losetup - Revision history

Woozle: /* Encryption */ removed initial space so text will wrap

2010-01-12T22:46:33Z

Encryption: removed initial space so text will wrap

← Older revision		Revision as of 22:46, 12 January 2010
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	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 loop_device argument is given, the status of the corresponding loop device is shown.		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 loop_device argument is given, the status of the corresponding loop device is shown.
	===Encryption===		===Encryption===
	It is possible to specify transfer functions (for encryption/decryption or other purposes) using one of the '''-E''' and '''-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 finds the module that knows how to perform that encryption. (Thus, either one uses a number different from 18 with the '''-E''' option, or one uses a name with the '''-e''' option.)		It is possible to specify transfer functions (for encryption/decryption or other purposes) using one of the '''-E''' and '''-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 finds the module that knows how to perform that encryption. (Thus, either one uses a number different from 18 with the '''-E''' option, or one uses a name with the '''-e''' option.)

	===OPTIONS===		===OPTIONS===
	'''--delete''', '''--detach''', '''-d'''		'''--delete''', '''--detach''', '''-d'''

Woozle: moved Losetup to losetup: command name is not capitalized; this was a holdover from before I turned off the first-letter-cap flag

2010-01-12T22:42:48Z

moved Losetup to losetup: command name is not capitalized; this was a holdover from before I turned off the first-letter-cap flag

← Older revision	Revision as of 22:42, 12 January 2010
(No difference)

Woozle: template name is capitalized because Linux is capitalized

2010-01-12T22:42:13Z

template name is capitalized because Linux is capitalized

← Older revision		Revision as of 22:42, 12 January 2010
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	{{~~linux~~ shell commands\|losetup}}		{{Linux shell commands\|losetup}}
	==Documentation==		==Documentation==
	*Section: [[Linux manpages section 8\|MAINTENANCE COMMANDS (8)]]		*Section: [[Linux manpages section 8\|MAINTENANCE COMMANDS (8)]]

Woozle: post-import navbar cleanup

2005-10-14T20:03:47Z

post-import navbar cleanup

← Older revision		Revision as of 20:03, 14 October 2005
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	~~[[Category:Linux Shell Commands]]~~		{{linux shell commands\|losetup}}
	~~[[Techniques]]: [[Linux]]: [[~~losetup]]
	==Documentation==		==Documentation==
	*Section: [[Linux manpages section 8\|MAINTENANCE COMMANDS (8)]]		*Section: [[Linux manpages section 8\|MAINTENANCE COMMANDS (8)]]

Woozle at 14:59, 25 June 2005

2005-06-25T14:59:16Z

New page

[[Category:Linux Shell Commands]]
[[Techniques]]: [[Linux]]: [[losetup]]
==Documentation==
*Section: [[Linux manpages section 8|MAINTENANCE COMMANDS (8)]]
===NAME===
[[losetup]] - set up and control loop devices
===SYNOPSIS===
*Get info:
:[[losetup]] ''loop_device''
*Delete loop:
:[[losetup]] '''-d''' ''loop_device''
* Print name of first unused loop device:
:[[losetup]] '''-f'''
*Setup loop device:
:[[losetup]] [{'''-e'''|'''-E'''} ''encryption''] ['''-o''' ''offset''] ['''-p''' ''pfd''] {-f|''loop_device''} ''file''
===DESCRIPTION===
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 loop_device argument is given, the status of the corresponding loop device is shown.
===Encryption===
It is possible to specify transfer functions (for encryption/decryption or other purposes) using one of the '''-E''' and '''-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 finds the module that knows how to perform that encryption. (Thus, either one uses a number different from 18 with the '''-E''' option, or one uses a name with the '''-e''' option.)
===OPTIONS===
'''--delete''', '''--detach''', '''-d'''
:detach the file or device associated with the specified loop device.
'''-E''' ''encryption_type''
:Enable data encryption with specified number.
'''--encryption''', '''-e encryption'''
:Enable data encryption with specified name.
'''-f'''
:Find the first unused loop device. If a ''file'' argument is present, use this device. Otherwise, print its name.
'''--nohashpass''', '''-N'''
:Do not hash the password. By default, Debian systems run the password through a hash function, non-Debian systems tend not to.
'''--offset''', '''-o''' ''offset''
'''-o''' ''offset''
:The data start is moved ''offset'' bytes into the specified file or device.
'''--pass-fd''', '''-p''' ''num''
:Read the passphrase from file descriptor with number ''num'' instead of from the terminal.
'''--keybits''', '''-k''' ''num''
:set the number of bits to use in key to ''num''.
===RETURN VALUE===
losetup returns 0 on success, nonzero on failure. When 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 losetup from determining the status of the device.
===FILES===
/dev/loop0, /dev/loop1, ... loop devices (major=7)
===EXAMPLE===
If you are using the loadable module you must have the module loaded first with the command
# [[insmod]] loop.o
Maybe also encryption modules are needed.
# [[insmod]] des.o
# [[insmod]] cryptoloop.o
The following commands can be used as an example of using the loop device.
# [[dd]] if=/dev/zero of=/file bs=1k count=100
# [[losetup]] -e des /dev/loop0 /file
Password:
Init (up to 16 hex digits):
# [[mkfs]] -t ext2 /dev/loop0 100
# [[mount]] -t ext2 /dev/loop0 /mnt
...
# [[umount]] /dev/loop0
# [[losetup]] -d /dev/loop0
If you are using the loadable module you may remove the module with the command
# [[rmmod]] loop
===RESTRICTION===
DES encryption is painfully slow. On the other hand, XOR is terribly weak. Both are insecure nowadays. Some ciphers may require a licence for you to be allowed to use them.
==Edit History==
* '''2005-06-25''' Transcribed from Linux man page (Ubuntu hoary) via Konqueror man:/losetup.