Cannot resolve hostname in Linux terminal? Start here

1. DNS server address is wrong or missing

This is the big one. I've seen this on fresh Ubuntu 22.04 installs, CentOS 7 boxes, even RHEL 9 servers. The DNS resolver isn't set, or it's pointing to something dead.

First check what DNS you're using right now:

cat /etc/resolv.conf

If you see a line like nameserver 127.0.0.53, that's systemd-resolved running. That's normal on Ubuntu 22.04. But if it says 127.0.0.1 and you don't run a local DNS server, that's your problem.

Fix it temporarily to test:

echo "nameserver 8.8.8.8" | sudo tee /etc/resolv.conf

If ping google.com works now, you nailed it. Make it permanent by editing your network config file. On Ubuntu with Netplan:

sudo nano /etc/netplan/00-installer-config.yaml

Add or change the nameservers section:

nameservers:
  addresses:
    - 8.8.8.8
    - 1.1.1.1

Then apply:

sudo netplan apply

On older systems with /etc/network/interfaces, you add a line like dns-nameservers 8.8.8.8 1.1.1.1 under your interface.

2. systemd-resolved is interfering

If your /etc/resolv.conf looks like a symlink to /run/systemd/resolve/stub-resolv.conf, systemd-resolved is in charge. It's supposed to be smart, but I've seen it get confused — especially after a network change or VPN disconnect.

Check what it thinks:

resolvectl status

Look for the DNS Servers line. If it's empty or shows something weird like 127.0.0.1:53, you need to fix it.

The blunt fix is to disable systemd-resolved and use a plain /etc/resolv.conf:

sudo systemctl stop systemd-resolved
sudo systemctl disable systemd-resolved
sudo rm /etc/resolv.conf
echo "nameserver 8.8.8.8" | sudo tee /etc/resolv.conf

That'll get you running. But if you want to keep systemd-resolved, configure it properly:

sudo nano /etc/systemd/resolved.conf

Uncomment and set DNS=8.8.8.8 and FallbackDNS=1.1.1.1. Then restart:

sudo systemctl restart systemd-resolved

Don't bother with resolvconf package. It's old and rarely needed now. systemd-resolved handles everything if you set it right.

3. Network interface DNS settings are wrong in NetworkManager

You might have DNS set correctly in /etc/resolv.conf, but NetworkManager overrides it on reboot. This is common on Fedora and RHEL.

Check your connection:

nmcli dev show | grep DNS

If it shows wrong servers, fix it per interface. List your active connections first:

nmcli con show

Then set DNS for the connection (replace "Wired connection 1" with yours):

nmcli con mod "Wired connection 1" ipv4.dns "8.8.8.8 1.1.1.1"
nmcli con mod "Wired connection 1" ipv4.ignore-auto-dns yes

Bring it down and up:

nmcli con down "Wired connection 1" && nmcli con up "Wired connection 1"

Now check again:

cat /etc/resolv.conf

It should show your new DNS servers. If not, you might have a race condition with systemd-resolved. In that case, disable systemd-resolved (fix #2) or set dns=default in /etc/NetworkManager/NetworkManager.conf and restart.

Quick-reference summary table

Try these in order. Fix #1 works for 70% of cases. Fix #2 covers another 20%. Fix #3 is the last 10%. Don't waste time restarting network services or reinstalling packages — it's almost always a DNS config issue.