How to fix W: Failed to fetch URL Could not connect to hostname:port in APT

First, verify your system can reach the internet:

ping -c 4 google.com

If ping fails:
- Check your network interface is up: ip link show
- Check you have an IP address: ip addr show
- Restart networking: sudo systemctl restart networking (or NetworkManager if using NetworkManager)
- Check WiFi/ethernet is connected

If ping works but apt still fails, move to the next step.

DNS resolution converts repository hostnames to IP addresses. Test it:

nslookup archive.ubuntu.com
# or
host archive.ubuntu.com
# or
dig archive.ubuntu.com

If DNS fails:
1. Check your current DNS servers:

cat /etc/resolv.conf

2. Try using a public DNS server (Google's 8.8.8.8 or Cloudflare's 1.1.1.1):

sudo nano /etc/resolv.conf
   # Add or replace with:
   nameserver 8.8.8.8
   nameserver 1.1.1.1

3. Test DNS again after updating the file.

Some systems have broken IPv6 support. Force apt to use IPv4 only:

sudo apt-get -o Acquire::ForceIPv4=true update

If this works, make it permanent:

echo 'Acquire::ForceIPv4 "true";' | sudo tee /etc/apt/apt.conf.d/99-ipv4

Then try updating again:

sudo apt update

Ensure your firewall allows outbound HTTP and HTTPS connections:

sudo ufw status

If ufw is active, allow outbound traffic on ports 80 and 443:

sudo ufw allow out 80/tcp
sudo ufw allow out 443/tcp

If using iptables directly:

sudo iptables -L -n
# Check OUTPUT chain rules; ensure they allow port 80/443 or are set to ACCEPT by default

After updating firewall rules, test apt again.

Sometimes corrupted cache causes issues. Clean and retry:

sudo apt clean
sudo apt autoclean
sudo apt update

The apt clean command removes all cached package files, forcing apt to re-download fresh package lists from repositories.

If the default mirror is down, try an alternative:

sudo nano /etc/apt/sources.list

If using Ubuntu, you can replace the mirror URL. For example, change:

deb http://archive.ubuntu.com/ubuntu/ jammy main restricted

To use a different region mirror (e.g., your country's mirror). Check [Ubuntu Mirror List](https://launchpad.net/ubuntu/+archivemirrors) for available mirrors.

After editing, test:

sudo apt update

If your network requires a proxy, configure apt:

sudo nano /etc/apt/apt.conf.d/proxy.conf

Add your proxy details:

Acquire::http::Proxy "http://proxy.example.com:8080/";
Acquire::https::Proxy "http://proxy.example.com:8080/";

For authenticated proxies:

Acquire::http::Proxy "http://username:[email protected]:8080/";

Save the file and retry:

sudo apt update