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Old 08-27-2014, 04:42 PM   #1
thegoldeneagle
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How to run multiple display managers simultaneously?


Peace be upon you,

I have gdm and kdm, i want to run both of them at the same time but i don't know how?

I know that this is possible from this message when configuring gdm3

"Multiple display managers can run simultaneously if they are configured to manage different servers; to achieve this, configure the display managers accordingly, edit each of their init scripts in /etc/init.d, and disable the check for a default display manager."

Last edited by thegoldeneagle; 08-27-2014 at 04:46 PM.
 
Old 08-27-2014, 05:33 PM   #2
jpollard
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Depends on your distribution.

Several no longer have an init.d directory...

Some don't install kdm, even if you install KDE.

You don't really need to run both of them anyway. They both carry out the same function - getting logged in via a GUI.

The main advantage for kdm is when you DON'T have any part of Gnome installed. Using gdm in this case causes all Gnome libraries to be installed. The same is true for kdm.

Last edited by jpollard; 08-27-2014 at 05:35 PM.
 
Old 08-27-2014, 07:02 PM   #3
thegoldeneagle
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First of all, thank you jpollard for your reply

I use debian jessie and it have /etc/init.d which in it i found gdm3 and kdm shell script file

with a lock inside /etc/init.d/gdm3 i think this is the important part for me in the file
# To start gdm even if it is not the default display manager, change
# HEED_DEFAULT_DISPLAY_MANAGER to "false."
HEED_DEFAULT_DISPLAY_MANAGER=true
DEFAULT_DISPLAY_MANAGER_FILE=/etc/X11/default-display-manager

i can't find any explanation for example how i get gdm3 on :0 display and kdm on :1 display?

Last edited by thegoldeneagle; 08-27-2014 at 07:08 PM.
 
Old 08-27-2014, 10:13 PM   #4
jpollard
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Never did this (I don't use debian)... but the reason you have to set the HEED_DEFAULT_DISPLAY_MANAGER to false is to stop it from starting one.

You have to have two configuration files, with each one specifying a different display. By default the configuration files will both use 0 (especially if none are specified at all).

Then BOTH have to be started.
 
Old 08-27-2014, 10:35 PM   #5
frankbell
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Maybe I'm missing something, but, assuming that one has only one display, I can't see anything but conflict and trouble if one tries to run two display managers at the same time.
 
Old 08-27-2014, 11:43 PM   #6
jpollard
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That is why you have to have two configuration files.

Normally, the Linux kernel has multiple virtual displays. When one of them is in use, X server will grab the first unused virtual displays (or virtual terminals).

In this case, running two X servers is not a problem - the first unused display gets :0 (or whatever display number the X server is directed to use), and the second will grab the next unused display.

What is shown on the physical display is selected by the alt-fx key (x being 1 through 12). Frequently 1-6 are desigated for use as terminals (via agetty initialization, which has the terminal marked busy). Thus the first unused virtual terminal is 7.

The X server interprets the selection via the ctrl-alt-fx sequence (and hopefully it will still be configured that way here).

gdm has supported the use of multiple X servers for quite a while - screen savers usually have a "New Login" button which directs gdm to start another X server. Selecting between them is done via the ctrl-alt-fx sequence. All this is doing is using two different display managers to manage two different displays.

Not real sure why, but it should be possible for two display managers to run; though both have to be given configurations for different X display names. This is mostly due to the nature of X. It uses a domain socket in /tmp/.X11-unix for communication. The display number is used to identify the two displays. Normally one will be X0, and the second would be X1. When a single display manager is used, it decides the next number to use... usually by incrementing a simple internal counter, then starting a new display. My system currently has X0 (which happens to be used by my wife), and I get the next one (which is now X26, because each time I logout and login I get the next bigger number).

Last edited by jpollard; 08-27-2014 at 11:45 PM. Reason: typo - put /etc where /tmp should be
 
3 members found this post helpful.
Old 08-28-2014, 08:58 PM   #7
frankbell
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Thanks.

Now I get that it's possible. I will concede I was thinking of the boot-up display manager.
 
Old 08-29-2014, 01:07 AM   #8
EDDY1
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@jpollard is this being displayed on 1 machine or on remote terminals?
 
Old 08-29-2014, 05:31 AM   #9
jpollard
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This would be on one machine.

Normally, remote machines would be using their own X server to display windows forwarded by ssh, no need for the overhead of multiple layers of X servers.

Using something like vnc is a different option, but I'm not sure how you would even do a single display manager for that. From

http://wiki.centos.org/HowTos/VNC-Server

it would appear that the vnc server itself handles the login, thus a display manager isn't needed.

Last edited by jpollard; 08-29-2014 at 05:45 AM.
 
  


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