Differences between revisions 6 and 7
Revision 6 as of 2006-04-30 05:42:32
Size: 3008
Editor: 70-57-193-50
Revision 7 as of 2006-06-19 16:06:35
Size: 55
Editor: 127
Deletions are marked like this. Additions are marked like this.
Line 1: Line 1:
MD5SUMs are a type of checksum, which are used to verify data integrity, in other words, they can detect errors. When you download a large file like a CD .iso, it is possible that there are errors, simply because the probability of an error in a file is proportional to the size of the file. When you have a file that ''must'' be correct, e.g. an install CD for an operating system, it is a very good idea to run a check on it. In addition, checksums provide a measure of authenication, so you know that your copy is the same as the official copy, and has not been altered in some way. There are actually better ways of authentication than simple checksums, but they are better than nothing.

== MD5SUM on Ubuntu ==

Most Linux distributions come with the {{{md5sum}}} utility, so there is usually no need to install it. When you download a CD .iso file, on the same page there should be an md5sum file. If your .iso file is named ''my_cd.iso'', then the md5sum file is generally named ''my_cd.iso.md5sum'', ''my_cd.md5sum'', ''my_cd.txt'', or some similar variant. The Ubuntu CDs all have a common md5sum file named "MD5SUM". Download this file to the same place as the .iso file. When you have both files, run
cd download_directory
md5sum --check md5sum_file
This will cause {{{md5sum}}} to look at all the files listed in the md5sum file (one of which should be your .iso), and compare the checksum of the .iso with the checksum recorded in the md5sum file. If they match, you're good to go. If they don't, redownload the .iso file.

You can check files without an md5sum file as well (but you still need to get the checksum from somewhere!). Just run
md5sum file_to_check
and manually compare the output of that command with the checksum from the website.

== MD5SUM on Windows ==

Windows does not come with an md5sum utility. You must download one from another location, and preferably a location that you trust. There is a commandline {{{md5sum.exe}}} that works similarly to the Unix utility, and a graphical version that you may be more comfortable with. Some of the links in the External Links section have additional howtos and offer checksum utility downloads.

== MD5SUM on CD ==

There is a fool-proof way to see that your (install or live) CD is uncorrupted. First mount the CD, if it isn't already

sudo mount /dev/hda /cdrom

Then use the supplied md5sum file on the CD

cd /cdrom
md5sum -c md5sum.txt | grep -v 'OK$'

If the command outputs any errors, you'll know either the burn was bad or the .iso is bad.

== External Links ==
 * [ Linux .iso How To]
 * [ Etree] is a site for sharing legitmate live sound recordings. They are in the business of sharing large files, thus MD5SUMs are useful for them.
 * [ Open Office MD5SUM How to]


HowToMD5SUM (last edited 2008-08-06 16:35:54 by localhost)