Comments on: Copy hard disk or partition image to another system using a network and netcat (nc)

By: Scott

Scott — Sat, 02 Jul 2011 13:32:44 +0000

Great site and follow through by everybody. I wonder about the output destination partition/file. Is the output partition created before the
dd of=/dev/sdb
if so how is this done?
Can you instead just send this to a file on the receiving end?
dd of=/tftp/HOSTA.img

So far the discussion is about device or hard drive NOT a partition.
If one wants to make a bootable image of the source partition wouldn’t you copy the?
if=/dev/sda1 (if that is it).

Thanks everybody.

By: David Bain

David Bain — Sun, 23 May 2010 10:52:14 +0000

Hmmmm.. when I follow these instructions everything works except it appears to “hang” when no more data is left to pass from the source machine. I added pv to the command “chain”, as noted above, so I pretty much know when no more data is being passed. Isn’t it supposed to close the connection once all the bytes have been moved?

By: Salah

Salah — Sat, 15 May 2010 13:25:54 +0000

I see that everyone is recommending dd/nc but I wonder if there’s another solution that provide workarounds for network problems (unstable connections => disconnect/resume, bandwidth limitation => schedule,.. etc). While I’m not if it’s possible to use dd/nc that way.

I don’t mind spending days copying a harddisk from a remote location to another if that will go automatically and error free. Anyone?

By: Ksh

Ksh — Sat, 27 Feb 2010 21:41:18 +0000

Why not gzip? In my experience bzip2 take 3-4 times more cpu cycles than “gzip -3″ ;on the other side compression factor could be only 10-20% better.

By: Hari

Hari — Thu, 28 Jan 2010 02:48:15 +0000

I meant to say “hostA” (ie., the source device is a lowend device like iphone)

By: Hari

Hari — Thu, 28 Jan 2010 02:32:28 +0000

Thanks for putting this together. This is a good alternative to have in case ssh option doesn’t workout for some reason. This should also be better than ssh when the hostB is a very lowend device (like iphone).

By: richard

richard — Sun, 24 Jan 2010 08:45:32 +0000

An excellent HOWTO. Thank you. Take heed of ‘me’ advice. bzip2 will cause a cpu/memory bottleneck on old machines and under utilise the network. I also found using pv to add a progress meter was useful:
Target host (HOST B):
nc -p 2222 -l -vv | pv -r | dd of=/dev/sda bs=16M

Source host (HOST A):
dd if=/dev/sda bs=16M | nc 2222

By: Paul Johnson

Paul Johnson — Tue, 14 Jul 2009 20:33:21 +0000

I have new version of netcat. I wonder if there is a way to use something like the bs option with this new style of command in order to speed it up. Adapting your instruction to my case, here is what I do:

On the TARGET machine, 129.237.61.XX, make sure port 12345 is unfirewalled. Then set netcat to grab the incoming on 12345 and divert it to disk /dev/sdb. Can also replace with particular partition /dev/sdb2:

nc -l 12345 | bzip2 -d > /dev/sdb

After that, go to the SOURCE machine and compress the source disk /dev/sda and pipe it to through nc over to the other system:

bzip2 -c /dev/sda | nc 129.237.61.XX 12345

That does work, but not speedy.

Also, in your instructions, I wonder if you ought to add some information on whether this should be done on a “live” (mounted) file system. From what I can tell, one ought to do this only after booting from a rescue disk or external drive or some sort.

By: Me

Me — Mon, 25 May 2009 17:32:12 +0000

Just skipping the bzip2, is MUCH faster on slower systems..

By: casparoo

casparoo — Fri, 01 May 2009 05:38:18 +0000

How can I copy a hard disk image of a Windows machine to a Linux machine through network ( using netcat and dd). Could you please provide the details. Thanks in advance…

By: rickx

rickx — Thu, 19 Mar 2009 07:37:08 +0000

A bit messy tackling errors in the instructions, but doing
sudo su
nc -l -p 2222 | dd of=/dev/sda bs=16M
on the receiver (192.168.0.2) and
sudo su
dd if=/dev/sda bs=16M | nc 192.168.0.2 2222
on the source (192.168.0.1) works.
Use
ifconfig eth0 192.168.0.1[or 2] netmask 255.255.255.0
to configure the nics from the shell on the fly.
Problem is grub then: the entries with GUIDs will not work, so edit the menu.list before rebooting or you’ll get error 2.
Thanks anyway.

By: Florian

Florian — Tue, 06 Jan 2009 01:42:18 +0000

The command works fine, but if you use netcat to make a diskdump of two directly connected machines, you should avoid the compression, because it will slow down everything.

Works fine for the following scenario:
Host A Host B (with twisted pair)

By: Hannes

Hannes — Thu, 04 Sep 2008 20:30:24 +0000

Thanks a lot for this article.
But like Anuarag said, “hostA” should be “hostB” here:

(on hostA, type) # bzip2 -c /dev/sda | netcat hostA 2222

We connect not to ourself, yes? :)

By: S

Sat, 23 Aug 2008 02:10:42 +0000

in response to #11(ben);

why would you first netcat the data uncompressed and only then compress it into an image?

By: chains

chains — Wed, 13 Aug 2008 16:10:30 +0000

I tried what Ben suggested:

# BACKUP – to backupserver (192.168.1.1)
nc -p 2222 -l | bzip2 -c > Image.bz2
# BACKUP – from clienthost (192.168.1.2)
dd if=/dev/sda bs=16M | nc 192.168.1.1 2222

# RESTORE – to clienthost (192.168.1.2)
nc -p 2222 -l > /dev/sda
# RESTORE – from backupserver (192.168.1.1)
dd if=Image.bz2 bs=16M | bunzip2 -c | nc 192.168.1.2 2222

but when restoring i’m getting the error:
“bunzip2: (stdin) is not a bzip2 file.”

Any suggestions?

By: Brian Trauger

Brian Trauger — Wed, 25 Jun 2008 04:51:54 +0000

This looks very helpful. Can I also specify just 1 partition instead of the whole drive? I have a dual-boot with Xp and want to just backup the Windows partition.. Or should I just use partimage?

By: Ben

Ben — Fri, 28 Mar 2008 14:08:56 +0000

I don’t see any good about using ssh in local network and it would produce extra traffic. Here’s my contrib to backup and restore a linux parition:

# BACKUP – to backupserver (192.168.1.1)
nc -p 2222 -l | bzip2 -c > Image.bz2
# BACKUP – from clienthost (192.168.1.2)
dd if=/dev/sda bs=16M | nc 192.168.1.1 2222

# RESTORE – to clienthost (192.168.1.2)
nc -p 2222 -l > /dev/sda
# RESTORE – from backupserver (192.168.1.1)
dd if=Image.bz2 bs=16M | bunzip2 -c | nc 192.168.1.2 2222

By: The Cog

The Cog — Tue, 05 Feb 2008 08:46:33 +0000

Useful hint, thanks.
There is some confusion betwen host A and B though. All the examples are copying from B to A, but the headings: “Command to type on host…” indicate you are copying from A to B.
Nit-picking, I know.

By: g4b

g4b — Mon, 28 Jan 2008 15:01:42 +0000

-l also takes a host as option, so if you really want to be sure, no one else just streams in your data you can add like
nc -l HostSource -p 2222…

also maybe update the whole thing to use “HostSource” and “HostDest” because HostA and HostB is a bit confusing maybe.

thanx for the tutorial, g4b

By: Anuarag

Anuarag — Fri, 31 Aug 2007 04:08:42 +0000

Thanks for this guide.

I am confused!! on the host A (i.e. source disk host) command to be typed is:
# bzip2 -c /dev/sda | netcat hostA 2222

Should it be hostA or hostB.

Similarly I am confused about the commands given for the new version of nc: It seems to me commands for host A and B exchanged?

Please correct me.

Thanks
Anurag