Categories
Interior

How to switch between gdm and kdm on ubuntu

What is gdm3, kdm, lightdm? How to install and remove and repair them? Can anyone explain in details?

5 Answers 5

gdm3 , kdm , and lightdm are all display managers. They provide graphical logins and handle user authentication.

From a Wiki article,:

A display manager presents the user with a login screen. A session starts when a user successfully enters a valid combination of username and password.

GNOME Display Manager ( gdm3 )

gdm3 is the successor of gdm which was the GNOME display manager. The newer gdm3 uses a minimal version of gnome-shell , and provides the same look and feel of as GNOME3 session. Is the Canonical choice since Ubuntu 17.10. You can install it with:

and remove it with:

KDE Display Manager ( kdm )

kdm was KDE’s display manager. But it’s been deprecated in KDE5 in favor of SDDM , which is more capable as a display manager, and hence comes by default with Kubuntu. You can install it with:

and remove it with:

LightDM

LightDM was Canonical’s solution for a display manager. It was supposed to be lightweight and comes by default with Ubuntu (until 17.04), Xubuntu, and Lubuntu. It’s configurable, with various greeter themes available.

You can install it with:

And remove it with:

Repairing is broad term. However, if you have multiple display managers installed, you can choose between them using:

You can use any display manager’s name in place of gdm3 in the above command, and it will allow you to choose between them. You must reboot for the change to take affect.

To check which display manager is currently being used, run this command:

One important point to note that, currently due to a bug (I checked in 16.04) you cannot start GNOME3 or Ubuntu Unity session using SDDM. So, if you have both KDE and Unity or GNOME3 installed, make sure your display manager is either gdm3 or lightdm .

I hope you are aware of the concept of display managers in Linux. Because I am going to discuss how to change display manager in Ubuntu straightaway.

Ubuntu 20.04 comes with GDM3 as default display manager. But if you experiment with various display managers or various desktop environments, you may end up with Light DM or some other display manager as the default display manager. It is a matter of choice but if you want to get back to another display managers, you can easily do that.

In this quick post, we shall see how to switch between LightDM and GDM or othe r display managers in Ubuntu.

Switch between LightDM and GDM in Ubuntu

Open a terminal and use the following command:

You can in fact use lightdm instead of gdm, the procedure is same for both. Using the above mentioned command will take you to a warning page. Enter to get back to next screen:

How to switch between gdm and kdm on ubuntu

On the next screen, you’ll see all the available display managers. Use tab to select your preferred one and then press enter, Once you have selected it, press tab to go to ok and press enter again.

How to switch between gdm and kdm on ubuntu

Restart the system and you will find your selected display manager at login. The same procedure can be applied to switch between GDM, LightDM, MDM, KDM etc.

How do you switch back to your previous display manager in Ubuntu?

Basically, you follow the same steps as mentioned earlier. You just need to reconfigure a display manager and during this process, you’ll be presented with the option to choose from the available display managers on your system.

Easy, isn’t it? I hope you liked this quick Ubuntu beginner’s tip. Stay subscribed for more.

The best thing about an open source operating system, such as Linux, is that you can customize it as much as you want, ranging from default applications such as file managers, music players, web browsers, and text editors etc. to more vital system components such as the kernel, display managers, and terminal consoles. You can do this simply by downloading new application software and replacing the old ones with that, or editing system components by making changes in the source code of your operating system. The display manager is one such system component that you can replace simply by running a few commands mentioned in this article.

What is a display manager?

A display manager is the component of your Operating system responsible for launching your display server and the login session. This is the reason it is sometimes called the login manager. The layout of the screen that you see while entering your username and password(the greeter), your login session and user authorization are some of the tasks that the display manager performs. A few common types of default display managers are gdm, gdm3, lightdm, and kdm etc.

How to switch between gdm and kdm on ubuntu

The Login screen of LightDM

Why and how to switch between display managers?

While all display managers serve the same purpose, managing the look & feel and session management of user login, they vary in size, complexity, and operation. You will also notice that they almost, but not absolutely, look alike. You may wish to switch to a certain version depending on your OS and system specifications. For Example, a lighter weight display manager is perfect for a slightly old computer system. Another reason for switching to a new one might be the unavailability of catchy themes for the login background. A lighter and less complex display manager may lack this feature. A few days back, I changed my display manager because my default one broke due to some customization I was making. So, instead of wasting time and efforts on fixing that one, I preferred migrating to an alternative display manager.

While working with, and switching between display managers, you will be mostly using the following commands:

Check Current Display Manager

In order to check which display manager is currently running on your system, enter the following command in your Ubuntu terminal:

The above image shows that my system is currently running a gdm3 display manager.

Install/Remove a Display Manager

Use the following commands in order to add/remove a display manager from your system:

$ sudo apt-get install [displaymanagername]

$ sudo apt-get remove [displaymanagername]

Switch to another Display Manager

You can switch from one display manager to another by first installing that display manager if it is already not installed and then using the following command to switch to a new one:

When you enter your username and password, the following window will appear giving you an idea about how display managers run in a system.

How to switch between gdm and kdm on ubuntu

Press enter for OK; the following window will appear. You can configure a new display manager through the up and down arrow keys and then by pressing enter for OK.

How to switch between gdm and kdm on ubuntu

You selected display manager will be configured as the default one when you restart your system.

Some Common Display Managers for Ubuntu

Here are some popular Ubuntu display managers that you may wish to choose from:

GDM, the Gnome Display Manager is the default display manager for the popular Gnome desktop environment. It supports the windowing systems X11 and Wayland. You can easily customize it to allow passwordless login, hide list of other users and for configuring themes, custom sessions and login screens. Basic configurations to GDM can be done through the UI through System Settings. For advanced configurations, you need to edit GDM configuration files as an authorized user. Here is a list of some of the files that let you configure your login session and display settings:

GDM3 is the default display manager that comes with the latest versions of Ubuntu, for example, Ubuntu 18. It is a redesigned version of GDM; though its look & feel is almost the same as GDM, it is pretty different in the background. It is lighter and faster but lacks a few features that you could use in the legacy GDM. For example, most of the configurable features are accessible through the conf files rather than the user interface Settings utility. You can make changes in the following file in order to customize your Login UI and sessions tackling:

LightDM

LightDM is also an alternate display manager for the older GDM. It has various greeter themes available for configuration. It supports Canonical server and X.org, therefore, it is a good choice for Ubuntu. Through LightDM, you can customize login greeter sessions, disable guest account and show/hide the list of other users on login. Here is a list of the files that let you configure your login session and display settings in Ubuntu:

KDM is the default display manager for KDE. It comes with a lot of customizable functionality through the UI module: System Settings. You can customize minute details in your greeter such as welcome message, font, and background wallpaper. A powerful feature of KDM is that it prevents shutting down at the login screen so only logged in users can shut down the computer system. Other customization options include root shutdown, logging a user and auto-login feature.

After reading this article, you are hopefully familiar with the concept of a Linux Display manager and what is the need of choosing one over the other. You can download and switch between different display Manager installed on your system with the help of the simple commands we described in this article.

Karim Buzdar

About the Author: Karim Buzdar holds a degree in telecommunication engineering and holds several sysadmin certifications. As an IT engineer and technical author, he writes for various web sites. You can reach Karim on LinkedIn

When installing a display manager on a Debian-based Linux distribution, you’re asked which display manager should be used by default, but it may not be clear for some users how to change the display manager later on.

This can be useful in case you’re having issues with your current display manager and you want to use a different one, in case you installed a desktop environment that uses a different display manager by default and you want to switch to it, and so on.

How to switch between gdm and kdm on ubuntu

To change the default display manager on Debian, Ubuntu, Linux Mint, elementary OS and any Debian or Ubuntu-based Linux distribution we’ll use dpkg-reconfigure , a tool provided by debconf, which can be used to reconfigure an already installed package by asking the configuration questions, much like when the package was first installed.

So to change the default display manager, use this command:

In this command, replace some_installed_display_manager with one of the display managers installed on your system, for example gdm3 , lightdm , sddm , lxdm , etc.. After running this command, it will list all installed display managers, allowing you to select the one to be used. If only one display manager is installed, this command won’t work.

After selecting a new default display manager, reboot your system.

For example, if you have both LightDM and GDM3 installed on your system, the command to switch to either GDM3 or LightDM can be both:

Any of these two commands work if you want to switch to either LightDM or GDM3, since both are installed in this example.

For the old GDM (used a while back – pre Ubuntu 16.04 for example), use gdm instead of gdm3 in the command.

In the same way, if you have SDDM or LXDM installed, you can use this command to change the display manager:

Once the boot process gets completed, we get a prompt to enter user and password to login. The type of login manager would depend on our Ubuntu configuration. If we intend to use CLI (Command-line interface), then we would get a default shell to login. Or else, a Display Manager in case of GUI (Graphical User Interface). In this article, we would focus on how to switch between different Display Manager in Ubuntu 20.04 release.

Although there are numerous Display Manager (both GUI and CLI) available, but we would focus on three prominent ones – GDM, LightDM and SDDM. In Ubuntu, GDM has been the default Display Manager in Ubuntu 16.10 and later. Many Ubuntu flavors still prefer to choose LightDM as default display manager.

Note: Following operations would require you to have superuser privileges. In case you don’t have one, then contact your System Administrator for assistance.

First, we will discuss how to install each Display Manager mentioned above.

Install GDM in Ubuntu

To install GDM (GNOME Display Manager), open a terminal and issue the following –

Install LightDM in Ubuntu

To install LightDM, open a terminal and issue the following –

Install SDDM in Ubuntu

To install SDDM (Simple Desktop Display Manager), open a terminal and issue the following –

Switch Display Manager in Ubuntu 20.04

Its not necessary to install all of the above mentioned Display Manager. Any two will suffice. First, we need to identify our default display manager. Therefore, issue the following in terminal –

This would return

for GDM3

for LightDM

and SDDM

Or, you can simply issue to get the status of active Display Manager –

Now, to switch between them – run the following command with active (or default) Display Manager –

for instance (opt any one of three as per your System’s configuration),

And, press OK. Next, you will be asked to select your default Display Manager (gdm3, lightdm or sddm).

On running – sudo dpkg-reconfigure gdm3, you may get following error –

In our case, we just needed to reboot our System. And, everything worked as it should.

In conclusion, we have discussed how to switch Display Manager in Ubuntu 20.04 release.

How do I switch from the default display manager (Lightdm) to the older display manager (GDM)?

Best Answer

Switching from LightDM to the "older" GDM is very easy, and need not even involve opening a terminal.

  • If you need/want to do this from a terminal (e.g. recovery console), please scroll below the screenshots for a how-to.
  • Also, the "new" GDM is not covered here because it is not officially available for 12.04 and the unofficial packages do not work for most users.

Easily switch to GDM with the Software Centre

Open the Software Center, type "gdm" in the search box, and click on Install as shown below, or click on this button: gdm

How to switch between gdm and kdm on ubuntu

After you enter your password, you will get the configuration screen shown below. Change lightdm to gdm and click on Forward:

How to switch between gdm and kdm on ubuntu

Restart your computer, and you should now have the "old" GDM login screen; note that you can still select from any available session, including Ubuntu (3D), Ubuntu 2D, Gnome, Gnome Classic, etc.

How to switch between gdm and kdm on ubuntu

Switch to GDM via the terminal

Open a terminal with Ctrl + Alt + T if you are on the desktop and not in the recovery console.

Type sudo apt-get install gdm , and then your password when prompted or run sudo dpkg-reconfigure gdm then sudo service lightdm stop, in case gdm is already installed.

A "Package Configuration" dialog will be displayed; click OK to proceed to the below screen. Use the arrow-keys to select gdm instead of lightdm , press Tab to move to OK, and press Enter.

How to switch between gdm and kdm on ubuntu

Reboot the computer (you can do this with sudo reboot if in the recovery console).

One of Linux strong points over Windows is the capability to switch desktops. Several exist, but the two most popular are Gnome and KDE. For Windows users, KDE will have a familar Windows XP feel, while Gnome may seem dull.

If you have been using Ubuntu, which uses Gnome as the default desktop, or Kubuntu which uses KDE as the desktop, and have been wondering what the other desktop looks like, you can easily install KDE or Gnome and switch back and forth before logging on to Ubuntu.

If you are running Ubuntu, you can install KDE by opening a terminal window and type:

sudo apt-get install kubuntu-desktop

When prompted, enter your password, and then answer yes (Y) when asked if you want to install. The install may take some time to complete, so be patient.

To install Gnome in Kubuntu, open a Terminal window and type:

sudo apt-get install ubuntu-desktop

When prompted, enter your password and continue with the install until it has been completed.

Now reboot either Ubuntu or Kubuntu. Then at the logon screen you can either press F10 or click on the Options logo at the bottom (left side) of the login screen. Then click on Select Session…

How to switch between gdm and kdm on ubuntu

Here you can select Gnome (2) or KDE (3) by selecting the radio button.

How to switch between gdm and kdm on ubuntu

During the next logon, you will see a prompt asking if you want to use the same desktop manager Just For This Session or Make Default (so you don't have to be bother with the prompt again).

How to switch between gdm and kdm on ubuntu

To change back to either KDE or Gnome, press F10 and select the desktop manager of your choice.

If you changed from the previous desktop manager, you can make it the default at the next logon.

What Next?

Comments on Switch Between Gnome And KDE Desktops In Ubuntu Or Kubuntu

Oliver @ 3:43 am

Perfect information. Very well explained. Exactly what I was looking for quite some time. Thx a lot and thumbs up for BlogRush. πŸ™‚

Mike @ 5:58 am

Thanks, now that I've determined that Gnome sucks, how do I get it off my system?

miksuh @ 10:25 am

h"Now reboot either Ubuntu or Kubuntu."

I really don't understand what you mean, Why should you reboot? That's not nesessary, just logout and login again using different desktop. Actually it's not even nesessary to logout, you can start a new X-session, which can be full screen or nested in window. You can also run Gnome apps from KDE-desktop and KDE apps from Gnome-desktop. All you need to do is install both gnome and kde. Nothing of what I said is ubuntu related. This is how X works no matter which Linux-distro you use.

I really don't understand why there must be Ubuntu (Gnome), Kubuntu (KDE) and Xubuntu (XFCE). In Debian and in most of the other distros too you just install desktop you want and then you use it.

miksuh @ 10:35 am

And by the way. Those screenshots are from GDM (gnome display manager). There is similar for KDE (kdm). Usually you don't need to worry about that but if you use mostly KDE you might want to replace gdm with kdm. Again this is how it works no matter what distro you use. So if you someday try another distro this tutorial mostly applies for it too. Only the command/package name which installs kde/gnome will be different.

Watching The Net @ 12:25 pm

You just described Linux. A bunch of ways to do the same task. There is no wrong way to do it!

Brad @ 7:24 pm

When I did this, FYI, from Kubuntu, the installer actually asked me which manager I wanted to use by default during the install of the package.

Jim Sowers @ 4:16 pm

This is helpful IF you have to login. I set up my system some time ago such that it doesn't require me to login since I am the only user. Now, I cannot figure out/remember how to force a login, thus I cannot change between desktops. Please help πŸ˜‰

Watching The Net @ 6:22 pm

This should help you remember πŸ˜‰

connor @ 10:35 pm

hey, thanks heaps, i just started using ubuntu. one thing though, when you do it and enter that code (for newbies here) just go Applications, Accessories, Terminal. and also when it asks you to enter your password it's exactly the same except you cant see what your writing. just punch it in and press enter

suraya @ 2:48 am

Me also not understand why we have Ubuntu (Gnome), Kubuntu (KDE) and Xubuntu (XFCE) ? I know only one fit in one CD. Why just make cd ubuntu-kde, ubuntu-gnome, ubuntu-xfce ?

Valentine @ 5:29 pm

Great. It helped me a lot. Thanx!

quorlia @ 10:15 am

If, like me, you can't even get Gnome working (fresh Wubi install and I've spent the last 4 hours slaving over a hot command line πŸ˜‰ you might need to do an apt-get update before you can even FIND the kubuntu-desktop package.

Mark @ 4:56 pm

I can confirmed that there were too many unresolved dependencies, at least under Ubuntu 6.06 . This was a nightmare and even trying to satisfy the dependencies hammered the system. I am now preparing a reformat, after attempting this, BE WARNED!

Chris @ 10:32 am

@Mark – Try updating your outdated Ubuntu OS, of course it caused problems! We're all mostly on 8.04 or 8.10 and you tried with 6.06?

Tim @ 2:51 am

KDE and Gnome are only window interfaces to Linux a sort of 'front end' display – in Ubuntu, gnome is most like Microsoft XP, KDE is more like unix. Both have their good and bad points, so for new users of Linux, it may be a good idea to try both. First, you have to load both (there are lots of posts about how to do this)Thereafter KDE will run Gnome applications, and Gnome will run KDE applications (both sorts appear in the 'applications launcher of either) or either sort of application can be run from the dreaded 'command line' The easiest way to swap between the blue KDE desktop and the usual orange Gnome display is via the login window go to in the bottom left.

Some tasks require a bit more skill, and require 'old fashioned' command line entry (usuakkl Alt-F2, or an application such as Terminal or my favourite, Konsole). Here Ubuntu offers both super-user access and sudo (super user – DO), which allows users to perform some super-user tasks. For this, I find that KDE is best, because Konsole allows 'clipboard cut and paste' (e.g. from internet posts like this), but only using the right mouse button (this is a bit awkward at first, as you can not paste anywhere but at the end – it is not possible to paste in the middle of a part-entered command).

Finally, Linux environments may be cash light, but they can be labor intensive and challenging to master. So back-up your work regularly, and do not be afraid to play. Remember though that super-user is scary, and try not to use it unless you HAVE recently backed up somewhere safe – like a memory stick or USB disk that you can unplug!

How to switch between gdm and kdm on ubuntu

Ubuntu 20.04 Gnome desktop uses GDM3 as the default display manager. If you installed other desktop environments in your system, then you may have different display managers.

To change the default display manager, open terminal from system application launcher, and do following steps one by one.

1.) Check the current running display manager by running command:

How to switch between gdm and kdm on ubuntu

You may also run cat /etc/X11/default-display-manager to get the result.

2. Run command to reconfigure the default manager:

NOTE: replace gdm3 in the command with the one you got in step 1).

How to switch between gdm and kdm on ubuntu

3.) It will bring up the package configuration screen, if you have more than one display managers installed:

How to switch between gdm and kdm on ubuntu

4.) Hit enter in the previous screen, then press Up / Down arrow keys to switch the display manager and hit Enter.

How to switch between gdm and kdm on ubuntu

The change will be applied in next boot. Enjoy!

Share this:

I’m a freelance blogger who started using Ubuntu in 2007 and wishes to share my experiences and some useful tips with Ubuntu beginners and lovers. Please notify me if you find any typo/grammar/language mistakes. English is not my native language. Contact me via [email protected]

  • Sweet Home 3D 6.4 Released.
  • How to Install Deepin Desktop.

4 responses to How to Change the Default Display Manager in Ubuntu 20.04

Hi Ji, Welcome to Ubuntu!. It is good to ditch the Windows rubbish and get into the real OS where one can change anything you want, yet have a global community who can support the OS. I run the latest kernel almost every 2 weeks ob X64 platform while on Arm platform running V5.8 as they are not as stable nor fast. My Arm machines are Rasp Pi4 (naturally), OrangePi Pc, Orange Pi Zero, BananaPi ZeroM2. Those little nixes are very good and fun to use.

Hello Ji;
I can hardly fault your English. It is actually very good. I take your statement as invitation for corrections. This (being corrected by others) was the most helpful when I came to live in this my country and had to learn English very quickly. Swim or Sink, I was told.
Regarding this article, I have few questions: Perhaps others encountered the same problems and you may provide us with some answers:
I installed this Ubuntu:
Linux Nomis-Revival-Ubu 5.8.0-30-generic #32-Ubuntu SMP Mon Nov 9 21:03:15 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
I am running Gnome with several extensions. The gdm3 worked for a say or so, then this
problem cropped up:
When booting, the screen turns black. Within seconds the Philips monitor announces it is going to sleep for lack of signal. Indeed it does (goes to sleep), Most times, I can do a three-fingers salute 2 or 3 (Ctl-Alt-F2, Ctl-Alt-F2). and get a console login. This happens in a very tiny font, so small my tired old eyes cannot read the screen. Once I login, I can use startx(1), to start a gnome session, xinit(1) will NOT work (lack of permission to write (false!).) This is very strange!. Anyway, once startx starts, Gnome session will start and run as well as Gnome knows how. Screen resolution is always the same 3840×2160, which is perfect for me.
Last night this ability to get a text console stopped working. I have no idea why.
However, while the screen is black and looks turned off, I can actually login! Just like with invoking startx from the console shell, it starts the session just perfectly.
I really want to have gdm work properly and visibly. Normally I would have been able to solve the problem by myself. But now my health is too run down, and my eyesight is too poor for serious reading – I have to ask for help πŸ™ I apologize for making this too long, I simply wanted to provide you with useful information, not just “it does not work.”
Oh, the dialog you quote, samples and all, does not display at all. The script pauses for a second or two, then exits without any output. Exit status is zero.
Thank you.
Simon

Ubuntu 20.04
systemctl status display-manager.service give me this output:

Jan 15 18:09:45 Ubuntu gdm-password][2653]: pam_unix(gdm-password:auth): Couldn’t open /etc/securetty: No such file or directory
Jan 15 18:09:52 Ubuntu gdm-password][2653]: pam_unix(gdm-password:auth): Couldn’t open /etc/securetty: No such file or directory
Jan 15 18:09:52 Ubuntu gdm-password][2653]: gkr-pam: unable to locate daemon control file
How do I correct the misspelled word “security” , so that gdm finds the correct directory?

Hi. I have been using gnome for a couple of years now, and I think it’s time to give kde a try. So I installed it, and now it want me to configure it! In a window called Debconf on debian, I have to choose between gdm and kdm. Which should I choose and why? Will there be an easy way to switch back and forth once I’ve chosen?

Re: gdm vs. kdm

#2 Post by BioTube » 2010-08-27 00:15

Re: gdm vs. kdm

#3 Post by Satanic Atheist » 2010-08-27 01:53

I’ve been using Linux for years now and I’ve still never figured out much about the differences between GDM and KDM other than (on the surface, at least) log-in managers for their respective GUIs. That said, both will quite happily load other window managers such as FluxBox, BlackBox and (of course) eachother to name but a few.

I’ve only ever had one reason to run GDM and that was so that I could get the Crystal Rose theme running. The differences on the surface really are (to me, anyway) trivial.

Still, if anyone we like to enlighten me.

Re: gdm vs. kdm

#4 Post by Absent Minded » 2010-08-27 02:41

Re: gdm vs. kdm

#5 Post by driller » 2010-08-27 10:11

Re: gdm vs. kdm

#6 Post by Satanic Atheist » 2010-08-27 11:39

It used to be a lot more complicated than using dpkg-reconfigure to change Desktop Manager. If I remember right, you couldn’t use the DM that wasn’t set as the “default” – it would not load and print a warning. I’m not sure if this is true anymore. I haven’t had a reason to play around with this stuff for a while.

I believe that simply changing /etc/X11/default-display-manager is enough to switch between DMs (it’s just a pointer to the DM of choice).

Re: gdm vs. kdm

#7 Post by AMLJ » 2010-08-27 17:02

Re: gdm vs. kdm

#8 Post by shathaway » 2010-08-29 02:05

A Historical Perspective:

KDE and Gnome have different design lineages and licensing criteria. The truly open-source communities (GNU et.al.) did not like the the KDE commercial licensing encumbrances. The Gnu (Gnome) design refused to use the KDE underpinings but tried to accommodate the same applications.

If you are embracing a specific Linux distribution (Debian, Red Hat, Ubuntu, Suse, Slackware, TurboLinux, Fedora, etc.) and wish the greatest compatibility with the distribution, then it is wise to stick with the default GUI manager for that distribution because it has undergone the most stringent integration tests.

If the distribution allows you to choose either, and your choice is not the default GUI manager — you should be ready to understand the management issues related to your GUI choice.

If you are looking for games and other commercial software, then your choice of software may dictate that a specific GUI should be used.

Re: gdm vs. kdm

#9 Post by nadir » 2010-08-29 03:30

shathaway wrote: A Historical Perspective:

KDE and Gnome have different design lineages and licensing criteria. The truly open-source communities (GNU et.al.) did not like the the KDE commercial licensing encumbrances. The Gnu (Gnome) design refused to use the KDE underpinings but tried to accommodate the same applications.

If you are embracing a specific Linux distribution (Debian, Red Hat, Ubuntu, Suse, Slackware, TurboLinux, Fedora, etc.) and wish the greatest compatibility with the distribution, then it is wise to stick with the default GUI manager for that distribution because it has undergone the most stringent integration tests.

If the distribution allows you to choose either, and your choice is not the default GUI manager — you should be ready to understand the management issues related to your GUI choice.

If you are looking for games and other commercial software, then your choice of software may dictate that a specific GUI should be used.

Huh?
Must have taken the wrong turn again
(there really ought to be a sign at the end of the universe to tell that it stops there. )

Gnu is free software, not open-source software (not that it would matter that much, or that it would relate somehow to this thread, but if one feels the urge to talk about it. et.al and all that latin stuff).

Back on track:
Like the others say. It doesn’t matter that much. In case you use kde using kdm would be a good choice (not that gdm would not work), if you are using gnome gdm would be a good choice ( not that kdm would not work).