problem with display settings on Centos7 KDE control module

[kristijonas]

I have a 3 monitor setup. I think I have KDE installed, latest Centos7 with updates.

Everything is default!

This is what I get when I go to display settings:

https://pasteboard.co/I5rNYXU.png

I am not an advanced user.

[desertcat]

I have a 3 monitor setup. I think I have KDE installed, latest Centos7 with updates.

Everything is default!

This is what I get when I go to display settings:

https://pasteboard.co/I5rNYXU.png

I am not an advanced user.

I have been using KDE for some 19 years and have never seem something called a "KDE CONTROL MODULE" What you should have along the bottom of ONE of your three monitors is a bar called The Panel (also sometimes called the Task Bar). On the far left side of the the Panel you should see something like a multi-colored 8-pointed star or two squares one offset over the other. This is the Application Launcher. If you were to click on this it will give you Drop Down Menus which contain all your applications and sub-applications. Somehow you -- don't ask me how -- have ended up where you need to set up your monitors, though normally it would list the various monitors.

You need to locate the Monitor which contains the Panel and Application Launcher. Click on the Application Launcher and you will see along the menu bottom things that say Favourites, Applications, Computer, Recently Used, Leave. Click on Application and it will give a drop down menu. Find SETTINGS and Click on it. Locate SYSTEM SETTINGS and Click on it. Under HARDWARE find DISPLAY and MONITOR. Click on it, and you should now see Something called DISPLAY CONFIGURATION. Click on it and you *should* now see the Names of all 3 of your Monitors. The Monitor that has the Panel on it should be located in the Middle and the other two should be located to the right and left of it.

I don't have a CLUE how you reached where you are. If you are using a third party Control Panel, TrevorH will read you the riot act that CentOS does NOT support 3rd Party Control Panels and that you are on your own, and to contact them for support. If you are NOT using a 3rd Party Application the best advice is to troubleshoot your situation. The best way to do that would be to disconnect the two monitors that do not have the Panel and start from there. If you are using multiple video cards, find out which one is being used.

Given that I don't know HOW you got where you are or have seen anything that even remotely looks like your jpeg, all I can do is wish you luck, but hope I have provided you with some starting points.

[kristijonas]

Hey, so this is a stock thingy. I did not install anything third party anything. Fresh CentOS7.

I also have a very simple setup. A laptop with Intel graphics with vga and hdmi displays connected (three displays in total).

https://pasteboard.co/I6cqqDk.png Here is how I opened the KDE control module. I press Alt+F2 and type "display".
In this picture, it is the second option

Hope that helps.

I should also note I am experiencing another, possibly related problem with displays:

When I power on the laptop, I cannot log in Centos7 as I can't see the authentication screen.
This only happens when the external displays are not attached.
When I attach the mentioned external displays and power on, I can see the authentication screen...

Let me know if I can provide any further information or if you have any suggestions.

[desertcat]

Hey, so this is a stock thingy. I did not install anything third party anything. Fresh CentOS7.

I also have a very simple setup. A laptop with Intel graphics with vga and hdmi displays connected (three displays in total).

https://pasteboard.co/I6cqqDk.png Here is how I opened the KDE control module. I press Alt+F2 and type "display".
In this picture, it is the second option

Hope that helps.

I should also note I am experiencing another, possibly related problem with displays:

When I power on the laptop, I cannot log in Centos7 as I can't see the authentication screen.
This only happens when the external displays are not attached.
When I attach the mentioned external displays and power on, I can see the authentication screen...

Let me know if I can provide any further information or if you have any suggestions.

Well I stand corrected -- learn something NEW everyday. I have gone back and checked your ORIGINAL post. I did find using -- Alt+F2 -- you need to select the first option, the one that says Display CONFIGURATION "Manage and configure monitors and displays". That *should* allow you to see all three displays. It *should* allow you to select the MASTER monitor which more likely than not will be the laptop's screen.

Which brings me to Question #2: What do you mean by "Authentication Screen"?? Do you mean the Login Page?? -- The page where you select the User and enter the User's Password?? Or is this something else?!?

Which brings me to Observation #1: I noticed that you said LAPTOP... and then you run two external monitors. I run a traditional WORKSTATION with dual monitors.... in a four computer network. The Graphics card in my Workstation which, in theory, can drive 4 monitors at once -- 1VGA, 2 DVI, and 1 HDMI. Some of these computers are so old (they are hand-me-downs, or one was found by the dumpster) they can only use VGA, and the KVM switch uses ONLY a VGA input/output. Thus all four computers have a VGA input, while the Workstation with its graphics card allows me to also utilize the second monitor which is hooked to one of the DVI inputs. Thus ONLY the Workstation and utilize the DUAL Monitors, while the other 3 computers a SINGLE Monitor (VGA). This brings me back to your case. I have a very limited amount of experience with laptops, which my buddy and I hacked and rebuilt from the ground up, and it was built in 2007. My experience with laptops is that it can use EITHER the laptop monitor OR an External monitor, but NOT both at the same time. But my limited experience with Laptops and the age of the one we rebuilt the situation may have changed.

Which brings me to Question #3: When you installed CentOS 7, did you have all three monitors hooked up, or did you just use the Laptop's monitor? During the install it *should* have found the Laptop's monitor and made it the DEFAULT. After you finished the install you should have rebooted, it it will -- if I remember correctly -- asked you to agree to the GPL license agreement, etc., etc., etc. after which I usually would shutdown the machine, reboot from the ground up, it then shows you the Kernel versions, defaults to the top one after 5-10 seconds, then it leads you to the login page where you enter your users Password, it then goes through the KDE StartUp, and finally dumps you into your Users' Home Directory, where you can have all the fun of Configuring the computer (or in your case Laptop) to your heart's desire. Does this sound familiar? Have you gotten as far as this?? If NOT then chances are good you screwed up the install, at which point the best thing to do is to simply do a re-install. Use ONLY the Laptop's Monitor during the install otherwise it might not know which monitor is suppose to be the MASTER. You can always add the external monitors later. The MASTER Monitor will be designated by the presence of the Panel (Taskbar) bar on the BOTTOM of the Screen.

Final Question (#4): During the install did you select a Minimal Install or an install + GUI?!? By DEFAULT the GUI for RHEL and CentOS is GNOME, though you can select to add KDE during your package selection phase of the install. That Alt+F2 command is one I did not know, which makes me think you might have done a MINIMAL Install and the selectively added KDE post install from the CLI using the yum grouplist, and the yum groupinstall "KDE Plasma Workspaces" commands. Once KDE is installed the easiest way to check, configure, etc., etc., monitors and displays is from the application launcher [ Settings => System Settings => Hardware => Display and Monitor] or if you are REALLY LAZY and have an Nvidia Graphics Card you can put the launch icon on your Panel (Taskbar) and then it is a simple matter of clicking on it to launch and then configure your monitors.

Without seeing your setup it *sounds* as though you have something wrong ie. you first need to CONFIGURE the monitors and the way to do that is to use Alt+F2 Display CONFIGURATION that should show you ALL the monitors that the Laptop can see ie 1, 2, or all 3.

[kristijonas]

Thank you for your reply! It seems that your experience with laptops is really old! You can indeed use laptop display together with any external ones at the same time. A modern laptop is more like a desktop PC. That being said:

#1. I can select the first selection and I can configure the displays there. I only wanted to report a problem with that second option which appears to be malfunctioning.
#2. Yes, Login screen, where I can choose my desktop environment, login and pass.
#3. I install Centos with all 3 displays connected.
#4 It is not a minimal installation. I did select KDE modules.

My own other observation:
I cannot use the laptop unless I have external displays hooked up. If I boot it without external laptops, the login screen is not visible. The laptop screen is indeed selected as the primary screen, though. Not sure what is wrong, but Centos7 appears to be really misbehaving with multiple displays. I have had so many problems. For example, with one screen, I could not set it to its full resolution (It worked on other OSs). I should also like to add, this is a fresh, untampered installation for educational purposes.

[desertcat]

Thank you for your reply! It seems that your experience with laptops is really old! You can indeed use laptop display together with any external ones at the same time. A modern laptop is more like a desktop PC. That being said:

#1. I can select the first selection and I can configure the displays there. I only wanted to report a problem with that second option which appears to be malfunctioning.
#2. Yes, Login screen, where I can choose my desktop environment, login and pass.
#3. I install Centos with all 3 displays connected.
#4 It is not a minimal installation. I did select KDE modules.

My own other observation:
I cannot use the laptop unless I have external displays hooked up. If I boot it without external laptops, the login screen is not visible. The laptop screen is indeed selected as the primary screen, though. Not sure what is wrong, but Centos7 appears to be really misbehaving with multiple displays. I have had so many problems. For example, with one screen, I could not set it to its full resolution (It worked on other OSs). I should also like to add, this is a fresh, untampered installation for educational purposes.

OK Now we are are getting somewhere.

#1. When you did the initial install you say you did it with all three monitors hooked up, not just the Laptop Screen?? You Can ADD monitors , but I'm not so sure you can SUBTRACT monitors which may explain your problem. In short this is a config problem.

#1a. "The Monitor Setting" likewise was a bust for me too using Alt+F2. That is a most uncommon way to access the monitors from a GUI.

#2. As to the default resolution, probably a config problem too ie. the MINIMAL res that is common to all monitors is the DEFAULT say 1920x1080. You might have a monitor that can do better than 1920x1080, but if the max of one monitor is 1920x1080 then that will be the default. You *MIGHT* be able to change the individual resolutions and customize each monitor. Here is how you do it: [a] Go to the Panel (Taskbar) and click on System Settings Click on System Settings and locate Hardware and click on Display and Monitors [c] Click on Display Configurations. You should now see -- in your case -- 3 gray boxes, and the name of the monitor's maker ex. ViewSonic Corporation plus the type of connection ex DVI-D, VGA, HDMI... [d] under the ID you will see a pair of squares one will be Blue the other White. This either turns ON or OFF the monitor/s after a reboot. The BLUE box tells you that that monitor can be seen, and accessed. Otherwise it will appear as a "ghost" monitor. [e] Under the ON/OFF boxes you will see 3 small icons: 1) a Purple semi-circle Arrow going counter clockwise 2) a Star 3) a White box with four Green symbols in it. Here is what they do: The Purple Arrow will Rotate the Output by 90 degrees in a Counter Clockwise Direction. ONE of the -- in your case -- three stars will be YELLOW this is your PRIMARY (Master) Output. The icon -- the White Box with the four GREEN Symbols in it will give you a list of ALL the Available Screen Resolutions. In *THEORY* this is where you would set the monitors screen resolution. [f] Once you have configured all your monitors and are happy click on APPLY.

#3. Say you are not a happy camper and the monitors don't appear in the desired order. EX You have a ViewSonic Monitor, the Laptop Display, and a BenQ Monitor and you want them in that order. You want the Laptop Monitor to be the Master Monitor -- This is going to be the Monitor that will contain the Panel (Taskbar). Currently the Panel is found on the BenQ Monitor that is Physically on the Right Side of the of the set setup, but the BenQ shows up on the Virtual Representation on the Left side, the ViewSonic is shown to be in the Virtual Middle, and the Laptop on the Right side. Here is how we solve that problem: [1] On the Laptop Monitor representation click on the Star, it will turn YELLOW. This is now your MASTER Monitor [2] Now the ONLY problem is the display ORDER. [a] Click and HOLD the ViewSonic Monitor and DRAG it to the LEFT side. Click and HOLD the BenQ Monitor and DRAG to the RIGHT side. The Laptop Display will now fall in between the two monitors, and the laptop Display will be the Master. Now click on Apply and the monitors should now be correctly configured. Thus even if you disconnect the two EXTERNAL monitors the Laptop Monitor will still work as it is the MASTER.

This of course ASSUMES you can log into your Users account and Start KDE, once there it is simply a matter of clicking on the Application Launcher, finding Settings, System Settings. etc., as outlined above. The Alt+F2 CLI command was a new one for me, and don't know where you found that, though it is nice to know as obscure knowledge. [Shrug].