FreeBSD 15 – resolv.conf gets overwritten by dhclient and breaks internal DNS

📖 ~1 min read

Table of contents

1. Symptom & Impact
2. Environment & Reproduction
3. Root Cause Analysis
4. Quick Triage
5. Step-by-Step Diagnosis
6. Solution – Primary Fix
7. Solution – Alternative Approaches
8. Verification & Acceptance Criteria
9. Rollback Plan
10. Prevention & Hardening
11. Related Errors & Cross-Refs
12. References & Further Reading

Symptom & Impact

Host intermittently loses access to internal zones after DHCP renew events.

Environment & Reproduction

Common on mixed static+DHCP environments where custom DNS is required.

cat /etc/resolv.conf
ps aux | grep '[d]hclient'
service netif status

Root Cause Analysis

dhclient replaces resolver file on lease renewal, discarding enterprise DNS search/domain configuration.

Quick Triage

Confirm resolver file timestamp changes align with DHCP events.

ls -lT /etc/resolv.conf
grep -i dhclient /var/log/messages | tail -n 50

Step-by-Step Diagnosis

Review dhclient scripts and lease options that manage resolv.conf generation.

cat /etc/dhclient.conf
cat /var/db/dhclient.leases.* | tail -n 80
grep -R resolv /sbin/dhclient-script*

Solution – Primary Fix

Supersede DNS values in dhclient.conf or lock resolv management strategy.

echo 'supersede domain-name-servers 10.0.0.53, 10.0.0.54;' >> /etc/dhclient.conf
service netif restart
service routing restart

Solution – Alternative Approaches

Disable DHCP on critical interfaces and define static resolver settings.

sysrc ifconfig_='inet  netmask '
cat > /etc/resolv.conf <<EOF
nameserver 10.0.0.53
search corp.example
EOF

Verification & Acceptance Criteria

Lease renew no longer removes internal resolver entries.

dhclient -r  && dhclient 
cat /etc/resolv.conf
drill internal.corp.example

Rollback Plan

Remove supersede directives and return to provider DNS if required for compatibility.

sed -i '' '/supersede domain-name-servers/d' /etc/dhclient.conf
service netif restart

Prevention & Hardening

Track resolver integrity with file checksum monitoring and alerting.

sha256 /etc/resolv.conf

Related Errors & Cross-Refs

Often appears with split-DNS VPN routing and search domain order issues.

Related tutorial: View the step-by-step tutorial for freebsd-15.

View all freebsd-15 tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

dhclient.conf man page and FreeBSD network interface configuration docs.