How to check an Ubuntu .iso file

After downloading an .iso file from ubuntu.com (please tick the box under the “Start Download” green button if you want the alternate version and choose a mirror close to your location), you need to verify that the .iso file is not corrupted before you can use it to install Ubuntu.

Ubuntu provides the md5 hashes of all the released .iso files. Please read here for more information about md5 (Message-Digest algorithm 5). To check the file, we’ll use md5sum.

  • md5sum on the downloaded file
    Go to the directory the file is located and run md5sum. In the example below, I had downloaded the file to the desktop:

    :~ $cd Desktop/
    :~/Desktop $ md5sum ubuntu-7.10-alternate-i386.iso 
    9a4ae3cfd68911a861d094ec834c9b48  ubuntu-7.10-alternate-i386.iso

    Then verify it matches the hash from the Ubuntu release.

  • md5sum on the burnt file
    Once you have burnt the .iso file to a CD, it is a good idea to check it too, and verify nothing happened during the process. By default, Ubuntu mounts the cdrom to /media:

    :~ $ cd /media/cdrom0/
    :/media/cdrom0 $ md5sum -c md5sum.txt | grep -v 'OK$'
    :/media/cdrom0 $ 

    If the match is good, there will be no error on the output.

You can then use the disk to install Ubuntu :)

Reference

Shamelessly inspired from the Ubuntu Community Documentation page. Please refer to this page if you are downloading and burning the .iso file on Windows.