Agent Configuration: Linux
In order to use an OpenPGP smart card for SSH, the
environment variable needs to point at a GnuPG agent (
Getting this right can be tricky.
Debian 9 (stretch) and Xfce
If you use Xfce on Debian stretch or newer (including buster), getting this working is actually quite straightforward.
TL;DR (quick setup):
xfconf-query -c xfce4-session -p /startup/ssh-agent/enabled -n -t bool -s false echo use-standard-socket >> ~/.gnupg/gpg-agent.conf echo enable-ssh-support >> ~/.gnupg/gpg-agent.conf
Xfce starts both
ssh-agent instances for you at login,
but you want to avoid the standalone
ssh-agent and instead configure just
gpg-agent for SSH. In fact, the
gpg-agent is likely started for you as
a systemd user service: you probably want to keep that setup.
To make sure Xfce doesn't start
ssh-agent for you, you need to disable it
in your settings. Unfortunately this isn't presented anywhere in the GUI that I
can find, but can be easily disabled on the command-line:
xfconf-query -c xfce4-session -p /startup/ssh-agent/enabled -n -t bool -s false
Then you need to tell
gpg-agent to always enable its SSH support, and
ideally for it to use a standard (stable) socket path rather than something
/tmp. The latter is particularly useful if you need to restart
gpg-agent for any reason, as the environment variables get baked into your
desktop session, and is the default in GnuPG 2.2 which is in buster.
To set this up, you need to add the following two lines to your
~/.gnupg/gpg-agent.conf file, creating it if it doesn't exist:
You can omit the first line on Debian buster as it is the default there.
You then need to logout and log back into your session for the changes to take effect.
If your Xfce setup uses a systemd user session, as is the default on Debian stretch, you should see something like the following:
$ echo $SSH_AUTH_SOCK /run/user/1000/gnupg/S.gpg-agent.ssh $ gpgconf --list-dirs agent-ssh-socket /run/user/1000/gnupg/S.gpg-agent.ssh $ systemctl --user show-environment | grep SSH_AUTH_SOCK SSH_AUTH_SOCK=/run/user/1000/gnupg/S.gpg-agent.ssh
If so, you're all set!