nautilus not generating thumbnails anymore

[Ralf Hildebrandt]

After the upgrade to 24.04, nautilus is not generating thumbnails for new files.
Old thumbnails are displayed ok.

I cleaned out $HOME/.cache/thumbnails/ and found that only a subdirectory "fail" is being generated.
It contains a subdirectory "gnome-thumbnail-factory" which in turn contains lots of PNG files:

ece577c54f5ca98e1f7aaa5b4e932aa4.png: PNG image data, 1 x 1, 8-bit/color RGBA, non-interlaced
ee638c64b1c285684412717bf120e295.png: PNG image data, 1 x 1, 8-bit/color RGBA, non-interlaced
ef811735cfb8e69447b5d3a53f361c63.png: PNG image data, 1 x 1, 8-bit/color RGBA, non-interlaced
f0b3ab2f77c342daa3579bfcf9c72481.png: PNG image data, 1 x 1, 8-bit/color RGBA, non-interlaced
f0ddb101b8342e4b298b4c7121881422.png: PNG image data, 1 x 1, 8-bit/color RGBA, non-interlaced

ProblemType: Bug
DistroRelease: Ubuntu 24.04
Package: nautilus 1:45.2.1-4ubuntu1
ProcVersionSignature: Ubuntu 6.6.0-14.14-generic 6.6.3
Uname: Linux 6.6.0-14-generic x86_64
NonfreeKernelModules: zfs
ApportVersion: 2.27.0-0ubuntu6
Architecture: amd64
CasperMD5CheckResult: unknown
CurrentDesktop: ubuntu:GNOME
Date: Sat Feb 17 08:49:55 2024
EcryptfsInUse: Yes
InstallationDate: Installed on 2019-04-16 (1767 days ago)
InstallationMedia: Ubuntu 18.04.2 LTS "Bionic Beaver" - Release amd64 (20190210)
SourcePackage: nautilus
UpgradeStatus: Upgraded to noble on 2024-02-14 (3 days ago)
usr_lib_nautilus:
 file-roller 43.1-1
 nautilus-extension-gnome-terminal 3.49.92-2ubuntu1

[Ralf Hildebrandt (ralf-hildebrandt)]

I id some tests, and while root was able to create thumbnails in nautilus, I checked the logs and found:

Feb 17 09:20:51 comet kernel: audit: type=1400 audit(1708158051.561:1699): apparmor="DENIED" operation="userns_create" class="namespace" info="User namespace creation restricted" error=-13 profile="unconfined" pid=142479 comm="bwrap" requested="userns_create" denied="userns_create"
Feb 17 09:20:51 comet kernel: audit: type=1400 audit(1708158051.565:1700): apparmor="DENIED" operation="userns_create" class="namespace" info="User namespace creation restricted" error=-13 profile="unconfined" pid=142480 comm="bwrap" requested="userns_create" denied="userns_create"
Feb 17 09:20:51 comet kernel: audit: type=1400 audit(1708158051.569:1701): apparmor="DENIED" operation="userns_create" class="namespace" info="User namespace creation restricted" error=-13 profile="unconfined" pid=142481 comm="bwrap" requested="userns_create" denied="userns_create"

This coincides with me deleting the bogus 1x1 thumbnails an re-entering the folder...

[Ralf Hildebrandt (ralf-hildebrandt)]

After some digging I found
https://github.com/flatpak/flatpak/issues/5462
and alas:
sudo sysctl -w kernel.apparmor_restrict_unprivileged_userns=0
makes thumbnail generation work again.

[Launchpad Janitor (janitor)]

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

[corrado venturini (corradoventu)]

Suggested command seems ok but thumbnail generation still does not work (also after reboot)
corrado@corrado-n4-nn-0215:~$ sudo sysctl -w kernel.apparmor_restrict_unprivileged_userns=0
[sudo] password for corrado:
kernel.apparmor_restrict_unprivileged_userns = 0
corrado@corrado-n4-nn-0215:~$

[corrado venturini (corradoventu)]

In my system not upgraded but installed from ISO Ubuntu 24.04 LTS "Noble Numbat" - Daily amd64 (20240215) I have the same problem but my .cache/thumbnails is as follows
corrado@corrado-n4-nn-0215:~/.cache/thumbnails$ tree -d
.
├── fail
│   └── gnome-thumbnail-factory
├── large
└── normal

gnome-thumbnail-factory contains more than 200 .png files 1 × 1 pixel
large and normal contains few .png files

[Ralf Hildebrandt (ralf-hildebrandt)]

* corrado venturini <email address hidden>:
> Suggested command seems ok but thumbnail generation still does not work (also after reboot)

A reboot resets the "kernel.apparmor_restrict_unprivileged_userns" back
to its default value, so you must not reboot :)

[corrado venturini (corradoventu)]

THANKS, I hadn't emptied the folder ~/.cache/thumbnails/fail/gnome-thumbnail-factory

[olive (chenet07)]

the solution to not lose the configuration after the reboot :

sudo nano /etc/rc.local

The bash:
#!/bin/bash
# Votre commande ici
sudo sysctl -w kernel.apparmor_restrict_unprivileged_userns=0

sudo chmod +x /etc/rc.local

[Ralf Hildebrandt (ralf-hildebrandt)]

* olive <email address hidden>:

> the solution to not lose the configuration after the reboot :

by creating a file in /etc/sysctl.d, e.g.
/etc/sysctl.d/10-fix_nautilus
containing
kernel.apparmor_restrict_unprivileged_userns=0

[Sebastien Bacher (seb128)]

it seems another fallout from the new apparmor restriction described in bug #2046844 and probably a conflict with the sandboxing in https://gitlab.gnome.org/GNOME/gnome-desktop/-/blob/master/libgnome-desktop/gnome-desktop-thumbnail-script.c