Ubuntu – How to recover USB flash drive functionality after having used dd

live-usbmountusb-drive

I have been installing Linux on my laptop via a bootable USB flash drive and I was having difficulty, so I ran the following command:

dd if=/dev/zero of=/dev/sdb

Was this a huge mistake? Did I wipe out some of the software that allows the USB drive to properly function?

Now my computer no longer recognizes my device (which was previously in /media/USERNAME), although it makes a sound when I plug it in. I tried to mount it via How to access a USB flash drive from the terminal?. The following output shows up when I use sudo fdisk -l :

Disk /dev/sdb: 14.7 GiB, 15728640000 bytes, 30720000 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: 0x003e98d7

Device     Boot Start      End  Sectors  Size Id Type
/dev/sdb1  *       32 30719999 30719968 14.7G  c W95 FAT32 (LBA)

When I try to mount it I get the following results: 

mkdir /media/usb
sudo mount /dev/sdb1 /media/usb

mount: wrong fs type, bad option, bad superblock on /dev/sdb,
   missing codepage or helper program, or other error

       In some cases useful info is found in syslog - try
       dmesg | tail or so.

I found this question, but this and its references don't answer my question.

Best Answer

In the following steps I am assuming as an example that you want to restore an 8GB USB flash drive to usable condition after writing the Ubuntu iso to it using dd, although of course the exact size of the USB flash drive is not important. The results of these steps are reproducible. I reformatted 2 USB flash drives with the following steps after writing Ubuntu ISOs to them with dd. As a side remark, it's kind of annoying to use dd instead of a GUI program like Startup Disk Creator, but dd is the only program I have found that works for writing the Ubuntu Minimal CD to a bootable USB flash drive.

  1. Remove all of your USB devices except for the 8GB USB flash drive that you want to reformat, so you won't get confused about the device name of the USB flash drive later on.

  2. List all the partitions.

     sudo fdisk -l

    Search the results of the command for output that looks like this:

     Disk /dev/sdc: 7864 MB, 7864320000 bytes
 30 heads, 33 sectors/track, 15515 cylinders, total 15360000 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
 Disk identifier: 0x00016288

    Device Boot      Start         End      Blocks   Id  System
 /dev/sdc1   *        2048    15359999     7678976    b  W95 FAT32

    If you see something like 7864 MB (8GB) in the output (see the example output above), then that is your 8GB USB flash drive. In this example it is called /dev/sdc. Now open the Disks application from the Dash and check again to make sure that the device name of your 8GB flash drive is the same as what you got from running the command: sudo fdisk -l.

  3. Create a partition table on the disk of type msdos, sometimes known as Master Boot Record (MBR).

     sudo parted /dev/sdc mklabel msdos

    In this example I used /dev/sdc for the name of the device which is what was found in the results of step 2. I can't stress strongly enough how important it is to verify the device name before running this step!

    Warning: If you type the wrong device name you may overwrite your operating system or another one of your partitions containing important personal files!!! So be careful and check the device name a second time. Open the Disks application and check the device name of your 8GB USB flash drive in Disks. It should be the same device name!!! Now check again! You don't want to accidentally type the wrong device name!

  4. Add an empty "primary" partition, which will hold a FAT filesystem later.

     sudo parted -a none /dev/sdc mkpart primary fat32 0 8192

    Once again in this example I used /dev/sdc for the name of the device which is what was found in the results of step 2. The command specifies the start point (from 0 MB) to the end point (8192 MB). If the 8GB USB flash drive does not have the full 8192 MB space, parted will adjust it automatically. If the terminal returns a message that the start point can't start at 0 MB and you have to use some other small number close to 0 MB, type Y to accept this. Note the command is creating a single, primary partition on the whole disk.

    This newly created partition will have the ID /dev/sdc1. That is because the device name in this example is /dev/sdc and the 1 at the end is because it is the first partition on that device.

  5. Create a FAT filesystem on the /dev/sdc1 partition by formatting the partition.

     mkfs.vfat -n "8GB-USB" /dev/sdc1

    /dev/sdc1 is the partition ID from step 4. "8GB-USB" is the partition label, which can be your own choice of label, just enclose the label inside two double quote characters.

You now have a ready-to-use reformatted USB flash drive with an 8GB FAT partition.

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