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

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

By: foobar

foobar — Mon, 13 Aug 2007 15:41:41 +0000

this is basically copying a compressed partition or disk over the network, unencrypted. you may consider using ssh for safety reasons, e.g:

foo:# cat /dev/sda | bzip | ssh remotehost “cat > /backup/foo.sda.bz2″

By: Karl O. Pinc

Karl O. Pinc — Mon, 13 Aug 2007 14:52:11 +0000

You forgot to mention _why_ someone would want to use netcat to do these things, instead of just plain old ssh which is easier because it can be done in one command from one system. You’d want it when you don’t want the overhead of ssh, and don’t need encryption. (It’s also good to have articles like this because netcat is so useful and if you’ve another problem it’s nice to start with something that you know works.)

By: Anonymous

Anonymous — Mon, 13 Aug 2007 13:52:23 +0000

You should definitely use bs=16M or something like that. Otherwise, the copy will take forever. Copying a 300 GB hard drive over a 1 Gbps cross-over cable took about 1 1/2 hours or so using bs=16M Without this option, the same thing would have taken about 7 hours