NCViewer - CNC GCode Simulator - Fails to Open File on Lubuntu

Lubuntu 22.04.3 LTS

I have a CNC Mill with LinuxCNC on a RPi 4B (works well).

Two support laptops:

  • office Lubuntu doesn’t show the drop-down browse dialog box when “Open File” selected,
  • workshop Ubuntu Mate shows the dialog box.

On Lubuntu, I Copy/Paste the file contents and NCViewer displays correctly.
On Ubuntu Mate, the Browse allows file selection then correct display.

Any suggestions on what it is in Lubuntu that prevents the dialog box showing ?

Keep well,

Lubuntu doesn’t have media for Pi’s, thus your creation of a arm64 system for Pi may cause differences, and we won’t know what that procedure was.

I’d not expect any differences with a Lubuntu system, and Ubuntu-MATE of the same release, though we do have some differences in seed that can cause different kernel stacks to be installed for some media; but that won’t impact how applications run, just system level detail such as kernel stack, kernel modules (aka drivers) etc. You gave no details of install media, and none at all of Ubuntu-MATE release.

There was no development of arm64 software.
The Lubuntu machine simply searched for the RPi 4B image on the Net, then burned it to an SD card, which was then inserted in the RPi.

The Ubuntu Mate is 22.04.3 LTS.

Thanks for the hint about kernel modules.
Can you provide any guidance on search criteria.
I will check both machines for their kernel details.

NCViewer is not installed, it is a Net-based tool, accessed directly on the Firefox browser.

There are numerous sites on the web offering images, one is legitimate (alas has no Pi images), one is fan (it’ll also have no images except links for EOL maybe) plus many fake sites (that provide who knows what).

We don’t provide support for fake or illegitimate images that may say they’re Lubuntu. Lubuntu ISOs & images are built on Ubuntu infrastructure, and are thus downloaded by Canonical or Ubuntu sites ( etc… even points you to the Ubuntu official site).

As Canonical only keep specific ISO/images, we are aware of some on 3rd party sites that are valid; but there won’t be Pi images there either.

Thanks guiverc for taking the time to help.
But, I don’t think this problem is related to the RPi at all.

The GCode file was generated by CamBam and is a simple editable text file that is transported between the machines on a Flash USB card.

The issue is simply two legitimate Linux images, Lubuntu and Ubuntu Mate, taken from the standard legitimate sources that behave differently when interacting with a well-known Net inter-active application (NCViewer) running on the standard Linux browser (Firefox).

There is some subtle difference that results in Lubuntu not working in a minor way.
I am sure the difference can be identified, and a correction or work-around implemented.
Just hoping I can get some hints on where to look.

I don’t see any differences, at least as far as firefox on standard systems.

Ubuntu-MATE use the MATE desktop, which is GTK3, where Lubuntu uses LXQt which uses Qt5, but that shouldn’t impact the modern firefox used given it’s the identical snap package on both.

Ubuntu-MATE & Lubuntu have the equivalent install defaults with regards releases (ie. GA for 22.04 & 22.04.1, but default to newer HWE for 22.04.2 & later; which is different to Ubuntu Desktop), but if the system as upgraded and not clean installed, the defaults for both will depend on installation media - this won’t impact firefox behavior though (closest being how its shown on screen due to kernel modules).

There will be theming differences of course; Qt5 versus GTK3, but that’s not behavior. At most it could impact how displayed, making things harder to see meaning you could miss something that’s there but hard to see; but that’s unlikely (with browsers usually ignoring desktop theming often anyway).

I don’t see any differences though, and whilst I’m using Ubuntu MATE far less often, I’m still doing some QA with it semi-regularly.

If it was me, I’d look for changes made to the browsers, the system, or if one was a fresh install of 22.04 where the other was an earlier release upgraded to 22.04 (thus uses defaults of prior releases as those do not change) then they won’t be identical systems.

I would expect both to respond the same.

The stack differences are likely of no interest, but my install on this my primary box used to include Ubuntu-MATE too, and the stack differences made the only real difference I noticed; ie. kernel module & video card differences; which is why I mention that. Ubuntu-MATE uses ubiquity as its installer, which can react differently if specific hardware is detected (switching to OEM & other kernel stacks as default) which Lubuntu doesn’t have (one reason our ISO is smaller!) but I’ve never had hardware that triggered it thus haven’t explored it much.

Thanks for that in-depth description.

Reluctant to do a fresh install on a functioning system.
I know I followed the advice for the 22.04 release, but cannot remember if that was a fresh install.

I have a work-around, the copy/paste approach on Lubuntu.

Your list of possible areas to check is a bit daunting to me at the moment, but I will try to make some time for those.

The safest may be to live with what I have, and wait for the 24.04 releases.


With luck you’ll get more from other (in time)… I’m limited to my own experience, and I have no experience with NCViewer.

A picture of the difference may help others (& myself) understand too, when we’re not familiar with the tool. Provide a link if you can’t upload the picture to this site.

I’d likely boot a Lubuntu thumb-drive & test it live, and contrast how it performs there with Ubuntu-MATE (of the same release/period) also running live), ie. no installation necessary; just the download & write of ISO to thumb-drives; or download & contrast as a VM too.

If you get different experiences in this testing (between the live system and your installed system experience*), it’s likely related to a configuration change made to your system post-install; but you’ve got more you can work with.

ps: you don’t have to use the 22.04.3 ISO, but can download a daily ISO which includes all upgrades pre-applied to a few hours before ISO creation. I’ll provide where it’s the jammy daily I’m referring to… follow links if you’re unfamiliar with Ubuntu ISOs.

That’s probably the safest bet.
If on the other hand you a feeling adventurous, you could try this fix.

It seems 22.04 may have left out
xdg-desktop-portal-gtk (ref)
which allow snap apps to request gtk services (which firefox seems to prefer).
(I did not see this problem with 23.10 live).

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Thanks, that could be a specific line of attack.

guiverc provided a test, live USB, a great idea.
Searched my library of USBs and found Ubuntu 20.04 and Lubuntu 18.04.
Both react correctly on NCViewer displaying the dialog box.

Thanks for all the help.

A comment:
Firing up Lubuntu 18 was like meeting an old friend.
I much prefer the look and feel of the old install compared with the new.

I suffered the same problem on a metalwork forum in Australia
So I installed your suggested package using the standard Lubuntu Package Manager, Muon.
As it was listed as available and supported by Canonical, I thought it to be a safe one.

Success, both NCViewer and the forum now browse for a file.
Thank you.

Keep well,