Ubuntu: Why does integrity check fail for the 12.04.1 Alternate ISO?



Question:

I have followed various recommendations from the Ubuntu Documentation to create a bootable Ubuntu USB flash drive using the 12.04.1 Alternate install ISO-file for 64-bit PC. But the integrity test of the USB stick has failed and I do not see why.

These are the steps I have made:

  1. Download of the 12.04.1 Alternate install ISO-file for 64-bit PC (ubuntu-12.04.1-alternate-amd64.iso) from http://releases.ubuntu.com/12.04.1/, as well as the MD5, SHA-1 and SHA-256 hash files and related PGP signatures
  2. Verification of the data integrity of the ISO-file using the MD5, SHA-1 and SHA-256 hash files, after having verified the hash files using the related PGP signature files (see e.g. https://help.ubuntu.com/community/HowToSHA256SUM and https://help.ubuntu.com/community/VerifyIsoHowto)
  3. Creation of a bootable USB stick using Ubuntu's Startup Disk Creator program (see http://www.ubuntu.com/download/help/create-a-usb-stick-on-ubuntu)
  4. Boot of my computer using the newly made 12.04.1 Alternate install on USB stick
  5. Selection of the option "Check disc for defects" (see https://help.ubuntu.com/community/Installation/CDIntegrityCheck)

Steps 1, 2, 3 and 4 went without any problem or error messages. However, step 5 ended with an error message entitled "Integrity test failed" and with the following content:

The ./install/netboot/ubuntu-installer/amd64/pxelinux.cfg/default file failed the MD5 checksum verification. Your CD-ROM or this file may have been corrupted.

I have experienced the same (might only be similar since I have no exact notes) error message in previous attempts using the 12.04 (i.e. not the maintenance release) Alternate install ISO-file. I have in these cases tried to install anyway and have so far not experienced any problems to my knowledge.

  • Is failed integrity check described above a serious error?
  • What is the solution?
  • Or can it be ignored without further problems?


Solution:1

This is an error in mastering the ISO, but can safely be ignored

  • You get this error because the install/netboot/ubuntu-installer/amd64/pxelinux.cfg/default file does not exist in the 64-bit alternate ISO image, although it does in the ISO's file-checksum list (md5sum.txt):

    • 573bf62a1f14cdcef0e8299863547a5a ./install/netboot/ubuntu-installer/amd64/pxelinux.cfg/default

    • See this pastebin for the actual contents of the install/netboot folder.

  • It can be ignored because the files refer to the minimal "netboot" ISO version, which is irrelevant when you are using a full alternate ISO.

  • If you really want to "solve" the error, you can download the missing file into the appropriate folder; beware that this may not be the last though because apparently there are six such missing files...


Solution:2

This stopped my installation dead in its tracks doing an alternate install with an encrypted volume. Using unetbootin to create the image, the six files mentioned above were missing. I am convinced this is an issue with filename and path length restrictions causing these long filenames to be missing. This issue is marked as an invalid bug here: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1041911

Ultimately adding the files didn't help. And I had to boot into an incomplete installation and install ubuntu-desktop manually.


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