Examples of the dd command usage
dd is a file copying utility you can use for a lot of useful tasks. I will teach you some of them.
Table of Contents
- Backup disks/filesystems
- Wipe partitions/disks
- Copy an ISO file to a USB drive
- Create files with a random content
- Create filesystems inside files
- Create a swap file
You can wipe a partition (or an entire drive) in a way that will be hard to recover deleted files, by overwriting all space with zeros.
dd if=/dev/zero of=/dev/sdb1
- This is the basic command. You must kill the process when
ddshows that there is no space left on the device. You can specify the device space with
bs=<bytes>(read and write up to
<bytes>bytes at a time) and
<n>input blocks) parameters, so it will terminate automatically.
dd if=/dev/zero of=/dev/sdb1 bs=1M count=512
After this command, you will need to recreate the filesystem (by running
# e.g.: mkfs.vfat -F32 /dev/sdb1
Copy an ISO file to a USB drive
The following command is one of the recommended methods of installing Arch Linux ISO file on a USB. You can use it as an example.
dd bs=4M if=path/to/archlinux-version-x86_64.iso of=/dev/sdx conv=fsync oflag=direct status=progress
Create files with a random content
You can create files with any size to do tests. You can use
/dev/random/ to fill these files with random data.
dd if=/dev/random of=some_file bs=1M count=100
Create filesystems inside files
/dev/zero you can create files that can contain filesystems inside them.
dd if=/dev/zero of=system.img bs=1M count=512
Once created, you can make a filesystem and mount the file as any other partition:
mkfs.ext4 system.img mount system.img /mnt/test/
Create a swap file