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date excerpt tags title toc
2017-08-22 This is why I love linux! [linux netcat] Cloning a hard disk over the network false

This is going to be short: My old trusty laptop began showing signs of old age. The screen started flickering, a problem I already knew. Last time, I bought a new screen from Alibaba for ~100€, but wasn't going to spend that much on a three year old laptop.

So, new laptop it is. The Lenovo V110-15IAP looked nice, so I ordered it online. It arrived today, but I wasn't going to spend hours to set up a new OS, copy all files over, check if everything is ok --- and I also didn't have an external drive to hold all files during transfer ... there must be an easier way.

Well, there is, and it's called netcat and some pipes. Netcat is a nice, simple tool that reads and writes data over the network, using TCP by default (more info here).

I connected old and new laptop via ethernet, booted the old laptop into recovery mode, booted the new laptop with a Arch live USB drive I had laying around, and got to work.

First, the two computers need a network connection. On the old laptop:

[~]# ip addr add dev enp1s0f0
[~]# ip l set dev enp1s0f0 up

and on the new laptop:

[~]# ip addr add dev enp1s0
[~]# ip l set dev enp1s0

Notice the different interface names. Check connectivity:

[~]$ ping -c 3
PING ( 56(84) bytes of data.
64 bytes from icmp_seq=1 ttl=64 time=2.33 ms
64 bytes from icmp_seq=2 ttl=64 time=2.34 ms
64 bytes from icmp_seq=3 ttl=64 time=2.33 ms

--- ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2003ms
rtt min/avg/max/mdev = 2.335/2.340/2.346/0.004 ms

Looks good!

On the "receiving" (new) laptop, I made netcat listen on the network, together with pv to get an idea of the transmission rate:

[~]# nc -l -p 4000 | pv -pterab -s 117g >/dev/sda

The switches for pv give us some nice metrics, see pv(1) for more info. The 117g is the size of the disk, this is necessary to get an ETA and a progress meter.

Now, start the transfer on the old laptop:

[~]# nc 4000 </dev/sda

The transfer took around 20 minutes at about 100 MB/s, which means the Ethernet is actually the bottleneck).

After that, I verified the first few bytes of the disk to make sure they are actually the same:

[~]# dd if=/dev/sda bs=1M count=1 status=none | md5sum
d4bf772aa861fef76ff777aa52ec6800  -

This output was the same on both machines, which means we are good!

After a reboot, the new machine booted straight into my trusted fedora, and everything worked out of the box (except I had to re-enter the WiFi password, which I guess has something to do with changing MAC addresses). And not even five minutes later, I started writing this post.

I also eperimented a bit with compression (lz4 and lzop), but even though the network was the bottleneck, the transfer didn't complete any faster. Not sure why, but I got what I wanted, so I didn't bother to investigate further.

You could do the same over any network, but with the netcat transfer being unencrypted, you'd need some kind of encryption, for example by piping through ssh.

Anyway, thank you for reading!