1LOSETUP(8) System Administration LOSETUP(8)
2
6 losetup - set up and control loop devices
7
9 Get info:
10 losetup [loopdev]
12 losetup -l [-a]
14 losetup -j file [-o offset]
16 Detach a loop device:
18 losetup -d loopdev...
20 Detach all associated loop devices:
22 losetup -D
24 Set up a loop device:
26 losetup [-o offset] [--sizelimit size] [--sector-size size]
28 [-Pr] [--show] -f|loopdev file
29 Resize a loop device:
31 losetup -c loopdev
33
35 losetup is used to associate loop devices with regular files or block
36 devices, to detach loop devices, and to query the status of a loop
37 device. If only the loopdev argument is given, the status of the cor‐
38 responding loop device is shown. If no option is given, all loop
39 devices are shown.
40 Note that the old output format (i.e., losetup -a) with comma-delimited
42 strings is deprecated in favour of the --list output format.
43 It's possible to create more independent loop devices for the same
45 backing file. This setup may be dangerous, can cause data loss, cor‐
46 ruption and overwrites. Use --nooverlap with --find during setup to
47 avoid this problem.
48
51 The size and offset arguments may be followed by the multiplicative
52 suffixes KiB (=1024), MiB (=1024*1024), and so on for GiB, TiB, PiB,
53 EiB, ZiB and YiB (the "iB" is optional, e.g., "K" has the same meaning
54 as "KiB") or the suffixes KB (=1000), MB (=1000*1000), and so on for
55 GB, TB, PB, EB, ZB and YB.
56 -a, --all
59 Show the status of all loop devices. Note that not all informa‐
60 tion is accessible for non-root users. See also --list. The
61 old output format (as printed without --list) is deprecated.
62 -d, --detach loopdev...
64 Detach the file or device associated with the specified loop
65 device(s). Note that since Linux v3.7 kernel uses "lazy device
66 destruction". The detach operation does not return EBUSY error
67 anymore if device is actively used by system, but it is marked
68 by autoclear flag and destroyed later.
69 -D, --detach-all
71 Detach all associated loop devices.
72 -f, --find [file]
74 Find the first unused loop device. If a file argument is
75 present, use the found device as loop device. Otherwise, just
76 print its name.
77 --show Display the name of the assigned loop device if the -f option
79 and a file argument are present.
80 -L, --nooverlap
82 Check for conflicts between loop devices to avoid situation when
83 the same backing file is shared between more loop devices. If
84 the file is already used by another device then re-use the
85 device rather than a new one. The option makes sense only with
86 --find.
87 -j, --associated file [-o offset]
89 Show the status of all loop devices associated with the given
90 file.
91 -o, --offset offset
93 The data start is moved offset bytes into the specified file or
94 device. The offset may be followed by the multiplicative suf‐
95 fixes; see above.
96 --sizelimit size
98 The data end is set to no more than size bytes after the data
99 start. The size may be followed by the multiplicative suffixes;
100 see above.
101 -b, --sector-size size
103 Set the logical sector size of the loop device in bytes (since
104 Linux 4.14). The option may be used when create a new loop
105 device as well as stand-alone command to modify sector size of
106 the already existing loop device.
107 -c, --set-capacity loopdev
109 Force the loop driver to reread the size of the file associated
110 with the specified loop device.
111 -P, --partscan
113 Force the kernel to scan the partition table on a newly created
114 loop device.
115 -r, --read-only
117 Set up a read-only loop device.
118 --direct-io[=on|off]
120 Enable or disable direct I/O for the backing file. The optional
121 argument can be either on or off. If the argument is omitted,
122 it defaults to on.
123 -v, --verbose
125 Verbose mode.
126 -l, --list
128 If a loop device or the -a option is specified, print the
129 default columns for either the specified loop device or all loop
130 devices; the default is to print info about all devices. See
131 also --output, --noheadings, --raw, and --json.
132 -O, --output column[,column]...
134 Specify the columns that are to be printed for the --list out‐
135 put. Use --help to get a list of all supported columns.
136 --output-all
138 Output all available columns.
139 -n, --noheadings
141 Don't print headings for --list output format.
142 --raw Use the raw --list output format.
144 -J, --json
146 Use JSON format for --list output.
147 -V, --version
149 Display version information and exit.
150 -h, --help
152 Display help text and exit.
153
156 Cryptoloop is no longer supported in favor of dm-crypt. For more
157 details see cryptsetup(8).
158
161 losetup returns 0 on success, nonzero on failure. When losetup dis‐
162 plays the status of a loop device, it returns 1 if the device is not
163 configured and 2 if an error occurred which prevented determining the
164 status of the device.
165
168 /dev/loop[0..N]
169 loop block devices
170 /dev/loop-control
172 loop control device
173
176 The following commands can be used as an example of using the loop
177 device.
178 # dd if=/dev/zero of=~/file.img bs=1024k count=10
180 # losetup --find --show ~/file.img
181 /dev/loop0
182 # mkfs -t ext2 /dev/loop0
183 # mount /dev/loop0 /mnt
184 ...
185 # umount /dev/loop0
186 # losetup --detach /dev/loop0
187
189 LOOPDEV_DEBUG=all
190 enables debug output.
191
193 Karel Zak <kzak@redhat.com>, based on the original version from
194 Theodore Ts'o <tytso@athena.mit.edu>
195
197 The losetup command is part of the util-linux package and is available
198 from https://www.kernel.org/pub/linux/utils/util-linux/.
199util-linux November 2015 LOSETUP(8)