Fix Chrome Install Errors In CircleCI Builds

Dec 9, 2025 by Alex Johnson 45 views

Mirror Sync in Progress? How to Fix Chrome Installation Errors in CircleCI

Have you ever been in the middle of a crucial deployment or test run, only to have it crash and burn because of a seemingly obscure error message like "Mirror sync in progress?" when trying to update Chrome in your CircleCI environment? It’s frustrating, right? Especially when it happens intermittently, making it even harder to pinpoint the cause. If you’re using the cimg/ruby:3.4.5-browsers image and have encountered this issue, you're not alone. This article will dive deep into what this error means, why it happens, and most importantly, how you can effectively resolve it to get your CircleCI builds back on track.

Understanding the "Mirror Sync in Progress?" Error

The "Mirror sync in progress?" error, as seen in the provided example log, typically occurs during the package update process in Debian-based Linux systems, which includes Ubuntu. When your CircleCI job tries to install or update Chrome, it relies on the Advanced Packaging Tool (APT) to fetch the necessary files from software repositories. These repositories are essentially mirrors of the official software packages. The error message indicates that APT tried to download a package list or a specific package file, but the file it received had an unexpected size compared to what the repository server indicated. This discrepancy often happens when the repository mirror itself is in the process of updating its files. Think of it like trying to download a document from a server that’s currently being edited; you might get an incomplete or corrupted version. In the context of CircleCI, where build environments are spun up and torn down rapidly, this transient state of the repository mirrors can lead to these frustrating failures.

The core of the problem lies in the timing. Ideally, APT should fetch a complete and consistent set of package information. However, if a mirror is undergoing an update, certain files might be temporarily unavailable, partially downloaded, or corrupted. APT detects this inconsistency by comparing the checksums and file sizes. When the downloaded file doesn't match the expected attributes, it throws this error. This is particularly problematic in automated CI/CD pipelines because a failed package installation can halt the entire build process, leaving your tests unexecuted and your deployments stalled. The error message itself, "File has unexpected size... Mirror sync in progress?", is APT’s way of telling you that it suspects the source it’s trying to download from is in an inconsistent state. This is why it often occurs when Canonical's repositories are being updated, as these are the primary sources for Ubuntu-based systems like the one used in the cimg/ruby:3.4.5-browsers image. The dependency on external repositories, while necessary for software management, introduces an external factor that can occasionally disrupt your build pipeline.

Furthermore, the error log shows that this is happening during the installation of Chrome. Chrome, being a popular and frequently updated browser, relies on Google's own repositories, which are added to the system's APT sources. The dl.google.com/linux/chrome/deb stable/main amd64 Packages line in the log points to this. When this repository is also experiencing its own update cycles simultaneously with the system's main Ubuntu repositories, the chances of encountering a synchronization issue increase. The specific error about restricted/binary-amd64/Packages.gz and main/binary-amd64/Packages.gz indicates that the package index files themselves are the ones being affected. These files are crucial for APT to know what packages are available and how to download them. If these index files are corrupted or incomplete due to a mirror sync, APT cannot proceed correctly. The subsequent errors about fetching main/binary-amd64/Packages.gz are direct consequences of the initial failure, as APT tries to recover but finds the situation still unresolved. The final line, "Some index files failed to download. They have been ignored, or old ones used instead," is APT’s fallback mechanism, but it's not reliable and often leads to further issues or failed installations, as seen by the Exited with code exit status 100.

Why Does This Happen in CircleCI?

CircleCI builds run in ephemeral environments. This means that each build starts with a fresh, clean environment based on the specified Docker image (cimg/ruby:3.4.5-browsers in this case). While this offers consistency, it also means that the environment is subject to the state of external resources at the precise moment the build runs. The "Mirror sync in progress?" error surfaces in CircleCI primarily because:

Timing is Everything: Your build might be scheduled at the exact moment one of the Ubuntu or Google Chrome package repositories is undergoing an update. This is a race condition that’s hard to predict and control.
Network Instability/Latency: Although less common, network issues between CircleCI's runners and the repository mirrors could theoretically contribute to incomplete downloads, mimicking the effects of a mirror sync.
Apt-get's Behavior: The apt-get install command, by default, doesn't have robust error handling for transient network or mirror issues. When it encounters an inconsistent file, it fails. The provided log clearly indicates that the install_chrome.sh script within the browser-tools-orb lacks specific error handling for the apt-get install command.

The ephemeral nature of CI/CD environments like those in CircleCI is a double-edged sword. On one hand, it guarantees a clean slate for every build, preventing configuration drift and ensuring reproducibility. On the other hand, it makes the build process highly dependent on the availability and integrity of external resources at the exact time the build executes. When these external resources, such as package repositories, are in a transitional state – like during a mirror synchronization – the build can fail. The error message "Mirror sync in progress?" is a classic symptom of this dependency. It's not that your CircleCI configuration is inherently wrong, but rather that the timing of your build coincided with a temporary inconsistency in the software mirrors it relies on. Imagine trying to read a book while someone is actively rewriting pages; you might end up with a jumbled mess. Similarly, APT, when fetching package metadata, expects stable files. If these files are being updated by the mirror, the download might be incomplete or corrupted, leading to the size mismatch error. The fact that this error occurs when "Canonical's repos are being updated" strongly suggests that the Ubuntu base image's package sources are the primary culprits. These are the fundamental sources from which many other packages, including potentially Chrome's dependencies or even Chrome itself if installed via a general package manager, are fetched. The problem is exacerbated because the browser-tools-orb attempts to install Chrome, which involves interacting with these system-level repositories. If these underlying repositories are unstable, the subsequent Chrome installation is likely to fail.

Moreover, the specific error related to Packages.gz files indicates that the problem is at the index level. APT uses these compressed files to maintain a catalog of available packages. If these catalogs are not properly synchronized across mirrors, APT might download a version that is out of sync with the actual package files. This can lead to failed installations because APT believes a package should exist or have certain properties, but the reality is different. The error message File has unexpected size (6280648 != 6287328) is a direct manifestation of this problem. APT downloaded a Packages.gz file that is smaller than expected, implying that the download was interrupted or the file on the mirror is incomplete. The subsequent Err:25 http://archive.ubuntu.com/ubuntu jammy-updates/main/binary-amd64/Packages.gz error shows that the problem persists even when APT tries to fetch another critical index file. This chain reaction of errors highlights how a single transient issue in a repository mirror can cascade and bring down the entire package installation process. The Exited with code exit status 100 at the end of the log is a generic indicator of failure, confirming that the script could not complete its intended task due to these underlying APT errors.

Strategies to Resolve the Error

Fortunately, this isn't an insurmountable problem. Several strategies can help mitigate or resolve the "Mirror sync in progress?" error in your CircleCI builds. The key is to make your package installation process more resilient to these transient issues.

1. Implement Retries and Cleanup (The Most Direct Solution)

The most straightforward approach, as suggested in the original issue description, is to add error handling to the script responsible for installing Chrome. Specifically, after an apt-get install command fails, you can:

Clean the APT cache: Run sudo apt-get clean to remove downloaded package files that might be corrupted.
Update the package list again: Execute sudo apt-get update to refetch the package lists from the repositories.
Force a clean update (if necessary): In more stubborn cases, you might need to remove all cached package lists by running sudo rm -rv /var/lib/apt/lists/* before running sudo apt-get update.
Retry the installation: After cleaning and updating, retry the apt-get install command for Chrome.

This approach essentially gives APT a chance to recover from the temporary inconsistency by clearing out potentially bad data and fetching fresh information.

Implementing retries and cleanup is often the most effective way to combat transient errors like the "Mirror sync in progress?" issue. The original problem arises because apt-get install fails on the first attempt due to a temporary glitch in the repository mirror. Instead of letting the build fail outright, we can instruct the system to try again after performing some housekeeping. The apt-get clean command is vital here; it removes any .deb files from the /var/cache/apt/archives/ directory, freeing up disk space and removing potentially corrupted downloaded packages. Following this with apt-get update refreshes the package lists, ensuring that APT has the latest information about available packages and their locations. If the mirror issue was truly temporary, this second attempt should succeed. For more persistent issues, or to ensure a completely fresh start, the command sudo rm -rv /var/lib/apt/lists/* followed by apt-get update is a more aggressive way to clear the APT state. It forcibly removes all cached package index files, compelling APT to download everything anew. This can be particularly useful if APT is holding onto outdated or corrupted index information. By wrapping these cleanup and update steps within a retry loop around the Chrome installation command, you significantly increase the chances of a successful build, even when encountering temporary mirror synchronization problems. This makes your CI pipeline more robust and less susceptible to the unpredictable nature of external package repositories.

Within the CircleCI configuration, this could look something like:

if ! sudo apt-get install -y google-chrome-stable; then
  echo "Chrome installation failed, attempting recovery..."
  sudo apt-get clean
  sudo rm -rv /var/lib/apt/lists/*
  sudo apt-get update
  if ! sudo apt-get install -y google-chrome-stable; then
    echo "Chrome installation failed again after recovery. Exiting."
    exit 1
  fi
fi

This basic if/then structure can be expanded into a more sophisticated retry loop for even greater resilience.

2. Use a Different Mirror (Advanced)

While apt-get usually selects a suitable mirror automatically, you can sometimes specify a different mirror in your /etc/apt/sources.list file or by creating a file in /etc/apt/sources.list.d/. If you consistently face issues with a particular mirror, switching to a geographically closer or known-to-be-stable mirror might help. However, this is more complex to manage within a dynamic CircleCI environment and might not be practical.

3. Pinning Package Versions (Less Ideal for Chrome)

For system packages, you can sometimes