This post describes the process of verifying Ubuntu Operating System ISO file for authenticity and integrity. Whenever you download an ISO file of Ubuntu operating system, you should first ensure that it has not been tampered and is same as provided by Ubuntu before using it for creating bootable media. Once download of Ubuntu ISO file is complete follow the below steps to check integrity and authenticity of Ubuntu ISO file.
After Ubuntu Desktop ISO file download is complete, click on the “verify your download” link on the thank you for download page.
The SHA256 sum of the ISO file provided by Ubuntu will be displayed.
Here the SHA256 sum is: e5b72e9cfe20988991c9cd87bde43c0b691e3b67b01f76d23f8150615883ce11
So, now you have the ISO file and its SHA256 checksum. Now you need to generate the SHA256 checksum of the downloaded ISO file with the one mentioned in the checksum file. Let us see the method of generating SHA256 checksum on windows and Linux PC and matching them in following steps:
A. Check SHA256 checksum on Linux
Open the Terminal by Right Clicking on the ISO file download location and select ‘Open in Terminal’ or open it from applications menu and change the present working directory to Download Directory where Ubuntu ISO file is downloaded.
Copy the echo command (e.g. given below) piping with SHA256 generator displayed on Ubuntu website:
echo “e5b72e9cfe20988991c9cd87bde43c0b691e3b67b01f76d23f8150615883ce11 *ubuntu-20.04-desktop-amd64.iso” | shasum -a 256 –check
Paste the command in Terminal and hit enter:
If the terminal produces OK in output with Ubuntu ISO file then the ISO file downloaded is verified for integrity and authenticity.
B. Generate and match SHA256 checksum on Windows
Open Windows PowerShell and change the directory to Downloads folder (or location where you have kept Ubuntu Desktop ISO file). Run the CertUtil -hashfile [Ubuntu Desktop ISO file name] SHA256 command as shown in below image.
The above commands will generate the SHA256 Sum of Ubuntu Desktop ISO file. It may take some time as the file size will be large ~2.52 GB.
The SHA256 sum would be a long string with arbitrary characters e.g. e5b72e9cfe20988991c9cd87bde43c0b691e3b67b01f76d23f8150615883ce11. Let’s say it is the KeyGenerated.
Go back to Ubuntu download page and copy SHA256 sum provided by Ubuntu official site in the echo command.
For e.g. the key provided on Ubuntu download page is e5b72e9cfe20988991c9cd87bde43c0b691e3b67b01f76d23f8150615883ce11. Let’s say it is KeyProvided.
Now visually compare this KeyProvided with KeyGenerated in previous section character by character. It is a simple way to compare the key however, time consuming.
Another efficient and quick method is to use a sheet (Microsoft Excel or Libre Office Calc) to compare the SHA256 sum. Open a sheet in Excel or Calc, label the cells to identify each SHA key viz. the one generated in Powershell and second that is provided on Ubuntu official website.
Copy SHA256 sum keys viz. KeyGenerated and KeyProvided. Switch to Excel / Calc sheet and paste the keys. In one of the cells (Let’s say E5) paste the KeyGenerated in Powershell and in another cell (Let’s say E7) paste the KeyProvided on Ubuntu download page. Ensure that both sums are in same format and of same length. Remove any extra blank space if visible to make strings equal length.
Now use the ‘=’ (equal to) operator to compare the value of both cells. For e.g. type ‘=E5=E7’ in another cell.
If both values will match the result will be ‘True’ else the result will be ‘False’. If the result is ‘True’, the integrity and authenticity of the Ubuntu ISO file is verified to be maintained while downloading from the source.
Else if, the result is False, you should download the ISO file again preferably on a reliable computer and Network.
You can proceed to create Ubuntu bootable media (USB or DVD) with the ISO file upon successful verification. If verification fails, re-download the ISO file from an authentic source.
This article is a part of Ubuntu Desktop – The Complete Installation Guide series. You need to visit Previous (download Ubuntu Desktop ISO) and Next (create Ubuntu bootable USB) chapters to understand the topic in entirety.
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