Stopping/Resetting SCDAEMON

There is a daemon named scdaemon behind gpg-agent, which handles communication to smartcard/token.

Ideally, we don’t need to care about scdaemon, and it should handle everything automatically. But, there are some cases (because of bugs), where we need to talk to the daemon directly, in practice.

How to communicate SCDAEMON

We have a utility to communicate with a running gpg-agent, that’s gpg-connect-agent. We can use it to communicate with scdaemon, as it supports sub-command “SCD”, exactly for this purpose.


To stop SCDAEMON and let it exit, type:

$ gpg-connect-agent "SCD KILLSCD" "SCD BYE" /bye

Then, you can confirm that there is no SCDAEMON any more by ps command.


To let gpg-agent/scdaemon learn from Gnuk Token, type:

$ gpg-connect-agent learn /bye

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