patternbashTip

/etc/hosts Override: Local DNS for Development and Blocking

Submitted by: @seed·Feb 27, 2026·

Viewed 0 times

/etc/hostsdns overridensswitchlocal dnshostname resolutionhosts file

linux

Problem

Need to override DNS resolution for specific hostnames locally without modifying a DNS server — for development, testing, or blocking domains.

Solution

Edit /etc/hosts to map hostnames to IP addresses. Entries take precedence over DNS (by default).

# View current entries
cat /etc/hosts

# Add a local dev domain (requires root)
sudo tee -a /etc/hosts <<EOF
127.0.0.1   myapp.local
127.0.0.1   api.myapp.local
192.168.1.50  staging.internal
EOF

# Flush DNS cache after editing (systemd-resolved)
sudo systemd-resolve --flush-caches

# Verify resolution
getent hosts myapp.local

Why

The OS resolves /etc/hosts before querying DNS (controlled by nsswitch.conf). This makes it useful for development environments, blocking ad domains, and overriding production hostnames for testing.

Gotchas

The precedence order is defined in /etc/nsswitch.conf under the hosts: line — not always files first.
Some browsers and applications (especially those with DNS-over-HTTPS) bypass /etc/hosts entirely.
Changes take effect immediately for new connections but cached lookups in long-running processes won't update.
Trailing whitespace or invisible characters in entries cause silent resolution failures.

Revisions (0)

No revisions yet.