I'm looking for an incremental backup tool to use on a running, disk based linux system, such as ubuntu or the like, and a tool which is freeware.
Clonezilla can do accurate backups but only when the system is idle.
Acronis for linux can do accurate backups on a running system, but it's not freeware. There are methods that Acronis and BTRFS use to capture file system changes as it runs, so as to emulate the effect of stopping the OS while it is working. I'm looking for something that does this.
rsync, dump and many other ill-suited tools are suggested and even used for this purpose, but they can not be trusted to accurately capture a running OS. rsync, is fine when used on a static file-system, but not on a multi-threaded running file-system.
It is surprising to me how many are under the belief that one can do an accurate backup of a running file system just by copying it in some fashion or another. Having built a small multi-tasking engine some years ago I am well aware of the danger of one task polluting another's work. Only if a backup runs as an atomic task, with all other tasks stopped while it works, can it be assured to capture a 100% accurate restorable backup. There is nothing worse than having a backup that you rely upon, and believe will save you, only to have it corrupt when you try to use it.
I need this for a plain old desktop linux, and not for a virtual setup.