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

The kpartx command is a powerful utility used to create device maps from partition tables. This is particularly useful in scenarios where disk images, which contain multiple partitions, need to be individually accessed and manipulated. The command can perform several functions such as adding, deleting, and listing partitions from these disk images, thereby providing granular control over the memory mapping of each partition to a device node.

Add partition mappings

Code:

kpartx -a whole_disk.img

Motivation:

The primary motivation for using the kpartx -a command is when you have a disk image file (for example, whole_disk.img) that contains multiple partitions and you need to access or modify each partition separately. This is often necessary in environments where direct manipulation of individual partitions within a disk image is required, such as system recovery, forensic analysis, or virtual machine setup.

Explanation:

• kpartx: This is the command that initiates the operation of creating device maps from partition tables.
• -a: This argument tells kpartx to add partition mappings for all partitions found within the specified disk image.
• whole_disk.img: This is the path to the disk image file which contains the partition table that you wish to map.

Example Output:

add map loop0p1 (254:0): 0 204800 linear 7:10 2048
add map loop0p2 (254:1): 0 307200 linear 7:10 206848

This output indicates that two partitions have been mapped from the whole_disk.img file, with device nodes loop0p1 and loop0p2 now available for further operations.

Delete partition mappings

Code:

kpartx -d whole_disk.img

Motivation:

The need to use the kpartx -d command arises when you are done with operations on the partition device nodes and wish to clean up by removing the mappings. This can help prevent confusion or accidental manipulation of device nodes no longer needed and can also be useful for system resource management, especially in environments that dynamically create and destroy disk images.

Explanation:

• kpartx: The command used for device map manipulation.
• -d: This option stands for “delete,” instructing kpartx to remove partition mappings created from the specified disk image.
• whole_disk.img: Refers to the disk image from which partition mappings should be deleted.

Example Output:

loop deleted : /dev/loop0

The output confirms the deletion of device mappings associated with the specified disk image, indicating that /dev/loop0 and its associated partitions have been successfully removed.

List partition mappings

Code:

kpartx -l whole_disk.img

Motivation:

Utilizing the kpartx -l command is crucial when you need an overview of the partitions present within a disk image. This is particularly useful for preliminary analysis before performing operations on specific partitions, and ensures that you correctly identify the partition layout and corresponding device mappings.

Explanation:

• kpartx: The main command invoking the partition table manipulation utilities.
• -l: Represents “list,” used to display existing partition mappings without making any changes to them.
• whole_disk.img: Specifies the disk image whose partition mappings you wish to list.

Example Output:

loop0p1 : 0 204800 /dev/loop0 2048
loop0p2 : 0 307200 /dev/loop0 206848

This output lists the partition mappings, showing device nodes like loop0p1 and loop0p2, as well as the blocks they represent, which provides clarity on the partition setup within the disk image.

Conclusion

The kpartx command is an essential tool for accessing and managing partitions within a disk image. By understanding how to add, delete, and list these mappings, users can perform intricate disk operations efficiently, doing so in a manner that helps to maintain system stability and resource management. Each of these use cases highlights the flexibility and control offered by kpartx, and underscores its importance in scenarios involving complex disk image management tasks.