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289619bd | 1 | .TH LOSETUP 8 "November 2015" "util-linux" "System Administration" |
fd6b7a7f KZ |
2 | .SH NAME |
3 | losetup \- set up and control loop devices | |
4 | .SH SYNOPSIS | |
5 | .ad l | |
d162fcb5 KZ |
6 | Get info: |
7 | .sp | |
8 | .in +5 | |
fd6b7a7f | 9 | .B losetup |
76493ceb | 10 | [\fIloopdev\fP] |
d162fcb5 | 11 | .sp |
896352d3 OO |
12 | .B losetup -l |
13 | .RB [ \-a ] | |
8b125fae | 14 | .sp |
26ea6eb1 KZ |
15 | .B losetup -j |
16 | .I file | |
17 | .RB [ \-o | |
18 | .IR offset ] | |
259fcc57 | 19 | .sp |
d162fcb5 | 20 | .in -5 |
c372860d | 21 | Detach a loop device: |
d162fcb5 KZ |
22 | .sp |
23 | .in +5 | |
24 | .B "losetup \-d" | |
f7963004 | 25 | .IR loopdev ... |
d162fcb5 KZ |
26 | .sp |
27 | .in -5 | |
f1453d52 | 28 | Detach all associated loop devices: |
34f9b684 PU |
29 | .sp |
30 | .in +5 | |
31 | .B "losetup \-D" | |
32 | .sp | |
33 | .in -5 | |
c372860d | 34 | Set up a loop device: |
d162fcb5 KZ |
35 | .sp |
36 | .in +5 | |
37 | .B losetup | |
d162fcb5 KZ |
38 | .RB [ \-o |
39 | .IR offset ] | |
7bcefc7f | 40 | .RB [ \-\-sizelimit |
ca1e1363 | 41 | .IR size ] |
76493ceb KZ |
42 | .RB [ \-\-sector\-size |
43 | .IR size ] | |
26ea6eb1 | 44 | .in +8 |
c372860d BS |
45 | .RB [ \-Pr ] |
46 | .RB [ \-\-show ] " \-f" | \fIloopdev\fP | |
d162fcb5 | 47 | .I file |
d34ac93a | 48 | .sp |
d162fcb5 | 49 | .in -13 |
c372860d | 50 | Resize a loop device: |
d34ac93a KZ |
51 | .sp |
52 | .in +5 | |
53 | .B "losetup \-c" | |
54 | .I loopdev | |
55 | .in -5 | |
fd6b7a7f KZ |
56 | .ad b |
57 | .SH DESCRIPTION | |
58 | .B losetup | |
59 | is used to associate loop devices with regular files or block devices, | |
c372860d | 60 | to detach loop devices, and to query the status of a loop device. If only the |
26ea6eb1 | 61 | \fIloopdev\fP argument is given, the status of the corresponding loop |
c372860d BS |
62 | device is shown. If no option is given, all loop devices are shown. |
63 | .sp | |
ec3624aa | 64 | Note that the old output format (i.e., \fBlosetup -a\fR) with comma-delimited |
c372860d | 65 | strings is deprecated in favour of the \fB--list\fR output format. |
9a94b634 KZ |
66 | .sp |
67 | It's possible to create more independent loop devices for the same backing | |
68 | file. | |
69 | .B This setup may be dangerous, can cause data loss, corruption and overwrites. | |
ec3624aa | 70 | Use \fB\-\-nooverlap\fR with \fB\-\-find\fR during setup to avoid this problem. |
14576644 | 71 | |
fd6b7a7f | 72 | .SH OPTIONS |
c372860d BS |
73 | The \fIsize\fR and \fIoffset\fR |
74 | arguments may be followed by the multiplicative suffixes KiB (=1024), | |
75 | MiB (=1024*1024), and so on for GiB, TiB, PiB, EiB, ZiB and YiB (the "iB" is | |
76 | optional, e.g., "K" has the same meaning as "KiB") or the suffixes | |
77 | KB (=1000), MB (=1000*1000), and so on for GB, TB, PB, EB, ZB and YB. | |
ca1e1363 | 78 | |
c372860d BS |
79 | .TP |
80 | .BR \-a , " \-\-all" | |
81 | Show the status of all loop devices. Note that not all information is accessible | |
82 | for non-root users. See also \fB\-\-list\fR. The old output format (as printed | |
83 | without \fB--list)\fR is deprecated. | |
84 | .TP | |
c372860d | 85 | .BR \-d , " \-\-detach " \fIloopdev\fR... |
60eedb0a KZ |
86 | Detach the file or device associated with the specified loop device(s). Note |
87 | that since Linux v3.7 kernel uses "lazy device destruction". The detach | |
88 | operation does not return EBUSY error anymore if device is actively used by | |
89 | system, but it is marked by autoclear flag and destroyed later. | |
c372860d | 90 | .TP |
b06c1ca6 | 91 | .BR \-D , " \-\-detach\-all" |
c372860d BS |
92 | Detach all associated loop devices. |
93 | .TP | |
ec3624aa FG |
94 | .BR \-f , " \-\-find " "\fR[\fIfile\fR]" |
95 | Find the first unused loop device. If a \fIfile\fR argument is present, use | |
96 | the found device as loop device. Otherwise, just print its name. | |
97 | .IP "\fB\-\-show\fP" | |
98 | Display the name of the assigned loop device if the \fB\-f\fP option and a | |
99 | \fIfile\fP argument are present. | |
289619bd | 100 | .TP |
9a94b634 KZ |
101 | .BR \-L , " \-\-nooverlap" |
102 | Check for conflicts between loop devices to avoid situation when the same | |
103 | backing file is shared between more loop devices. If the file is already used | |
104 | by another device then re-use the device rather than a new one. The option | |
105 | makes sense only with \fB\-\-find\fP. | |
106 | .TP | |
ec3624aa FG |
107 | .BR \-j , " \-\-associated " \fIfile\fR " \fR[\fB\-o \fIoffset\fR]" |
108 | Show the status of all loop devices associated with the given \fIfile\fR. | |
c372860d BS |
109 | .TP |
110 | .BR \-o , " \-\-offset " \fIoffset | |
784e9d9e KZ |
111 | The data start is moved \fIoffset\fP bytes into the specified file or device. The \fIoffset\fP |
112 | may be followed by the multiplicative suffixes; see above. | |
ec3624aa | 113 | .IP "\fB\-\-sizelimit \fIsize\fP" |
784e9d9e KZ |
114 | The data end is set to no more than \fIsize\fP bytes after the data start. The \fIsize\fP |
115 | may be followed by the multiplicative suffixes; see above. | |
c372860d | 116 | .TP |
76493ceb KZ |
117 | .BR \-b , " \-\-sector-size " \fIsize |
118 | Set the logical sector size of the loop device in bytes (since Linux 4.14). The | |
119 | option may be used when create a new loop device as well as stand-alone command | |
120 | to modify sector size of the already existing loop device. | |
a1a41597 | 121 | .TP |
ec3624aa FG |
122 | .BR \-c , " \-\-set\-capacity " \fIloopdev |
123 | Force the loop driver to reread the size of the file associated with the | |
124 | specified loop device. | |
c372860d BS |
125 | .TP |
126 | .BR \-P , " \-\-partscan" | |
422f0e9f KZ |
127 | Force the kernel to scan the partition table on a newly created loop device. Note that the |
128 | partition table parsing depends on sector sizes. The default is sector size is 512 bytes, | |
129 | otherwise you need to use use the option \fB\-\-sector\-size\fR together with \fB\-\-partscan\fR. | |
c372860d | 130 | .TP |
b06c1ca6 | 131 | .BR \-r , " \-\-read\-only" |
c372860d | 132 | Set up a read-only loop device. |
ec3624aa FG |
133 | .TP |
134 | .BR \-\-direct\-io [ =on | off ] | |
135 | Enable or disable direct I/O for the backing file. The optional argument | |
136 | can be either \fBon\fR or \fBoff\fR. If the argument is omitted, it defaults | |
137 | to \fBon\fR. | |
c372860d BS |
138 | .TP |
139 | .BR \-v , " \-\-verbose" | |
140 | Verbose mode. | |
141 | .TP | |
ec3624aa FG |
142 | .BR \-l , " \-\-list" |
143 | If a loop device or the \fB-a\fR option is specified, print the default columns | |
144 | for either the specified loop device or all loop devices; the default is to | |
145 | print info about all devices. See also \fB\-\-output\fP, \fB\-\-noheadings\fP, | |
146 | \fB\-\-raw\fP, and \fB\-\-json\fP. | |
147 | .TP | |
148 | .BR \-O , " \-\-output " \fIcolumn\fR[,\fIcolumn\fR]... | |
149 | Specify the columns that are to be printed for the \fB\-\-list\fP output. | |
150 | Use \fB\-\-help\fR to get a list of all supported columns. | |
151 | .TP | |
289673b1 SK |
152 | .B \-\-output\-all |
153 | Output all available columns. | |
154 | .TP | |
ec3624aa FG |
155 | .BR \-n , " \-\-noheadings" |
156 | Don't print headings for \fB\-\-list\fP output format. | |
157 | .IP "\fB\-\-raw\fP" | |
158 | Use the raw \fB\-\-list\fP output format. | |
159 | .TP | |
160 | .BR \-J , " \-\-json" | |
161 | Use JSON format for \fB\-\-list\fP output. | |
162 | .TP | |
c372860d BS |
163 | .BR \-V , " \-\-version" |
164 | Display version information and exit. | |
165 | .TP | |
166 | .BR \-h , " \-\-help" | |
167 | Display help text and exit. | |
ba3809b0 | 168 | |
23b85230 | 169 | .SH ENCRYPTION |
c372860d | 170 | .B Cryptoloop is no longer supported in favor of dm-crypt. |
5593132a | 171 | .B For more details see cryptsetup(8). |
23b85230 | 172 | |
66ee8158 KZ |
173 | .SH RETURN VALUE |
174 | .B losetup | |
c372860d | 175 | returns 0 on success, nonzero on failure. When |
66ee8158 KZ |
176 | .B losetup |
177 | displays the status of a loop device, it returns 1 if the device | |
178 | is not configured and 2 if an error occurred which prevented | |
c372860d | 179 | determining the status of the device. |
66ee8158 | 180 | |
fd6b7a7f | 181 | .SH FILES |
23b85230 KZ |
182 | .TP |
183 | .I /dev/loop[0..N] | |
184 | loop block devices | |
185 | .TP | |
0d0d12ad | 186 | .I /dev/loop-control |
23b85230 KZ |
187 | loop control device |
188 | ||
fd6b7a7f | 189 | .SH EXAMPLE |
fd6b7a7f KZ |
190 | The following commands can be used as an example of using the loop device. |
191 | .nf | |
192 | .IP | |
bda26762 | 193 | # dd if=/dev/zero of=~/file.img bs=1024k count=10 |
23b85230 KZ |
194 | # losetup --find --show ~/file.img |
195 | /dev/loop0 | |
196 | # mkfs -t ext2 /dev/loop0 | |
197 | # mount /dev/loop0 /mnt | |
fd6b7a7f | 198 | ... |
d03dd608 | 199 | # umount /dev/loop0 |
23b85230 | 200 | # losetup --detach /dev/loop0 |
fd6b7a7f | 201 | .fi |
0bf03740 KZ |
202 | .SH ENVIRONMENT |
203 | .IP LOOPDEV_DEBUG=all | |
204 | enables debug output. | |
23b85230 | 205 | .SH AUTHORS |
c372860d | 206 | Karel Zak <kzak@redhat.com>, based on the original version from |
23b85230 | 207 | Theodore Ts'o <tytso@athena.mit.edu> |
86d62711 | 208 | .SH AVAILABILITY |
601d12fb | 209 | The losetup command is part of the util-linux package and is available from |
d673b74e | 210 | https://www.kernel.org/pub/linux/utils/util-linux/. |