# losetup

## NAME



           losetup - set up and control loop devices
    


## SYNOPSIS



           Get info:
    
           **losetup**[_loopdev_]
    
           **losetup -l**[**-a**]
    
           **losetup -j** _file_ [**-o** _offset_]
    
           Detach a loop device:
    
           **losetup -d** _loopdev_ ...
    
           Detach all associated loop devices:
    
           **losetup -D**
    
           Set up a loop device:
    
           **losetup**[**-o** _offset_] [**--sizelimit** _size_] [**--sector-size** _size_]
           [**--loop-ref** _name_] [**-Pr**] [**--show**] **-f** |_loopdev file_
    
           Resize a loop device:
    
           **losetup -c** _loopdev_
    


## DESCRIPTION



           **losetup** is used to associate loop devices with regular files or
           block devices, to detach loop devices, and to query the status of
           a loop device. If only the _loopdev_ argument is given, the status
           of the corresponding loop device is shown. If no option is given,
           all loop devices are shown.
    
           Note that the old output format (i.e., **losetup -a**) with
           comma-delimited strings is deprecated in favour of the **--list**
           output format.
    
           It is possible to create multiple independent loop devices for the
           same backing file. **This setup may be dangerous, can cause data**
           **loss, corruption, and overwrites.** Use **--nooverlap** with **--find**
           during setup to avoid this problem.
    
           The loop device setup is not an atomic operation when used with
           **--find** , and **losetup** does not protect this operation by any lock.
           The number of attempts is internally restricted to a maximum of
           16. It is recommended to use for example flock(1) to avoid a
           collision in heavily parallel use cases.
    


## OPTIONS



           The _size_ and _offset_ arguments may be followed by the
           multiplicative suffixes KiB (=1024), MiB (=1024*1024), and so on
           for GiB, TiB, PiB, EiB, ZiB and YiB (the "iB" is optional, e.g.,
           "K" has the same meaning as "KiB") or the suffixes KB (=1000), MB
           (=1000*1000), and so on for GB, TB, PB, EB, ZB and YB.
    
           **-a** , **--all**
               Show the status of all loop devices. Note that not all
               information is accessible for non-root users. See also **--list**.
               The old output format (as printed without **--list**) is
               deprecated.
    
           **-d** , **--detach** _loopdev_...
               Detach the file or device associated with the specified loop
               device(s). Note that since Linux v3.7 kernel uses "lazy device
               destruction". The detach operation does not return **EBUSY** error
               anymore if device is actively used by system, but it is marked
               by autoclear flag and destroyed later. Even if the device is
               not used, the loop device can be destroyed later. If you need
               to wait for a complete removal of the loop device, call
               **udevadm settle** after **losetup**.
    
           **-D** , **--detach-all**
               Detach all associated loop devices.
    
           **-f** , **--find**[_file_]
               Find the first unused loop device. If a _file_ argument is
               present, use the found device as loop device. Otherwise, just
               print its name.
    
           **--show**
               Display the name of the assigned loop device if the **-f** option
               and a _file_ argument are present.
    
           **-L** , **--nooverlap**
               Check for conflicts between loop devices to avoid situation
               when the same backing file is shared between more loop
               devices. If the file is already used by another device then
               re-use the device rather than a new one. The option makes
               sense only with **--find**.
    
           **-j** , **--associated** _file_ [**-o** _offset_]
               Show the status of all loop devices associated with the given
               _file_.
    
           **-o** , **--offset** _offset_
               The data start is moved _offset_ bytes into the specified file
               or device. The _offset_ may be followed by the multiplicative
               suffixes; see above.
    
           **--loop-ref** _string_
               Set the reference string. The backwardly compatible default is
               to use the backing filename as a reference in the loop setup
               ioctl (aka lo_file_name). This option overrides this default
               behavior and sets the reference to the _string_. The reference
               may be used by udevd in /dev/loop/by-ref. The Linux kernel
               does not use the reference at all, but it could be used by
               some old utils that cannot read the backing file from sysfs.
               The reference is readable only for the root user (see **--output**
               +REF) and it is restricted to 64 bytes.
    
           **--sizelimit** _size_
               The data end is set to no more than _size_ bytes after the data
               start. The _size_ may be followed by the multiplicative
               suffixes; see above.
    
           **-b** , **--sector-size** _size_
               Set the logical sector size of the loop device in bytes (since
               Linux 4.14). The option may be used when creating a new loop
               device as well as a stand-alone command to modify sector size
               of the already existing loop device.
    
           **-c** , **--set-capacity** _loopdev_
               Force the loop driver to reread the size of the file
               associated with the specified loop device.
    
           **-P** , **--partscan**
               Force the kernel to scan the partition table on a newly
               created loop device. Note that the partition table parsing
               depends on sector sizes. The default is sector size is 512
               bytes, otherwise you need to use the option **--sector-size**
               together with **--partscan**.
    
           **-r** , **--read-only**
               Set up a read-only loop device.
    
           **--direct-io**[**=on** |**off**]
               Enable or disable direct I/O for the backing file. The default
               is **off**. Specifying either **--direct-io** or **--direct-io=on** will
               enable it. But, **--direct-io=off** can be provided to explicitly
               turn it off.
    
           **-v** , **--verbose**
               Verbose mode.
    
           **-l** , **--list**
               If a loop device or the **-a** option is specified, print the
               default columns for either the specified loop device or all
               loop devices; the default is to print info about all devices.
               See also **--output** , **--noheadings** , **--raw** , and **--json**.
    
           **-O** , **--output** _column_[,_column_]...
               Specify the columns that are to be printed for the **--list**
               output. Use **--help** to get a list of all supported columns.
    
           **--output-all**
               Output all available columns.
    
           **-n** , **--noheadings**
               Don’t print headings for **--list** output format.
    
           **--raw**
               Use the raw **--list** output format.
    
           **-J** , **--json**
               Use JSON format for **--list** output.
    
           **-h** , **--help**
               Display help text and exit.
    
           **-V** , **--version**
               Display version and exit.
    


## ENCRYPTION



           **Cryptoloop is no longer supported in favor of dm-crypt.** For more
           details see cryptsetup(8).
    


## EXIT STATUS



           **losetup** returns 0 on success, nonzero on failure. When **losetup**
           displays the status of a loop device, it returns 1 if the device
           is not configured and 2 if an error occurred which prevented
           determining the status of the device.
    


## NOTES



           Since version 2.37 **losetup** uses **LOOP_CONFIGURE** ioctl to setup a
           new loop device by one ioctl call. The old versions use
           **LOOP_SET_FD** and **LOOP_SET_STATUS64** ioctls to do the same.
    


## ENVIRONMENT



           **LOOPDEV_DEBUG** =all
               enables debug output.
    


## FILES



           _/dev/loop[0..N]_
               loop block devices
    
           _/dev/loop-control_
               loop control device
    


## EXAMPLE



           The following commands can be used as an example of using the loop
           device.
    
               # dd if=/dev/zero of=~/file.img bs=1024k count=10
               # losetup --find --show ~/file.img
               /dev/loop0
               # mkfs -t ext2 /dev/loop0
               # mount /dev/loop0 /mnt
               ...
               # umount /dev/loop0
               # losetup --detach /dev/loop0
    


## AVAILABILITY



           The **losetup** command is part of the util-linux package which can be
           downloaded from Linux Kernel Archive
           <https://www.kernel.org/pub/linux/utils/util-linux/>. This page is
           part of the _util-linux_ (a random collection of Linux utilities)
           project. Information about the project can be found at 
           ⟨https://www.kernel.org/pub/linux/utils/util-linux/⟩. If you have a
           bug report for this manual page, send it to
           util-linux@vger.kernel.org. This page was obtained from the
           project's upstream Git repository
           ⟨git://git.kernel.org/pub/scm/utils/util-linux/util-linux.git⟩ on
           2025-08-11. (At that time, the date of the most recent commit that
           was found in the repository was 2025-08-05.) If you discover any
           rendering problems in this HTML version of the page, or you
           believe there is a better or more up-to-date source for the page,
           or you have corrections or improvements to the information in this
           COLOPHON (which is _not_ part of the original manual page), send a
           mail to man-pages@man7.org
    
    util-linux 2.42-start-521-ec46  2025-08-09                     _LOSETUP_(8)
    


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