sys-utils/losetup.8

   1 .TH LOSETUP 8 "November 2015" "util-linux" "System Administration"
   2 .SH NAME
   3 losetup \- set up and control loop devices
   4 .SH SYNOPSIS
   5 .ad l
   6 Get info:
   7 .sp
   8 .in +5
   9 .B losetup
  10 [\fIloopdev\fP]
  11 .sp
  12 .B losetup \-l
  13 .RB [ \-a ]
  14 .sp
  15 .B losetup \-j
  16 .I file
  17 .RB [ \-o
  18 .IR offset ]
  19 .sp
  20 .in -5
  21 Detach a loop device:
  22 .sp
  23 .in +5
  24 .B "losetup \-d"
  25 .IR loopdev ...
  26 .sp
  27 .in -5
  28 Detach all associated loop devices:
  29 .sp
  30 .in +5
  31 .B "losetup \-D"
  32 .sp
  33 .in -5
  34 Set up a loop device:
  35 .sp
  36 .in +5
  37 .B losetup
  38 .RB [ \-o
  39 .IR offset ]
  40 .RB [ \-\-sizelimit
  41 .IR size ]
  42 .RB [ \-\-sector\-size
  43 .IR size ]
  44 .in +8
  45 .RB [ \-Pr ]
  46 .RB [ \-\-show ]  " \-f" | \fIloopdev\fP
  47 .I file
  48 .sp
  49 .in -13
  50 Resize a loop device:
  51 .sp
  52 .in +5
  53 .B "losetup \-c"
  54 .I loopdev
  55 .in -5
  56 .ad b
  57 .SH DESCRIPTION
  58 .B losetup
  59 is used to associate loop devices with regular files or block devices,
  60 to detach loop devices, and to query the status of a loop device.  If only the
  61 \fIloopdev\fP argument is given, the status of the corresponding loop
  62 device is shown.  If no option is given, all loop devices are shown.
  63 .sp
  64 Note that the old output format (i.e., \fBlosetup \-a\fR) with comma-delimited
  65 strings is deprecated in favour of the \fB\-\-list\fR output format.
  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.
  70 Use \fB\-\-nooverlap\fR with \fB\-\-find\fR during setup to avoid this problem.
  71
  72 .SH OPTIONS
  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.
  78
  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
  85 .BR \-d , " \-\-detach " \fIloopdev\fR...
  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.
  90 .TP
  91 .BR \-D , " \-\-detach\-all"
  92 Detach all associated loop devices.
  93 .TP
  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.
 100 .TP
 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
 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.
 109 .TP
 110 .BR \-o , " \-\-offset " \fIoffset
 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.
 113 .IP "\fB\-\-sizelimit \fIsize\fP"
 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.
 116 .TP
 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.
 121 .TP
 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.
 125 .TP
 126 .BR \-P , " \-\-partscan"
 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 the option \fB\-\-sector\-size\fR together with \fB\-\-partscan\fR.
 130 .TP
 131 .BR \-r , " \-\-read\-only"
 132 Set up a read-only loop device.
 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.
 138 .TP
 139 .BR \-v , " \-\-verbose"
 140 Verbose mode.
 141 .TP
 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
 152 .B \-\-output\-all
 153 Output all available columns.
 154 .TP
 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
 163 .BR \-V , " \-\-version"
 164 Display version information and exit.
 165 .TP
 166 .BR \-h , " \-\-help"
 167 Display help text and exit.
 168
 169 .SH ENCRYPTION
 170 .B Cryptoloop is no longer supported in favor of dm-crypt.
 171 .B For more details see cryptsetup(8).
 172
 173 .SH EXIT STATUS
 174 .B losetup
 175 returns 0 on success, nonzero on failure.  When
 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
 179 determining the status of the device.
 180
 181 .SH FILES
 182 .TP
 183 .I /dev/loop[0..N]
 184 loop block devices
 185 .TP
 186 .I /dev/loop-control
 187 loop control device
 188
 189 .SH ENVIRONMENT
 190 .IP LOOPDEV_DEBUG=all
 191 enables debug output.
 192 .SH EXAMPLE
 193 The following commands can be used as an example of using the loop device.
 194 .nf
 195 .IP
 196 # dd if=/dev/zero of=~/file.img bs=1024k count=10
 197 # losetup \-\-find \-\-show ~/file.img
 198 /dev/loop0
 199 # mkfs \-t ext2 /dev/loop0
 200 # mount /dev/loop0 /mnt
 201  ...
 202 # umount /dev/loop0
 203 # losetup \-\-detach /dev/loop0
 204 .fi
 205 .SH AUTHORS
 206 Karel Zak <kzak@redhat.com>, based on the original version from
 207 Theodore Ts'o <tytso@athena.mit.edu>
 208 .SH AVAILABILITY
 209 The losetup command is part of the util-linux package and is available from
 210 https://www.kernel.org/pub/linux/utils/util-linux/.