gnupg2 fails, "Line passed to IPC too long"

[Chad Miller]

I have a key on a USB-plugged "smart card" in the form of a Yubikey 4 Nano.

$ gpg2 --sign noise
gpg: signing failed: Line passed to IPC too long
gpg: signing failed: Line passed to IPC too long

$ echo $?
2

In going to gpg-agent.conf and adding debug logging, Attaching.

If I kill "scdaemon" and "gpg-agent", they exit, and it has no effect. Next run causes the same message.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: gnupg2 2.1.11-6ubuntu2
Uname: Linux 4.5.0-040500-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.1
Architecture: amd64
CurrentDesktop: GNOME
Date: Thu Jun 2 17:15:42 2016
EcryptfsInUse: Yes
SourcePackage: gnupg2
UpgradeStatus: No upgrade log present (probably fresh install)

[Chad Miller (cmiller)]

Okay, the shell I was using to run gpg here didn't have GPG_TTY or DISPLAY environment variables set, which seems to be the cause of the problem.

That is a bewildering error message.