Beyond Compare won't start without root privilege (Exception at 000055C461983F92: EThread)

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1

Hello,

I’m using CachyOs for work for a few month now and so far everyting went fine. I’m currently running the Linux 6.18.21-1-cachyos-lts kernel with XFCE desktop. Since a few weeks there is a problem however, I was not able to resolve.

For diffing source code I’m using Beyond Compare. I installed it via yay from the AUR (bcompare). After initially installing it, it worked for some time. At the moment (i guess after a recent update) it’s not starting anymore. As far as I’m aware of it is the only program I have this problem with.

The program is normally launched via the script /usr/bin/bcompare. This sets some environment variables, specifacally some library-paths which ship with the program. After that it runs the executable /usr/lib/beyondcompare/BCompare.
For testing I set the environment manually and run the BCompare executable directly with my normal user login.

I made the following observations:

  • When having the default Adwaita Theme active the command just hangs (no UI comming up) and has to be canceled with ctrl-c.

  • When having the Materia-dark-compact theme (materia-gtk-theme) (installed via pacman), the command fails with exit code 217 and the following error message:

    Exception at 000055C461983F92: EThread:
Failed to create new thread.

  • Running the command with sudo will start the GUI with both themes and everything is working. When running with sudo however there are the following messages in the terminal (not sure if relevant):

    qt.qpa.theme.dbus: Session DBus not running.
qt.qpa.theme.dbus: Application will not react to setting changes.
 Check your DBus installation.
qt.qpa.theme.gnome: dbus connection failed. Last error:  QDBusError("org.freedesktop.DBus.Error.NotSupported", "Using X11 for dbus-daemon autolaunch was disabled at compile time, set your DBUS_SESSION_BUS_ADDRESS instead")
qt.qpa.theme.dbus: Session DBus not running.
qt.qpa.theme.dbus: Application will not react to setting changes.
 Check your DBus installation.
qt.qpa.theme.gnome: dbus connection failed. Last error:  QDBusError("org.freedesktop.DBus.Error.NotSupported", "Using X11 for dbus-daemon autolaunch was disabled at compile time, set your DBUS_SESSION_BUS_ADDRESS instead")
QThreadStorage: entry 1 destroyed before end of thread 0x55fbea01b250
QThreadStorage: entry 0 destroyed before end of thread 0x55fbea01b250

To make sure, I did not mess up my installation somehow I did the following:

  • Deinstallation of Beyond Compare (including purging all config files), installing it from AUR without yay → Same result.
  • Purging the intallation, installing the program directly from the provided TAR.GZ-File → Same result.
  • Installing older versions of BeyondCompare (I knew once worked) which did not yet depend on qt6-base → Same result
  • Trying other kernels (linux-cachyos, linux-cachyos-gcc, linux-cachyos-bore, linux (Arch Linux default)) → Nothing changed.
  • Making a fresh CachyOS install within a VirtualBox-VM and installing Beyond Compare (via yay) → Same result.
  • Installing Beyond Compare (via yay) on another PC running Arch Linux with the default kernel → Everything works.

I’m not sure how to debug the problem any further. But after the above testing I came to the conclusion, that it has to do something with CachyOS specifically since:

  • It’s working on Arch Linux - so the problem should neither be the AUR package nor Beyond Compare itself
  • It is reproducable with a fresh CachyOS installation in a VM

If anyone has an idea how to narrow down the problem further or how to make Beyond Compare run again, I’d be gratefull. If further information are needed, I’m happy to provide them.

Thanks and regards
Peter

2

Most likely a wayland issue, as mine works.

can you use it with:

export QT_GRAPHICSSYSTEM=native bcompare
3

Hi,

thanks for replying. I’m running XFCE with X11, so it’s not a Wayland issue.

I tried your suggestion nevertheless, but it’s not working.

4

XFCE? Ha no coffee yet. :sweat_smile:

The specific log entry Cannot set scheduler: "Operation not permitted" confirms that the program is attempting a restricted linux_sched_setscheduler call that fails without elevated privileges.

One more then:

LD_PRELOAD=./nosched.so bcompare

If that stiil don’t work check your /home permissions, as running GUI’s as root is not a good idea.

ls -al /home/$USER

Also check:

ls -al .Xauthority

Dang I’m forgetting a lot for X11 these days, this may also help as a normal user run:

xhost +si:localuser:$(whoami)

That should allow it to run as a non root user.

5

Hey,
thanks for answering again. Could you reproduce the error in an XFCE environment? Where did you get the error message from? I’d like to understand how to debug such a problem better in the future :).

Where would I get the nosched.so library? Just running the command as given (from my home), obviouslly only leads to an error

ERROR: ld.so: object './nosched.so' from LD_PRELOAD cannot be preloaded (cannot open shared object file): ignored.

I guess I have to install a package for this?

My home permissions look fine. I also made a new user trying to run Beyond Compare logged in as that user and it failed the same way. The permissions on the .Xauthority file are as follows:

-rw-------  1 peter peter   58 10. Apr 18:12 .Xauthority

Adding my user account to the access control list with xhost did not change the outcome either unfortunately.

6

It’s a dummy file to debug your issue.

But this seems to lay deeper on your system.

Please run a bug-report and return the link it gives you back here for the team to look at.

sudo cachyos-bugreport.sh

From this.

7

I have the bugreport from my PC here:

Here you’ll find the bugreport from the virtual machine running xfce on x11, where Beyond Compare also is not working (machine was setup today):

I just setup a virtual machine running CachyOS with KDE on wayland. There Beyond Compare is indeed working. But as I wrote, I have another PC running vanilla Arch with the default kernel and XFCE on X11 where Beyond Compare is also working.

For completeness: I also installed LXDE on the XFCE VM to see if it would work, but to no success.

Thanks again for looking into this!

8

I can also confirm XFCE4 and bcompare only runs as root user in a KVM along with VBox.

Thought it might have something in our Cachy kernels but Vanilla Arch kernel is the same.

9

At least it is reproducable.

Since bcompare is the only application with this problem (at least that I noticed), do you think it would be worth asking in the Beyond Compare support forum about this? Maybe they can debug their software on startup. Or do you think, the problem is definitly one that needs solving on the OS side?

10

Yes I do.

I just can’t say, it is a puzzler though.

Keep us updated if you come across anything.

11

I posted the issue on the Beyond Compare support forum: https://forum.scootersoftware.com/forum/beyond-compare-discussion/general-aa/98509-beyond-compare-requires-root-privilege-to-run-on-cachyos-on-a-desktop-using-x11

So far nothing really new, except me experimenting with different desktops and older versions of Beyond Compare - coming to the conclusion that it is most likely some problem with x11 on CachyOS.

If anything like a solution comes arround, I’ll post it here.

12

The guy over on the BC forum tried some things to debug the application but to no success.

From what I tested in the meantime and was verified here in this thread and on the BC forums, it can be summarized as follows:

  • On desktops using X11 (I tested XFCE4 and LXQt) BC5 is not working on CachyOS.
  • Old versions of BC5 (and 4) that worked on CachyOS in the end of february 2026 are not working anymore.
  • It’s not related to the kernel used, it’s not even working on the vanilla Arch Linux kernel.
  • On a freshly setup Arch Linux VM using XFCE4 on X11 BC5 works.
  • BC5 is the only application I noticed that has this problem.

It’s very likely that something broke on CachyOS during an update.

@anon15508052 do you think that would be worth making a bug report on the CachyOS Github issues? Would other people involved with the OS see it there and maybe try to find out what broke?

I’ll probably set up my PC with vanilla Arch during the coming weekend, but keep a CachyOS VM, so I could test BC5 from time to time.

13

I’d like to corroborate Andrezej’s observations, where attempting to launch Beyond Compare using the terminal results in it appearing to hang and needing to be cancelled with Ctrl + C. My attempts at resolving the issue are not as thorough as Andrezej’s, but I thought it worthwhile to share my own observations / configuration details.

Differentiators

There are several parts of my setup that differ from Andrezej, and so likely rules out several of the going theories.

  • DE / WM: KDE Plasma / KWin (Wayland) | OP: XFCE on X11.
  • Theme: Breeze (Dark) [Qt], Breeze-Dark [GTK2], Breeze [GTK3]
  • Kernel version: Linux 7.0.8-1-cachyos | OP: Linux 6.18.21-1-cachyos-lts

The installation method from AUR appears to have been ruled out already, but worth noting that I installed the application using paru as opposed to yay.

paru -S bcompare-kde6

Observations

The hang consistently occurs when attempting to launch Beyond Compare 5 from the terminal. Commands tested:

  • bcompare from any directory
  • /usr/bin/bcompare
  • ./bcompare from within /usr/bin/ directory
  • git difftool where git config --global diff.tool bc

However, if Beyond Compare 5 is ran using any methods that avoid using the terminal, it works consistently. This includes:

  • Running /usr/bin/bcompare script directly from Dolphin file manager
  • Running Beyond Compare 5 from the Application Launcher panel widget (configured simply to use bcompare as the launch command)

Also to help confirm that this is indeed the same issue, it is possible to run from the terminal but only when being ran as root i.e. sudo bcompare.

Final thought

I’m left wondering whether the root cause of this issue may lie within the configuration for the Terminal or Shell that’s shipped with CachyOS (Konsole / Fish)?

Configuration

Kernel: Linux 7.0.8-1-cachyos
Uptime: 5 hours, 55 mins
Packages: 1591 (pacman)
Shell: fish 4.7.1
Display (BenQ GL2760): 1920x1080 in 27", 60 Hz [External]
Display (BenQ GL2760): 1920x1080 in 27", 60 Hz [External] *
DE: KDE Plasma 6.6.5
WM: KWin (Wayland)
WM Theme: plastik
Theme: Breeze (Dark) [Qt], Breeze-Dark [GTK2], Breeze [GTK3]
Icons: breeze-dark [Qt], breeze-dark [GTK2/3/4]
Font: Noto Sans (8pt) [Qt], Noto Sans (8pt) [GTK2/3/4]
Cursor: breeze (24px)
Terminal: konsole 26.4.1
CPU: Intel(R) Core™ i7-7700K (8) @ 4.50 GHz
GPU: NVIDIA GeForce GTX 1080 Ti [Discrete]
Memory: 13.83 GiB / 31.26 GiB (44%)
Swap: 13.08 GiB / 31.26 GiB (42%)```
14

Thanks for sharing your observations. Interesting to see it fail on KDE/Wayland.When I tried this in VMs it worked. Though I did not use the VMs otherwise and did not install any aother things that might interfere.

As for my system: I used alacritty and zsh. In the VMs I tested with, I simply used the XFCE terminal and fish, as it comes out of the box. bcompare always hangs now and has to be killed witch ctrl+c. Launching BC5 via the XFCE-Application launcher or from Whiskermenu where it uses the desktop-file did not work on XFCE / X11. There was a process running I had to kill with htop but it seems to be the same hanging process as when it is launched via terminal.

Since I recently ran into other problems with my CachyOS system, I went back to vanilla arch and everything is working again. I keep a CachyOS VM and can check from time to time but I’m not actively looking for a solution anymore.

15

After spending the past hour throwing mud at the wall to see what sticks, I’ve managed to find out what was causing the hang for me.

For my own convenience, I’d added a startup command to Konsole:

ssh-agent /user/bin/fish.

Changing this back to just set /usr/bin/fish as the command results in Beyond Compare working correctly!

To confirm whether it was the start command, or specifically ssh-agent, I tested with the following:

❯ ssh-agent /usr/bin/fish
❯ bcompare

This consistently reproduces the issue. I also tried this with zsh and bash, with exactly the same results. Starting up additional nested shells - even different shells - but without using ssh-agent does not reproduce the issue.

It seems to be either tied to ssh-agent itself, or it could be a quirk with launching the shell with a wrapper like this.

Out of curiosity, and for giggles, I modified the bcompare script to launch the application using ssh-agent /bin/bash, and very curiously bcompare has a good chance to startup if it’s being run from a fresh terminal instance. When this happens, it’s usable for a while; but if the window is refocused - or just as the main window shows up for the first time - it hangs. I’ll forward this info to the Beyond Compare post, but thought it was interesting enough to share in case anyone else sleepwalks into this trap. (EDIT: Couldn’t seem to post on the Beyond Compare forum. Will do so if/when I am able)

16

Nice find. I never started bcompare via a wrapped shell, so it worked on the KDE VM. Since it, s not working on Xfce4 with X11 out of the box (and it used to work) and I don’t use a wrapper there either, I’m not sure if it’s the same issue. Maybe it’s related. I can try later on arch with Xfce4 and the ssh-agent wrapper.