How to use the command 'dd' (with examples)

The dd command is a powerful tool used for converting and copying files. It can be used for a variety of tasks, such as creating bootable USB drives, cloning drives, generating random files, benchmarking disk performance, and creating system backups. In this article, we will explore each of these use cases in detail, providing example commands and explanations for each.

Use case 1: Make a bootable USB drive from an isohybrid file

Code:

dd if=path/to/file.iso of=/dev/usb_drive

Motivation: Creating a bootable USB drive is often necessary when installing or troubleshooting operating systems. By using the dd command, you can easily copy an isohybrid file (such as archlinux-xxx.iso) to a USB drive and make it bootable.

Explanation:

• if=path/to/file.iso: Specifies the input file, in this case, the path to the isohybrid file you want to copy.
• of=/dev/usb_drive: Specifies the output file, which is the USB drive you want to make bootable. The /dev/usb_drive should be replaced with the correct device name of your USB drive.

Example output: The dd command will copy the contents of the isohybrid file to the USB drive. Once the process is complete, you will have a bootable USB drive that you can use to install or troubleshoot an operating system.

Use case 2: Clone a drive to another drive with 4 MiB block and ignore errors

Code:

dd if=/dev/source_drive of=/dev/dest_drive bs=4194304 conv=noerror

Motivation: Drive cloning can be useful when migrating to a new drive or creating backups. The dd command allows you to clone a source drive to a destination drive, with the added benefit of specifying the block size and ignoring any errors that may occur during the cloning process.

Explanation:

• if=/dev/source_drive: Specifies the input file, which is the source drive you want to clone.
• of=/dev/dest_drive: Specifies the output file, which is the destination drive where you want to clone the source drive. The /dev/dest_drive should be replaced with the correct device name of your destination drive.
• bs=4194304: Specifies the block size for copying data. In this example, the block size is set to 4 MiB.
• conv=noerror: Specifies that any errors encountered during the cloning process should be ignored.

Example output: The dd command will clone the contents of the source drive to the destination drive using a block size of 4 MiB. Any errors that occur during the process will be ignored.

Use case 3: Generate a file of 100 random bytes using the kernel random driver

Code:

dd if=/dev/urandom of=path/to/random_file bs=100 count=1

Motivation: Generating random files can be useful for various purposes, such as creating encryption keys or testing applications. The dd command can be used to generate a file of random bytes by utilizing the kernel random driver.

Explanation:

• if=/dev/urandom: Specifies the input file, which is the kernel random driver. This driver provides a source of random data.
• of=path/to/random_file: Specifies the output file, i.e., the path where you want to create the random file.
• bs=100: Specifies the block size for copying data. In this example, the block size is set to 100 bytes.
• count=1: Specifies the number of blocks to be copied. In this example, we are copying only one block.

Example output: The dd command will generate a file called random_file in the specified path, containing 100 random bytes sourced from the kernel random driver.

Use case 4: Benchmark the write performance of a disk

Code:

dd if=/dev/zero of=path/to/file_1GB bs=1024 count=1000000

Motivation: Benchmarking the write performance of a disk can help you determine its speed and efficiency. The dd command can be used to perform a write test by copying data from the /dev/zero device to a file.

Explanation:

• if=/dev/zero: Specifies the input file, which is the /dev/zero device. This device produces null bytes.
• of=path/to/file_1GB: Specifies the output file, i.e., the path where you want to create the benchmarking file.
• bs=1024: Specifies the block size for copying data. In this example, the block size is set to 1024 bytes (1 KiB).
• count=1000000: Specifies the number of blocks to be copied. In this example, we are copying 1000000 blocks, resulting in a 1 GB file.

Example output: The dd command will write 1 GB of null bytes to the specified file. The output will show the time taken to complete the write operation, which can be used to calculate the disk’s write performance.

Use case 5: Generate a system backup into an IMG file

Code:

dd if=/dev/drive_device of=path/to/file.img

Motivation: Creating system backups is crucial for protecting data and ensuring disaster recovery. The dd command can be used to generate a complete image backup of a drive, including all partitions and data.

Explanation:

• if=/dev/drive_device: Specifies the input file, which is the drive device you want to back up. The /dev/drive_device should be replaced with the correct device name.
• of=path/to/file.img: Specifies the output file, i.e., the path where you want to create the backup image file.

Example output: The dd command will create an IMG file in the specified path, containing a complete image backup of the specified drive. This backup file can be used to restore the drive or extract specific files if needed.

Use case 6: Restore a drive from an IMG file

Code:

dd if=path/to/file.img of=/dev/drive_device

Motivation: Restoring a drive from a previously created backup IMG file is essential for recovering data and system configurations. The dd command can be used to restore a drive using the data stored in the IMG file.

Explanation:

• if=path/to/file.img: Specifies the input file, which is the backup IMG file you want to restore from.
• of=/dev/drive_device: Specifies the output file, i.e., the drive device where you want to restore the backup. The /dev/drive_device should be replaced with the correct device name.

Example output: The dd command will restore the drive using the data stored in the specified IMG file. This process will overwrite any existing data on the drive, so caution should be taken when executing this command.

Conclusion:

The dd command is a versatile tool that can be used for a variety of tasks, from creating bootable USB drives to performing disk benchmarks and generating system backups. By understanding the different use cases and the arguments used in each command, you can leverage the power of dd to efficiently manage your files and drives.