APT Repository Issues and Fixes — Windows to Linux Guide

What This Guide Achieves

Goal	Status
Fix duplicate repository warnings	Done
Resolve GPG key errors	Done
Clean up old .list files (legacy format)	Done
Understand .list vs .sources file formats	Done
Safely remove PPAs	Done

The Problem (Windows User Perspective)

On Windows, software updates come from one place (Windows Update or the app itself). On Linux, software comes from repositories — external servers that apt checks for packages. When you install Chrome, Edge, Brave, or add PPAs, each one adds its own repository configuration. Over time, these can conflict, duplicate, or break — especially when repository formats changed from .list (old) to .sources (new) in Ubuntu 24.04.

Understanding the Two File Formats

Ubuntu 24.04 introduced a new repository format. Both formats work, but having both for the same repo causes problems.

Old Format: `.list` files

Location: /etc/apt/sources.list.d/*.list

deb [arch=amd64 signed-by=/usr/share/keyrings/google-chrome.gpg] https://dl.google.com/linux/chrome/deb/ stable main

New Format: `.sources` files (DEB822)

Location: /etc/apt/sources.list.d/*.sources

Types: deb
URIs: https://dl.google.com/linux/chrome/deb/
Suites: stable
Components: main
Architectures: amd64
Signed-By: /usr/share/keyrings/google-chrome.gpg

Key insight: When you install Chrome or Edge via .deb, the installer may create a .sources file. If you previously had a .list file from an older install or manual setup, you now have both — and apt update complains about duplicates.

Diagnosing Issues

Check for Duplicates

# List all repository config files
ls /etc/apt/sources.list.d/

# Look for pairs of .list and .sources for the same app
ls /etc/apt/sources.list.d/ | grep google
# Example problematic output:
# google-chrome.list
# google-chrome.sources

Check for Errors

sudo apt update 2>&1 | grep -E "W:|E:|Err"

Common error patterns:

W: Target ... is configured multiple times — duplicate repos
W: ...doesn't support architecture 'i386' — missing arch restriction
Err: ... NO_PUBKEY ... — missing GPG signing key

Fix: Duplicate Repository Entries

Chrome (Most Common)

# Check what exists
ls /etc/apt/sources.list.d/ | grep google

# If BOTH google-chrome.list AND google-chrome.sources exist:
sudo rm /etc/apt/sources.list.d/google-chrome.list

# Verify
sudo apt update

Edge

ls /etc/apt/sources.list.d/ | grep microsoft-edge

# If both formats exist:
sudo rm /etc/apt/sources.list.d/microsoft-edge.list

sudo apt update

Brave

ls /etc/apt/sources.list.d/ | grep brave

# If both formats exist:
sudo rm /etc/apt/sources.list.d/brave-browser-release.list

sudo apt update

General Rule

When both .list and .sources exist for the same app:

Keep the .sources file (new format)
Remove the .list file (old format)
Run sudo apt update to verify

Fix: Architecture Warnings (i386)

N: Skipping acquire of configured file 'main/binary-i386/Packages' as repository '...' doesn't support architecture 'i386'

This means a 64-bit-only repository is configured without specifying arch=amd64.

For .list files:

# Edit the file
sudo nano /etc/apt/sources.list.d/google-chrome.list

# Change:
deb https://dl.google.com/linux/chrome/deb/ stable main
# To:
deb [arch=amd64] https://dl.google.com/linux/chrome/deb/ stable main

For .sources files:

sudo nano /etc/apt/sources.list.d/google-chrome.sources

# Add this line if missing:
Architectures: amd64

Fix: GPG Key Errors

Missing Key (NO_PUBKEY)

W: GPG error: https://dl.google.com/linux/chrome/deb stable InRelease:
The following signatures couldn't be verified because the public key is not available: NO_PUBKEY ABCDEF1234567890

Fix — import the key:

# For Chrome
curl -fsSL https://dl.google.com/linux/linux_signing_key.pub | sudo gpg --dearmor -o /usr/share/keyrings/google-chrome.gpg

# For Edge
curl -fsSL https://packages.microsoft.com/keys/microsoft.asc | sudo gpg --dearmor -o /usr/share/keyrings/microsoft-edge.gpg

# For Brave
curl -fsSL https://brave-browser-apt-release.s3.brave.com/brave-browser-archive-keyring.gpg | sudo tee /usr/share/keyrings/brave-browser-archive-keyring.gpg > /dev/null

Deprecated apt-key Warning

W: Key is stored in legacy trusted.gpg keyring (/etc/apt/trusted.gpg)

This means a key was added with the old apt-key add method. Modern Ubuntu uses per-repo keyring files in /usr/share/keyrings/.

Fix — migrate to new format:

# Export the key from legacy keyring
sudo apt-key export KEYID 2>/dev/null | sudo gpg --dearmor -o /usr/share/keyrings/repo-name.gpg

# Update the .sources or .list file to reference the new keyring:
# signed-by=/usr/share/keyrings/repo-name.gpg

Safely Removing PPAs

# List installed PPAs
grep -r "ppa" /etc/apt/sources.list.d/

# Remove a PPA and its source file
sudo add-apt-repository --remove ppa:owner/repo-name

# Clean up afterward
sudo apt update

Full PPA Removal Example (Papirus icons)

sudo apt remove --purge papirus-icon-theme papirus-folders
sudo add-apt-repository --remove ppa:papirus/papirus
sudo apt autoremove
sudo apt update

Full PPA Removal Example (FSearch)

sudo apt remove --purge fsearch
sudo add-apt-repository --remove ppa:christian-boxdoerfer/fsearch-daily
sudo apt autoremove --purge
sudo apt update

Clean State Verification

After fixing repository issues, verify everything is clean:

# Check for errors
sudo apt update 2>&1 | grep -E "W:|E:|Err"

# List all configured repos
ls /etc/apt/sources.list.d/

# Check for duplicate entries
apt-cache policy | grep -E "http" | sort | uniq -d

# Check for orphaned keys
ls /usr/share/keyrings/

What Didn’t Work (and Why)

Approach Tried	Why It Failed
Having both `.list` and `.sources` for Chrome	Causes “Target is configured multiple times” duplicate warning
Using `apt-key add` to import GPG keys	Deprecated in Ubuntu 24.04 — use `/usr/share/keyrings/` instead
Not specifying `[arch=amd64]` in repo entry	Triggers i386 architecture warning on every `apt update`
Removing a PPA without removing its packages first	Packages remain installed but won’t get updates
Ignoring `apt update` warnings	Warnings accumulate and can eventually become errors

Package Management Basics — How apt works
Browser Setup — Chrome, Edge, Brave repository setup
Common Issues — General troubleshooting FAQ