Upgrading an Ubuntu system is usually a straightforward process, but when things go wrong, they can go very wrong. One of the most common and frustrating issues users face after upgrading to Ubuntu 18.04 LTS is a system plagued by broken packages, unmet dependencies, and package manager errors that seem impossible to resolve. These problems can prevent software installation, block security updates, and in severe cases make the system unstable or unusable.
This guide is designed to walk you through a complete, methodical recovery process. It explains why these issues occur, how Ubuntu’s package management system works, and exactly what steps you should take to repair broken packages and resolve unmet dependencies safely. The goal is not just to fix the immediate problem, but to restore your system to a healthy, maintainable state so future updates work as intended.
Whether you upgraded from 16.04 or another earlier release, used the graphical updater or the command line, or encountered errors halfway through the process, the steps below will help you regain control of your Ubuntu 18.04 system.
Why Broken Packages and Unmet Dependencies Happen After an Upgrade
Understanding the root causes of post-upgrade package issues makes troubleshooting far easier. Ubuntu relies on a complex dependency system where each package may depend on specific versions of other packages. During a release upgrade, thousands of packages are replaced, removed, or updated to newer versions, and any interruption or mismatch can cause conflicts.
One common cause is third-party repositories. Personal Package Archives and external software sources often target specific Ubuntu releases. After an upgrade, these repositories may not yet support Ubuntu 18.04, leading to incompatible package versions that conflict with official repositories.
Another frequent issue is a partially completed upgrade. Network interruptions, power failures, or forcibly closing the upgrade process can leave the package database in an inconsistent state. In such cases, some packages are upgraded while others remain tied to older dependencies.
How Ubuntu Package Management Works at a High Level
Ubuntu uses the Advanced Packaging Tool to manage software. APT resolves dependencies automatically, ensuring that all required libraries and supporting packages are installed in compatible versions. When everything works correctly, users rarely notice this complexity.
Problems arise when APT cannot find a compatible set of packages that satisfy all requirements. This results in errors such as “unmet dependencies” or “held broken packages.” These messages indicate that the package manager cannot proceed without manual intervention.
It is important to approach fixes carefully. Forcing removals or installing random packages can worsen the situation. The steps below follow a conservative, well-established recovery process recommended by experienced Ubuntu maintainers.
Initial System Preparation Before Making Fixes
Before attempting repairs, make sure your system environment is stable. Start by ensuring you have a reliable internet connection, as many fixes require downloading packages from official repositories.
Next, close any software center windows or background package managers. Only one package management process should run at a time. Running multiple tools simultaneously can lock the package database and cause additional errors.
Finally, open a terminal and ensure you have administrative access using sudo. Most repair commands require elevated privileges to modify system packages.
Step-by-Step Process to Fix Broken Packages
Step 1: Update the Package Lists
The first step is to refresh your package lists so APT knows what versions are available for Ubuntu 18.04. This does not install or remove anything; it simply updates metadata.
sudo apt update
If this command reports errors related to unsupported repositories, note them. These will be addressed later in the guide.
Step 2: Attempt an Automatic Repair
APT includes a built-in repair option that tries to fix broken dependencies automatically. This is often enough to resolve minor issues.
sudo apt --fix-broken install
This command installs missing dependencies and completes partially installed packages where possible. Carefully read the output to ensure it is not proposing the removal of critical system components.
Step 3: Configure Unfinished Packages
If the upgrade was interrupted, some packages may be unpacked but not fully configured. This command completes their configuration.
sudo dpkg --configure -a
Errors at this stage often indicate deeper dependency conflicts, which are addressed in the next steps.
Dealing with Third-Party Repositories and PPAs
Unsupported third-party repositories are a major source of post-upgrade problems. Ubuntu 18.04 requires repositories built specifically for its release. Older sources can introduce incompatible package versions.
Start by reviewing your software sources. You can list all configured repositories using the command line or the graphical “Software & Updates” tool.
ls /etc/apt/sources.list.d/
Temporarily disable third-party repositories by commenting them out or moving their list files to a backup location. After disabling them, update your package lists again and retry the repair commands.
Handling Held Packages
Held packages are packages marked to not be upgraded or modified. While useful in some scenarios, they can block dependency resolution after a major upgrade.
To identify held packages, use:
sudo apt-mark showhold
If packages are listed, consider unholding them to allow APT to resolve dependencies properly.
sudo apt-mark unhold package-name
Replace the placeholder with the actual package name. Proceed cautiously and unhold only packages you understand.
Advanced Dependency Resolution Techniques
In more complex cases, automatic tools may not succeed. Advanced techniques involve manually removing conflicting packages or downgrading problematic ones.
One approach is to remove packages that are no longer compatible with Ubuntu 18.04. APT will suggest removals during repair attempts. Review these suggestions carefully and confirm they are not essential system components.
Another option is to install a specific package version from the official repositories that satisfies dependency requirements. This should only be done when you clearly understand the dependency tree involved.
Cleaning and Rebuilding the Package Cache
Corrupted package caches can also cause errors. Cleaning the cache forces APT to re-download package data.
sudo apt clean
sudo apt autoclean
After cleaning, update the package lists and retry installation or upgrade commands. This step often resolves persistent but unexplained errors.
When to Use Distribution Upgrade Repair Tools
Ubuntu provides tools designed to complete or repair distribution upgrades. If standard package repairs fail, these tools can sometimes finish incomplete upgrade steps.
Running a release upgrade in repair mode can help align packages with the correct release versions. This process checks for mismatches and attempts to correct them automatically.
Use this option only after standard repair steps, as it makes broad system changes.
Common Errors and What They Mean
Understanding error messages reduces trial-and-error troubleshooting. Messages about unmet dependencies indicate version conflicts. Messages about broken packages usually mean incomplete installations.
Errors referencing specific libraries often point to a single conflicting package rather than a system-wide issue. Addressing that package can resolve multiple related errors.
Pro Tips for Preventing Future Upgrade Issues
- Disable third-party repositories before upgrading. This reduces the risk of incompatible packages interfering with the process. You can re-enable them after confirming they support the new release.
- Ensure sufficient disk space. Lack of storage can interrupt upgrades and leave packages half-installed. Always check available space beforehand.
- Keep backups. While upgrades are generally safe, having a recent backup allows recovery if something goes wrong.
- Upgrade from a fully updated system. Installing all updates before a release upgrade minimizes version conflicts.
- Read upgrade prompts carefully. The upgrader may warn about removed or replaced packages. Understanding these changes prevents surprises.
Frequently Asked Questions
Is it safe to remove packages suggested by APT?
In most cases, APT suggests removing packages that are no longer compatible or required. Always review the list carefully and avoid removing core desktop or system packages unless you are certain.
Can broken packages damage my system permanently?
Broken packages usually do not cause permanent damage, but they can prevent updates and installations. Resolving them promptly restores normal system operation.
Should I reinstall Ubuntu instead of fixing packages?
Reinstallation is a last resort. Most upgrade-related issues can be fixed using the methods described in this guide without losing data or settings.
Why does Ubuntu still reference old package versions?
This typically happens when old repositories remain enabled or when package lists were not updated correctly after the upgrade.
Conclusion
Broken packages and unmet dependencies after upgrading to Ubuntu 18.04 can feel overwhelming, but they are usually recoverable with a structured approach. By understanding why these issues occur, carefully repairing the package system, and addressing third-party repositories and held packages, you can restore stability and regain full control of your system. Following best practices before and after upgrades significantly reduces the risk of future problems, ensuring your Ubuntu installation remains reliable and easy to maintain.
