1. Create a new file under /etc/dconf/db/gdm.d/. The file should be named something like “10-local-gdm-settings”.
2. The contents of the file will contain the path to the schema and the value to be set:
Multiple entries can be made in the same file and multiple values can be placed under the same schema section.
3. Then after the file is in place run “dconf update” to have it take effect.