I want to backup my virtual machines (all Debian) with a cronjob. As the backups per machine can be pretty huge I only want to backup the system with its configuration itself (leaving out the directory where users mess around), which can be done with the exclude-dir-parameter.
I'm planning to run the cronjob once a week. But I really only want to backup the machine if something has changed in the system configuration or new packages have been installed. Is there a way to detect such changes in a virtual machine before running vzdump?