This is a tutorial on how to format a USB flash drive using the dd command.
You can format a flash drive using a number of GUI tools - such as Disk Utility. Unfortunately, this does not work properly all the time. If you have a flash drive which has some kind of Linux installed on it and it is split into various partitions, Disk Utility may not detect all partitions. In such scenarios, it's best to use the command line tool called dd.
Linux
First, find the flash drive mounted in the system:
fdisk -l
Assume the flash drive is mounted on /dev/sdb. Now, unmount the device:
umount /dev/sdb
Format the flash drive:
sudo dd if=/dev/zero of=/dev/sdb bs=1m
After several minutes, the formatting will be completed.
macOS
First, find the device:
diskutil list
Assume the flash drive is mounted on /dev/disk2. Now, unmount it:
diskutil unmountDisk /dev/disk2
Format the flash drive (note the rdisk2 instead of disk2):
sudo dd if=/dev/zero of=/dev/rdisk2 bs=1m
After several minutes, the formatting will be completed.
urandom instead of zero
You may also use this command to fill the filesystem with random numbers instead of 0s.
sudo dd if=/dev/urandom of=/dev/rdisk2 bs=1m
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