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md5sum

The md5sum command computes and checks the MD5 message digest. it alow to create the diget for the whole tree and then check it with one command, which is important  in WAN file tranferes.

md5sum [OPTION]... [FILE]...

without file it will try read standard input.

Options

-b, --binary Read in binary mode.
-c, --check Read MD5 sums from the FILE(s) and check them.
-t, --text Read in text mode (default).

NOTE: There is no difference between binary and text mode option in GNU implementation used in Linux.

The following four options are useful only when verifying checksums:

--quiet Don't print OK for each successfully verified file.
--status Don't output anything, status code shows success.
--strict Exit non-zero for improperly formatted checksum lines.
-w, --warn Warn about improperly formatted checksum lines.
--help Display this help and exit.
--version Output version information and exit.

The sums are computed as described in RFC 1321. When checking, the input should be a former output of this program. The default mode is to print a line with checksum, a character indicating input mode ('*' for binary, space for text), and name for each FILE.

Examples

All of the following files are assumed to be in the current directory.

Create MD5 hash file hash.md5

$ md5sum filetohashA.txt filetohashB.txt filetohashC.txt > hash.md5

File produced contains hash and filename pairs.

$ cat hash.md5
595f44fec1e92a71d3e9e77456ba80d1  filetohashA.txt
71f920fa275127a7b60fa4d4d41432a3  filetohashB.txt
43c191bf6d6c3f263a8cd0efd4a058ab  filetohashC.txt

NOTES:


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HowToMD5SUM - Community Help Wiki

Here is a shell script that will check the md5 hash of a burned disk and compare it to the hash of an iso image. Copy and paste it into your favorite text editor and save it as eg. hashcdrom.sh.

#Compares the checksums of an iso9660 image and a burned disk.
#This script is released into the public domain by it's author.
if [ -n "$BASH" ]; then
shopt -s expand_aliases
fi

if [ -n "$FILE" ]; then
FILE="$FILE"
else
FILE=`basename $0`
fi

if [ -n "$CHECKSUM" ]; then
alias CHECKSUM="$CHECKSUM"
elif which md5deep &> /dev/null; then
alias CHECKSUM='md5deep -e'
else
alias CHECKSUM='md5sum'
fi

if [ -n "$2" ]; then
DISKDEVICE="$2"
else
DISKDEVICE='/dev/cdrom'
fi

if [ -n "$1" ]; then
CSUM1=$(CHECKSUM "$1" | grep --only-matching -m 1 '^[0-9a-f]*')
echo 'checksum for input image:' $CSUM1
SIZE=$(stat -c '%s' "$1");
BLOCKS=$(expr $SIZE / 2048);
CSUM2=$(dd if="$DISKDEVICE" bs=2048 count=$BLOCKS 2> /dev/null | CHECKSUM | grep --only-matching -m 1 '^[0-9a-f]*')
echo 'checksum for output disk:' $CSUM2

if [ "$CSUM1" = "$CSUM2" ]; then
echo 'verification successful!'
else
echo 'verification failed!'
fi

else
echo ''
echo 'Usage:'
echo '  '$FILE' /path/to/iso [/path/to/cd/drive]'
echo ''
fi

Now open a terminal and type

sh /path/to/hashcdrom.sh /path/to/ubuntu-8.10-desktop-i386.iso /dev/mycdromdevice

Note that if your cdrom device is /dev/cdrom, you can omit that parameter.

It should print out something like

checksum for input image: 24ea1163ea6c9f5dae77de8c49ee7c03
checksum for output disk: 24ea1163ea6c9f5dae77de8c49ee7c03
verification successful!

If you verified that the iso image is okay (above), than you need not check the hash against UbuntuHashes.

This script has some nifty features. For example, if md5deep is installed (sudo aptitude install md5deep), it will use it to print out some progress information, such as how many bytes copied. You can also make it use different hashing algorithms such as sha256 and whirlpool by setting the CHECKSUM environment variable to the command you want to use to create the hash:

export CHECKSUM='whirlpooldeep -e'
sh /path/to/hashcdrom.sh /path/to/ubuntu-8.10-desktop-i386.iso /dev/mycdromdevice

This shell script depends on certain features found only in GNU grep, so it probably will not work on systems that do not ship the GNU utilities.

A method using wodim instead of dd

readom dev=/dev/scd0 sectors=0-352113 f=- |md5sum

where 352113 is result of dividing size of iso file in bytes by 2048.

Check the files on the CD

The MD5 hashes for every file on the CD are listed in a file called md5sum.txt. You can use this file to check the integrity of all the files on the CD.

  • cd /media/cdrom
    md5sum -c md5sum.txt | grep -v "OK$"

This will automatically check every file against the MD5 hashes stored in the file and outputs any failures. (Again, you may need to change cdrom, depending on your system). Beware, it can take a long time so don't worry if your terminal seems to have hung; provided the CD drive is still accessing, it is probably still working. It should not output anything if it there were no errors, and an error message if a file failed the check. The grep command option -v "OK$" filters out all of the files that pass the check, because there are usually a lot of them.

Success?

Congratulations, you now have a verified Ubuntu CD. Go ahead and use it (or play frisbee with it if you want).

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