.TH LOSETUP 8 "July 2003" "util-linux" "System Administration"
.SH NAME
losetup \- set up and control loop devices
.SH SYNOPSIS
.ad l
Get info:
.sp
.in +5
.B losetup
.I loopdev
.sp
.B losetup -a
.sp
.B losetup -j
.I file
.RB [ \-o
.IR offset ]
.sp
.in -5
Delete loop:
.sp
.in +5
.B "losetup \-d"
.IR loopdev ...
.sp
.in -5
Delete all used loop devices:
.sp
.in +5
.B "losetup \-D"
.sp
.in -5
Print name of first unused loop device:
.sp
.in +5
.B "losetup \-f"
.sp
.in -5
Setup loop device:
.sp
.in +5
.B losetup
.RB [{ \-e | \-E }
.IR encryption ]
.RB [ \-o
.IR offset ]
.RB [ \-\-sizelimit
.IR size ]
.in +8
.RB [ \-p
.IR pfd ]
.RB [ \-rP ]
.RB { \-f [ \-\-show ]| \fIloopdev\fP }
.I file
.sp
.in -13
Resize loop device:
.sp
.in +5
.B "losetup \-c"
.I loopdev
.in -5
.ad b
.SH DESCRIPTION
.B losetup
is used to associate loop devices with regular files or block devices,
to detach loop devices and to query the status of a loop device. If only the
\fIloopdev\fP argument is given, the status of the corresponding loop
device is shown.

.SH OPTIONS
+The \fIsize\fR and \fIoffset\fR arguments may be followed by the multiplicative
+suffixes KiB=1024, MiB=1024*1024, and so on for GiB, TiB, PiB, EiB, ZiB and YiB
+(the "iB" is optional, e.g. "K" has the same meaning as "KiB") or the suffixes
+KB=1000, MB=1000*1000, and so on for GB, PB, EB, ZB and YB.

.IP "\fB\-a, \-\-all\fP"
show status of all loop devices. Note that not all information are accessible
for non-root users.
.IP "\fB\-c, \-\-set-capacity\fP \fIloopdev\fP
force loop driver to reread size of the file associated with the specified loop device
.IP "\fB\-d, \-\-detach\fP \fIloopdev\fP..."
detach the file or device associated with the specified loop device(s)
.IP "\fB\-D, \-\-detach-all\fP"
detach all associated loop devices
.IP "\fB\-e, \-E, \-\-encryption \fIencryption_type\fP"
enable data encryption with specified name or number
.IP "\fB\-f, \-\-find\fP"
find the first unused loop device. If a
.I file
argument is present, use this device. Otherwise, print its name
.IP "\fB\-h, \-\-help\fP"
print help
.IP "\fB\-j, \-\-associated \fIfile\fP"
show status of all loop devices associated with given
.I file
.IP "\fB\-o, \-\-offset \fIoffset\fP"
the data start is moved \fIoffset\fP bytes into the specified file or
device
.IP "\fB\-\-sizelimit \fIsize\fP"
the data end is set to no more than \fIsize\fP bytes after the data start
.IP "\fB\-p, \-\-pass-fd \fInum\fP"
read the passphrase from file descriptor with number
.I num
instead of from the terminal
.IP "\fB\-P, \-\-partscan\fP"
force kernel to scan partition table on newly created loop device
.IP "\fB\-r, \-\-read-only\fP"
setup read-only loop device
.IP "\fB\-\-show\fP"
print device name if the
.I -f
option and a
.I file
argument are present.
.IP "\fB\-v, \-\-verbose\fP"
verbose mode

.SH ENCRYPTION
.B Cryptoloop is deprecated in favor of dm-crypt. For more details see
.B cryptsetup (8). It is possible that all bug reports regarding to -E/-e
.B options will be ignored.


It is possible to specify transfer functions (for encryption/decryption
or other purposes) using one of the
.B \-E
and
.B \-e
options.
There are two mechanisms to specify the desired encryption: by number
and by name. If an encryption is specified by number then one
has to make sure that the Linux kernel knows about the encryption with that
number, probably by patching the kernel. Standard numbers that are
always present are 0 (no encryption) and 1 (XOR encryption).
When the cryptoloop module is loaded (or compiled in), it uses number 18.
This cryptoloop module will take the name of an arbitrary encryption type
and find the module that knows how to perform that encryption.

.SH RETURN VALUE
.B losetup
returns 0 on success, nonzero on failure. When
.B losetup
displays the status of a loop device, it returns 1 if the device
is not configured and 2 if an error occurred which prevented
from determining the status of the device.

.SH FILES
.TP
.I /dev/loop[0..N]
loop block devices
.TP
.I /dev/loop-cotrol
loop control device

.SH EXAMPLE
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
# losetup --find --show ~/file.img
/dev/loop0
# mkfs -t ext2 /dev/loop0
# mount /dev/loop0 /mnt
 ...
# umount /dev/loop0
# losetup --detach /dev/loop0
.fi
.SH AUTHORS
Karel Zak <kzak@redhat.com>, based on 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/.