http://www.fsarchiver.org/Main_Page It's a filesystem imaging program, like a more advanced version of partimage. One of its more interesting featuers is that you can force it to do a hot backup of an RW-mounted filesystem. Is this a good idea? Probably not. Definitely not in production environments. However, I will also note that fsarchiver checksums every file it copies. So if it does fail to preserve a file, it will at least tell you that the file failed to copy... For whatever that's worth. That being said, I was able to take a hot backup of my Debian laptop's root partition (while mounted RW - no files failed) and restore it successfully on another computer. Yay. That being said, if you must do hot backups on UNIX, you should probably stick with tar or cpio anyway; those will offer you more flexibility. Unless you're using ACLs or something.