This was easier on Hostgator, where everything is “owned” by my user account and everything works. To get Ode addins to work, the /data directory is owned by my user and is in the www-data group. The /data/addins/state directory has the same ownership and permissions (755). The /data/addins/state/Indexette directory is owned by www-data and is in the www-data group and has permissions 755. The files created by Indexette in /data/addins/state/Indexette are aux_index_file and primary_index_file.