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.
 112 .IP "\fB\-\-sizelimit \fIsize\fP"
 113 The data end is set to no more than \fIsize\fP bytes after the data start.
 114 .TP
 115 .BR \-b , " \-\-sector-size " \fIsize
 116 Set the logical sector size of the loop device in bytes (since Linux 4.14). The
 117 option may be used when create a new loop device as well as stand-alone command
 118 to modify sector size of the already existing loop device.
 119 .TP
 120 .BR \-c , " \-\-set\-capacity " \fIloopdev
 121 Force the loop driver to reread the size of the file associated with the
 122 specified loop device.
 123 .TP
 124 .BR \-P , " \-\-partscan"
 125 Force the kernel to scan the partition table on a newly created loop device.
 126 .TP
 127 .BR \-r , " \-\-read\-only"
 128 Set up a read-only loop device.
 129 .TP
 130 .BR \-\-direct\-io [ =on | off ]
 131 Enable or disable direct I/O for the backing file.  The optional argument
 132 can be either \fBon\fR or \fBoff\fR.  If the argument is omitted, it defaults
 133 to \fBon\fR.
 134 .TP
 135 .BR \-v , " \-\-verbose"
 136 Verbose mode.
 137 .TP
 138 .BR \-l , " \-\-list"
 139 If a loop device or the \fB-a\fR option is specified, print the default columns
 140 for either the specified loop device or all loop devices; the default is to
 141 print info about all devices.  See also \fB\-\-output\fP, \fB\-\-noheadings\fP,
 142 \fB\-\-raw\fP, and \fB\-\-json\fP.
 143 .TP
 144 .BR \-O , " \-\-output " \fIcolumn\fR[,\fIcolumn\fR]...
 145 Specify the columns that are to be printed for the \fB\-\-list\fP output.
 146 Use \fB\-\-help\fR to get a list of all supported columns.
 147 .TP
 148 .BR \-n , " \-\-noheadings"
 149 Don't print headings for \fB\-\-list\fP output format.
 150 .IP "\fB\-\-raw\fP"
 151 Use the raw \fB\-\-list\fP output format.
 152 .TP
 153 .BR \-J , " \-\-json"
 154 Use JSON format for \fB\-\-list\fP output.
 155 .TP
 156 .BR \-V , " \-\-version"
 157 Display version information and exit.
 158 .TP
 159 .BR \-h , " \-\-help"
 160 Display help text and exit.
 161
 162 .SH ENCRYPTION
 163 .B Cryptoloop is no longer supported in favor of dm-crypt.
 164 .B For more details see cryptsetup(8).
 165
 166 .SH RETURN VALUE
 167 .B losetup
 168 returns 0 on success, nonzero on failure.  When
 169 .B losetup
 170 displays the status of a loop device, it returns 1 if the device
 171 is not configured and 2 if an error occurred which prevented
 172 determining the status of the device.
 173
 174 .SH FILES
 175 .TP
 176 .I /dev/loop[0..N]
 177 loop block devices
 178 .TP
 179 .I /dev/loop-control
 180 loop control device
 181
 182 .SH EXAMPLE
 183 The following commands can be used as an example of using the loop device.
 184 .nf
 185 .IP
 186 # dd if=/dev/zero of=~/file.img bs=1024k count=10
 187 # losetup --find --show ~/file.img
 188 /dev/loop0
 189 # mkfs -t ext2 /dev/loop0
 190 # mount /dev/loop0 /mnt
 191  ...
 192 # umount /dev/loop0
 193 # losetup --detach /dev/loop0
 194 .fi
 195 .SH ENVIRONMENT
 196 .IP LOOPDEV_DEBUG=all
 197 enables debug output.
 198 .SH AUTHORS
 199 Karel Zak <kzak@redhat.com>, based on the original version from
 200 Theodore Ts'o <tytso@athena.mit.edu>
 201 .SH AVAILABILITY
 202 The losetup command is part of the util-linux package and is available from
 203 https://www.kernel.org/pub/linux/utils/util-linux/.