How to enable PDF thumbnail preview on PCmanFM-qt on Lubuntu 20.04 LTS?

I installed Lubuntu 20.04 LTS and I did the upgrade of system (sudo apt upgrade).
But this function don’t work. I installed Evince and I setting as default PDF reader, but don’t work.

As you see in image above, the pdf thumbnail don’t show. I installed Nautilus and the thumbnails work well, just PCManFM that don’t work.

I tried with official Ubuntu 20.04 LTS on live mode and thumbnails work well. I installed PCManFM-qt on Ubuntu and worked too! See the picture:

Anyone knows some way to enable this feature on Lubuntu??? I am dummy in this subjects. I think is some problem on DBus or something like.

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You need another app to do that.


Hi man!

Thanks for response. I finally understood how thumbnails are produced.
The guy of your link use graphicsmagick to generate thumbnails, but in my tests its so slow to execute. Evince was more fast.

I tested against a book of 828 MB six times:

time gm convert -quality 100 -thumbnail 128 -flatten Biology.pdf[0] 1.png

real    0m15,729s
real    0m7,861s
real    0m10,055s
real    0m8,773s
real    0m8,416s
real    0m11,417s
# File generated had 23,6 KiB

time evince-thumbnailer -s 128 Biology.pdf 2.png

real    0m0,250s
real    0m0,250s
real    0m0,273s
real    0m0,249s
real    0m0,251s
real    0m0,249s
# File generated had 25,4KiB

Evince takes less 1 second to generate the thumbnail whereas graphicsmagick takes 10 seconds in average.

Do you know some alternative of thumbnailer for LXQt as fast as Evince ?

I really liked of qpdf and I want takes just one PDF reader in my machine, but I think that feature is essential when you have a lot of pdf documents to check in the work.

Another problem that I found is that evince-thumbnailer just work in Lubuntu 18/20.04 if I disable apparmor.
I did and restart:

sudo systemctl stop apparmor.service
sudo systemctl disable apparmor.service

All thumbnails start to work now.


I solved the problem! I used the pdftoppm that is already available in Lubuntu.

I created the file /usr/bin/pdftoppm-thumbnailer:


pdftoppm -png -singlefile -scale-to $1 "$2" "${out%".png"}"

Then I created the file /usr/share/thumbnailers/pdftoppm.thumbnailer:

[Thumbnailer Entry]
Exec=pdftoppm-thumbnailer %s %i %o

I restarted and everything worked good!

I created an debian package to fix this easy, you can download here!

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In my tests here, neither graphicsmagick nor pdftoppm can generate thumbnails on top of the SMB protocol. Evince-thumbnailer can if apparmor had disabled.
I will continue using pdftoppm, but if someone need this feature over SMB those people will have to change to Evince.

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