Can't sign ubuntu core model assertion

[Vadim Usoltsev]

I'm trying to create personal Ubuntu Core image performing all the steps from the tutorial here: https://docs.ubuntu.com/core/en/guides/build-device/image-building

At the step of signing the model assertion I got an error:
koldoon@ubuntu:~/snapcraft/ucore$ cat x86-model.json | snap sign > x86.model
error: cannot sign assertion: cannot sign using GPG: /usr/bin/gpg --personal-digest-preferences SHA512 --default-key 0x34F7072EEA5628D077D79942A196ADCB7D63B8AA --detach-sign failed: exit status 2 ("gpg: signing failed: No such file or directory\ngpg: signing failed: No such file or directory\n")

Then I tried to create named key:
snapcraft create-key koldoon

And after that I could sign the model but JUST ONCE! After that I got the same error as above with no result.

[Oliver Grawert (ogra)]

theer is a known issue with gpg-agent not freeing the lock ... see the discussion and workaround at:

https://forum.snapcraft.io/t/snap-sign-unable-to-invoke-gpg-agent-pinentry/10938