Demo Configuring Hostnames and Name Resolution

In this lesson you will learn how to view and change the system hostname, manage local host-to-IP mappings, and verify name resolution on a Linux system. Correct hostname configuration and reliable name resolution are important because many services and networked applications depend on resolving hostnames correctly.

A dark presentation slide reading "Demo" with the subtitle "Configuring Hostnames and Name Resolution" on the left. The right side shows a large empty dark panel with a small "Copyright KodeKloud" in the top-right.

Displaying the current hostname

Use the hostname command to print the current (runtime) hostname.
The persistent hostname is stored in /etc/hostname.
For detailed metadata and the canonical static/present hostname, use hostnamectl (systemd).

Example session:

root@control:~# hostname
control

root@control:~# cat /etc/hostname
control

root@control:~# hostnamectl
   Static hostname: control
   Icon name: computer-vm
   Chassis: vm
   Machine ID: 500d9331afaf4b96957586d4650b73e2
   Boot ID: 42b37518fa5c422991641e371a935270
   Product UUID: 8daa7ceb-1348-044b-929d-623364a7716a
   Virtualization: oracle
   Operating System: Red Hat Enterprise Linux 10.1 (Coughlan)
   CPE OS Name: cpe:/o:redhat:enterprise_linux:10.1
   Kernel: Linux 6.12.0-124.8.1.el10_1.x86_64
   Architecture: x86-64
   Hardware Vendor: innotek GmbH
   Hardware Model: VirtualBox
   Hardware Serial: VirtualBox-eb7caa8d-4813-4b04-929d-623364a7716a
   Firmware Version: VirtualBox
   Firmware Date: Fri 2006-12-01

Setting a new hostname

To change the persistent hostname (updates /etc/hostname automatically), use:

hostnamectl set-hostname control.example.com

Verify the change:

root@control:~# hostname
control.example.com

root@control:~# cat /etc/hostname
control.example.com

Note: hostnamectl updates the static hostname and is the recommended method on systemd-based distributions.

Local name resolution — /etc/hosts

The file /etc/hosts contains local host-to-IP mappings. This file is consulted before DNS when files appears before dns in /etc/nsswitch.conf.
Each line should contain an IP address, then one or more hostnames separated by whitespace.

Example (with a commented correction and a real mapping):

# Loopback entries; do not change.
# For historical reasons, localhost precedes localhost.localdomain:
127.0.0.1  localhost localhost.localdomain localhost4 localhost4.localdomain4
::1        localhost localhost.localdomain localhost6 localhost6.localdomain6
# See hosts(5) for proper format and other examples: https://man7.org/linux/man-pages/man5/hosts.5.html
# 192.168.1.10 foo.example.org foo
# 192.168.1.13 bar.example.org bar
10.0.2.6   node1

If you update a mapping (for example change node1 to node5 at a new IP), save /etc/hosts. The system will then resolve that hostname using the updated entry.

Testing resolution with ping

After editing /etc/hosts, use ping to confirm the hostname resolves to the expected IP:

root@control:~# ping node5
PING node5 (10.0.2.15) 56(84) bytes of data.
64 bytes from node5 (10.0.2.15): icmp_seq=1 ttl=64 time=1.25 ms
64 bytes from node5 (10.0.2.15): icmp_seq=2 ttl=64 time=0.647 ms
64 bytes from node5 (10.0.2.15): icmp_seq=3 ttl=64 time=0.640 ms
64 bytes from node5 (10.0.2.15): icmp_seq=4 ttl=64 time=0.465 ms
^C
--- node5 ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 3027ms
rtt min/avg/max/mdev = 0.465/0.749/1.246/0.295 ms

Tip: You can map arbitrary hostnames (e.g., google.com) to a chosen IP in /etc/hosts for testing, but avoid doing this for public hostnames in production.

Use getent to test resolver lookups

getent queries the system name service switch and respects the lookup order defined in /etc/nsswitch.conf. Use it to verify how the system resolves names without sending ICMP traffic:

root@control:~# getent hosts node5
10.0.2.15        node5

This shows the resolver result as the system sees it, following nsswitch.conf rules.

Name resolution order — /etc/nsswitch.conf

The file /etc/nsswitch.conf defines the order the system uses to resolve different databases, including hosts. A typical hosts line is:

hosts: files dns myhostname

Meaning:

files — check /etc/hosts
dns — query DNS servers
myhostname — fallback to local machine name methods

Example /etc/nsswitch.conf excerpt (with authselect comments corrected):

# Generated by authselect
# Do not modify this file manually, use authselect instead. Any user changes will be overwritten.
# You can stop authselect from managing your configuration by calling `authselect opt-out`.
# In order of likelihood of use to accelerate lookup.
passwd:         files systemd
shadow:         files
group:          files [SUCCESS=merge] systemd
hosts:          files dns myhostname
services:       files
netgroup:       files
automount:      files

aliases:        files
ethers:         files
gshadow:        files
networks:       files dns
protocols:      files
publickey:      files
rpc:            files

Quick reference

Item	Purpose	Example
View current hostname	Show runtime hostname	`hostname`
Persistent hostname file	Where static hostname is stored	`/etc/hostname`
Set persistent hostname	Change system hostname (systemd)	`hostnamectl set-hostname <name>`
Local overrides	Local host-to-IP mappings	`/etc/hosts`
Resolver test (no ICMP)	Check system resolution order	`getent hosts <name>`
Resolution order config	Define lookup order (files, dns, etc.)	`/etc/nsswitch.conf` (`hosts: files dns myhostname`)

Entries in /etc/hosts take precedence over DNS when files appears before dns in /etc/nsswitch.conf. Use /etc/hosts for local overrides and testing, but avoid modifying it for public hostnames unless you understand the implications.

Links and references

hostnamectl (systemd): https://www.freedesktop.org/software/systemd/man/hostnamectl.html
getent manual: https://man7.org/linux/man-pages/man1/getent.1.html
nsswitch.conf manual: https://man7.org/linux/man-pages/man5/nsswitch.conf.5.html
hosts file format: https://man7.org/linux/man-pages/man5/hosts.5.html
authselect (RHEL): https://man7.org/linux/man-pages/man8/authselect.8.html

This concludes the demo on configuring hostnames and managing local name resolution.

Introduction

Working with the Command Line

File Management

Working with Text Files

Output Redirection

User Management

Linux Permissions

Enhanced Command Line

Storage Management

Managing Services

Controlling the Boot Process

Scheduling Future Tasks

Working with Logs

Installing Software

Process Management & Tuning

Managing Network Configuration and Security

SELinux

Configuring SSH

Demo Configuring Hostnames and Name Resolution

Displaying the current hostname

Setting a new hostname

Local name resolution — /etc/hosts

Testing resolution with ping

Use getent to test resolver lookups

Name resolution order — /etc/nsswitch.conf

Quick reference

Links and references

Watch Video

​Displaying the current hostname

​Setting a new hostname

​Local name resolution — /etc/hosts

​Testing resolution with ping

​Use getent to test resolver lookups

​Name resolution order — /etc/nsswitch.conf

​Quick reference

​Links and references

Watch Video

Displaying the current hostname

Setting a new hostname

Local name resolution — /etc/hosts

Testing resolution with ping

Use getent to test resolver lookups

Name resolution order — /etc/nsswitch.conf

Quick reference

Links and references