How to force GPG to use console-mode pinentry to prompt for passwords?

To change the pinentry permanently, append the following to your ~/.gnupg/gpg-agent.conf:

pinentry-program /usr/bin/pinentry-tty

(In older versions which lack pinentry-tty, use pinentry-curses for a 'full-terminal' dialog window.)

Tell the GPG agent to reload configuration:

gpg-connect-agent reloadagent /bye

On a debian box:

sudo apt install pinentry-tty
sudo update-alternatives --config pinentry

(and set it to pinentry-tty)

I just had this problem on Ubuntu 16.04.3 when trying to generate/install a private key using gpg2 (2.1.11) on a system account without a password, and on a user account over ssh. Nothing worked giving:

gpg: key FE17AE6D/FE17AE6D: error sending to agent: Permission denied
gpg: error building skey array: Permission denied

I then found this which worked for me, so in brief:

pico ~/.gnupg/gpg-agent.conf
# add: allow-loopback-pinentry
gpg-connect-agent reloadagent /bye
gpg2 --pinentry-mode loopback --import private.key