Usage:
 losetup [options] [<loopdev>]
 losetup [options] -f | <loopdev> <file>

Set up and control loop devices.

Options:
 -a, --all                     list all used devices
 -d, --detach <loopdev>...     detach one or more devices
 -D, --detach-all              detach all used devices
 -f, --find                    find first unused device
 -c, --set-capacity <loopdev>  resize the device
 -j, --associated <file>       list all devices associated with <file>
 -L, --nooverlap               avoid possible conflict between devices
     --remove <loopdev>...     remove one or more devices

 -o, --offset <num>            start at offset <num> into file
     --sizelimit <num>         device is limited to <num> bytes of the file
 -b, --sector-size <num>       set the logical sector size to <num>
 -P, --partscan                create a partitioned loop device
 -r, --read-only               set up a read-only loop device
     --direct-io[=<on|off>]    open backing file with O_DIRECT
     --loop-ref <string>       loop device reference
     --show                    print device name after setup (with -f)

 -J, --json                    use JSON --list output format
 -l, --list                    list info about all or specified (default)
 -n, --noheadings              don't print headings for --list output
 -O, --output <cols>           specify columns to output for --list
     --output-all              output all columns
     --raw                     use raw --list output format

 -h, --help                    display this help
 -V, --version                 display version

Available output columns:
         NAME  loop device name
    AUTOCLEAR  autoclear flag set
    BACK-FILE  device backing file
     BACK-INO  backing file inode number
 BACK-MAJ:MIN  backing file major:minor device number
     BACK-MAJ  backing file major device number
     BACK-MIN  backing file minor device number
      MAJ:MIN  loop device major:minor number
          MAJ  loop device major number
          MIN  loop device minor number
       OFFSET  offset from the beginning
     PARTSCAN  partscan flag set
          REF  loop device reference string
           RO  read-only device
    SIZELIMIT  size limit of the file in bytes
          DIO  access backing file with direct-io
      LOG-SEC  logical sector size in bytes

For more details see losetup(8).