-.TH LOSETUP 8 "July 2014" "util-linux" "System Administration"
+.TH LOSETUP 8 "November 2015" "util-linux" "System Administration"
.SH NAME
losetup \- set up and control loop devices
.SH SYNOPSIS
.sp
.in +5
.B losetup
-.I loopdev
+[\fIloopdev\fP]
.sp
.B losetup -l
.RB [ \-a ]
.B "losetup \-D"
.sp
.in -5
-Print the name of the first unused loop device:
-.sp
-.in +5
-.B "losetup \-f"
-.sp
-.in -5
Set up a loop device:
.sp
.in +5
.IR offset ]
.RB [ \-\-sizelimit
.IR size ]
+.RB [ \-\-sector\-size
+.IR size ]
.in +8
.RB [ \-Pr ]
.RB [ \-\-show ] " \-f" | \fIloopdev\fP
\fIloopdev\fP argument is given, the status of the corresponding loop
device is shown. If no option is given, all loop devices are shown.
.sp
-Note that the old output format (i.e. \fBlosetup -a\fR) with comma-delimited
+Note that the old output format (i.e., \fBlosetup -a\fR) with comma-delimited
strings is deprecated in favour of the \fB--list\fR output format.
+.sp
+It's possible to create more independent loop devices for the same backing
+file.
+.B This setup may be dangerous, can cause data loss, corruption and overwrites.
+Use \fB\-\-nooverlap\fR with \fB\-\-find\fR during setup to avoid this problem.
.SH OPTIONS
The \fIsize\fR and \fIoffset\fR
for non-root users. See also \fB\-\-list\fR. The old output format (as printed
without \fB--list)\fR is deprecated.
.TP
-.BR \-c , " \-\-set-capacity " \fIloopdev
-Force the loop driver to reread the size of the file associated with the
-specified loop device.
-.TP
.BR \-d , " \-\-detach " \fIloopdev\fR...
-Detach the file or device associated with the specified loop device(s).
+Detach the file or device associated with the specified loop device(s). Note
+that since Linux v3.7 kernel uses "lazy device destruction". The detach
+operation does not return EBUSY error anymore if device is actively used by
+system, but it is marked by autoclear flag and destroyed later.
.TP
-.BR \-D , " \-\-detach-all"
+.BR \-D , " \-\-detach\-all"
Detach all associated loop devices.
.TP
-.BR \-f , " \-\-find"
-Find the first unused loop device. If a
-.I file
-argument is present, use the found device as loop device.
-Otherwise, just print its name.
-.IP "\fB\-j, \-\-associated \fIfile\fP"
-Show the status of all loop devices associated with the given
-.IR file .
+.BR \-f , " \-\-find " "\fR[\fIfile\fR]"
+Find the first unused loop device. If a \fIfile\fR argument is present, use
+the found device as loop device. Otherwise, just print its name.
+.IP "\fB\-\-show\fP"
+Display the name of the assigned loop device if the \fB\-f\fP option and a
+\fIfile\fP argument are present.
.TP
-.BR \-l , " \-\-list"
-If a loop device or the \fB-a\fR option is specified, print the default columns
-for either the specified loop device or all loop devices; the default is to
-print info about all devices. See also \fB\-\-output\fP, \fB\-\-noheadings\fP
-and \fB\-\-raw\fP.
+.BR \-L , " \-\-nooverlap"
+Check for conflicts between loop devices to avoid situation when the same
+backing file is shared between more loop devices. If the file is already used
+by another device then re-use the device rather than a new one. The option
+makes sense only with \fB\-\-find\fP.
.TP
-.BR \-n , " \-\-noheadings"
-Don't print headings for \fB\-\-list\fP output format.
+.BR \-j , " \-\-associated " \fIfile\fR " \fR[\fB\-o \fIoffset\fR]"
+Show the status of all loop devices associated with the given \fIfile\fR.
.TP
.BR \-o , " \-\-offset " \fIoffset
-The data start is moved \fIoffset\fP bytes into the specified file or device.
+The data start is moved \fIoffset\fP bytes into the specified file or device. The \fIoffset\fP
+may be followed by the multiplicative suffixes; see above.
+.IP "\fB\-\-sizelimit \fIsize\fP"
+The data end is set to no more than \fIsize\fP bytes after the data start. The \fIsize\fP
+may be followed by the multiplicative suffixes; see above.
.TP
-.BR \-O , " \-\-output " \fIcolumns
-Specify the columns that are to be printed for the \fB\-\-list\fP output.
+.BR \-b , " \-\-sector-size " \fIsize
+Set the logical sector size of the loop device in bytes (since Linux 4.14). The
+option may be used when create a new loop device as well as stand-alone command
+to modify sector size of the already existing loop device.
+.TP
+.BR \-c , " \-\-set\-capacity " \fIloopdev
+Force the loop driver to reread the size of the file associated with the
+specified loop device.
.TP
.BR \-P , " \-\-partscan"
Force the kernel to scan the partition table on a newly created loop device.
-.IP "\fB\-\-raw\fP"
-Use the raw \fB\-\-list\fP output format.
.TP
-.BR \-r , " \-\-read-only"
+.BR \-r , " \-\-read\-only"
Set up a read-only loop device.
-.IP "\fB\-\-sizelimit \fIsize\fP"
-The data end is set to no more than \fIsize\fP bytes after the data start.
-.IP "\fB\-\-show\fP"
-Display the name of the assigned loop device if the
-.B \-f
-option and a
-.I file
-argument are present.
+.TP
+.BR \-\-direct\-io [ =on | off ]
+Enable or disable direct I/O for the backing file. The optional argument
+can be either \fBon\fR or \fBoff\fR. If the argument is omitted, it defaults
+to \fBon\fR.
.TP
.BR \-v , " \-\-verbose"
Verbose mode.
.TP
+.BR \-l , " \-\-list"
+If a loop device or the \fB-a\fR option is specified, print the default columns
+for either the specified loop device or all loop devices; the default is to
+print info about all devices. See also \fB\-\-output\fP, \fB\-\-noheadings\fP,
+\fB\-\-raw\fP, and \fB\-\-json\fP.
+.TP
+.BR \-O , " \-\-output " \fIcolumn\fR[,\fIcolumn\fR]...
+Specify the columns that are to be printed for the \fB\-\-list\fP output.
+Use \fB\-\-help\fR to get a list of all supported columns.
+.TP
+.B \-\-output\-all
+Output all available columns.
+.TP
+.BR \-n , " \-\-noheadings"
+Don't print headings for \fB\-\-list\fP output format.
+.IP "\fB\-\-raw\fP"
+Use the raw \fB\-\-list\fP output format.
+.TP
+.BR \-J , " \-\-json"
+Use JSON format for \fB\-\-list\fP output.
+.TP
.BR \-V , " \-\-version"
Display version information and exit.
.TP
.SH ENCRYPTION
.B Cryptoloop is no longer supported in favor of dm-crypt.
-.B For more details see cryptsetup (8).
+.B For more details see cryptsetup(8).
.SH RETURN VALUE
.B losetup
The following commands can be used as an example of using the loop device.
.nf
.IP
-# dd if=/dev/zero of=~/file.img bs=1MiB count=10
+# dd if=/dev/zero of=~/file.img bs=1024k count=10
# losetup --find --show ~/file.img
/dev/loop0
# mkfs -t ext2 /dev/loop0
# umount /dev/loop0
# losetup --detach /dev/loop0
.fi
+.SH ENVIRONMENT
+.IP LOOPDEV_DEBUG=all
+enables debug output.
.SH AUTHORS
Karel Zak <kzak@redhat.com>, based on the original version from
Theodore Ts'o <tytso@athena.mit.edu>
.SH AVAILABILITY
The losetup command is part of the util-linux package and is available from
-ftp://ftp.kernel.org/pub/linux/utils/util-linux/.
+https://www.kernel.org/pub/linux/utils/util-linux/.
projects / thirdparty / util-linux.git / blobdiff