Using dd with a mounted drive

Hi all

I have a hackintosh based on an Acer box which is working fine.

In order to run Docker I need to boot with Yosemite. I have a Yosemite image, and these instructions to use:

"- Plug 8GB USB PENDRIVE and mount all partition of it (not eject)
- Use dd to transfer image to pendrive like this:
sudo dd if=~/Downloads/yosemite.img of=/dev/diskXX bs=1m
*** WHERE diskXX is your 8GB PENDRIVE, THIS PROCEDMENT ERASE ALL DATA OF YOUR PENDRIVE, IT IS IRREVERSIBLE!!!
- This take a few minutes, take a coffee
- Once dd finish write your PENDRIVE, you can reboot and boot with this pendrive"

(Author is Spanish)

I have had some success with an 8GB pendrive but it ran out of space. I am now using a 16GB but unmounting and doing the file transfer corrupts the usb partition.

Is it possible to do the dd with the partition mounted? If so how?

Thanks again, you guys are the best!

ML

Originally Posted by martinlangley In order to run Docker I need to boot with Yosemite. I have a Yosemite image, and these instructions to use: "- Plug 8GB USB PENDRIVE and mount all partition of it (not eject) - Use dd to transfer image to pendrive like this: sudo dd if=~/Downloads/yosemite.img of=/dev/diskXX bs=1m *** WHERE diskXX is your 8GB PENDRIVE, THIS PROCEDMENT ERASE ALL DATA OF YOUR PENDRIVE, IT IS IRREVERSIBLE!!! - This take a few minutes, take a coffee - Once dd finish write your PENDRIVE, you can reboot and boot with this pendrive"

That should almost certainly be, "unmount". It's bad enough to copy from a partition with dd while it is mounted (the image will have some mild, but correctable, filesystem corruption), but overwriting a partition with dd while it is mounted is sheer lunacy. Neither the filesystem that the kernel has mounted nor the image that you copied to the device will be intact.

Not sure what you have exactly to begin with.
Not sure about the block size. (goes with above)
Not sure you have a disk image.

I've never wanted to use dd to a mounted drive. On accident a few times. Seems to go correctly but if some file is locking the drive or some program has a lock on it then you could have issues.

Had to check but this is the way it should be done. http://www.thelinuxdaily.com/2010/01...c-osx-with-dd/

I'd think there would be a sync option in macos dd command so you might wish to use it too.

that dd will erase everything on the pendrive, so there is no any reason to keep that filesystem mounted (it will be lost/overwritten/destroyed completely). Furthermore if anything was mounted during dd that may corrupt the copied image on the pendrive too (and you will not able to recognize that easily).
(if you have anything important on the pendrive, save it)