To have a dual screen, I changed the graphics card, but the second screen doesn't light. Do I need to recompile the kernel or something?

Can you provide more information about:

- What distro/DE
- What graphics card(s) are involved
- Did you turn on the various monitor(s) and connect them up to known working output(s) with known working cable(s)?

The most 'obvious' guess/answer, since you put 'Xubuntu' in your profile, would be to go into Settings -> Display and see if the additional monitor (s) are present, and if so, set them to 'On' or 'Enabled' and then confirm the changes. If that's not useful, folks will probably need at least the information I requested, if not more (like the output of xrandr).

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additionally recompiling kernel will not help (but again, hard to say anything without details).

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The distro is CentOs7 in console mode, without graphical environment
No idea, I took it from a less old PC that was taking dust in a closet. The output is DMS-59 I think, and then a splitter cable gives two Vga output. The Bios only says "PEG" on the main monitor. The new card looks like this card and the former like this one
Extensively... And everything works
At the lab, the computer runs Xubuntu but I'm home hacking. If needed, I can reinstall everything but I'm trying to avoid coming to that end

Ok, so once more:
You have a computer at home, running Xubuntu and another one in the lab running CentOS 7. Which one do you want to use with two monitors?
lspci should give you some info about your VGA compatible controller (= video card).

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The hacked computer home runs CentOs 7 (as I started on the forum to learn using Xubuntu in the lab, I left it when I switched to Linux)
lspci says:
(if I unplug the vga cable that goes from output #2 on the computer to the screen with no signal and plug it to output #1, the screen lights and shows what the main screen was displaying)

So both displays are known to be working? But one graphics card is able to provide a video signal to whatever display it's connected to? And the other graphics card doesn't? I would assume that the card that was detected by "lspci" is the one that's providing the video output. Right?

Since both are nVidia-based, have you checked the driver that's being used? If it's one of nVidia's proprietary drivers, does it have support for both chips?

Have you gone into a system setting dialog (as previously suggested) to see if there's an option to select one or both screens for output? If so, are both selected?

I haven't run a dual-video-card system before -- other than on a system with a motherboard-based video chip that I disabled via the BIOS in favor of my (now-no-longer-supported) nVidia card -- but I'm wondering if this could be an Xorg-related problem, i.e., does Xorg detected the second "screen". If not, this could be due to that system configuration setting that enables both cards/displays. Have you taken a look at the Xorg log file to how many screens are defined? (On my system, it's /var/log/Xorg.0.log---and I only see a "Screen 0". YMMV.)

HTH...

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There is no graphical environment

Sorry... I read and immediately spaced off that information from your earlier post. I've never known anyone to use that sort of configuration before. Most folks would simply use Ctrl-Alt-F[1-6] but I can see how having two live monitors could be useful.

I wish you luck in finding a solution.

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FWIW: I've never known nVidia cards to drive multiple displays without some sort of GUI/DE running - e.g. they won't display the computer's BIOS/UEFI on multiple screens, display text installers on multiple screens, etc. I know some ATi/AMD cards will do this, but it would be a 1:1 clone (the same output on all screens), which you could also achieve with a 1x2 active splitter (for whatever connection of choice). I'm also not sure I'd spend the money on a Radeon just to test that theory, when you could get a splitter (if your goal is to just have the same output on many monitors). Like rnturn, I'm not sure how you'd do this without a DE - you could probably run X and a very basic wm like dwm and have (separate) terminals on each of the displays, but I don't know if that's possible in your environment (and I base this entirely on pictures I've seen of dwm in action and reading about it - see more here: https://dwm.suckless.org/ and example image here: https://en.wikipedia.org/wiki/Dwm#/m...l_monitor.jpeg - according to the caption of the Wikipedia image this relies on Xinerama as well).

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For example on a 32bits computer, if I change the processor, I need to reinstall Linux. Is it the same for graphics cards?

I don't think it is true.

You only need to install the driver for the new video card.

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How would you do then?

For example:
?

Just tryied
and nothing appears... Maybe there is no driver at all: it's a minimal installation

if you have a similar card (for example a better nvidia) you do not need to install/uninstall anything, that will work.
Also these are generic kernels and they work with almost any CPUs, so do not need to do anything.

Furthermore I think nvidia (or nouveau) required only for GUI, otherwise yes, there is a basic support in the kernel for non-graphical environments.

Also I think you can have only one console, so you cannot use 2 monitors in console mode, you need to run X to be able to do that. Or probably there is a kernel patch to do that (I think this is a quite uncommon request).

But correct me if I'm wrong, maybe I have misunderstood something.

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