Display resolution dropping when using KVM switch

[eggegick]

I have a "DELL U2412M", a 24 inch monitor. It is connected to a Windows 11 machine and a Linux Mint 21.3 machine via an Iogear displayport KVM switch. Both machines normally boot up with the monitor at a resolution of 1920x1200.

I mostly use the Linux machine. When I run "Preferences->Display", the "Resolution" choices range from 1920x1200 down to 800x600.

If I use the to KVM switch to switch from the Linux machine to the Windows machine, I get a resolution of 1920x1200. Great. But when I switch back to the Linux machine, the resolution suddenly drops to 1280x1024, and "Preferences->Display" shows that no higher resolution is available.

At this point if I switch back to the Windows machine, it's still at 1920x1200. Then if I switch back to Linux, it has now dropped to 1024x768! At this point things stabilize, and switching back and forth yields 1920x1200 for windows and 1024x768 for Linux (that is, the resolution for Linux is no longer dropping).

Rebooting the Linux machine fixes this, but that is a lousy work around. I'd like it to not happen in the first place, or at least have a command to set thing back to normal.

Any suggestions?

[SMG]

Any suggestions?

Welcome to the forum, eggegick.

Please open the System Reports app and click the System Information tab on the left. Your computer's information should come up in the right pane. Then click the Copy button in the lower right and paste the results into a reply window here so we can see how Linux Mint views your hardware.

[eggegick]

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System:
  Kernel: 5.15.0-101-generic x86_64 bits: 64 compiler: gcc v: 11.4.0 Desktop: Cinnamon 6.0.4
    tk: GTK 3.24.33 wm: muffin vt: 7 dm: LightDM 1.30.0 Distro: Linux Mint 21.3 Virginia
    base: Ubuntu 22.04 jammy
Machine:
  Type: Desktop System: Dell product: OptiPlex 9020 v: 00 serial: <superuser required> Chassis:
    type: 15 serial: <superuser required>
  Mobo: Dell model: 0XCR8D v: A03 serial: <superuser required> UEFI: Dell v: A25
    date: 05/30/2019
Battery:
  Device-1: hidpp_battery_0 model: Logitech Wireless Mouse serial: <filter>
    charge: 55% (should be ignored) rechargeable: yes status: Discharging
CPU:
  Info: quad core model: Intel Core i7-4790 bits: 64 type: MT MCP smt: enabled arch: Haswell
    rev: 3 cache: L1: 256 KiB L2: 1024 KiB L3: 8 MiB
  Speed (MHz): avg: 3919 high: 3989 min/max: 800/4000 cores: 1: 3803 2: 3989 3: 3914 4: 3934
    5: 3916 6: 3984 7: 3892 8: 3925 bogomips: 57465
  Flags: avx avx2 ht lm nx pae sse sse2 sse3 sse4_1 sse4_2 ssse3 vmx
Graphics:
  Device-1: Intel Xeon E3-1200 v3/4th Gen Core Processor Integrated Graphics vendor: Dell
    driver: i915 v: kernel ports: active: DP-2 empty: DP-1, HDMI-A-1, HDMI-A-2, VGA-1
    bus-ID: 00:02.0 chip-ID: 8086:0412 class-ID: 0300
  Device-2: Logitech Webcam C270 type: USB driver: snd-usb-audio,uvcvideo bus-ID: 3-4:2
    chip-ID: 046d:0825 class-ID: 0102
  Display: x11 server: X.Org v: 1.21.1.4 driver: X: loaded: modesetting unloaded: fbdev,vesa
    gpu: i915 display-ID: :0 screens: 1
  Screen-1: 0 s-res: 1920x1200 s-dpi: 96 s-size: 508x317mm (20.0x12.5") s-diag: 599mm (23.6")
  Monitor-1: DP-2 model: Dell U2412M serial: <filter> res: 1920x1200 hz: 60 dpi: 94
    size: 518x324mm (20.4x12.8") diag: 611mm (24.1") modes: max: 1920x1200 min: 720x400
  OpenGL: renderer: Mesa Intel HD Graphics 4600 (HSW GT2) v: 4.6 Mesa 23.2.1-1ubuntu3.1~22.04.2
    direct render: Yes
Audio:
  Device-1: Intel Xeon E3-1200 v3/4th Gen Core Processor HD Audio vendor: Dell
    driver: snd_hda_intel v: kernel bus-ID: 00:03.0 chip-ID: 8086:0c0c class-ID: 0403
  Device-2: Intel 8 Series/C220 Series High Definition Audio vendor: Dell driver: snd_hda_intel
    v: kernel bus-ID: 00:1b.0 chip-ID: 8086:8c20 class-ID: 0403
  Device-3: Logitech Webcam C270 type: USB driver: snd-usb-audio,uvcvideo bus-ID: 3-4:2
    chip-ID: 046d:0825 class-ID: 0102
  Sound Server-1: ALSA v: k5.15.0-101-generic running: yes
  Sound Server-2: PulseAudio v: 15.99.1 running: yes
  Sound Server-3: PipeWire v: 0.3.48 running: yes
Network:
  Device-1: Intel Ethernet I217-LM vendor: Dell driver: e1000e v: kernel port: f080
    bus-ID: 00:19.0 chip-ID: 8086:153a class-ID: 0200
  IF: eno1 state: up speed: 1000 Mbps duplex: full mac: <filter>
  Device-2: Realtek RTL8188FTV 802.11b/g/n 1T1R 2.4G WLAN Adapter type: USB driver: N/A
    bus-ID: 3-6:4 chip-ID: 0bda:f179 class-ID: 0000 serial: <filter>
RAID:
  Hardware-1: Intel SATA Controller [RAID mode] driver: ahci v: 3.0 port: f060 bus-ID: 00:1f.2
    chip-ID: 8086:2822 rev: N/A class-ID: 0104
Drives:
  Local Storage: total: 953.87 GiB used: 182.68 GiB (19.2%)
  ID-1: /dev/sda model: SSD size: 953.87 GiB speed: 6.0 Gb/s type: SSD serial: <filter> rev: 4A0
    scheme: GPT
Partition:
  ID-1: / size: 937.33 GiB used: 182.67 GiB (19.5%) fs: ext4 dev: /dev/sda3
  ID-2: /boot/efi size: 512 MiB used: 6.1 MiB (1.2%) fs: vfat dev: /dev/sda2
Swap:
  ID-1: swap-1 type: file size: 2 GiB used: 0 KiB (0.0%) priority: -2 file: /swapfile
USB:
  Hub-1: 1-0:1 info: Full speed or root hub ports: 3 rev: 2.0 speed: 480 Mb/s chip-ID: 1d6b:0002
    class-ID: 0900
  Hub-2: 1-1:2 info: Intel Integrated Rate Matching Hub ports: 6 rev: 2.0 speed: 480 Mb/s
    chip-ID: 8087:8008 class-ID: 0900
  Hub-3: 2-0:1 info: Full speed or root hub ports: 3 rev: 2.0 speed: 480 Mb/s chip-ID: 1d6b:0002
    class-ID: 0900
  Hub-4: 2-1:2 info: Intel Integrated Rate Matching Hub ports: 8 rev: 2.0 speed: 480 Mb/s
    chip-ID: 8087:8000 class-ID: 0900
  Hub-5: 3-0:1 info: Hi-speed hub with single TT ports: 15 rev: 2.0 speed: 480 Mb/s
    chip-ID: 1d6b:0002 class-ID: 0900
  Device-1: 3-4:2 info: Logitech Webcam C270 type: Video,Audio driver: snd-usb-audio,uvcvideo
    interfaces: 4 rev: 2.0 speed: 480 Mb/s power: 500mA chip-ID: 046d:0825 class-ID: 0102
  Hub-6: 3-5:3 info: Terminus Hub ports: 4 rev: 2.0 speed: 480 Mb/s power: 100mA
    chip-ID: 1a40:0101 class-ID: 0900
  Device-1: 3-5.1:5 info: Logitech Unifying Receiver type: Mouse,HID
    driver: logitech-djreceiver,usbhid interfaces: 2 rev: 2.0 speed: 12 Mb/s power: 98mA
    chip-ID: 046d:c52f class-ID: 0300
  Device-2: 3-5.2:6 info: Logitech Logitech Mechanical keyboard type: Keyboard,HID
    driver: hid-generic,usbhid interfaces: 3 rev: 2.0 speed: 12 Mb/s power: 250mA chip-ID: 046d:c341
    class-ID: 0300 serial: <filter>
  Device-3: 3-6:4 info: Realtek RTL8188FTV 802.11b/g/n 1T1R 2.4G WLAN Adapter type: WiFi
    driver: N/A interfaces: 1 rev: 2.0 speed: 480 Mb/s power: 500mA chip-ID: 0bda:f179
    class-ID: 0000 serial: <filter>
  Hub-7: 4-0:1 info: Super-speed hub ports: 6 rev: 3.0 speed: 5 Gb/s chip-ID: 1d6b:0003
    class-ID: 0900
Sensors:
  System Temperatures: cpu: 29.8 C mobo: 27.8 C
  Fan Speeds (RPM): N/A
Repos:
  Packages: 2440 apt: 2431 flatpak: 9
  No active apt repos in: /etc/apt/sources.list
  Active apt repos in: /etc/apt/sources.list.d/google-earth-pro.list
    1: deb [arch=amd64] http: //dl.google.com/linux/earth/deb/ stable main
  Active apt repos in: /etc/apt/sources.list.d/official-package-repositories.list
    1: deb http: //packages.linuxmint.com virginia main upstream import backport
    2: deb http: //archive.ubuntu.com/ubuntu jammy main restricted universe multiverse
    3: deb http: //archive.ubuntu.com/ubuntu jammy-updates main restricted universe multiverse
    4: deb http: //archive.ubuntu.com/ubuntu jammy-backports main restricted universe multiverse
    5: deb http: //security.ubuntu.com/ubuntu/ jammy-security main restricted universe multiverse
  Active apt repos in: /etc/apt/sources.list.d/protonvpn-stable.list
    1: deb [arch="all", signed-by=/usr/share/keyrings/protonvpn-stable-archive-keyring.gpg] https: //repo.protonvpn.com/debian stable main
  No active apt repos in: /etc/apt/sources.list.d/steam-beta.list
  Active apt repos in: /etc/apt/sources.list.d/steam-stable.list
    1: deb [arch=amd64,i386 signed-by=/usr/share/keyrings/steam.gpg] https: //repo.steampowered.com/steam/ stable steam
    2: deb-src [arch=amd64,i386 signed-by=/usr/share/keyrings/steam.gpg] https: //repo.steampowered.com/steam/ stable steam
Info:
  Processes: 277 Uptime: 6h 16m wakeups: 31 Memory: 31.25 GiB used: 4.97 GiB (15.9%) Init: systemd
  v: 249 runlevel: 5 Compilers: gcc: 11.4.0 alt: 11/12 Client: Unknown python3.10 client
  inxi: 3.3.13

[SMG]

If I use the to KVM switch to switch from the Linux machine to the Windows machine, I get a resolution of 1920x1200. Great. But when I switch back to the Linux machine, the resolution suddenly drops to 1280x1024, and "Preferences->Display" shows that no higher resolution is available.

I don't see anything in your output which would lead me to believe it is something related to your install.

I'm suspecting it has something to do with how the KVM is working? Can you switch the leads for the computers and see if it still happens? And/or switch the ports being used on the KVM?

The EDID is supposed to pass from the monitor through the cable to the computer. The options in the EDID are what should be seen in the Display app. Usually, when the options in the Display app are not correct, the EDID is not be properly passed.

Linux-based distros are supposed to hot-plug so one should not need to reboot the computer.

As a test to see if the EDID might be "disappearing", you can run

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xrandr --verbose

when you start (you should see the section for EDID) and then run it later on after you have switched and the resolution is no longer correct and see if it is now gone.