How to fix E: Unable to parse package file in APT

Run the check command to see detailed error information:

sudo apt-get check

This will show you which specific file is corrupted, usually a path in /var/lib/apt/lists or /var/lib/dpkg/status.

If the error points to a specific file in /var/lib/apt/lists, remove just that file:

sudo rm /var/lib/apt/lists/archive.ubuntu.com_ubuntu_dists_focal_InRelease

Replace the filename with the one shown in your error message. Then rebuild the cache:

sudo apt update

If multiple cache files are corrupted, clear the entire cache directory and regenerate it:

sudo rm -rf /var/lib/apt/lists/*
sudo mkdir -p /var/lib/apt/lists/partial
sudo apt update

This safely removes all cached package information and rebuilds it fresh from your repositories.

If the error mentions /var/lib/apt/extended_states, temporarily rename this tracking file:

sudo mv /var/lib/apt/extended_states /var/lib/apt/extended_states.bak
sudo apt update

The file will be automatically recreated when apt next runs.

If the error is in /var/lib/dpkg/status, you can restore from a recent backup:

sudo cp /var/backups/dpkg.status.0 /var/lib/dpkg/status
sudo apt update

The backup directory typically contains daily snapshots of the dpkg database.

If the error originated from /etc/apt/sources.list or /etc/apt/sources.list.d/, check for syntax errors:

sudo nano /etc/apt/sources.list

Verify entries follow correct format: deb https://repository.url/ ubuntu-codename main with proper spacing. Check for lines split across multiple lines (they should be on one line). Remove any malformed entries and save.

After making changes, test that apt works:

sudo apt update
sudo apt install -s test-package

The second command simulates an install without making changes. If both succeed, the issue is resolved.