Ubuntu – Use DD to clone only Linux partition to external USB drive

dddual-boothard drivepartitioning

I have a 1 TB internal drive that has two 1/2 TB partitions, one for Windows and the other for Ubuntu 14.04 LTS. The station has become primarily a Linux station and I never boot into Windows anymore.

I wanted to create an image backup so I used DD to clone the internal drive to an external 1 TB USB drive. Unfortunately the USB drive appears to be just a few Gigabytes shy of the internal drive and DD ended with a "Not enough space on drive" error message. Now I am seeing something odd. When I ejected the USB drive and plugged it back in, I see two 1/2 GB partitions that appear to be duplicates. They have identical GUID's and Nautilus shows identical directory structures and content. I'm guessing that something about the incomplete copy of one of the partitions has left the external drive in a broken state.

How can I use DD to just clone the Linux partition to the external drive? That's all I really want.

Best Answer

As first you need to find out data about your HDD, you can do this by typing in terminal:

sudo fdisk -l

You should get an output like this:

Disk /dev/sda: 149,1 GiB, 160041885696 bytes, 312581808 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x06bd4abe

Device     Boot     Start       End   Sectors   Size Id Type
/dev/sda1  *         2048 230055935 230053888 109,7G 83 Linux
/dev/sda2       292970494 312580095  19609602   9,4G  5 Extended
/dev/sda3       230055936 292968447  62912512    30G 83 Linux
/dev/sda5       292970496 312580095  19609600   9,4G 82 Linux swap / Solaris

Partition table entries are not in disk order.

So lets say /dev/sda3 is the drive you want to clone, then you can do:

dd bs=512 if=/dev/sda of=/dev/sdb1/partition.ddfile seek=230055936 count=$(expr 292968447 - 230055936)

Remind this here are only examples you would need to fit that to your situation.

Using dd to clone an Ubuntu installation

Yes, you can use dd to clone an installation, but it's not the fastest/easiest way to do it. It's better to do it via backup/restore with a live-tool such as Clonezilla.

If you wish to use dd, note that the target disk must be the same size or larger than the source.
Also, to make it bootable, you must copy from device-to-device (e.g. /dev/sdX), NOT from partition to partition (/media/...)
Use sudo fdisk -l or gparted to find out which block devices your target internal hard disk (usually /dev/sda) and external USB hard disk (usually /dev/sdb) are.
Then use dd with exactly the following syntax, where x is the letter for the USB drive and y the letter for the internal drive which you have determined in the previous step:
```
  sudo dd if=/dev/sdx of=/dev/sdy bs=8M && sync
```
and wait for it to complete.
To answer your other question, no, simply dd'ing to an ISO (or CD or DVD, etc.) will NOT work; it will be unbootable. For that, you need to use a tool such as remastersys. See this question for more information:

How do I convert my Ubuntu installation into a Live-USB or Live-CD?

Ubuntu – Is the command to clone a drive optimal

Progress

The command you listed

dd if=/dev/hda of=/dev/hdb & pid=$!
while kill -USR1 $pid; do sleep 1; done

is a nice two-liner to get the the progress of dd on a regular basis. I use a very similar one too. Looks good. Found it here perhaps?

Blocksizes with `dd`: alignment and performance

You can add a block size in which the operations take place. It does not matter what the block size of the underlying block device is to get the operation done equally well, but for performance reasons you might want to pick one that suits your needs.

First of all, there's the alignment thing. In case your block device operates as 512KiB (like flash drives do), it would be very unfortunate to run dd with bs=512 (bytes) as this will cause 1024 writes (!) for each block from the device perspective. In practise it won't be this bad as writes are buffered and taken into one go, but during syncs it can still amplify the amount of writes a lot.

Then also consider the plain CPU usage overhead when dealing with a very large amount of small operations. It's just more efficient to take megabytes at once when copying over large amounts of data.

My best practice is to start with 1MB as that is a nice multiple of most set ups, including RAID stripe sizes, LVM extent sizes, etc. On my laptop with SSD I tend to see a slight improvement using 10MB as block size, whereas I don't see it anymore on my physical hard drive.

Last block

Don't worry about the drive/volume size not being a multiple of the block size. The last block dd will copy will be adjusted to match the last bit of data on it. You can see whether the last block had a different size by looking at the output.

18335302+0 records out

The +0 means that it was an exact match, a +1 means that it wasn't. No big deal.

Best Answer

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Using dd to clone an Ubuntu installation

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Progress

Blocksizes with dd: alignment and performance

Last block

See also

Related Question

Blocksizes with `dd`: alignment and performance