losetup

Set up and control loop devices that expose regular files as block devices

TLDR

List all loop devices

$ losetup -a

Attach file to loop device

$ sudo losetup /dev/loop0 /path/to/file

Attach to free device with partition scan

$ sudo losetup --show -P -f /path/to/file

Attach read-only

$ sudo losetup -r /dev/loop0 /path/to/file

Detach all loop devices

$ sudo losetup -D

Detach specific loop device

$ sudo losetup -d /dev/loop0

SYNOPSIS

losetup [OPTIONS] [loopdev] [file]

DESCRIPTION

losetup sets up and controls loop devices, which allow regular files to be accessed as block devices. This is commonly used for mounting disk images, ISO files, or encrypted containers.

PARAMETERS

-a, --all

Show status of all attached loop devices.

-f, --find

Find the first unused loop device. With no other arguments, print its name; with a backing file, attach the file to it.

-P, --partscan

Force the kernel to scan the partition table on the newly created loop device.

-r, --read-only

Set up a read-only loop device.

-d, --detach loopdev

Detach the specified loop device.

-D, --detach-all

Detach all currently attached loop devices.

-j, --associated file

Show loop devices associated with file.

--show

Print the assigned device name (useful together with -f).

-o, --offset bytes

Start the loop device at bytes offset into the backing file.

--sizelimit bytes

Limit the loop device to bytes starting at offset.

-b, --sector-size bytes

Set the logical sector size (512, 1024, 2048, or 4096).

--direct-io[=on|off]

Enable or disable kernel direct I/O on the backing file.

-c, --set-capacity loopdev

Force the kernel to reread the size of the backing file.

-L, --nooverlap

Fail if any existing loop device already covers the same byte range of the backing file.

-O, --output columns

Specify which columns to print (use `--list --output list` to see available).

-l, --list

Use a listing format similar to `losetup -a` but with extra columns.

-J, --json

Output as JSON (use with --list).

--help

Display help information.

CAVEATS

Loop devices require root privileges to create and detach. The kernel has a limited number of loop devices available (configurable). Always detach loop devices when finished to free resources.

HISTORY

losetup is part of the util-linux package, providing loop device management on Linux systems.