117 lines
3.0 KiB
Groff
117 lines
3.0 KiB
Groff
.TH LOSETUP 8 "2003-07-01" "Linux" "MAINTENANCE COMMANDS"
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.SH NAME
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losetup \- set up and control loop devices
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.SH SYNOPSIS
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.ad l
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.B losetup
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[
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.RB [ \-e | \-E ]
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.I encryption
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] [
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.B \-o
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.I offset
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] [
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.B \-p
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.I pfd
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]
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.I loop_device file
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.br
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.B losetup
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[
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.B \-d
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]
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.I loop_device
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.ad b
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.SH DESCRIPTION
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.B losetup
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is used to associate loop devices with regular files or block devices,
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to detach loop devices and to query the status of a loop device. If only the
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\fIloop_device\fP argument is given, the status of the corresponding loop
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device is shown.
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.SS "Encryption"
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It is possible to specify transfer functions (for encryption/decryption
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or other purposes) using one of the
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.B \-E
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and
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.B \-e
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options.
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There are two mechanisms to specify the desired encryption: by number
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and by name. If an encryption is specified by number then one
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has to make sure that the Linux kernel knows about the encryption with that
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number, probably by patching the kernel. Standard numbers that are
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always present are 0 (no encryption) and 1 (XOR encryption).
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When the cryptoloop module is loaded (or compiled in), it uses number 18.
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This cryptoloop module wil take the name of an arbitrary encryption type
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and finds the module that knows how to perform that encryption.
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(Thus, either one uses a number different from 18 with the
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.B \-E
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option, or one uses a name with the
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.B \-e
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option.)
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.SH OPTIONS
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.IP \fB\-d\fP
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Detach the file or device associated with the specified loop device.
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.IP "\fB\-E \fIencryption_type\fP"
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Enable data encryption with specified number.
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.IP "\fB\-e \fIencryption_name\fP"
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Enable data encryption with specified name.
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.IP "\fB\-o \fIoffset\fP"
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The data start is moved \fIoffset\fP bytes into the specified file or
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device.
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.IP "\fB\-p \fInum\fP"
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Read the passphrase from file descriptor with number
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.I num
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instead of from the terminal.
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.SH RETURN VALUE
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.B losetup
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returns 0 on success, nonzero on failure. When
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.B losetup
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displays the status of a loop device, it returns 1 if the device
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is not configured and 2 if an error occurred which prevented
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.B losetup
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from determining the status of the device.
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.SH FILES
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.nf
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/dev/loop0, /dev/loop1, ... loop devices (major=7)
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.fi
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.SH EXAMPLE
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If you are using the loadable module you must have the module loaded
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first with the command
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.IP
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# insmod loop.o
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.LP
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Maybe also encryption modules are needed.
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.IP
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# insmod des.o
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# insmod cryptoloop.o
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.LP
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The following commands can be used as an example of using the loop device.
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.nf
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.IP
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# dd if=/dev/zero of=/file bs=1k count=100
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# losetup -e des /dev/loop0 /file
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Password:
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Init (up to 16 hex digits):
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# mkfs -t ext2 /dev/loop0 100
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# mount -t ext2 /dev/loop0 /mnt
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...
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# umount /dev/loop0
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# losetup -d /dev/loop0
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.fi
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.LP
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If you are using the loadable module you may remove the module with
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the command
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.IP
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# rmmod loop
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.LP
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.fi
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.SH RESTRICTION
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DES encryption is painfully slow. On the other hand, XOR is terribly weak.
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.\" .SH AUTHORS
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.\" .nf
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.\" Original version: Theodore Ts'o <tytso@athena.mit.edu>
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.\" Original DES by: Eric Young <eay@psych.psy.uq.oz.au>
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.\" .fi
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