On Mar 2, 2017, at 6:36 PM, Robert Moskowitz <rgm at htt-consult.com> wrote: > > I want to image the drive at various 'checkpoints' so I can go back and redo from a particular point… > what dd params work? > > dd if=/dev/sdb of=os.img bs=1M count=3210 That looks plausible. (I haven’t verified your count parameter exactly.) However, I wonder why you’re trying to reinvent snapshots, a technology now built into several advanced filesystems, such as btrfs and ZFS? https://en.wikipedia.org/wiki/Btrfs#Subvolumes_and_snapshots btrfs is built into CentOS 7. While there have been some highly-publicized bugs in btrfs, they only affect the RAID-5/6 features. You don’t need that here, so you should be fine with btrfs. And if you really distrust btrfs, ZFS is easy enough to integrate into CentOS on-site. And if *that* is also out of the question, you have LVM2 snapshots: http://tldp.org/HOWTO/LVM-HOWTO/snapshots_backup.html Why reinvent the wheel?