I am struggling to get dd to restore a disk image across a network. I imaged a hard drive using dd to an external drive but no longer have that drive. The image file itself is on another machine and the only drives I have are the single internal drives of each machine so I am trying to run the command over the network

Running the command I'm prompted for the password for 'user' and after entering it get the error:I've tried booting the machine I need to restore from a Knoppix disc then used the "root terminal". I have also tried a standard terminal on both Knoppix and Ubuntu (in both cases running the OS from CD) running "sudo -i" before the ssh/dd combination.

The permissions on /dev/sda appear to be correct - root has rw access.

I assume the problem is that the credentials for the remote account "user" are being used for "dd". Is this a syntax problem or do I have to change the permissions on sda to give write access to everyone? I don't know if changing the permissions affects only the running Linux or if anything is written to disk so I'd prefer not to make changes until I'm sure I'll be able to restore the image.

Thanks

http://www.ndchost.com/wiki/server-a...etcat-over-ssh
Try something like this maybe.


dd if=/dev/sda | ssh username@servername.net "dd of=/dev/sdb"

Thanks for the tip jefro.

I had a look at the link you included and tried netcat first but couldn't get it to work.

Going back to ssh I had to jump through a couple of hoops - running the command from the machine where the image was stored didn't work at first because something somewhere did not like the fact that Knoppix has a nul root password, once I changed it I managed to get it running with Now I just have to keep my fingers crossed that it will finish in less time than it would have taken me to order a USB drive and do everything locally 'cos it's a large, uncompressed image.

I know you have marked this post as "solved", but you may be in for a l-o-n-g wait for that command to finish.

netcat really is the way to go if you are on your LAN (this basic method isn't safe over the big bad interweb).

Boot the laptop from a live CD.
On the laptop (the destination for the image), as root:

1] Make sure /dev/sda has no partitions mounted, unmount them if necessary.
2] Start netcat listening on port 1010:
On server (as root)
When the server has finished sending, dd will report the number of bytes transferred but the laptop will still be listening, so you need to do a CTRL-C on the laptop to terminate the listening command.

That's it.

Cross fingers and reboot the laptop.

Yep, I realise it is going to take time. I tried netcat earlier but couldn't get it to work. The method I used was almost identical to the one you suggest, I just chose a different port and used a relative path to the image file rather than an absolute one. There were no error messages when I started the laptop listening, nor when I started sending the file. The terminals did not return to a prompt as expected, but when I checked the port using tcpdump there didn't seem to be any traffic and the laptop hard disk showed no activity. I'm using Mac OS X on the 'server' - only the laptop is running Linux - but as far as I know there is no difference in netcat on OS X. What I didn't do was make sure /dev/sda wasn't mounted. I can't remember if running Knoppix from CD automatically mounts the machine's hard drive or not (and can't test it until the restore has finished).

I will give it another go if the ssh method fails but it's been running for a few hours now and judging by Activity Monitor, may only have an hour or two to go (as long as it doesn't slow down).

Thanks for the advice anyway.

Thanks for the update.

Looks like you have been running for about 6hrs now.

Be patient, or try netcat. I have used it to do exactly what you are trying (but in reverse: I imaged a friend's virus-broken windows laptop [booted to a live linux distro] over my LAN to recover their personal data), it worked, and was very fast.

For the record, setting bs=a_big_number (16M in my post above) for the dd command speeds things up a lot, never mind the netcat business, which also helps.

Please let us know how you get on.

Best wishes.

It finally finished - after nearly 8 hours! ... which I suppose isn't bad as the image was 250GB and I had forgotten to specify the block size (I noticed about 2 hours in and decided to let it run) so it was using the default 512. The 100Mb connection was almost saturated (one way at least) for the whole time.

... and the machine boots

While I was not in a hurry the lessons I've learnt from this are:

- don't forget to set block size for dd
- zero slack space before imaging and compress to reduce the size of the image - the aim was a backup of config and applications not data which I backup separately

I'll try netcat next time.

Thanks for the help. I don't use Linux (nor the OS X terminal) often enough for these things to come to me without thinking and tend to forget what I know so all guidance is useful and welcome.