Configure Hostname Resolution in Linux

Tested on RHEL 10.2 (Coughlan) — vm1.lab.example (192.168.56.116), vm2.lab.example (192.168.56.117)
Package systemd 257-23.el10_2.2
bind-utils 9.18.33-15.el10_2.2
Applies to Ubuntu, Debian, Kali Linux, Linux Mint, Pop!_OS, Raspberry Pi OS, elementary OS, Zorin OS, Parrot OS, MX Linux, RHEL, Rocky Linux, AlmaLinux, Oracle Linux, CentOS Stream, Fedora, Arch Linux
Privilege Normal user for lookups; sudo or root to edit /etc/hosts, nsswitch.conf, and NetworkManager profiles
Scope Name resolution flow, hostname vs FQDN, /etc/hosts, nsswitch.conf, getent hosts, dig and host, DNS servers and search domains with NetworkManager, resolv.conf, and ordered troubleshooting. Does not cover BIND server setup, changing the local hostname with hostnamectl, or full DNS protocol theory.
Related guides hostnamectl command
dig and host commands
nmcli command examples
RHCSA tutorial
Linux command line
IMPORTANT
This guide explains how Linux turns hostnames into IP addresses and how to fix resolution failures. It does not install or operate a DNS server, and it does not replace the dedicated hostnamectl command article for setting this machine’s static hostname.

When you ssh vm2.lab.example, the shell does not magically know 192.168.56.117. Applications ask the Name Service Switch (NSS) layer, which may read /etc/hosts, query DNS, or consult other backends configured on your system. This walkthrough uses two lab hosts: vm1.lab.example resolves peers through local files and DNS depending on the name you test.

How Linux Hostname Resolution Works

text
Application (ssh, curl, ping)
   ↓
libc / getent
   ↓
Name Service Switch (nsswitch.conf)
   ├── files      → /etc/hosts
   ├── dns        → DNS servers (resolv.conf / stub resolver)
   ├── myhostname → local machine name (RHEL/Fedora)
   └── other backends if configured (LDAP, etc.)

Resolution is not one fixed path. The hosts: line in /etc/nsswitch.conf defines which sources NSS tries and in which order. The first source that returns an answer wins for getent hosts.

Hostname Resolution Quick Reference

Task Command or file
Show local hostname hostnamectl
Test NSS hosts database getent hosts NAME
Test closer to modern apps getent ahosts NAME
Query DNS directly dig NAME
Simple DNS lookup host NAME
Local static mappings /etc/hosts
Resolution order /etc/nsswitch.conf
NetworkManager DNS nmcli device show
Resolver file (often generated) /etc/resolv.conf

Hostname vs DNS Name vs FQDN

Term Meaning
Static hostname Name this machine uses for itself (hostnamectl)
Short name Single label such as vm2 or server
FQDN Host plus domain, such as vm2.lab.example
DNS domain Suffix published in DNS zones (lab.example)
Alias Extra name in /etc/hosts or DNS pointing at the same address

On the lab client:

bash
hostnamectl status
output
Static hostname: vm1.lab.example
       Icon name: computer-vm
         Chassis: vm 🖴
      Machine ID: 23b7a5ba4a464d768c37c2b2990e7d06
         Boot ID: a15989ae19014058b9f02b857023ac9f
    Product UUID: d5f4d06c-44bf-4b46-b216-ff4f3472c78d
  Virtualization: oracle
Operating System: Red Hat Enterprise Linux 10.2 (Coughlan)
     CPE OS Name: cpe:/o:redhat:enterprise_linux:10.2
          Kernel: Linux 6.12.0-211.42.1.el10_2.x86_64
    Architecture: x86-64
 Hardware Vendor: innotek GmbH

Static hostname is how this VM names itself. Remote peers you ssh to are separate DNS or /etc/hosts entries. To change the local hostname, see hostnamectl command.

Configure Local Name Resolution with /etc/hosts

/etc/hosts maps addresses to names before DNS is consulted when files appears first in nsswitch.conf.

Syntax:

text
192.0.2.10   server.example.com server
Piece Role
Address IPv4 or IPv6
Canonical name First hostname after the address
Aliases Additional names on the same line

This lab already maps vm2:

bash
grep vm2 /etc/hosts
output
192.168.56.117  vm2.lab.example vm2

Add a temporary peer entry:

bash
sudo tee -a /etc/hosts <<'EOF'
192.168.56.118  labpeer.lab.example labpeer
EOF

IPv6 entries use the same layout with an address such as 2001:db8::10 in the first column.

Understand /etc/nsswitch.conf

The hosts: line controls NSS order for hostname lookups:

bash
grep '^hosts:' /etc/nsswitch.conf
output
hosts:      files  dns myhostname
Source Typical role
files /etc/hosts
dns DNS servers from resolver configuration
myhostname Resolves the local static hostname (common on RHEL and Fedora)

Distributions differ. Some systems add resolve for systemd-resolved or mdns4_minimal for multicast DNS. Read the actual line on the host you troubleshoot rather than assuming a universal template.

Test the Complete Linux Resolution Path

getent hosts tests the NSS hosts database and shows whether /etc/hosts, DNS, or another configured NSS backend can resolve the name. It uses the legacy gethostbyname2() / gethostbyaddr() interfaces—not getaddrinfo(), which many modern applications call instead.

bash
getent hosts labpeer.lab.example
output
192.168.56.118  labpeer.lab.example labpeer

Short names resolve when an alias or search domain applies:

bash
getent hosts labpeer
output
192.168.56.118  labpeer.lab.example labpeer

Compare with a name that exists only in /etc/hosts but not in public DNS:

bash
getent hosts vm2.lab.example
output
192.168.56.117  vm2.lab.example vm2

Query DNS for the same FQDN with full dig so you can read the response status in the header (+short hides it):

bash
dig vm2.lab.example
output
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 62341
;; flags: qr rd ra ad; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 1

;; QUESTION SECTION:
;vm2.lab.example.		IN	A

status: NXDOMAIN means the DNS server reports that name does not exist in DNS. An empty dig +short result alone is weaker—it only shows no address in the answer section and can also appear when the name exists but the queried record type has no data.

getent succeeded from the NSS files source; dig queried DNS and therefore did not use /etc/hosts. That split is normal and is why both tools matter in troubleshooting.

Remove the temporary mapping:

bash
sudo sed -i '/labpeer/d' /etc/hosts

Query DNS Directly

dig and host speak to DNS servers configured in resolver settings, not to NSS file order.

Public name through DNS:

bash
dig +short google.com
output
142.250.67.46

NSS should return the same address when dns is in the hosts: line:

bash
getent hosts google.com
output
142.250.67.46   google.com

When both agree, NSS reached DNS successfully.

DNS failure for a hosts-only name:

bash
host vm2.lab.example
output
Host vm2.lab.example not found: 3(NXDOMAIN)
Observation Likely meaning
dig/host work, getent fails for the same FQDN NSS order, missing dns in nsswitch, or bracketed NSS actions such as [NOTFOUND=return]
dig/host work, getent fails for a short name only Search-domain mismatch or no /etc/hosts alias for the short form
getent works, dig returns NXDOMAIN Answer came from /etc/hosts or another non-DNS NSS source
Both fail Name missing everywhere, or DNS/network path broken

More query patterns live in dig and host commands.

Configure DNS Servers with NetworkManager

On RHEL and Fedora desktops and servers with NetworkManager, DNS servers and search domains usually come from connection profiles—not hand-edited resolv.conf. RHEL 10 documents ipv4.dns and ipv4.dns-search as the NetworkManager properties for these settings.

List active connection profiles so you know which name to edit:

bash
nmcli -t -f NAME,DEVICE con show --active
output
enp0s3:enp0s3
Internal-LAN:enp0s8
lo:lo

Set a static DNS server and search suffix on the lab LAN profile (Internal-LAN on this host). The address 192.0.2.53 is documentation TEST-NET space—replace it with a resolver that exists on your network:

bash
sudo nmcli con mod Internal-LAN ipv4.dns "192.0.2.53"

Add the search domain on the same profile:

bash
sudo nmcli con mod Internal-LAN ipv4.dns-search "lab.example"

Reactivate the profile so NetworkManager regenerates resolver data:

bash
sudo nmcli con up Internal-LAN
output
Connection successfully activated (D-Bus active path: /org/freedesktop/NetworkManager/ActiveConnection/6)

Confirm DNS and domain settings on the interface that uses that profile:

bash
nmcli device show enp0s8 | grep -E 'IP4\.(DNS|DOMAIN)'
output
IP4.DNS[1]:                             192.0.2.53

When the profile still uses DHCP (ipv4.method auto), NetworkManager may merge manually configured DNS and search values with values supplied automatically by DHCP. The system-wide /etc/resolv.conf can list nameservers from more than one active connection:

bash
grep -E '^(search|nameserver)' /etc/resolv.conf
output
search nsn-intra.net lab.example
nameserver 192.168.0.1
nameserver fd17:625c:f037:2::3
nameserver 192.0.2.53

To replace DHCP-provided DNS entirely on that profile instead of merging with it, set:

bash
sudo nmcli con mod Internal-LAN ipv4.ignore-auto-dns yes

Then reactivate the connection. NetworkManager documents this property explicitly for profiles that should use only the DNS servers you configure.

For more connection editing patterns, see nmcli command examples.

Understand DNS Search Domains

Search domains let applications resolve short names by appending suffixes from search or domain lines in resolver configuration. glibc applies the search list to names with fewer dots than the ndots threshold (often 1), so server.example.com is queried as written while server may expand to server.lab.example.

With search lab.example in /etc/resolv.conf, an application may expand server to server.lab.example before querying DNS.

You type Resolver may try
vm2.lab.example Exact FQDN first
vm2 vm2.lab.example if lab.example is in search
server server.lab.example, then other search suffixes

/etc/hosts aliases can make short names work without DNS. vm2 resolves here because the line includes the vm2 alias, not because DNS published it.

Check Resolver Configuration

Read the active resolver file the system uses:

bash
cat /etc/resolv.conf
output
# Generated by NetworkManager
search nsn-intra.net lab.example
nameserver 192.168.0.1
nameserver fd17:625c:f037:2::3

On NetworkManager-managed systems, the header Generated by NetworkManager means manual edits may be overwritten when a connection reactivates. Change DNS on the connection profile instead.

Some installations use systemd-resolved with a stub file at /etc/resolv.conf pointing to 127.0.0.53. The troubleshooting pattern is the same: find which component owns DNS (nmcli, resolved, or static files) before you edit.

Troubleshoot Hostname Resolution

Work in order:

  1. Confirm the exact name the application uses (FQDN vs short name).
  2. Check /etc/hosts for a static mapping.
  3. Read hosts: in /etc/nsswitch.conf.
  4. Inspect DNS servers and search in nmcli device show and /etc/resolv.conf.
  5. Query DNS directly with dig or host.
  6. Verify search domains expand short names as you expect.
  7. Confirm routing to the DNS server (ip route) when errors mention timeouts.
  8. Check firewalls only when DNS UDP/TCP to the server is blocked.

When you want behavior closer to modern applications (including IPv4/IPv6 address selection), getent ahosts uses getaddrinfo():

bash
getent ahosts vm2.lab.example
output
192.168.56.117  STREAM vm2.lab.example
192.168.56.117  DGRAM  
192.168.56.117  RAW
Symptom Likely cause Next step
Name or service not known No NSS source returned an answer getent hosts NAME; check hosts file and nsswitch
Temporary failure in name resolution DNS unreachable or timeout dig NAME; check routes and nameserver reachability
NXDOMAIN from dig Name absent in DNS Add DNS record or use /etc/hosts for lab names
Wrong IP returned Stale /etc/hosts entry wins over DNS Compare getent vs dig; fix files line or order
FQDN works, short name fails Missing or wrong search domain, or no /etc/hosts short alias Check search in /etc/resolv.conf, ipv4.dns-search, and /etc/hosts aliases
Short name works, expected FQDN fails Short name likely from a /etc/hosts alias or another NSS source Compare getent for both forms; inspect hosts file before blaming search domains
dig works, application fails for same FQDN NSS path or bracketed NSS actions differ from direct DNS Test getent hosts and getent ahosts with the exact string the app uses

Practical Resolution Examples

Two-host lab workflow on vm1.lab.example:

  1. Map the peer in /etc/hosts:
bash
grep vm2 /etc/hosts
  1. Confirm NSS resolution:
bash
getent hosts vm2
output
192.168.56.117  vm2.lab.example vm2
  1. Confirm DNS does not publish the lab name (expected in this lab)—read status: in the dig header:
bash
dig vm2.lab.example +noall +comments +answer
output
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 53019
;; flags: qr rd ra ad; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 1

  1. Set DNS servers and search suffixes on the connection profile with nmcli (ipv4.dns and ipv4.dns-search on Internal-LAN in this lab).

  2. Connect by name (resolution succeeds before SSH authenticates):

bash
getent hosts vm2.lab.example

Use getent to prove the name resolves; use ssh, curl, or your application to test the full connection after that.

References

Summary

Linux hostname resolution is a chain: applications call NSS, NSS reads nsswitch.conf, and sources such as /etc/hosts and DNS answer in order. getent hosts tests the NSS hosts database; getent ahosts follows getaddrinfo() closer to what modern apps use. dig and host query DNS directly and can disagree when /etc/hosts or another NSS source answers first.

On this lab, vm2.lab.example resolves through /etc/hosts while DNS returns NXDOMAIN in the dig header—a pattern you will see for internal names until you publish DNS records or keep static mappings. Configure DNS servers with ipv4.dns and search domains with ipv4.dns-search on NetworkManager connection profiles; use ipv4.ignore-auto-dns when you must replace DHCP DNS instead of merging with it. Treat generated /etc/resolv.conf as output rather than the primary edit target.

When troubleshooting, compare getent hosts, getent ahosts, full dig status lines, nsswitch.conf, and resolver settings before you blame the application. For changing this machine’s hostname, use hostnamectl command. For DNS query syntax, see dig and host commands. For connection profiles, see nmcli command examples.

Frequently Asked Questions

1. What is the difference between getent hosts and dig?

getent hosts follows the Name Service Switch order in nsswitch.conf, so local files can answer before DNS. dig is a DNS query utility and queries DNS servers directly; it does not consult /etc/hosts in normal use.

2. Why does dig work but ssh says Name or service not known?

dig queries DNS directly, while SSH and most applications resolve through NSS. If dig works but getent or SSH fails for the same FQDN, inspect the hosts line in nsswitch.conf, including bracketed NSS actions, and confirm the application uses the exact same hostname. For short unqualified names, also check configured search domains.

3. Should I edit /etc/resolv.conf by hand on NetworkManager systems?

Usually no. NetworkManager generates resolv.conf on many RHEL and Fedora systems. Change DNS servers and search domains on the connection profile with nmcli instead of overwriting the generated file.

4. Can I use ping to test DNS?

ping only shows whether some address was resolved and whether packets reach the host. It does not show which resolver answered or why getent and dig disagree, so use getent, dig, and host for diagnosis.

5. Where does the system hostname differ from DNS names?

hostnamectl sets the local static hostname for the machine identity. DNS names live in zones and /etc/hosts and are what applications resolve when you ssh or curl a remote host.
Deepak Prasad

R&D Engineer

Founder of GoLinuxCloud with more than 15 years of expertise in Linux, Python, Go, Laravel, DevOps, Kubernetes, Git, Shell scripting, OpenShift, AWS, Networking, and Security. With extensive experience, he excels across development, DevOps, networking, and security, delivering robust and efficient solutions for diverse projects.

Expertise
  • Go (programming language)
  • Python (programming language)
  • DevOps
  • Computer Security
  • Cloud Computing
  • Kubernetes
  • Linux
  • Ansible (software)

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