(For more resources related to this topic, see here.)
In this article we will learn how to download and confirm the checksum of one or more CentOS 6 disk image(s) using a typical Windows desktop computer.
CentOS is made available in various formats by HTTP, FTP, or via a Torrent-based client from a series of mirror sites located across the world. It supports both the 32-bit and 64-bit architectures, and having downloaded one or more image files, it is often a good idea to validate those files’ checksum in order to ensure that any resulting media should function and perform as expected.
To complete this recipe it is assumed that you are using a typical Windows-based computer (Windows 7, Windows Vista, or similar) with full administration rights. You will need an Internet connection to download the required installation files and access to a standard DVD/CD disk burner with the appropriate software in order to create the relevant installation disks.
Regardless as to what type of installation files you download, the following techniques can be applied to all image files supplied by the CentOS project:
This URL was correct at the time of writing this article, but if it’s no longer functional or is not available, then simply visit http://www.centos.org and navigate to Downloads Mirrors | CentOS Public Mirror List| or review the links associated with the latest release announcements made on the home page.
As this is a standard text file, place your mouse on the link, right-click and choose Save As to download a copy of md5sum.txt.When finished, store this file in a safe place for future reference. For the purpose of this recipe, it is assumed that all downloads will be stored in your C:Users<username>Downloads folder.
If you are new to CentOS or are intending to follow the recipes found throughout this article, then the minimal installation is ideal. However, you should be aware that there are other options available to you.
For a full 64-bit DVD-based installation, you will need both:
CentOS-6.X-x86_64-bin-DVD1.iso
CentOS-6.X-x86_64-bin-DVD2.iso
For a full 32-bit DVD-based installation, you will need both:
CentOS-6.X-i386-bin-DVD1.iso
CentOS-6.X-i386-bin-DVD2.iso
For a minimal installation, you should choose either:
CentOS-6.X-i386-minimal.iso (32-bit version)
CentOS-6.X-x86_64-minimal.iso (64-bit version)
For a network installation, you should choose either:
CentOS-6.X-i386-netinstall.iso (32-bit version)
CentOS-6.X-x86_64-netinstall.iso (64-bit version)
If you choose to download a torrent file, then you will need to extract these files in the usual way in order to build the appropriate ISO image file(s).
md5sum.exe
The full URL is http://mirror.centos.org/centos/dostools/md5sum.exe.
cd downloads
dir
md5sum.exe your_image_file_name_here.iso
For example, you can type md5sum.exe CentOS-6.X-x86_64-minimal.iso
087713752fa88c03a5e8471c661ad1a2 *CentOS-6.X-x86_64-minimal.iso
The act of downloading an installation image and validating the file’s integrity is just the first step towards building the perfect server, and although the process of downloading CentOS is very simple, many do forget the need to confirm the checksum.
So what have we learned from this experience?
We began this recipe by showing you how to download CentOS by outlining the various optionsavailable to you. It is not expected that you will need to do this often, but during the course of this recipe you also learned how to navigate the CentOS Project website and select the best download location based on your current location.
Having done this, our next step was to obtain a copy of md5sum.txt before downloading the preferred image files.
The choice as to whether you selected a 32-bit or 64-bit version is largely dependent on the specification of your intended server. However, given the abilities of most modern computers, for most people the obvious choice will be the 64-bit version in order that you can take advantage of the improved code base and support more than 4 GB of RAM.
The time required to complete the task of downloading the relevant files will depend largely on the speed of your Internet connection, but it was important that we obtained a copy of md5sum.exe in order to confirm file integrity and compare the value given against those listed in md5sum.txt.
The DOS-based tool was obtained from
http://mirror.centos.org/centos/dostools/md5sum.exe.
Having completed these steps, we then proceed to open a command prompt session and navigate to the expected destination of all the files by typing:
cd downloads
We then proceeded to view the contents of C:Users<username>Downloads by typing the following command:
dir
This action lists the filenames concerned, thereby enabling us to modify the following command in order to validate the appropriate ISO files:
md5sum.exe your_image_file_name_here.iso
The resulting response provides us with the checksum value of the file in question in order that we can compare it with the corresponding value found in md5sum.txt.
For example,the content of md5sum.txt may look like this:
087713752fa88c03a5e8471c661ad1a2 CentOS-6.X-x86_64-minimal.iso
Whereas the display in command prompt may show:
087713752fa88c03a5e8471c661ad1a2 *CentOS-6.X-x86_64-minimal.iso
You should repeat this process for all image files, and if these values match, then you can be confident that your download is verified. A fact that not only reduces the chance of wasting optical disks, but with security in mind, it also implies that what you downloaded is what you were expecting to download (and not something else).
So remember, with every new release the CentOS team will update the main website and enable you to download the required image files. Unless the CentOS project states otherwise, you will only need to do this once, as all minor updates can be managed like any other operating system. However, if you do intend to download them again, then it is always a good idea to check the integrity of your image files with the md5sum checksum tool.
Further resources on this subject:
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