My goal is to have a certain directory to be available as tmpfs. There will be some modifications during server uptime in this dir and those modifications must be synced to non-tmpfs persistent dir on HDD over rsync.

After server boot the latest version from non-tmpfs persistent dir must be moved to tmpfs and rsync syncing to be started.

I'm afraid that rsync will erase non-tmpfs backup if tmpfs dir will be empty..

I'm doing it in this way right now:

1. create tmpfs partition in /etc/fstab

2. cat /etc/rc.local (pseudocode)

   delete "tmpfs rsync" cronjob from /var/spool/cron/crontabs if there is any

   cp -r /path/to/non-tmpfs-backup /path/to/tmpfs/dir

   append /var/spool/cron/crontabs with "tmpfs rsync" cronjob

What do you think?