Setting up dual screens on CentOS 7 X.org Adjust settings for two displays at once
Setting up dual screens on CentOS 7 X.org Adjust settings for two displays at once
Hey there, I’m here for my Linu x Tech Tips. I’ve got a question that should be straightforward, but my search didn’t yield an answer. I have two 24" Dell P2418HT touchscreens linked to a CentOS 7 PC with X.org and MATE desktop. The setup has the desktop extended across both screens—left and right. The issue is that touch input isn’t scaling properly, and movement on one screen causes double the horizontal shift on the other. I think this is because the system treats the whole desktop as controlled by a single input zone. Since both screens are connected via USB, I’m wondering how to restrict pointer movement to each monitor’s area. I believe adjusting a mapping will help. The specs are: Shuttle DH370 with i5-8400, Intel UHD Graphics 630, DP resolution 1920x1080 on CentOS 7.6.1810. I’m unsure where to start configuring touchscreen bounds or mappings. This machine is meant for use without a mouse or keyboard—any guidance would be greatly appreciated.
You might have to adjust how the touch screen input moves between screens, making sure each side starts at the correct position. For example, if the left screen begins at pixel 0,0, the right should start at a different offset like 1921,0. The exact settings are likely in /etc/X11/xorg.conf, though the details aren’t clear yet.
According to my understanding, Linux currently supports only one touch input and displays a fixed desktop size. In X, the main screen is at position 0, which means it should only accept input from that specific area. This aligns with what I've learned.
Well, X or X11 isn't the only option anymore; CentOS 7 hasn't embraced Wayland, while Wayland 8 finally arrived but isn't available as an alternative in my setup. In my general grasp of the situation, this could mean: identifying touchscreen devices via USB port locations to decide left/right, using lsusb for assistance, possibly checking device files, and employing xinput with coordinate spaces for each input device. I've seen talks about it from years ago (really old), but no one has shared a detailed guide on it.
I developed a method to solve the issue on my own. The challenge was that a touch digitizer connected via USB appears normal, making it hard for the system to identify which screen it belongs to. My goal was to map each touch input to a specific monitor using commands like xinput map-to-output. I wrote a script initially, but it wasn’t ideal. Now I explain my process in detail. If you have multiple touchscreens of the same model, distinguishing them requires knowing which USB port they connect to—usually based on physical connections. I identified the correct port by checking /proc/bus/input/devices and noting the ports (e.g., 6 and 9). I then searched for event handlers linked to those controllers during login setup. By analyzing xinput logs, I extracted numeric IDs for each touch controller. Using xrandr, I captured monitor port assignments that remained consistent after reboots. Finally, I matched these IDs with the appropriate monitor ports (e.g., DP3 and DP1). This approach lets you dynamically associate physical USB locations with specific input IDs. It’s a workaround that works best when you maintain stable port mappings.