Checking the integrity of a Live CD

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Verify CD

Cdrom unmount.png

When burning a CD with K3b make sure you compare the MD5 sum calculated by K3b with the one in the downloaded .md5sum file. Don't forget to select the verify written data checkbox if you want K3b to check if the CD was burnt correctly.

After burning a Live CD, you may want to verify the integrity of the CD. Here's how you can do that:

On Linux

In terminal type:

 md5sum /dev/cdrom

Depending on your system you might need to replace cdrom with cdrom1 or another device name like hdc (/dev/cdrom is the first CD drive, /dev/cdrom1 is the second one, etc.)

Wait for 2 to 5 minutes, depending on your CDROM speed, for your CD to be read and MD5 sum to be calculated, compare the MD5 sum obtained with the one that you got from the download site, they should be the same.

(This test fails for CD recorded 'track at once'. Use 'session at once' mode. When using cdrecord, use -dao switch.)

Iso-md5sum.png

You can use this verify method for CDs burned (using dao) with any software, not just K3B.

K3B Verify Errors

If K3B reports a verify error you should check the md5sum from the command line as described above. There have been reports of K3b erroneously reporting a failed verify after burning. Summary of fixes: install

libk3b3-extracodecs 
libk3b-dev
quodlibet-plugins

KDE 4 and Mepis 8.5 will verify correctly using the version of K3b that comes with it.

Finding your device name

With a CD or DVD in the device right click on the icon on the desktop and select properties from the menu that pops up.

Device-name.png

For KDE 4 and 8.5 simple open K3b --> Settings --> Configure K3b --> Devices and all CD/DVD/R/RW drives will be listed. Look for the line that starts /dev/xxxxx

Use a script to verify the image

Some burning software writes extra bytes when burning .iso images onto DVD disks, causing the checksum of a DVD disk to be different than the checksum of the .iso image. To get around this problem, the md5sum should be calculated using only the number of bytes copied from the .iso file itself, rather than calculating the md5sum of the entire DVD.

Copy and paste the below script into a blank text file, save it with a name like checkiso.sh and mark it as executable.

#!/bin/bash
#shell script to verify a burned iso

# Sets the path to iso
if  -e $1 ; then 
	ISOFILE=$1
else
	echo "Enter the complete path to the iso you want to use as a reference"
	read -e ISOFILE
	echo
	if  ! -e $ISOFILE ; then
		echo -e "Path or file doesn't exist, please try again \n" 
		get_iso_path
	fi
fi 

echo "Isofile: " $ISOFILE
DVDDRIVE=/dev/dvd
BYTES=2048

#Get the number of extends
NROFEXTENDS=$(($(ls -l $ISOFILE | awk '{ print $5 }') / $BYTES ))
echo "Nr of extends: " $NROFEXTENDS

#Get MD5 sum of DVD
dd if=$DVDDRIVE bs=$BYTES count=$NROFEXTENDS | md5sum

#Get MD5 sum of iso file
md5sum $ISOFILE 

If you saved the script into your /home/<you> folder, you can run it by opening a konsole window and type ./checkiso.sh, then follow the prompts.

On Windows

  1. Get the free version of the Windows application IsoBuster, available at isobuster.com.
  2. Insert CD in drive.
  3. Run IsoBuster as Administrator.
  4. In registration dialog, select "Free funct. only".
  5. In left pane, right-click on CD (top line) to get context menu, and select: "MD5 Checksum file" >> "Create MD5 Checksum" >> "For image file with 2048 bytes/block".
  6. Compare the MD5 in the .tao line of the output with the MD5 in the downloaded .md5sum file.

Alternate method of checking CD: Use IsoBuster to create an .iso file from the CD, and then do a binary comparison of that file with the downloaded .iso (using fc /b from a command prompt); the files should be identical.


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