apt command is used to install, update, remove packages in Linux distributions like Ubuntu, Debian, Mint, Kali. apt is mainly used with the deb packages.  With the apt update or apt-get update command the repository information is downloaded to from the deb repositories to the local repositories. Hash is used to checking if the downloaded file is valid. If there is a problem we may face with the Hash Sum mismatch error.

“Hash Sum mismatch” Error

First, we will look at how the  Hash Sum mismatch error occurs during the apt update or  apt-get update command usage.

$ apt update && apt dist-upgrade -y

We can see that following errors and warnings are printed during the update repository information.

• Last modification reported: Wed, 26 Jun 2019 12:03:10 +0000
• Hashes of expected file:
• – Filesize:17059946 [weak]
• Last modification reported: Wed, 26 Jun 2019 12:03:10 +0000
• Release file created at: Wed, 26 Jun 2019 12:04:12 +0000
• E: Some index files failed to download. They have been ignored, or old ones used instead.

“Hash Sum mismatch” Solution

In order to solve the Hash Sum mismatch error, we need to remove downloaded repository information from the /var/lib/apt/lists/ directory. We will use rm -rf command for this. We will also provide the sudo command.

$ sudo rm -rf /var/lib/apt/lists/*

Then the update command like below will work.

$ sudo apt update