A customer reported (and I was able to reproduce) getting an error when using snapcraft validate. The key to reproducing (for me at least - still awaiting confirmation from customer) was doing this on a remote headless system. Sounds like gpg is trying to invoke something that isn't present on the system to get the passphrase and then fails. But it seems to happen only when gpg is invoked by snapcraft - so perhaps gpg is detecting something about its running environment or stdin/out redirection when running under snapcraft, and trying to ask for the password differently, and one thing to do would be forcing gpg to ask for the password a different way or something. To reproduce: 1- ssh into a system that has snapcraft. I used a VM installed from an ubuntu server cloud image. snapcraft validate allyoursnaparebelongtous1 allyoursnaparebelongtous2=2 --key-name an-example-three Getting details for allyoursnaparebelongtous2 Signing validations assertion for allyoursnaparebelongtous2=2 Error signing validations assertion for allyoursnaparebelongtous2=2: error: cannot sign assertion: cannot sign using GPG: /usr/bin/gpg --personal-digest-preferences SHA512 --default-key 0x4A7677B256FB90F61B91C061C3E6F877EC048DD3 --detach-sign failed: exit status 2 ("gpg: signing failed: No such file or directory\ngpg: signing failed: No such file or directory\n") The workaround is to first run the gpg command outside of snapcraft, so the key is unlocked: echo "lalal" > a-file /usr/bin/gpg --homedir=.snap/gnupg --personal-digest-preferences SHA512 --default-key 0xE185A8404D4CCDA151FA4AC51F5108DA9CD52BC6 --detach-sign a-file then the snapcraft operation succeeds: snapcraft validate allyoursnaparebelongtous1 allyoursnaparebelongtous2=2 --key-name an-example-two Getting details for allyoursnaparebelongtous2 Signing validations assertion for allyoursnaparebelongtous2=2 snapcraft version snapcraft, version 4.5.4 lsb_release -a No LSB modules are available. Distributor ID: Ubuntu Description: Ubuntu 18.04.4 LTS Release: 18.04 Codename: bionic snap version snap 2.49 snapd 2.49 series 16 ubuntu 18.04 kernel 4.15.0-136-generic This is likely related to: https://forum.snapcraft.io/t/snap-sign-unable-to-invoke-gpg-agent-pinentry/10938 and: https://bugs.launchpad.net/snapcraft/+bug/1866257 from the latter, "there is a known issue with gpg-agent not freeing the lock"