docker run --rm guacamole/guacamole:1.4.0 /opt/guacamole/bin/initdb.sh > guac_db.sql

Hello,

I want to install Guacamole and get an error when using the following command.

docker run --rm guacamole/guacamole:1.4.0 /opt/guacamole/bin/initdb.sh --mysql > guac_db.sql

Error:

cat guac_db.sql
Bad database type: --mysql
USAGE: /opt/guacamole/bin/initdb.sh [--postgres | --mysql]

Am I using the command incorrectly? What have I overlooked?

With kind regards