gpg: signing failed: Inappropriate ioctl for device

When trying to use the bash+curl verifying method on a server, this cryptic error message might happen:

> gpg: signing failed: Inappropriate ioctl for device

Since this is a fatal error and also quite difficult to debug, maybe the fix could be put somewhere (in the provided command line?):
```bash
export GPG_TTY=$(tty)
```

[source](http://unix.stackexchange.com/a/257065)

Start by locating the bash+curl verification command referenced in the issue and reproduce the GPG signing failure on a server. Check how the command establishes the terminal environment, then confirm that the documented verification flow handles GPG_TTY. Done means the provided command no longer produces the reported error in the relevant server setup.

Written by the indexing model from the issue text.