the pcmanfm-qt crashes on an inexistant image background

[amer]

I describe whole the issue on this link: https://askubuntu.com/q/1238736/305703

But I describe here too:

 1. I right-click on desktop and choose desktop properties to change the background image
 2. choose the background image and close all opened windows
 3. permanently delete the set image from my PC
 4. re-open the desktop properties to change the Wallpaper mode
 5. suddenly the desktop properties crashed and a black tiny window alert me
 6. I didn't read it and press yes
 7. after it the pcmanfm-qt and many system apps doesn't work (doesn't work means dead completely, clicking on them or running from terminal is like doing nothing)
 8. then by the suggestion of AskUbuntu user I change the background image from terminal by changing the ~/.config/pcmanfm-qt/lxqt/settings.conf Wallpaper variable
 9. then everything became ok

So I believe crashing pcmanfm-qt just for an nonexistent image is a bug, it should show the solid background color or something else.

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: lubuntu-default-settings 20.04.4
ProcVersionSignature: Ubuntu 5.4.0-29.33-generic 5.4.30
Uname: Linux 5.4.0-29-generic x86_64
ApportVersion: 2.20.11-0ubuntu27
Architecture: amd64
CasperMD5CheckResult: skip
CurrentDesktop: LXQt
Date: Wed May 13 09:48:47 2020
InstallationDate: Installed on 2020-05-03 (10 days ago)
InstallationMedia: Lubuntu 20.04 LTS "Focal Fossa" - Release amd64 (20200423)
PackageArchitecture: all
SourcePackage: lubuntu-default-settings
UpgradeStatus: No upgrade log present (probably fresh install)

[Chris Guiver (guiverc)]

Thank you for taking the time to report this bug and helping to make Ubuntu better.

I had a fresh groovy install running (QA-test on first boot) and confirmed the issue on that box, so it impacts groovy too.

I see no evidence of a crash (step 5); no crash dump in /var/crash/, lxqt-panel still operates normally, however htop shows (`ps -elf` output)

0 R guiverc 1114 1039 9 80 0 - 347758 - 15:48 ? 00:03:56 /usr/bin/pcmanfm-qt --desktop --profile=lxqt

hovers around 100%, desktop preferences window is still on my display and can be dragged around, but it's contents are whatever window last covered it, and it's unusable. I can use `firefox` to enter this detail correctly, qterminal & other apps start & operate fine from menu (but NOT pcmanfm-qt; it remains at ~100% cpu looping..).

A bug yes, but should I have suggested pcmanfm-qt? I'm not sure.

[Chris Guiver (guiverc)]

Changed package to `pcmanfm-qt` as per @aptghetto's recommendation

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Chris Guiver (guiverc)]

I do not get this behavior on Debian Bullseye/11

On my debian, after the file is deleted on disk the background goes black on any subsequent change to Wallpaper mode, and `pcmanfm-qt` doesn't appear anywhere near the top of `htop` (ie. no 100% cpu thread)

guiverc@dc780-deb:~/wallpapers$ apt-cache policy pcmanfm-qt
pcmanfm-qt:
  Installed: 0.14.2~166-g74a6f4d-1
  Candidate: 0.14.2~166-g74a6f4d-1
  Version table:
 *** 0.14.2~166-g74a6f4d-1 500
        500 https://lxqt.debian.net/debian experimental-snapshots/main amd64 Packages
        100 /var/lib/dpkg/status
     0.14.1-3+b1 500
        500 http://ftp.iinet.net.au/debian/debian testing/main amd64 Packages

however this maybe a later package than I tested on Lubuntu; the command `pcmanfm-qt --version` both report the same version

guiverc@dc780-deb:~/wallpapers$ pcmanfm-qt --version
pcmanfm-qt 0.14.1
// identical version reported on Lubuntu 20.10

[Chris Guiver (guiverc)]

I'd not noticed the loss of lxqt.debian.net in prior comment, until I tried to `apt source` today.

Thus I replaced package with standard debian package

guiverc@dc780-deb:~$ apt-cache policy pcmanfm-qt
pcmanfm-qt:
  Installed: 0.14.1-3+b1
  Candidate: 0.14.1-3+b1
  Version table:
 *** 0.14.1-3+b1 500
        500 http://deb.debian.org/debian testing/main amd64 Packages
        500 http://ftp.iinet.net.au/debian/debian testing/main amd64 Packages
        100 /var/lib/dpkg/status

I've now RE-CREATED the issue on debian testing (bullseye/11), though it took some play as it changing the settings a number of times as the deleted image was sometimes visible, sometimes shown as black-screen (behavior felt different to Lubuntu but that could be my memory). To achieve issue this session I had to logout (image deleted last session) & login again before 100% thread could be re-created.

guiverc@dc780-deb:~$ ps -elf |grep pcmanfm
0 R guiverc 3146 2932 86 80 0 - 392369 - 11:45 ? 00:04:44 /usr/bin/pcmanfm-qt --desktop --profile=lxqt

Either way that thread is now pretty steady at 100% CPU; same issue as with Lubuntu.

Given it took me a bit of play on this box to accomplish (what I recall being easy on Lubuntu), maybe I'd just followed the instructions exactly in comment #5 and not re-created it thus giving debian-testing using the 0.14.2~166-g74a6f4d-1 package a faulty not-impacted (I doubt I logged out & logged back in comment #5 which is what I think allowed the issue to occur this time).

[Chris Guiver (guiverc)]

my attempts to have https://github.com/lxqt/pcmanfm-qt/issues/1120 linked with pcmanfm-qt failed, sorry.