Install gtk-common-themes on Raspberry Pi Offline

Question

I am trying to install "gtk-common-themes" for Snap offline on a Raspberry Pi 2B. It is imperative the device stays offline. On another Raspberry Pi 3 (online) machine, running the same OS (raspbian buster 10), I used snap download gtk-common-themes, copied the files to a USB drive, and put them on the Raspberry Pi 2. After running:

sudo snap ack gtk-common-themes_1515.assert

followed by

sudo snap ack gtk-common-themes_1515.snap

I get

error: cannot assert: cannot decode request body into assertions: parsing assertion headers: header is not utf8.

Can somebody please help me understand why this is happening? I have not had trouble with other snap packages.

Answer 1

The process for installing a snap offline is as follows:

1. Download both the snap as well as the assertion (the signed document that asserts this particular snap came from the snap store):

   $ snap download <snap name>
   

2. Transfer both the .snap and the .assert over to the other machine.

3. Load the assertion into snapd (so it knows that the snap you're about to install came from the store):

   $ sudo snap ack <snap name>.assert
   

4. Finally, install the snap:

   $ sudo snap install <snap name>.snap
   

Note how you don't use --dangerous in that last command-- that's only needed if you don't have an assertion for the snap, and you have one.

It seems that you understand this process, but instead of using snap install on step 4, you're using snap ack again, which expects an assertion and isn't going to actually install a snap.