How to fix fatal: unable to access 'https://github.com/': Could not resolve host: github.com in Git

First, check if you have general internet connectivity and can resolve DNS:

Test internet connectivity:

# Test if you can reach the internet at all (uses IP, no DNS needed)
ping -c 4 8.8.8.8

Test DNS resolution:

# Test if DNS is working
host github.com
# or
nslookup github.com
# or
dig github.com

Test connectivity to GitHub:

ping -c 4 github.com

If ping 8.8.8.8 works but host github.com fails, you have a DNS problem. If even ping 8.8.8.8 fails, your network connection is down.

Incorrect proxy configuration is a common cause of this error. Check and clear proxy settings:

View current proxy settings:

git config --global --get http.proxy
git config --global --get https.proxy

Remove proxy settings if they exist:

git config --global --unset http.proxy
git config --global --unset https.proxy

Also check for environment variables:

env | grep -i proxy

If you see HTTP_PROXY, HTTPS_PROXY, or similar variables, unset them temporarily:

unset HTTP_PROXY
unset HTTPS_PROXY
unset http_proxy
unset https_proxy

Then try your Git command again.

On Linux, DNS settings are controlled by /etc/resolv.conf. Check and fix it:

View current DNS configuration:

cat /etc/resolv.conf

You should see one or more nameserver entries. If the file is empty or contains only comments, add public DNS servers:

Add Google and Cloudflare DNS:

# Backup the existing file
sudo cp /etc/resolv.conf /etc/resolv.conf.backup

# Add working nameservers
echo "nameserver 8.8.8.8" | sudo tee /etc/resolv.conf
echo "nameserver 1.1.1.1" | sudo tee -a /etc/resolv.conf

If using NetworkManager, restart the network:

sudo systemctl restart NetworkManager
# or
sudo service network-manager restart

Note: On some systems (like Ubuntu with systemd-resolved), you may need to configure DNS through /etc/systemd/resolved.conf instead.

WSL2 has known DNS issues. The auto-generated resolv.conf often points to the wrong nameserver:

Step 1: Disable auto-generation of resolv.conf

Create or edit /etc/wsl.conf:

sudo tee /etc/wsl.conf << EOF
[network]
generateResolvConf = false
EOF

Step 2: Shutdown WSL completely from Windows:

# Run in Windows PowerShell or CMD
wsl --shutdown

Step 3: Restart WSL and recreate resolv.conf:

# Remove the old symlink
sudo rm /etc/resolv.conf

# Create a new file with working DNS
sudo tee /etc/resolv.conf << EOF
nameserver 8.8.8.8
nameserver 1.1.1.1
EOF

Step 4: Test:

ping github.com
git clone https://github.com/octocat/Hello-World.git

DNS uses port 53 (both TCP and UDP). Ensure it's not blocked:

On Linux with ufw:

# Check firewall status
sudo ufw status

# Ensure DNS is allowed (should be by default)
sudo ufw allow out 53

On Linux with firewalld:

sudo firewall-cmd --list-all
sudo firewall-cmd --add-service=dns --permanent
sudo firewall-cmd --reload

On Windows:
1. Open Windows Firewall (search "firewall" in Start menu)
2. Click "Allow an app or feature through Windows Firewall"
3. Ensure your Git client (Git Bash, Git GUI) is allowed

Check if your network/VPN is blocking DNS:

# Try using a specific DNS server directly
nslookup github.com 8.8.8.8

If this works but regular nslookup github.com fails, your network's default DNS is the problem.

VPN clients often interfere with DNS resolution:

Temporary test - disconnect VPN:
1. Temporarily disconnect your VPN
2. Try the Git command again
3. If it works, your VPN is the cause

VPN DNS solutions:

- Use the VPN's DNS servers: Many VPNs require you to use their DNS for security. Check your VPN's documentation.

- Configure split DNS: Some VPN clients let you exclude certain domains from the VPN tunnel.

- Cisco AnyConnect specific fix:

# Check if VPN is overriding DNS
cat /etc/resolv.conf
# If it shows VPN DNS, you may need to manually add public DNS

On Windows, check if VPN is modifying adapter settings:

# View DNS servers for all adapters
Get-DnsClientServerAddress

A bad entry in the hosts file can prevent DNS resolution:

On Linux/macOS:

cat /etc/hosts | grep -i github

On Windows (run as Administrator):

Get-Content C:\Windows\System32\drivers\etc\hosts | Select-String github

If you see any entries for github.com, remove them (unless you specifically added them for a reason):

On Linux/macOS:

sudo nano /etc/hosts
# Comment out or delete any github.com lines

On Windows:
1. Open Notepad as Administrator
2. Open C:\Windows\System32\drivers\etc\hosts
3. Remove or comment out any github.com entries
4. Save the file

Sometimes resetting the network stack resolves persistent DNS issues:

On Windows (run as Administrator):

# Reset TCP/IP stack
netsh int ip reset

# Reset Winsock
netsh winsock reset

# Flush DNS cache
ipconfig /flushdns

# Release and renew IP
ipconfig /release
ipconfig /renew

Restart your computer after running these commands.

On macOS:

# Flush DNS cache
sudo dscacheutil -flushcache
sudo killall -HUP mDNSResponder

On Linux:

# Flush DNS cache (systemd-resolved)
sudo systemd-resolve --flush-caches

# Or restart the network
sudo systemctl restart NetworkManager

Simple fixes to try:
- Toggle your WiFi off and on
- Disconnect and reconnect your Ethernet cable
- Restart your router/modem

If HTTPS continues to have issues, switching to SSH may help as it uses a different network path:

Step 1: Generate an SSH key (if you don't have one):

ssh-keygen -t ed25519 -C "[email protected]"

Step 2: Add the SSH key to your GitHub account:

# Copy the public key
cat ~/.ssh/id_ed25519.pub

Go to GitHub Settings > SSH and GPG keys > New SSH key, and paste the key.

Step 3: Test SSH connectivity:

ssh -T [email protected]

Step 4: Clone using SSH:

git clone [email protected]:username/repository.git

Step 5: Change existing remotes from HTTPS to SSH:

# View current remote
git remote -v

# Change from HTTPS to SSH
git remote set-url origin [email protected]:username/repository.git