How to resolve DNS and use /etc/hosts

Topic: Servers linux

Configure and test DNS resolution: set nameservers in resolv.conf or netplan, use getent and dig to verify; add static entries in /etc/hosts when you need a fixed name without DNS. Use this when the server cannot resolve hostnames or you need to override a name.

Intent: How-to

Quick answer

  • Nameservers: /etc/resolv.conf (nameserver 8.8.8.8) or in netplan/NetworkManager; getent hosts example.com or dig example.com to test.
  • /etc/hosts: add line 'IP FQDN shortname'; checked before DNS by default (nsswitch.conf order); use for local overrides or when DNS is down.
  • If resolv.conf is overwritten: set nameservers in netplan (resolve section) or in NM; avoid editing resolv.conf directly on systems that manage it.

Prerequisites

Steps

  1. Check current DNS config

    cat /etc/resolv.conf; cat /etc/nsswitch.conf (hosts: files dns); getent hosts example.com; dig example.com +short.

  2. Set nameservers

    Netplan: nameservers.addresses in the interface; NM: nmcli con mod ID ipv4.dns '8.8.8.8 1.1.1.1'; then netplan apply or NM reload; verify resolv.conf.

  3. Add /etc/hosts entry

    echo '192.168.1.10 myapp.local myapp' | sudo tee -a /etc/hosts; getent hosts myapp.local; use for local dev or overrides.

  4. Verify and debug

    getent hosts name; dig name; nslookup name; if fail check resolv.conf and firewall (outbound 53); check /etc/hosts for wrong entry.

Summary

You will configure DNS (resolv.conf or netplan/NM), test resolution with getent and dig, and add static entries in /etc/hosts when needed. Use this when the server cannot resolve names or you need a local override.

Prerequisites

  • Root or sudo; network connectivity.

Steps

Step 1: Check current DNS config

cat /etc/resolv.conf
getent hosts google.com
dig google.com +short

Step 2: Set nameservers

In netplan add under the interface: nameservers: addresses: [8.8.8.8, 1.1.1.1]. Then netplan apply.

Step 3: Add /etc/hosts entry

echo '192.168.1.10 myapp.local' | sudo tee -a /etc/hosts
getent hosts myapp.local

Step 4: Verify and debug

  • getent and dig succeed; wrong or stale entry in hosts can break resolution—edit or remove it.

Verification

  • Resolution works for a test name; /etc/hosts used when expected (order in nsswitch.conf).

Troubleshooting

resolv.conf overwritten — Managed by systemd-resolved or NM; set DNS in netplan or NM, not directly in resolv.conf.

Slow resolution — Check DNS server reachability; reduce timeout or use a closer DNS; check for IPv6 attempts that hang.

Next steps

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