I'm looking for an incremental backup tool to use on a plain old running disk based linux system, such as ubuntu or the like, and a tool which is freeware.
This is for a plain old desktop linux, and not for a virtual setup.
I'm already aware of tools that can be used to do backups when the system is idle like clonezilla.
I'm also already aware of many tools that are suggested for this purpose but which can not be trusted to accurately capture a running OS, like for example rsync, which is fine for a static file-system, but not for a running file-system.
An example of what I'm looking for is Acronis for linux and windows, but it's not freeware.
I also read somewhere that Btrfs (Butter-file-system) has some of this capability.
This is a similar question, but does not ask about an incremental backup.