Infosec Scribbles

October 14, 2017, updated on April 21, 2019

Linux Woes and 4K Hell

Note: this post has now been updated for 18.04 LTS.

Recently I got a new Dell Precision 5520 and a TB16 dock. It came with Windows 10, and as I was quick to learn, “10” is the number of minutes it took me to decide that I would rather use anything else. This is coming from someone who has been using Windows on all non-server machines since age 7. Given the available options, I went for Ubuntu Linux.

As it turned out, Linux came with its own set of problems, and 4K or HiDPI has below usable support no matter which OS you choose.

I will maintain this post with status updates on the issues listed so that others can reuse my solutions. Another reason is that a bunch of my coworkers have decided to follow suit upon seeing Windows 10 and this is the most efficient way of helping them with the issues they are about to face.

Current setup: Ubuntu GNOME 18.04 LTS, 5.0 mainline kernel.

For the purposes of this page, a solution fixes the problem fully, a workaround fixes it partially and unwanted side effects can be introduced in both cases.

Disk Detection

In order for Linux to detect your disk, set SATA mode in BIOS to AHCI.

Secure Boot

VMware and Nvidia are two offenders that require you to turn off Secure Boot, because their code is not signed.

Solution: (not tested yet) sign nvidia and vmware kernel modules manually for every kernel update.

HiDPI Support

The laptop comes with a 4K UHD screen. Overall, HiDPI support on Linux exists. As long as you don’t mix DPI on monitors and only use GTK3+ applications.

As soon as you connect 1080p monitors, you are in trouble. X Org does not support different DPI settings for different screens.

Where Linux does support 4K on non-mixed screens, it varies per application. Pretty much anything based on GTK2, QT4, Mono/DotNET or Java won’t work or will give you a partially/fully broken UI. Examples: KeePass, VMware, Burp Suite, HipChat to name a few.

If it makes you feel any better, Windows is just as much hit and miss. 4K technology is just not ready for daily use without making more trade-offs than it solves.


1. Run all screens at their native resolutions

Unwanted side effect: DPI setting for the UI remains the same across screens. If your external monitors are not 4K and you set DPI based on your laptop monitor, everything will be massive on them. If you set DPI based on your external monitors, everything will be tiny on your laptop monitor.

2. XRandR-based downscaling of external monitors

Unwanted side effect: increased GPU load. Applications will be rendered in 4K and scaled down, so all 4K support issues will remain. Fonts will be distorted and/or blurry on screens where downscaling takes place.

3. Run laptop screen at 1080p

Unwanted side effect: in theory, this should work without problems. 1080p is exactly half of 2160p and scaling should not introduce any artifacts. In practice, for whatever reason Dell decided that the laptop monitor should use interpolation instead, so everything is blurry.

I currently use the latter option and only use the laptop screen for background things like Spotify and IM. I tried using it on the go and it gave me a splitting headache within an hour. Too much eye strain. For on the go use, I have to switch to 2160p and restart all graphical applications. Applications that are not based on GTK3 (plenty) require workarounds which have their own bugs, i.e. cursor falling out of sync with the scaled application.

The counter-intuitive thing with this option is to not touch the HiDPI window scaling setting in GNOME Tweak Tool! By default it is set to auto-adjust to your selected resolution. The moment you touch it, it will become fixed in the value you set it to.

UPDATE 10/17/2017: I am currently attempting to get the newly released nearest neighbour rendering option to work.

UPDATE 10/20/2017: nearest neighbour scaling is not supported for hybrid graphics devices.

Docking Station / Linux Kernel

Support for Thunderbolt docking stations in Linux kernels available in Ubuntu is sub par.


As of kernel 4.15, it just works. 18.04 LTS comes with it out of the box and 16.04 LTS received it in the .5 point release, so I removed the lengthy description of the issue and the workarounds from this post. Thanks to all the open source developers that were involved in fixing this for good!

UPDATE 4/21/2019: apparently the issue comes back with every new TB dock released to market and requires someone to go and include the new hardware in the original patch. Le sigh.


Hot-plugging devices into the dock works if you disable Thunderbolt Security and use either nouveau drivers or only the Intel GPU.

On nVidia drivers, booting up with the dock, disconnecting it (e.g. for a meeting) and plugging it back in again causes the entire system to freeze. You can unfreeze it by unplugging the dock again, but even if it does come back to life, save all your work and reboot because sometimes it will crash shortly after.

This problem does not affect XPS 15 as it comes with a different nVidia GPU.

Solution: none. This was reported on launchpad.

UPDATE 4/21/2019: At some point (kernels 4.18.0 through 4.18.15) it was working, but then it broke again. Current workaround is to use 5.x mainline kernels with very specific versions of nVidia drivers - see the ticket for latest.

Thunderbolt Security

By default, devices plugged into the dock won’t work. Or so says the concept of Thunderbolt security. In reality, you still get a 50/50 chance of it working without this hack. But if you want devices plugged into the dock at boot to work, you should disable Thunderbolt Security in BIOS. Support for this feature is coming was introduced in kernel 4.13, but I haven’t tested it yet.

Solution: disable Thunderbolt security in BIOS.

Unwanted side effect: no Thunderbolt security.

Middle Click Paste

In X Org, middle click pastes from “Selection Buffer”. This buffer holds whatever your last selection was. The functionality is hard coded into X Org with no switch, GNOME Tweak Tool does not help.

Workaround: some apps allow you to disable this for them. For me, this is Firefox and Sublime Text.

Unwanted side effect: doesn’t help apps that don’t support this.

Solution: patch and recompile X Org.

Unwanted side effect: can’t get automatic updates for X Org. You will have to make it part of your daily routine to check for new versions, recompile them and install them manually.


GNOME has a couple of problems where settings from the GUI get completely ignored by the system. Some examples:

  • “Show All Input Sources” does nothing. Fixed in 18.04 LTS.
  • “Middle Click Paste” does nothing.
  • “Show Location of Pointer” breaks hotkeys.
  • Touchpad/mouse are treated the same in terms of GUI settings. Fixed in 18.04 LTS, along with other significant improvements for touchpads being added.

Window Focus Glitches

Fixed in 18.04 LTS. Kudos to GNOME team!

Window focus logic in GNOME (or maybe X Org, I haven’t bothered testing KDE to confirm yet) is weird.

Say I have a text editor full-screened on one of my monitors. If I focus a different window on a different monitor and move it to that screen, I expect it to retain focus and appear on top of the full screen window. The full screen window should stay in the background until focused.

What happens in reality is that full screen windows bully all other windows. When you move something onto a screen with a full screen window, you will not see it until you Alt+Tab into it. The moment you unfocus that window by calling up a drop-down terminal or clicking on the task bar or clicking on anything that is not the window you just Alt+Tabbed into, the full screen window gains focus. This makes no logical sense at all: clearly the full screen window should stay quiet until called upon.

Solution: upgrade to 18.04 LTS.


All fonts are fat. Sub-pixel aliasing is dirty on all settings. Decimal point font sizes, i.e. 13.4 get rounded up to .5 and render incorrectly. Standard fonts are not the same as on Windows, resulting in incorrect wildly different rendering of a large portion of websites.

Solution: I wrote a detailed blog post with how-tos and references. It is trivial and the end result is better font rendering than on any other OS.

Invisible Key Bindings

Some key bindings are not exposed in the key bindings UI. For example, Ctrl+Alt+Arrow will switch workspaces, but does not show up in the keyboard UI. I am used to having this hotkey reserved for expanding vertical selections in my text editor.

Solution: manually edit dconf under org/gnome/desktop/wm/keybindings/switch-to-workspace*.

Mouse Acceleration

The cursor will accelerate when you don’t expect it to and will refuse to accelerate when you do want it to do so: 1, 2, 3.

Solution: upgrade to 18.04 LTS, it exposes acceleration profile settings in the UI.

Workaround for 16.04 LTS: disable mouse acceleration by installing libinput and selecting flat acceleration profile in X Org config files.

Unwanted side effect: severely decreased accuracy. Your mouse pointer will be too sensitive when moving it slowly.

Input Devices Configuration

Fixed in 18.04 LTS. Kudos to GNOME team!

The OS does not allow you to configure your touchpad and mouse in the GUI. If you want tapping enabled, you have to edit dconf. If you want to configure gestures, you have to travel seven circles of hell with config files and different input drivers.

Solution for 16.04 LTS: manual config using Xorg files and dconf.

VMware and KeePass

VMware has its own mechanism for handling keystrokes and as such will not allow you to auto-type your passwords from KeePass. They will all be typed in lowercase.

Copy and pasting is hit or miss, depending on whether or not the target field allows it fully functional as of VMware 14 as long as you do it through VMware context menu and not via shared clipboard.

Workaround: auto-type using VNC built into VMware. Keep it on a separate workspace when not in use.

Unwanted side effect: decreased responsiveness, extra rendering load, extra jumping back and forth between workspaces.

True Color in tmux

The version of tmux bundled in 18.04 LTS does not have True Color support enabled by default.

The version of tmux bundled in Ubuntu LTS repositories is old enough not to have true color support.

Solution: add set-option -ga terminal-overrides ",YOUR_TERM_OUTSIDE_TMUX:Tc" to your ~/.tmux.conf.

f.lux and “Night Light” Not Working

To eliminate one of the big sleep disruption factors, for years I have been using f.lux to adjust the color of my monitors after sunset. On Linux, it does nothing due to still being behind changes to the kernel that were made in 4.4.

18.04 LTS comes with a “Night Light” display setting. Unfortunately, it only works occasionally and doesn’t work on whichever monitor I have plugged in via HDMI as opposed to USB-C.

Solution: use redshift-gtk instead.

Unwanted side effect: occasionally, especially when switching between full-screen applications, redshift effect will disappear for a few seconds, but it always comes back.

Random Things

These are things that have occurred more than once to me, but I could not reproduce them or did not have the time to hunt them down enough for a full write-up. They may get their own sections or blog posts in the future.

  • For secure RDP with TLS, build the latest FreeRDP and ditch rdesktop. use Remmina.


Works out of the box on 18.04 LTS both for headphones and peripherals.

For 16.04 LTS: a separate blog post on how to get Bluetooth to work, as this task is rather involved.

I do still have a massive complaint: the only available codec is the ancient, low-quality SBC, and PulseAudio guys would rather keep it this way indefinitely than simply re-pair a device or add a configuration option to force codec selection for devices that misbehave. Wow.


This section had four times as many points for 16.04 LTS. 18.04 LTS is a big improvement.

  • Some time after startup GNOME forgets that it is running in HiDPI mode and stops scaling newly launched applications. I observe this most frequently with Wireshark and HipChat.
  • Sometimes the system freezes in text mode when shutting down and you have to hard reset it.


  • Audio on the laptop gets strong noise, both on Windows and Linux. This is really, really bad DAC design. Apr ‘19: Firmware updates for the BIOS and the dock somehow fixed this, audio is fine now. The 3.5mm headphone out sounds great even on TOTL headphones.
  • Sometimes audio on the dock cuts off or becomes semi-functional, i.e. only one ear working. When this happens, usually both channels sound in the left ear and become distorted. Feb ‘18: I have been using an external DAC/amp combo for the last few months and will not be tracking this issue further. Apr ‘19: Fixed with latest firmwares and 18.04 LTS.
  • LibreOffice randomly crashes regularly. Feb ‘18: I am using a VM with Office 2016 when I need it and will not be tracking this issue further. There are so many issues with FOSS office suites that they are barely usable for read-only, let alone editing.


This section had 3 more issues with VMware 12 and 16.04 LTS. VMware 14 and 18.04 LTS both provided big improvements here.

  • VMware Linux (Kali) guest screen becomes offset into blank space and unusable when guest 3D acceleration is enabled; mouse pointer becomes out of sync with screen in the guest. Jul ‘18: I haven’t had a chance to test this out on newer versions yet.


I'm Georgi (Russian: Георгий). Although I do various software security things for work, I particularly enjoy reverse engineering and breaking native code on Android and embedded systems. Check out more about me.