I seem make a mistake

I type " dd if=xxx.iso of=/dev/sdb " wich /dev/sdb is a 4G usb disk

and now, I want this usb disk become normal disk

So I type " dd if=/dev/zero of=/dev/sdb "

and then reinsert the usb disk, but it still show that it is a iso usb disk

is there a method to revocer back to normal usb disk ?? thank you

I follow your step 1 [partition table], it got errors bellow :

I can not create the partition table !! :(


Command (m for help): n

Command action

e extended

p primary partition (1-4)


Partition number (1-4): 1

First cylinder (1-1020, default 1):

Using default value 1

Last cylinder, +cylinders or +size{K,M,G} (1-1020, default 1020):

Using default value 1020

Command (m for help): w

The partition table has been altered!

Calling ioctl() to re-read partition table.

WARNING: Re-reading the partition table failed with error 2: no such file or folder.

The kernel still uses the old table. The new table will be used at the next reboot or after you run partprobe(8) or kpartx(8) Syncing disks.


2 Answers 2


open up gparted, delete the existing partitions on your usb disk, create a new partition and format it to fat32


I assume you have write privilegies to /dev/sdb. Almost everything later in the answer requires it. Most likely you want to prefix everything with sudo and do it as root.


After you have zeroed you usb drive, you'll need to create one or more filesystems on it before you can use it. If you only want one filesystem, you don't need a partition table. This is (afaik) the default in Windows, and is sometimes called a "Superfloppy". In the *bsd world it is known as "dangerously dedicated". If you want that, skip the next paragraph.

Partition table

If you want a partition table, you almost certainly want an mbr table to have compatibility with 32-bit Windows. There are a lot of other options, among them GPT which is accepted as The Future, but it's advances are mostly unnecessary on a small device like a usb disk.

We'll use fdisk to create the partition table and a single partition spanning the whole drive. Fdisk will tell you what it does and how it works, you should read and learn, but I'll just tell you the keys you need to push. You can hit m to get a main menu.

Start fdisk with fdisk /dev/sdb. Hit n to create a new parition, p for primary, 1 for partition number, enter to accept the default start, enter to accept the default end and w to write the partition table.

Creating a filesystem

Now you have to choose a filesystem. If you just need it to work for transferring files, you probably want fat32. Other popular choices supporting modern filesystem features like permissions and reasonable platform support are ntfs and ufs.

To create a fat32 filesystem on the partition you created, do the following:

mkfs.vfat -f 32 /dev/sdb1

If you chose the "superfloppy" setup, do this in stead:

mkfs.vfat -f 32 /dev/sdb

Your usb disk should now work as expected.

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