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How To Fix “Malformed entry” Error in Ubuntu 18.04’s sources.list File

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In this article, we will discuss an issue that many Ubuntu 18.04 users may encounter: the “Malformed entry” error in the sources.list file. We’ll provide a detailed guide on how to fix this error, explaining each step along the way.

Quick Answer

To fix the "Malformed entry" error in Ubuntu 18.04’s sources.list file, you need to correct the syntax in the file. This can be done by running the command sudo sed -i 's|/bionic|/ bionic|g' /etc/apt/sources.list in the terminal. This command replaces any occurrence of "/bionic" with "/ bionic" in the file, resolving the syntax error.

Understanding the Error

The error message “E: Malformed entry 52 in list file /etc/apt/sources.list (Component)” can be quite confusing if you’re not familiar with the inner workings of Ubuntu. In essence, this error indicates that there is a syntax error in line 52 of your sources.list file.

The sources.list file is a critical component of your Ubuntu system. It contains the list of repositories that your system uses to download and install software. If there’s a syntax error in this file, it can prevent your system from updating correctly.

Identifying the Error

In our example, the problematic line in the sources.list file is:

deb main

At first glance, this line might seem fine. However, the correct syntax should be:

deb bionic main

The issue here is the missing space between “ubuntu/” and “bionic”. This small mistake is enough to cause the “Malformed entry” error.

Fixing the Error

To fix this error, you need to correct the syntax in your sources.list file. This can be done by running a command in the terminal.

Here’s the command you need to run:

sudo sed -i 's|/bionic|/ bionic|g' /etc/apt/sources.list

Let’s break down this command:

  • sudo: This prefix gives the command administrative privileges, which are necessary to modify the sources.list file.
  • sed: This is the command that will perform the actual modification. It’s a stream editor for filtering and transforming text.
  • -i: This option tells sed to edit files in place (i.e., save the changes to the original file).
  • 's|/bionic|/ bionic|g': This is the instruction that sed will follow. It tells sed to replace all occurrences of “/bionic” with “/ bionic”.
  • /etc/apt/sources.list: This is the file that sed will modify.

After running this command, the syntax error in your sources.list file should be fixed, and you should be able to update your system without encountering the “Malformed entry” error.


The “Malformed entry” error in Ubuntu 18.04’s sources.list file can be a headache, but it’s relatively easy to fix once you understand what’s causing it. By correcting the syntax in your sources.list file, you can get your system back to updating correctly.

Remember, it’s crucial to be careful when modifying system files. Always double-check your commands before running them, and consider backing up important files before making changes.

For more information on the sed command and its usage, you can check out the official documentation. If you have any further questions or issues, feel free to ask in the comments section below.

How can I identify if I have a “Malformed entry” error in my sources.list file?

You can identify a "Malformed entry" error by checking the error message that appears when you try to update your system using the apt command. The error message will specify the line number and the component where the error occurred.

Can I manually edit the sources.list file to fix the error?

Yes, you can manually edit the sources.list file to fix the error. However, it is recommended to use the provided command (sudo sed -i 's|/bionic|/ bionic|g' /etc/apt/sources.list) to avoid any syntax mistakes. If you choose to edit the file manually, make sure to use a text editor with administrative privileges.

What are repositories in Ubuntu?

Repositories in Ubuntu are servers that contain a collection of software packages. These packages can be downloaded and installed on your system using package management tools like apt. Repositories provide a convenient way to access and update software on your Ubuntu system.

How can I back up my sources.list file before making changes?

To back up your sources.list file, you can simply make a copy of it in a different location. For example, you can use the following command to create a backup in your home directory:

sudo cp /etc/apt/sources.list ~/sources.list.backup

This command will create a backup file named "sources.list.backup" in your home directory.

What should I do if the “Malformed entry” error persists after fixing the syntax?

If the error persists after fixing the syntax in the sources.list file, it could indicate a different problem. In such cases, it is recommended to seek assistance from the Ubuntu community forums or ask for help from experienced Ubuntu users. They can provide guidance and help troubleshoot the issue further.

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