Public bug reported:
(Perhaps this should be reported at Ubuntu 26.10 instead?)
After upgrading to Ubuntu 26.10 (GNOME 51), Nautilus showed PDF thumbnails
only for files with an embedded thumbnail. All other PDFs got the generic icon.
The cause was a leftover evince package, version 49~alpha-2ubuntu3, from an
earlier release. It was not upgraded or removed during the upgrade, so both
evince.thumbnailer and papers.thumbnailer were registered for application/pdf.
gnome-desktop picks between them in no defined order, and here
evince-thumbnailer
was used.
The evince 49~alpha package dates from Ubuntu 25.10 (GNOME 49), when Papers
replaced Evince as the default. Upgrade path on this machine:
25.10 -> 26.04 -> 26.10. The obsolete package survived both upgrades. Both
upgrades have been quite early, so it could be that which triggered the problem.
evince-thumbnailer now uses glycin, which runs its loaders under bwrap. The
AppArmor profile /usr/bin/evince-thumbnailer from this old package does not
allow that. Denials seen:
```
apparmor="DENIED" operation="exec" profile="/usr/bin/evince-thumbnailer"
name="/usr/bin/bwrap" comm="blocking-1" requested_mask="x"
apparmor="DENIED" operation="file_perm" class="net"
profile="/usr/bin/evince-thumbnailer" family="unix" sock_type="seqpacket"
peer="bwrap"
apparmor="DENIED" operation="file_perm" class="net"
profile="/usr/bin/evince-thumbnailer" family="unix" sock_type="seqpacket"
peer="unpriv_bwrap"
```
After allowing bwrap via a local override, the next denial was:
```
apparmor="DENIED" operation="exec" profile="/usr/bin/evince-thumbnailer"
name="/usr/libexec/glycin-loaders/2+/glycin-image-rs" comm="gly-hdl-editor"
requested_mask="x"
```
Putting the profile in complain mode made thumbnails appear, which confirms
AppArmor as the cause.
The current papers profile (/etc/apparmor.d/usr.bin.papers) already handles
this through a bwrap_trans child profile stacked with bwrap and a glycin child
profile. The old evince profile has nothing equivalent.
Workaround: `sudo apt purge evince`. Nothing installed depended on it (only an
Enhances from nautilus-sendto). After purging, papers-thumbnailer took over and
works in enforce mode.
Expected: on upgrade to 26.10, the obsolete evince 49~alpha package should be
upgraded to a version whose AppArmor profile supports glycin, or removed or
transitioned to papers.
Versions:
Ubuntu 26.10, GNOME 51
evince 49~alpha-2ubuntu3 (now removed)
papers <version>
kernel.apparmor_restrict_unprivileged_userns = 1
** Affects: evince (Ubuntu)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/2172692
Title:
Leftover evince 49~alpha-2ubuntu3 after update to Ubuntu 26.10 blocks
thumbnailing
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