Understanding DNS Resolution: Key Differences Between /etc/hosts and /etc/resolv.conf in Linux Systems


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While both files handle name resolution in Linux systems, they serve fundamentally different purposes:

# Example /etc/hosts entry
127.0.0.1   localhost
192.168.1.5 myserver.local

The /etc/hosts file provides static hostname-to-IP mappings that take precedence over DNS lookups. It's typically used for:

  • Local development environments
  • Network isolation scenarios
  • Blocking specific domains
# Example /etc/resolv.conf
nameserver 8.8.8.8
nameserver 1.1.1.1
search example.com

The /etc/resolv.conf configures the system's DNS resolver, specifying:

  • DNS server IP addresses
  • Search domains for hostname completion
  • Resolution options like timeout and attempts

The resolution order follows the nsswitch.conf configuration (usually files dns), meaning:

  1. First check /etc/hosts
  2. Then query DNS servers specified in /etc/resolv.conf

For local development with Docker:

# /etc/hosts
127.0.0.1   myapp.local
172.17.0.2  docker-mysql

For custom DNS resolution in a corporate network:

# /etc/resolv.conf
nameserver 10.0.0.53
search internal.corp.example.com
options timeout:2 attempts:2
  • /etc/resolv.conf may be automatically managed by network services (NetworkManager, systemd-resolved)
  • Modern systems may use systemd-resolve --status to view actual DNS configuration
  • Changes to /etc/hosts take effect immediately

The best references are the man pages:

man 5 hosts
man 5 resolv.conf

For deeper understanding, consult the glibc documentation on name service switch.

Both /etc/hosts and /etc/resolv.conf handle hostname resolution in Linux systems, but they operate at different layers of the networking stack and serve distinct purposes.

This static file contains manual IP-to-hostname mappings that bypass DNS resolution entirely. Example entry:

127.0.0.1   localhost
192.168.1.5   myserver.local

This dynamic file configures how the system interacts with DNS servers. Example:

nameserver 8.8.8.8
nameserver 1.1.1.1
search example.com
  • Resolution Order: /etc/hosts is checked before DNS (configured in /etc/nsswitch.conf)
  • Persistence: /etc/hosts changes remain until manually edited, while /etc/resolv.conf may be overwritten by DHCP or network managers
  • Scope: /etc/hosts is machine-specific, while DNS affects all resolvers

For local development environments, I often use:

# In /etc/hosts
127.0.0.1   api.staging.local
127.0.0.1   web.staging.local

For custom DNS configuration in Docker containers:

# In /etc/resolv.conf
nameserver 10.0.0.2
options ndots:0

Modern systems often use systemd-resolved or NetworkManager which dynamically manage /etc/resolv.conf. To check actual DNS configuration:

systemd-resolve --status

For authoritative references:

  • man 5 hosts
  • man 5 resolv.conf
  • The Linux Documentation Project (tldp.org)