How to Flush DNS Cache on Linux: A Complete Step‑by‑Step Guide

Why Flush DNS Cache on Linux?

Local DNS cache can become corrupted, causing HTTP errors or DNS spoofing; refreshing forces the system to retrieve fresh records.

How to View Local DNS Cache

Before systemd, most Linux distributions lacked a system‑wide DNS cache unless dnsmasq or nscd were installed. systemd‑resolved now provides caching.

Viewing systemd‑resolved cache

Send SIGUSR1 to dump the cache, then use journalctl to save the output.

sudo killall -USR1 systemd-resolved

sudo journalctl -u systemd-resolved > ~/cache.txt

Open the file with a text editor and search for “CACHE:” to see cached entries.

Viewing nscd cache

sudo strings /var/cache/nscd/hosts | uniq

Viewing dnsmasq cache

Send USR1 to dnsmasq and capture its log.

sudo pkill -USR1 dnsmasq

sudo journalctl -u dnsmasq > ~/cache.txt

How to Flush DNS Cache on Linux

Using systemd‑resolved

sudo resolvectl flush-caches

On Ubuntu 17.04/18.04 you can also run:

sudo systemd-resolved --flush-caches

Flushing nscd cache

Restart the nscd service or invalidate hosts.

sudo /etc/init.d/nscd restart

sudo nscd -i hosts

Flushing dnsmasq cache

sudo systemctl restart dnsmasq

or

service dnsmasq restart

Clearing Chrome DNS Cache

Open chrome://net-internals/#dns and click “Clear host cache”.