Ubuntu – dd: Operation not supported (on unmounted, but not ejected drive)

ddmountunmountusb-drive

I have looked through the other questions here on AU, and none of them seem to help me deal with this particular problem, so I am starting a new question.

For some context, all I am trying to do is install the Ubuntu Rescue Remix image onto an external USB drive. I am currently running these commands on my iMac, according to the steps made available via the Ubuntu Rescue Remix instructions.

My problem is that even after I unmount [but not eject] the destination USB drive (assigned to /dev/disc4); I still get the Operation not supported error, which (I think) is the error someone gets when trying to run a dd operation on a mounted drive (or "Resource Busy" error).

So here is the command I run:

sudo dd if=ubuntu-rescue.img of=/dev/disc4 bs=1m

And here is the result I get:

dd: /dev/disc4: Operation not supported

The output I get from running diskutil list:

...
/dev/disk4
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:     FDisk_partition_scheme                        *8.3 GB     disk4
   1:                 DOS_FAT_32 8GBUSBFLASH             8.3 GB     disk4s1

So can anyone help me understand why I can't seem to run the dd command on /dev/disc4, even after it has been unmounted, yet not ejected?

Thanks!

Update: Someone cited this answer as a potential solution to my question, so perhaps someone might find an answer there, but my question is unique, because it is asking in the context of dd operations, and the errors resulting from my dd operations — the suggested answer doesn't talk about dd operations at all, so it can't serve as an answer to my problem.

Best Answer

Solution

There is (normally) no device called /dev/discY.

You will have to find your device using ls /dev|grep sd

this will return you someting like 

$ ls /dev|grep sd
sda
sda1
sda2
sdb
sdb1
sdc
sdc1

then you mount the partition, of wich you think it could be your usb-stick

and see if it is the right device.

mount /dev/sdc1 /mnt && ls /mnt

if it is it, unmount it 

umount /mnt

and use 

dd if=whatever.img of=/dev/sdc

to write the image to the device.

Explanation

Ubuntu seperates four kind of device types:

  1. scsi drives

    these are today the most common. They are under the name sdX

    (sd = scsi drive) the the partitions are called sdXY.

    X is always a small letter starting from a and Y always an integer starting from 1 .

    usb works with a kind of scsi protocoll, too.

  2. parallel drives

    these are called hdX for hard drive.

  3. removable devices (without usbs)

    these are called srY for optical drives, Y is here an integer starting from 0.

    fdY are floppys and so on..

  4. Tapes

    are called nstY (guess what Y is) but you will most likely never face a tape.

The are all listed in the directory /dev/ dev for device.

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