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I have hard a hard time finding good information on the performance difference between display managers on Ubuntu (specifically between lightdm and gdm3).

With Ubuntu switching to Gnome, I would assume that it would also be recommended to switch to gdm3 instead of lightdm but I can't find any information one way or the other.

So:

  • Is this the case? Will lightdm still be developed?
  • Is lightdm faster than gdm3? (Answers like this say lightdm is "lightweight and fast" but do not say whether or not gdm3 is slow....)
Startec
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    I had to stop using gdm3. It got corrupted too easily. I couldn't start graphical sessions. Lightdm is more reliable. YMMV – ahoffer Jul 18 '20 at 01:51

4 Answers4

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GDM is the default DM in Ubuntu as of 17.10. LightDM is still the default for some other flavours, like Xubuntu or Lubuntu, and I doubt either of these projects will move to GDM, so LightDM should continue to be supported in Ubuntu.

See this mailing list post from June 2017:

As you might be aware the Ubuntu desktop has decided to switch to using GNOME and this means we will be using GDM instead of LightDM Unfortunately this means there is likely to be a reduction in development effort from Canonical.

However, I want to assure you that we are not abandoning LightDM:

  • We continue to ship LightDM in our existing Ubuntu desktop releases and we will support those for many years to come (see below).
  • Many Ubuntu derivatives use LightDM and we continue to support them in doing that.
  • Ultimately we think that LightDM is the right cross-desktop solution for display management, it's just not something we can make use of in Ubuntu desktop at this time. Who knows how the future will pan out :)

I will continue to do release management for LightDM and review and merge branches as I can. If anyone else is capable and interested in helping out with these jobs I'd love to hear from you - I don't want to be a blocker on development just because my focus is elsewhere.

The LightDM greeter is configurable, and a barebones greeter might well be faster than GDM, but a complex one might be slower.

muru
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gdm3 has an annoying bug for Nvidia Optimus users not using wayland. If you run your nvidia driver kernel modeset (modeset=1), you enable "prime sync" which means you no longer have tearing on your laptop screen. prime sync only works with modeset=1, so most Optimus users will want to enable this, unless they don't use their laptop's display, or don't care about tearing.

In Ubuntu 18.10, the nvidia packages activated modeset=1 by default, and the upgrade to 19.04 preserves this setting.

19.04 (new install) does not activate modeset=1, to avoid a big gdm3 bug.

Problem: gdm3 kills the nvidia card from displaying to external monitors when your use modeset=1. Bug still exists in Ubuntu 19.04. Speculation is that gdm3 sees the driver in modesetting operation, and decides wayland must be in use, and there is no way to get it to behave otherwise. It must be a hard bug to fix. An Ubuntu dev (Daniel van Vugt) says that is really a nvidia bug: something about the nvidia driver requires root access, which gdm3 denies to it (unlike all the other display managers).

Reference: https://bugs.launchpad.net/ubuntu/+source/gdm3/+bug/1716857

https://devtalk.nvidia.com/default/topic/1042774/nvidia-drivers-390-77-no-external-display-on-ubuntu-18-04-and-quadro-m1000m/?offset=24

lightdm does not have this problem (sddm from KDE also does not have this problem).

EDIT: Apart from using lightdm, there is a workaround for gdm3 (which Pop!OS uses out of the box. System76 sells Optimus hardware so a good Nvidia experience is mission-critical). The fix is a one-liner, see the 'Jeremy Soller' comment on the relevant Ubuntu bug report.

https://bugs.launchpad.net/ubuntu/+source/gdm3/+bug/1716857/comments/26

Note that this means Pop!OS decided to keep gdm3 and use this workaround, instead of using lightdm, which I suppose is an authoritative vote on which is the best approach.

Tim Richardson
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  • That;s some useful information for me. I have been facing issues of ubuntu 18.04 stopping at ppm init and never reaches to login screen. This workaround saved the day. – mrigendra Apr 20 '20 at 11:20
  • So what is the downside to using lightdm then? – Josh Jan 15 '21 at 07:40
  • This advice (my answer) is quite old now and may not be correct. (I no longer have any nvidia hardware after too many bad experiences). gnome shell has some intergrations with gdm3 such as showing notifications on the lock screen; once you are logged in, I don't think there is any difference. – Tim Richardson Jan 16 '21 at 08:52
  • I spent several days trying to support the various Cuda drivers for an external GPU on my laptop. Eventually, by educated guesswork, I disabled gmd3 and switched to lightdm and everything worked. This was on ubuntu 18.04 with Cuda 11.2, for what it is worth. – John Powell Feb 23 '21 at 10:20
  • some distributions run the gdm greeter (the login) in wayland, even when you then login to an X session (Ubuntu 20.10 does this). Which means a lot more people are using wayland than they think, at least for one moment. But it could also cause the problems you have. You can turn that off somewhere in gdm3 configuration. Using lightdm certainly turns it off. – Tim Richardson Feb 25 '21 at 04:58
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  1. Ubuntu GNOME uses the gdm3, which is the default GNOME 3.x desktop environment greeter.

  2. As its name suggests LightDM is more lightweight than gdm3 and it's also faster.

  3. LightDM will continue to be developed. Ubuntu MATE 17.10's default Slick Greeter (slick-greeter) uses LightDM under the hood, and as its name suggests it is described as a slick-looking LightDM greeter. The default Slick Greeter in Ubuntu MATE 18.04 also uses LightDM under the hood. Ubuntu MATE 20.04 switched from Slick Greeter to LightDM Arctica Greeter, so LightDM will not be going away any time in the near future.

karel
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  • How do you know this? I've looked all over the internet and can't find any proof that Lightdm is more "lightweight" (whatever this means) or faster. – Startec Feb 09 '18 at 06:25
  • I had a problem booting to Unity for a while, so I tried switching from lightdm to gdm and it solved my booting problem. Later after a few kernel updates I switched back from gdm to lightdm which I hadn't uninstalled and lightdm worked again. When I was researching lightdm vs. gdm on the web I learned that lightdm is more lightweight than gdm which is why I switched back to it in order to get a faster a boot time. – karel Feb 09 '18 at 06:29
  • Please read this answer about gdm vs. lightdm: https://askubuntu.com/questions/54847/why-use-a-display-manager/54848#54848 . – karel Feb 09 '18 at 06:52
  • LightDM always felt rather sluggish to me. gdm3 appears to be a lot more snappy. – Raphael May 05 '18 at 16:50
  • GDM3 requires an X restart to switch between nvidia and intel GPUs, while lightDM works with just a login\logout. – Mr.WorshipMe Jul 16 '18 at 09:04
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I use Ubuntu 22.10 server with slick-greeter and muffin to get only one window manager installed. When I install lightdm(-greeter) or gdm3, it seems it also installs the window manager. I see at the login screen - more choices as cinnamon are then available.

A little explanation about my little experience of it:

I much like the Cinnamon Desktop Environment, so I did some tests and research on how it works and came from Linux MINT. I’ve got used to Linux on the Ubuntu kernel and commands. I didn’t like the desktop environment that was much different to Windows for me.

I installed Ubuntu with the Cinnamon Desktop in many different ways to get it how I prefer. My goal was to make my desktop environment use as little as possible of my system, or at least as much as it needs to run the tools I like on it.

I learned with it that you need 3 things to run à desktop environment:

I discovered that Cinnamon uses the muffin display manager and the slick-greeter by default. Now these packages are directly available these days from ubuntu repositories. which makes it a lot more convenient for my own purposes.

gdm3 is also a gnome display manager, not only a greeter. and so it's the case for lightdm.

muffin(click the link for all the information) Mutter is a Wayland display server and X11 window manager and compositor library.

When used as a Wayland display server, it runs on top of KMS and libinput. It implements the compositor side of the Wayland core protocol as well as various protocol extensions. It also has functionality related to running X11 applications using Xwayland.

When used on top of Xorg it acts as a X11 window manager and compositing manager. …

slick-greeter(click the link for all the information) Slick Greeter started as a fork of Unity Greeter 16.04.2, a greeter developed for Ubuntu by Canonical, which used indicators and unity-settings-daemon. …

I’ve two desktop computers:

  • One on Ubuntu server 22.10 with ubuntucinnamon-desktop package installed with gdm3 for gaming with wine. I can see it installed the slick-greeter and muffin files after installation.
  • The other uses lightdm for system tools, repairs and tests.installed with muffin, slick-greeter and cinnamon no recommends. so it uses in à way lightdm.
  • I've a last installation of Ubuntu server 22.10 on an usb key and it uses a lightdm desktop environment.

I say, it depends on what you intend to do with your computer.

Therefore it’s great to use a linux operating system.