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GnuPG can, with gpg-agent, cache access to a private key. How can I keep that cache active for the entire user session?

When I unlock the key for gpg-agent, it only stays cached for a limited time. With SSH's agent, I enter the passphrase one time and it stays cached for the whole session. I want the same behaviour from gpg-agent.

So, ssh-agent doesn't suffer from a limited cache lifetime. But gpg-agent has limits the cache lifetime, at least by default. How can I eliminate the limit on cache time from gpg-agent?

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The user configuration (in ~/.gnupg/gpg-agent.conf) can only define the default and maximum caching duration; it can't be disabled.

The default-cache-ttl option sets the timeout (in seconds) after the last GnuPG activity (so it resets if you use it), the maximum-cache-ttl option set the timespan (in seconds) it caches after entering your password. The default value is 7200 (2 hours) for both.

Set it to a year or so – say, 34560000 seconds (400 days) – and you should be fine:

default-cache-ttl 34560000
maximum-cache-ttl 34560000

But for this change to take effect, you need to end the session by restarting gpg-agent.

If you want to limit to your session length, you'd need to kill the daemon at logout. This is very different between operating systems, so I'm referring to another question/answer containing hints for different systems.

You could also restart the gpg-agent during login, but this does not limit caching time to the session length, but logins of a user. Decide yourself if this is a problem in your case.

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Is this a “you can't do what you're asking” response? It's not clear, since you're talking about limiting the session length or limiting caching time. I want exactly the opposite of that: no arbitrary limit on the cache time or session length. –  bignose Jul 29 '13 at 0:58
    
Kind of that, you can only workaround by setting a rather huge ttl. Set it to a year or so and you should be fine - but need to end the session by restarting gpg-agent. –  Jens Erat Jul 29 '13 at 8:12
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