Quigley 
wrote:

>
> Lastly, I wanted to know if there are any security differences in how
> the login/lock screens work?
> Specifically:
> Is their a process I can kill from a user session to break the lock?
> If I'm able to crash the lock screen, is the user session destroyed or
> unlocked?
> Which would be easier to add functionality to block new USB
> drives/other devices from being connected when the screen is locked?
>
>
I'm not 100% familiar with the source but as I understand it gnome-shell is
the lock screen, so killing the lock screen could only be done by killing
the whole shell. A bug in the lock screen code will cause the session to be
unlocked. This is the same behaviour as Unity since Yakkety (I think?).

--Robert
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Re: lightdm or gdm?

[Bryan Quigley]

I did some testing in a VM with switching different flavors to/from
the default dm.  Mostly I found that my current VM setup isn't stable
(it's my own virt package I'm working on).

But I did also see:
Lubuntu -> gdm, Lock screen now falls to black screen
Gnome -> Lightdm, Wayland failed on the first run, worked on the second.

Now again, this could be my setup, my Unity tests simply didn't work.


One of my concerns for a gdm change is are we ready to reorg our VTs?
GDM appears to default to VT-1, and then the actual desktop session
usually goes to VT-2, but I also managed to get it to VT-4 (without
changing settings).  This appears to make it somewhat harder from a
debugging perspective and we would be doing that at the same time as
switching to wayland.
Lightdm - Both dm and desktop are on VT-7.


Looking at support requests the only one of note that I find is an
issue that came up with having both lightdm and gdm3 installed.  We
didn't debug to a root cause, just determined that we needed to purge
gdm3 (it was some NFS related, avahi, lightdm, dbus problem).  Will
look into it again as this would likely affect a lot more people
either way.


Lastly, I wanted to know if there are any security differences in how
the login/lock screens work?
Specifically:
Is their a process I can kill from a user session to break the lock?
If I'm able to crash the lock screen, is the user session destroyed or unlocked?
Which would be easier to add functionality to block new USB
drives/other devices from being connected when the screen is locked?

Thanks!
Bryan


On Wed, Apr 19, 2017 at 10:32 AM, Sebastien Bacher  wrote:
> Hey there,
>
> That's a topic that was mentioned during the meeting yesterday and
> something we need to decide on early in the cycle since there is going
> to be work needed on that front to have a fully working session.
>
> I'm doing a small summary of what I think are the pro (+) and con (-) of
> each
>
> * lightdm
>
> + well tested in Ubuntu
> + we have people in the team knowing the codebase
> + shared with other flavors/greeters selection
> + guest session
> - divergence from upstream
> - we are the maintainers so it's more work for us
> - gnome-shell uses gdm for its lockscreen so work is needed to make it
> work with lightdm
>
> * gdm
>
> + that's the GNOME solution, works today with wayland & gnome-shell
> - we started lightdm because we found the gdm codebase not easy to work
> on, that might still be true
> - ?keeps an active session from the greeter even after logging which
> uses resources? (it was mentioned on IRC, to be confirmed, is that
> needed due to the lockscreen?)
> - no guest session, we need to work on that or decide to drop the
> feature from Ubuntu
>
>
> I talked a bit with Robert yesterday who said he could make lightdm use
> the gdm greeter (he has some work started on that a few cycles ago)
> which means it could be used as GNOME lockscreen instead of gdm. He's
> probably the best placed to comment on the work and pro/con of the
> solutions though so I'm going to let him go into the details when he
> replies.
>
> Cheers,
> Sebastien Bacher
>
>
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Re: lightdm or gdm?

[Robert Ancell]

On Fri, Apr 21, 2017 at 12:57 AM Tim  wrote:

>
>
> On 20/04/17 00:32, Sebastien Bacher wrote:
> > - gnome-shell uses gdm for its lockscreen so work is needed to make it
> > work with lightdm
> That is not entirely right, the GUI for gdm is actually a cut-down
> gnome-shell session, this applies to both lock screen and greeter. gdm
> does however handle all user authentication, which is a little different
> from how lightdm work afaict (Robert correct me on this If I am wrong).
>
>
Support for allowing lock screens to do authentication was added in LightDM
1.20 and Unity used this (i.e. the same as the GDM lock screen). Running a
cut-down gnome-shell session is no different from runing any greeter (Unity
Greeter was effectively a cut-down Unity session with a simple shell).

--Robert
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Re: lightdm or gdm?

[Sebastien Bacher]

Hey,

Le 20/04/2017 à 14:56, Tim a écrit :
> What technical reasons remain ? So far as I can tell its really only
> the tests? 

Robert made the list in his replies, not sure how configuration
systems/logging/remote login/etc compared and how useful they are but we
have several flavors relying on lightdm and having their own greeters,
it would be nice to be able to keep supporting those communities and
share that piece of infrastructure between Ubuntu variants (it's not
likely that we invest work on several codebases so if we switch to gdm
we are likely going to stop working on lightdm)

Cheers,

Sebastien Bacher


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Re: lightdm or gdm?

[Tim]

On 20/04/17 00:32, Sebastien Bacher wrote:

- gnome-shell uses gdm for its lockscreen so work is needed to make it
work with lightdm
That is not entirely right, the GUI for gdm is actually a cut-down 
gnome-shell session, this applies to both lock screen and greeter. gdm 
does however handle all user authentication, which is a little different 
from how lightdm work afaict (Robert correct me on this If I am wrong).


When we started Ubuntu GNOME, gdm was problematic on Ubuntu, I spent 
alot time working with halfline (ray) to iron out the issues and 
everything is upstream. These days its pretty stable and works perfectly 
in most cases. Although lightdm does seem to handle better the corner 
cases where openGL config is broken for whatever reason.


I probably don't know enough about lightdm code to make a proper 
comparison, but if you have lightdm running the gnome-shell greeter, and 
replicating the auth channels and user switching interfaces to make it 
compatilbe with gnome shell (without patches). What technical reasons 
remain ? So far as I can tell its really only the tests?






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Re: lightdm or gdm?

[Robert Ancell]

On Thu, Apr 20, 2017 at 3:58 AM Jeremy Bicha  wrote:

> On Wed, Apr 19, 2017 at 10:32 AM, Sebastien Bacher 
> wrote:
> > - gnome-shell uses gdm for its lockscreen so work is needed to make it
> > work with lightdm
>
> Generally, lightdm works with GNOME, but it hasn't been tested much so
> it sometimes take a while before bugs are noticed and fixed. Here's
> some lightdm with GNOME bugs I just learned about:
>
> https://launchpad.net/bugs/1632772 (No Wayland support)
> https://launchpad.net/bugs/1684205 (Missing lock button)
>


LightDM has supported Wayland since 1.16 (Ubuntu 15.10). This has however
not been actively used or enhanced by me due to the conflict of interest
with the development of Mir. Now we are using Wayland on the desktop I
expect to be much more involved in this feature.

--Robert

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Re: lightdm or gdm?

[Robert Ancell]

Thanks Seb,

= Disclaimer =

Firstly, I should disclose my interests - I am the founder and maintainer
of LightDM. I'll try and minimise any biases I might have. Ultimately I
want the best outcome and I'm happy with either way we go as long as it
makes sense.

= History (simplified) =

In the beginning there was one Display Manager - XDM. Various desktops
forked this project to produce their own display managers that displayed
appropriate UI for their desktop (e.g. Qt on KDE with KDM, GTK+ on GNOME
with GDM).

LightDM was started for two reasons:
- We were having quality / maintenance issues with GDM in Ubuntu. GDM was
highly complex.
- None of the display managers allowed you to change greeter technology
outside of a bit of themeing.

The goal was to have a common display manager daemon (LightDM) and allow
each desktop to develop their own greeter against a stable greeter API
(liblightdm).

Ubuntu switched to LightDM in 11.10 and developed Unity Greeter. I gave up
pushing LightDM in GNOME (which I regret) amidst the Unity-GNOME flamewars.
KDE came super close to picking LightDM as a replacement for KDM with a
huge list of positives (including having the second most active LightDM
developer being from KDE). The major point against it was the CLA. That was
very disappointing. Most of the small desktops seem to have chosen LightDM
and seem quite happy with it.

= Pros and cons =

In addition to Seb's list:

* LightDM
+ an extensive test suite that contains 370 test cases. The test cases run
a full LightdDM setup and simulate all components.
+ a sophisticated configuration system that allows packagers and sysadmins
to override configuration. Some sysadmins may have work in switching from
LightDM to GDM (I can't quantify how significant this is).
+ Extensive logging that helps in debugging issues.
+ Support for greeters in multiple languages / platforms (C, Qt, Python etc
via GIR, Vala).
+ VNC support.
+ Remote login support (this has not been used for sometime and may or may
not be useful in the future).
+ Support for Mir (I don't know if this is important anymore, but dropping
LightDM would mean no DM supports it).

* GDM
- no significant tests (make check runs one thing from 2007)

= My conclusion =

My preference is to continue with LightDM for the following reasons:
- I think the tests and features of LightDM are superior to GDM (I could be
biased here).
- To switch would create some work for sysadmins who use existing features.
- I think the amount of work to get LightDM to work with GNOME Shell is
roughly equivalent to getting new features into GDM.
- LightDM is not an enormous amount of work to maintain - it's quite mature.
- If we were to stop developing LightDM this would be a huge loss to the
community outside of GNOME. Being used across various projects means we
have a larger pool of developers testing and fixing bugs. I'll have to
defer to my manager(s) to decide if this investment / divergence is
considered worth it.
- We always have the option of switching to GDM in the future if we want
to, the switch back would be harder.

Finally a clarification - when you refer to "LightDM" this never means any
UI that you see (LightDM is a daemon and contains no UI code). So
continuing with LightDM does not mean using Unity Greeter. The Unity
Greeter code has bitrotted to such a point we clearly would not use it (it
was to be replaced with Unity8 Greeter).

--Robert

On Thu, Apr 20, 2017 at 2:32 AM Sebastien Bacher  wrote:

> Hey there,
>
> That's a topic that was mentioned during the meeting yesterday and
> something we need to decide on early in the cycle since there is going
> to be work needed on that front to have a fully working session.
>
> I'm doing a small summary of what I think are the pro (+) and con (-) of
> each
>
> * lightdm
>
> + well tested in Ubuntu
> + we have people in the team knowing the codebase
> + shared with other flavors/greeters selection
> + guest session
> - divergence from upstream
> - we are the maintainers so it's more work for us
> - gnome-shell uses gdm for its lockscreen so work is needed to make it
> work with lightdm
>
> * gdm
>
> + that's the GNOME solution, works today with wayland & gnome-shell
> - we started lightdm because we found the gdm codebase not easy to work
> on, that might still be true
> - ?keeps an active session from the greeter even after logging which
> uses resources? (it was mentioned on IRC, to be confirmed, is that
> needed due to the lockscreen?)
> - no guest session, we need to work on that or decide to drop the
> feature from Ubuntu
>
>
> I talked a bit with Robert yesterday who said he could make lightdm use
> the gdm greeter (he has some work started on that a few cycles ago)
> which means it could be used as GNOME lockscreen instead of gdm. He's
> probably the best placed to comment on the work and pro/con of the
> solutions though so I'm going to let him go into the details when he
> replies.
>
> Cheers,
> Sebastien Bacher
>
>
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Re: lightdm or gdm?

[Jeremy Bicha]

On Wed, Apr 19, 2017 at 10:32 AM, Sebastien Bacher  wrote:
> - gnome-shell uses gdm for its lockscreen so work is needed to make it
> work with lightdm

Generally, lightdm works with GNOME, but it hasn't been tested much so
it sometimes take a while before bugs are noticed and fixed. Here's
some lightdm with GNOME bugs I just learned about:

https://launchpad.net/bugs/1632772 (No Wayland support)
https://launchpad.net/bugs/1684205 (Missing lock button)

Jeremy

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Re: lightdm or gdm?

[Dimitri John Ledkov]

On 19 April 2017 at 15:32, Sebastien Bacher  wrote:
> Hey there,
>
> That's a topic that was mentioned during the meeting yesterday and
> something we need to decide on early in the cycle since there is going
> to be work needed on that front to have a fully working session.
>
> I'm doing a small summary of what I think are the pro (+) and con (-) of
> each
>
> * lightdm
>
> + well tested in Ubuntu
> + we have people in the team knowing the codebase
> + shared with other flavors/greeters selection
> + guest session
> - divergence from upstream
> - we are the maintainers so it's more work for us
> - gnome-shell uses gdm for its lockscreen so work is needed to make it
> work with lightdm
>
> * gdm
>
> + that's the GNOME solution, works today with wayland & gnome-shell
> - we started lightdm because we found the gdm codebase not easy to work
> on, that might still be true
> - ?keeps an active session from the greeter even after logging which
> uses resources? (it was mentioned on IRC, to be confirmed, is that
> needed due to the lockscreen?)
> - no guest session, we need to work on that or decide to drop the
> feature from Ubuntu
>

Currently, in ubiquity we maintain a barebones ubiquity-dm which is
very DE which somewhat mimiced unity experience - it has a panel and
launches indicators, and offers users to run ubiquity installer under
it, or click the "Try Ubuntu" to skip through lightdm into a live
desktop session.

Ideally, I would like to drop that code in-favor of using gdm +
gnome-shell in the installer/app mode. As far as I understand during
live-session we use "ubuntu" user, and we do not by default show login
manager (lightdm) UI nor offer guest session.

(Well, the system indicator allows one to switch into guest session
mode, but said indicator will not be available anyway)

>
> I talked a bit with Robert yesterday who said he could make lightdm use
> the gdm greeter (he has some work started on that a few cycles ago)
> which means it could be used as GNOME lockscreen instead of gdm. He's
> probably the best placed to comment on the work and pro/con of the
> solutions though so I'm going to let him go into the details when he
> replies.
>

I think that would be nice, if we could use gdm as a lightdm greeter
to get the guest sessions. I did enquire if that is at all possible
during release sprint too.

Or try again for GDM to provide guest sessions?

Can guest sessions be improved with lxd containers at all? E.g. spawn
an ephemeral container that pretends to be user ubuntu, when in fact
it is namespaced away and self-destructs on log out?

-- 
Regards,

Dimitri.

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lightdm or gdm?

[Sebastien Bacher]

Hey there,

That's a topic that was mentioned during the meeting yesterday and
something we need to decide on early in the cycle since there is going
to be work needed on that front to have a fully working session.

I'm doing a small summary of what I think are the pro (+) and con (-) of
each

* lightdm

+ well tested in Ubuntu
+ we have people in the team knowing the codebase
+ shared with other flavors/greeters selection
+ guest session
- divergence from upstream
- we are the maintainers so it's more work for us
- gnome-shell uses gdm for its lockscreen so work is needed to make it
work with lightdm

* gdm

+ that's the GNOME solution, works today with wayland & gnome-shell
- we started lightdm because we found the gdm codebase not easy to work
on, that might still be true
- ?keeps an active session from the greeter even after logging which
uses resources? (it was mentioned on IRC, to be confirmed, is that
needed due to the lockscreen?)
- no guest session, we need to work on that or decide to drop the
feature from Ubuntu


I talked a bit with Robert yesterday who said he could make lightdm use
the gdm greeter (he has some work started on that a few cycles ago)
which means it could be used as GNOME lockscreen instead of gdm. He's
probably the best placed to comment on the work and pro/con of the
solutions though so I'm going to let him go into the details when he
replies.

Cheers,
Sebastien Bacher


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