unable to use gnupg on a read-only filesystem

[Martin Vegter]

Dear list,
I am working on a read-only filesystem and I am using following command:

     echo "hello" | gpg -e -a -r martin at example.com

This command fails with the following errors:

gpg: failed to create temporary file `/root/.gnupg/.#lk0x847421':
Read-only file system
gpg: fatal: can't create lock for `/root/.gnupg/trustdb.gpg'

I don't have the option "use-temp-files" enabled in my config. Even when
I explicitly disable it, I get the same errors:

     echo "asdf" | gpg --keyserver-options no-use-temp-files -e -a -r
martin at example.com

Could somebody please advice how I can use gpg without temporary files ?

many thanks,
Martin