You tried to install a certain software, but Ubuntu couldn't complete the installation. The APT prompts " No Installation Candidate ". What exactly does this mean? What is the root cause of the problem? Can it be solved? Here are several effective solutions.

Table of contents

• What does "Package has no installation candidate" mean?
• How to fix "No Install Candidate" error in Ubuntu
• Update and upgrade the system
• Add a third-party repository
• Make sure your Ubuntu version is still supported
• Try other installation methods
• FAQ

What does "Package has no installation candidate" mean?

When you try to install a software package that is not recognized by APT, the system prompts it to not find the software. This may be because you misspelled the package name, or the program you are trying to install is not in the default software source.

Another situation is: APT knows that this package exists (because other software relies on it), but it cannot be obtained under the current configuration. This is usually because you do not enable the necessary repository (such as universe or multiverse). Additionally, some software may be provided only through third-party PPAs, or does not support your system architecture.

For example, in newer Ubuntu versions, some packages commonly used in older projects or tutorials, such as python-pip (Python 2), ruby, or php5, have been deprecated or removed from the default source. This can lead to problems when building an old development environment or following outdated tutorials.

How to fix "No Install Candidate" error in Ubuntu

Ubuntu's package name is very accurate, even if one missing hyphen or the version number is written incorrectly, it may cause the installation to fail. Before in-depth investigation, please carefully check the package name you entered. It seems simple, but a letter error will make the APT unable to find the correct software.

If you are not sure of the exact name, you can use the apt search command to find similar packages. For example, if you want to install the Flameshot screenshot tool but don't know the exact name, you can run it:

 <code>apt search flameshot</code> 

If there are too many results, you can narrow the scope by:

 <code>apt search "^PACKAGE_NAME*"</code>

This command lists all packages starting with PACKAGE_NAME. If you replace PACKAGE_NAME with Firefox, you will see all packages starting with Firefox and may find the alternative you need. If there is still no result, the package may not be in the currently enabled source, or the name is different.

Update and upgrade the system

First check whether the target package was removed for the most recent update/upgrade. No need to flip through complex log files, just execute update commands to synchronize the latest software information. Run the following command to update the APT database:

 <code>sudo apt update && sudo apt upgrade</code> 

The root of this problem is that APT does not automatically detect whether the local source is synchronized with the remote server. Once the system update is lagging, the remote link will fail, resulting in a No Installation Candidate error.

After the update is completed, you can install all the packages available in the default source normally.

Add a third-party repository

If the above method is invalid, the target software is likely to be located in an unadded repository. You need to find and add it to the system's software source list.

The Internet is a good helper in finding missing warehouses. For example, you can copy its Personal Package Archive (PPA) link from the software official website and add it to your local APT configuration.

Once found, add the repository using the following command:

 <code>sudo add-apt-repository REPOSITORY_PPA</code>

Then refresh the local APT cache to load all packages in the new repository:

 <code>sudo apt update && sudo apt upgrade</code>

Check your software source (repository)

If updating and adding PPAs still fail to resolve the issue, the next step should check if the correct software source is enabled. Ubuntu's software comes from multiple channels, including main, universe, multiverse and restricted. Some software (especially niche tools) can only be installed after these sources are enabled.

You can operate through the graphical interface: open the "Software and Update" application, enter the "Ubuntu Software" tab, and make sure that main, universe, restricted and multiverse are all checked.

After clicking "Close", run the following command to reload the software list:

 <code>sudo apt update</code>

You can also enable these sources through the terminal, for example:

 <code>sudo add-apt-repository universe<br>sudo add-apt-repository multiverse<br>sudo add-apt-repository restricted<br>sudo apt update</code>

This allows for more comprehensive software resources. These repositories contain thousands of additional software beyond the main source. Universe contains open source software maintained by the community, while multiverse contains programs that may be license-restricted.

Make sure your Ubuntu version is still supported

If you are using an old or discontinued version of Ubuntu, some packages may have been removed or cannot be retrieved. Check the current system version and run:

 <code>lsb_release -a</code> 

If the version is no longer supported, it is recommended to upgrade to an updated distribution. Unsupported systems no longer receive updates and new packages, and they will encounter more and more problems over time.

It should be noted that the new version of Ubuntu may use different package names for the same software. For example, python in the older version may now be python3. Although the functions are the same, the packaging naming specification has changed.

Try other installation methods

If none of the above methods work, you can try using a universal package manager such as Snap or Flatpak. They are common software formats across Linux distributions.

Using Snap to install software is similar to APT:

 <code>sudo snap install <package_name></package_name></code>

Flatpak needs to install and configure the environment first, and then you can use a single command to install the required tools.

Another method is to directly download the software from the developer's official website and install it according to the instructions. Some developers provide installation packages (.deb files) in Debian format. After downloading from the official website, you can install it through the following command:

 <code>sudo apt install ./package_file.deb</code>

For open source software, you may need to download the source code, decompress and execute it in turn:

 <code>./configure<br>make<br>sudo make install</code>

Please note that compiling from source code is likely to cause dependency problems, so be cautious when operating.

FAQ

Can I list all available Ubuntu PPAs?

Can! Although the system does not have built-in tools to list all PPAs, Canonical allows users to submit personal repository information through Launchpad. You can search for the package name or repository name, and then use sudo add-apt-repository plus the Launchpad link to add the repository, and then run <code>sudo apt update</code> to refresh the cache.

However, please note that the repository on Launchpad is submitted by the user and it is important to verify its security and trustworthiness before adding.

My custom repository was not loaded during the update. What's the problem?

This is usually due to the lack of the repository's GPG signature key. Ubuntu uses apt-key to verify package integrity of all repositories, including Canonical official sources and Launchpad's third-party PPA. For repositories that are not Canonical or non-Launchpad, you must manually obtain and add the official signature key, otherwise the system will refuse to load.

I am using Ubuntu LTS, but I get the "no installation candidate" error. Is the system broken?

No! This error may also be because the software you are installing is only available in the updated Ubuntu version. At this point you can try using the Ubuntu Backports repository - a special source that allows users to maintain newer software versions for older systems. If you don't want to upgrade your system but need new features, backports is ideal. It can be installed by combining the version name and -backports through the -t parameter, for example:

 <code>sudo apt install -t jammy-backports <package_name></package_name></code>

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