Md5sum is a software utility used to check the integrity of an ISO image before the file is used to create a CD. Computers running Linux will have this utility installed on their default system. Users of other operating systems may need to download an md5sum utility before being able to check the integrity. If you are using Linux or a distro of Linux, you can run md5sum and the name of the ISO file as shown below to display the MD5 information.
The above command would give you output similar to the example below, which shows an alphanumeric hash or MD5 in front of the file.
Once you have gathered the hash, you can compare it with the hash information from where you downloaded the .iso file. In our example, we have an Ubuntu .iso file their MD5 hash information is listed in our UbuntuHashes overview. If the MD5 does not match the file is either incomplete, been changed, or is otherwise compromised.