DVD md5sum - Revision history

Rwh: /* The Easiest way to test if an ISO has been correctly backed up is as follows: */

2011-08-19T17:29:36Z

The Easiest way to test if an ISO has been correctly backed up is as follows:

← Older revision		Revision as of 13:29, 19 August 2011
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	4660920320 bytes (4.7 GB) copiedcmp: '''EOF on ISOFILENAME.ISO'''		4660920320 bytes (4.7 GB) copiedcmp: '''EOF on ISOFILENAME.ISO'''

	''~~{because and~~ EOF on the ISO Image is specified, this output indicates that for all bytes read, the file is equal (Bytes in and out are the same for the full size of the ISO Image!) and that the only error that occured was that the End of the ISO file was reached before the end of the CD/DVD, which is usually irrelevant as we try to test accuracy of the burned image against a ISO Image. The reason for the EOF is that the written medium may exceed the ISO filesize (I assume this is padding/information for ISO, UDF and other extensions. I did not go into this as I am a Greenhorn myself). This example illiminates the use of md5sum command in which a file size in bytes must be provided to ensure that the bytes compared are the exact length of the ISO image which we are comparing to). In the CMP command case, size is not required as the comparison will end as soon as either the CD/DVD or ISO file have reached their end or an difference was encountered, whichever takes place 1st. '''''If the ISO and CD/DVD differ''''', the result will tell you so by specifying - '''differ: char xxx, line xxx''' The advantage above md5sum is that the test will end immediately on determining an error which illiminates waiting until the very end should an error exist!'' md5sum does have its advantages but in this case the "cmp" command wins.		''Because an EOF on the ISO Image is specified, this output indicates that for all bytes read, the file is equal (Bytes in and out are the same for the full size of the ISO Image!) and that the only error that occured was that the End of the ISO file was reached before the end of the CD/DVD, which is usually irrelevant as we try to test accuracy of the burned image against a ISO Image. The reason for the EOF is that the written medium may exceed the ISO filesize (I assume this is padding/information for ISO, UDF and other extensions. I did not go into this as I am a Greenhorn myself). This example illiminates the use of md5sum command in which a file size in bytes must be provided to ensure that the bytes compared are the exact length of the ISO image which we are comparing to). In the CMP command case, size is not required as the comparison will end as soon as either the CD/DVD or ISO file have reached their end or an difference was encountered, whichever takes place 1st. '''''If the ISO and CD/DVD differ''''', the result will tell you so by specifying - '''differ: char xxx, line xxx''' The advantage above md5sum is that the test will end immediately on determining an error which illiminates waiting until the very end should an error exist!''. The '''md5sum''' utility does have its advantages but in this case the "cmp" command wins.

	= External links =		= External links =

	* [http://linux.die.net/man/1/md5sum md5sum man page]		* [http://linux.die.net/man/1/md5sum md5sum man page]

Rwh: /* Examples */

2011-01-22T02:27:38Z

Examples

← Older revision		Revision as of 22:27, 21 January 2011
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	$ md5sum tmp.iso		$ md5sum tmp.iso

	= ~~Examples~~ =		= Example DVD md5sum Calculations =
	You can use the -c option to md5sum to check the files against the md5sum file as below.		You can use the -c option to md5sum to check the files against the md5sum file as below.
	$ md5sum -c md5sum.txt		$ md5sum -c md5sum.txt
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	So for example:		So for example:
	$ dd if=/dev/dvd \| head --bytes=3621957632 \| md5sum		$ dd if=/dev/dvd \| head --bytes=3621957632 \| md5sum


	= The Easiest way to test if an ISO has been correctly backed up is as follows: =		= The Easiest way to test if an ISO has been correctly backed up is as follows: =

Rwh: /* Overview */

2011-01-22T02:23:06Z

Overview

← Older revision		Revision as of 22:23, 21 January 2011
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	This page was derived from: [http://wiki.linuxquestions.org/wiki/Md5sum LQWiki: Md5sum]		This page was derived from: [http://wiki.linuxquestions.org/wiki/Md5sum LQWiki: Md5sum]

	'''md5sum''' is a program for verifying that contents of a file have been exactly reproduced without having access to the original file. It is often used for large files like [[ISO]] images that must be verified before they are used. A large number called the MD5 checksum (MD5sum) is calculated from the file's contents in a reproducible way that, with extremely high probability, will never produce the same MD5sum for different files. The user compares the MD5sum of the downloaded file to that obtained separately from the original source.		'''md5sum''' is a program for verifying that contents of a file have been exactly reproduced without having access to the original file. It is often used for large files like '''ISO''' images that must be verified before they are used. A large number called the MD5 checksum (MD5sum) is calculated from the file's contents in a reproducible way that, with extremely high probability, will never produce the same MD5sum for different files. The user compares the MD5sum of the downloaded file to that obtained separately from the original source.

	The algorithm is designed to make it difficult to tamper with the file while still producing the same MD5sum for the tampered file. If two instances of a file have the same MD5sum, the user is assured that the instances are identical. If one is the official version, so is the other.		The algorithm is designed to make it difficult to tamper with the file while still producing the same MD5sum for the tampered file. If two instances of a file have the same MD5sum, the user is assured that the instances are identical. If one is the official version, so is the other.

Rwh: /* Overview */

2011-01-22T02:22:39Z

Overview

← Older revision		Revision as of 22:22, 21 January 2011
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	= Overview =		= Overview =

	This page was ~~copied~~ from: [http://wiki.linuxquestions.org/wiki/Md5sum LQWiki: Md5sum]		This page was derived from: [http://wiki.linuxquestions.org/wiki/Md5sum LQWiki: Md5sum]

	'''md5sum''' is a program for verifying that contents of a file have been exactly reproduced without having access to the original file. It is often used for large files like [[ISO]] images that must be verified before they are used. A large number called the MD5 checksum (MD5sum) is calculated from the file's contents in a reproducible way that, with extremely high probability, will never produce the same MD5sum for different files. The user compares the MD5sum of the downloaded file to that obtained separately from the original source.		'''md5sum''' is a program for verifying that contents of a file have been exactly reproduced without having access to the original file. It is often used for large files like [[ISO]] images that must be verified before they are used. A large number called the MD5 checksum (MD5sum) is calculated from the file's contents in a reproducible way that, with extremely high probability, will never produce the same MD5sum for different files. The user compares the MD5sum of the downloaded file to that obtained separately from the original source.

Rwh: /* Overview */

2011-01-22T02:21:10Z

Overview

← Older revision		Revision as of 22:21, 21 January 2011
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	= Overview =		= Overview =

			This page was copied from: [http://wiki.linuxquestions.org/wiki/Md5sum LQWiki: Md5sum]

	'''md5sum''' is a program for verifying that contents of a file have been exactly reproduced without having access to the original file. It is often used for large files like [[ISO]] images that must be verified before they are used. A large number called the MD5 checksum (MD5sum) is calculated from the file's contents in a reproducible way that, with extremely high probability, will never produce the same MD5sum for different files. The user compares the MD5sum of the downloaded file to that obtained separately from the original source.		'''md5sum''' is a program for verifying that contents of a file have been exactly reproduced without having access to the original file. It is often used for large files like [[ISO]] images that must be verified before they are used. A large number called the MD5 checksum (MD5sum) is calculated from the file's contents in a reproducible way that, with extremely high probability, will never produce the same MD5sum for different files. The user compares the MD5sum of the downloaded file to that obtained separately from the original source.

Rwh at 02:19, 22 January 2011

2011-01-22T02:19:00Z

← Older revision		Revision as of 22:19, 21 January 2011
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	~~___TOC___~~		__TOC__

			= Overview =
	'''md5sum''' is a program for verifying that contents of a file have been exactly reproduced without having access to the original file. It is often used for large files like [[ISO]] images that must be verified before they are used. A large number called the MD5 checksum (MD5sum) is calculated from the file's contents in a reproducible way that, with extremely high probability, will never produce the same MD5sum for different files. The user compares the MD5sum of the downloaded file to that obtained separately from the original source.		'''md5sum''' is a program for verifying that contents of a file have been exactly reproduced without having access to the original file. It is often used for large files like [[ISO]] images that must be verified before they are used. A large number called the MD5 checksum (MD5sum) is calculated from the file's contents in a reproducible way that, with extremely high probability, will never produce the same MD5sum for different files. The user compares the MD5sum of the downloaded file to that obtained separately from the original source.

Rwh at 02:18, 22 January 2011

2011-01-22T02:18:23Z

← Older revision		Revision as of 22:18, 21 January 2011
Line 1:		Line 1:
			___TOC___

	'''md5sum''' is a program for verifying that contents of a file have been exactly reproduced without having access to the original file. It is often used for large files like [[ISO]] images that must be verified before they are used. A large number called the MD5 checksum (MD5sum) is calculated from the file's contents in a reproducible way that, with extremely high probability, will never produce the same MD5sum for different files. The user compares the MD5sum of the downloaded file to that obtained separately from the original source.		'''md5sum''' is a program for verifying that contents of a file have been exactly reproduced without having access to the original file. It is often used for large files like [[ISO]] images that must be verified before they are used. A large number called the MD5 checksum (MD5sum) is calculated from the file's contents in a reproducible way that, with extremely high probability, will never produce the same MD5sum for different files. The user compares the MD5sum of the downloaded file to that obtained separately from the original source.

Rwh: Created page with ''''md5sum''' is a program for verifying that contents of a file have been exactly reproduced without having access to the original file. It is often used for large files like [[…'

2011-01-22T02:15:23Z

Created page with ''''md5sum''' is a program for verifying that contents of a file have been exactly reproduced without having access to the original file. It is often used for large files like [[…'

New page

'''md5sum''' is a program for verifying that contents of a file have been exactly reproduced without having access to the original file. It is often used for large files like [[ISO]] images that must be verified before they are used. A large number called the MD5 checksum (MD5sum) is calculated from the file's contents in a reproducible way that, with extremely high probability, will never produce the same MD5sum for different files. The user compares the MD5sum of the downloaded file to that obtained separately from the original source.

The algorithm is designed to make it difficult to tamper with the file while still producing the same MD5sum for the tampered file. If two instances of a file have the same MD5sum, the user is assured that the instances are identical. If one is the official version, so is the other.

To compute the MD5sum of a file (e.g., tmp.iso) and display it as a [http://en.wikipedia.org/wiki/Hexadecimal hex] number, execute the command:
$ md5sum tmp.iso

= Examples =
You can use the -c option to md5sum to check the files against the md5sum file as below.
$ md5sum -c md5sum.txt

To check the md5sum from a just burned dvd:
$ md5sum /dev/dvd

Trailing zero's and nuls at the end can change the MD5 hash.
So to calculate the md5sum we need to:
# find the size of the ISO in bytes
# run dd with this exact size in bytes: dd if=/dev/dvd | head --bytes=<size> | md5sum

So for example:
$ dd if=/dev/dvd | head --bytes=3621957632 | md5sum

= The Easiest way to test if an ISO has been correctly backed up is as follows: =

I though the md5sum would be the best option and was proven wrong by myself. My conclusion was that the cmp command better answered my demands for testing CD or DVD disks after writing (It does not waste any time informing you whenever an error was found).

dd if=/dev/dvd | cmp tmp.iso
or
dd if=/dev/sr0 | cmp "Whatever my Long ISO Filename may be.ISO"

''Testing should reveal that if the ISO Image is the same as the CD/DVD, you will have a result as follows:''

9103360+0 records in

9103360+0 records out

4660920320 bytes (4.7 GB) copiedcmp: '''EOF on ISOFILENAME.ISO'''

''{because and EOF on the ISO Image is specified, this output indicates that for all bytes read, the file is equal (Bytes in and out are the same for the full size of the ISO Image!) and that the only error that occured was that the End of the ISO file was reached before the end of the CD/DVD, which is usually irrelevant as we try to test accuracy of the burned image against a ISO Image. The reason for the EOF is that the written medium may exceed the ISO filesize (I assume this is padding/information for ISO, UDF and other extensions. I did not go into this as I am a Greenhorn myself). This example illiminates the use of md5sum command in which a file size in bytes must be provided to ensure that the bytes compared are the exact length of the ISO image which we are comparing to). In the CMP command case, size is not required as the comparison will end as soon as either the CD/DVD or ISO file have reached their end or an difference was encountered, whichever takes place 1st. '''''If the ISO and CD/DVD differ''''', the result will tell you so by specifying - '''differ: char xxx, line xxx''' The advantage above md5sum is that the test will end immediately on determining an error which illiminates waiting until the very end should an error exist!'' md5sum does have its advantages but in this case the "cmp" command wins.

= External links =

* [http://linux.die.net/man/1/md5sum md5sum man page]