Intermediate · 12 min · practise every command in the built-in terminal

🎯 Mission Briefing: The Internet Is Down?

Since this morning nothing on this server can reach the outside world: apt update fails, the nightly job can't call its API, and a colleague swears "the internet is down". Is it, though? Your job is to find out what is really broken and fix it.

Your objective

Tell a network problem from a name resolution (DNS) problem, find the misconfiguration, fix it and prove that names resolve again.

Investigation toolkit

ping -c 2 google.com                 # Does a NAME work?
ping -c 2 8.8.8.8                    # Does the network itself work? (an IP needs no DNS)
cat /etc/resolv.conf                 # Which DNS server does the system ask?
dig google.com                       # Ask the configured DNS server
dig @1.1.1.1 google.com              # Ask a different DNS server directly

Fix and verify

ls -l /etc/resolv.conf*              # Is there a known-good copy?
sudo cp /etc/resolv.conf.bak /etc/resolv.conf
# or edit it:  sudo nano /etc/resolv.conf   →   nameserver 1.1.1.1
ping -c 2 google.com

💡 If an IP address works but a name doesn't, the network is fine — DNS is the problem. "Temporary failure in name resolution" is the classic message.

Practice tasks

  1. Show that names don't resolve: ping a website by its name
  2. Prove the network itself works by pinging an IP address
  3. Find out which DNS server the system is using
  4. Point the system at a working DNS server (and remove the dead one)
  5. Confirm that names resolve again

Missions