Covered Topics

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Sunday, August 15, 2010

Verifying Checksums for LINUX Downloads - Part 2

On August 6, 2010, I posted an entry on how to verify checksums for downloaded LINUX CD .iso files. Herein is my own refinement on using the md5sum command.

The md5sum command:
For verifying the md5 chscksums [for Ubuntu 10.04, in this case], here is the basic command:

md5sum ubuntu-10.04-desktop-i386.iso

This generates an output like this to the command line:
d044a2a0c8103fc3e5b7e18b0f7de1c8 ubuntu-10.04-desktop-i386.iso

You then visually compare this to a similar string of letters and numbers taken from the md5 checksum file you downloaded along with the CD .iso file itself. Reading and comparing lines of gibberish like this can make you crosseyed. There IS a simple way to do this without spending a bunch of time or driving yourself crazy.

The way I do it:
As I pointed out in the August 6 post, I like to paste the output to a text file, along with the contents of the md5 file. To make this easier, I use the > symbol for UNIX redirect as follows:

md5sum ubuntu-10.04-desktop-i386.iso > sumcheck.txt

This creates a text file called "sumcheck.txt", then redirects the results from the md5sum command to it, rather than outputting to the command line as normal. You could actually use whatever name you want for the text file as long as it doesn't conflict with (and possibly over-write) something else on the system. I just happen to like the descriptive name "sumcheck". UNIX/LINUX allows you to forego using the .txt extension; I just do it to help when I'm looking at a directory listing from the command line.

Open "sumcheck.txt" in your "gedit" text editor wondow - you should see the output string generated by md5sum. Then, open the md5sum file you (hopefully) downloaded when you downloaded the cd .iso image. Copy the string seen there and paste it into your "sumcheck.txt" file on the line below your output string. Doing this results in the following:

d044a2a0c8103fc3e5b7e18b0f7de1c8 ubuntu-10.04-desktop-i386.iso
d044a2a0c8103fc3e5b7e18b0f7de1c8 *ubuntu-10.04-desktop-i386.iso

The top line was the output generated from the command I listed above.
The second line, the one with the asterisk, was the line copied and pasted from the downloaded md5 checksum file. See how at a glance you can quickly and easily compare the two strings?

After I'm done and am satisfied the files are not corrupted, I DELETE "sumcheck.txt" so I can use that filename again in the future.

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