signd is a little daemon that listens for sign requests from sign, and either calls gpg to do the signing or forwards the request to another signd. The -f option makes signd fork on startup.
signd uses the same configuration used for sign, /etc/sign.conf. It needs a gpg implementation that understands the "--file-is-digest" option to work correctly.
Unless the allow-unprivileged-ports option is set to true in /etc/sign.conf, signd allows only connections from reserved ports and the ip addresses, subnets expressed in CIDR notation, and hostnames listed in the "allow" field of the configuration.