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losetup

disk managementLinux/Unix

The losetup command is one of the most frequently used commands in Linux/Unix-like operating systems. losetup Set up and control loop devices

See Examples View Syntax

Quick Reference

Command Name:

losetup

Category:

disk management

Platform:

Linux/Unix

Basic Usage:

losetup [options] [arguments]

Common Use Cases

Syntax

losetup [options] [loopdev] [file]

Options

Option	Description
`-a, --all`	Show the status of all loop devices
`-d, --detach [loopdev...]`	Detach one or more loop devices
`-f, --find [file]`	Find the first unused loop device
`-c, --set-capacity loopdev`	Reread the size of the file associated with the loop device
`-j, --associated file`	Show loop devices associated with the given file
`-l, --list`	List information about all loop devices
`-o, --offset offset`	Start at the specified offset in the file
`--partscan`	Force the kernel to scan the partition table on the loop device
`-r, --read-only`	Set up a read-only loop device
`--show`	Display the name of the assigned loop device
`-v, --verbose`	Verbose mode
`-h, --help`	Display help information and exit
`-V, --version`	Display version information and exit

Examples

How to Use These Examples

The examples below show common ways to use the losetup command. Try them in your terminal to see the results. You can copy any example by clicking on the code block.

# Basic Examples Basic

losetup /dev/loop0 disk.img

Associate the loop device /dev/loop0 with the file disk.img.

losetup -d /dev/loop0

Detach the loop device /dev/loop0.

# Advanced Examples Advanced

losetup --find --show disk.img Find the first unused loop device and associate it with disk.img, then display the device name. losetup --offset 512 /dev/loop1 disk.img Set up a loop device with an offset of 512 bytes. losetup --partscan --find --show disk.img Set up a loop device for disk.img and scan for partitions. losetup -l List information about all loop devices. losetup -a Show the status of all loop devices. losetup -j disk.img Show loop devices associated with disk.img. losetup --read-only /dev/loop2 disk.img Set up a read-only loop device. losetup -c /dev/loop0 Update the status of a loop device after modifying the backing file.

Try It Yourself

Practice makes perfect! The best way to learn is by trying these examples on your own system with real files.

Understanding Syntax

Pay attention to the syntax coloring: commands, options, and file paths are highlighted differently.

Notes

The 'losetup' command in Linux is used to set up and control loop devices, which are special block devices that map to regular files or block devices. Loop devices make it possible to use regular files as if they were block devices, enabling operations like mounting filesystems from disk images. Key features of the losetup command: 1. Disk Image Mounting: One of the primary uses of losetup is to enable mounting of disk images (like .iso, .img, or virtual disk files) as if they were physical devices. 2. Virtual Block Devices: Loop devices create a virtual block device interface that can be used with other tools that operate on block devices, like filesystem utilities or encryption tools. 3. Partition Table Scanning: The --partscan option allows the kernel to scan for and set up partition mappings within the loop device, making individual partitions accessible. 4. Offset and Size Control: losetup can be configured to map only a portion of a file by specifying offsets and sizes, which is useful for accessing specific partitions within a disk image. 5. Device Management: The command provides options for listing, finding, and detaching loop devices, simplifying the management of multiple loop device configurations. 6. Read-Only Setup: Loop devices can be configured as read-only, preventing any modifications to the underlying file. 7. Encryption Support: In combination with cryptsetup, losetup can be used to access encrypted disk images or create encrypted containers. Common use cases for losetup include: - Mounting ISO files or disk images without burning them to physical media - Creating and managing virtual disks for testing and development - Setting up encrypted containers using files instead of partitions - Accessing individual partitions within a complete disk backup - Performing filesystem operations on images before writing them to physical media - Creating and testing filesystem images for embedded systems It's important to note that many modern Linux distributions now provide simpler tools for mounting disk images, such as the '-o loop' option with the mount command, which automatically handles the loop device setup. However, losetup remains valuable for more complex scenarios requiring specific configuration of loop devices.

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These commands are frequently used alongside losetup or serve similar purposes:

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Use Cases

Learn By Doing

The best way to learn Linux commands is by practicing. Try out these examples in your terminal to build muscle memory and understand how the losetup command works in different scenarios.

See Examples Try Lab Exercises

$ losetup

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