Pages refuse to load. A site still resolves to the old server hours after a migration. Both usually trace back to stale records sitting on your own machine. Linux stores the addresses it looks up, and those entries go bad with time. A linux flush dns clears them so the next lookup starts clean. Which command you need depends on the resolver running on your box.
What the DNS Cache Stores on Linux
Each cached entry pairs a domain name with an IP address. Reusing that entry skips a full lookup, so the page opens faster.
Problems start when the stored answer stops matching reality. Common signs:
- sites that will not open at all
- connection errors on domains that worked yesterday
- slow first loads
- tabs that fail again and again
Plain glibc caches nothing. A local DNS cache exists only when systemd-resolved, nscd or dnsmasq runs, which is why one universal command does not exist on Linux.
Find Your Resolver Before You Linux Flush DNS
Check which program answers queries on port 53 first. Open a terminal and run:
sudo lsof -i :53 -S| Piece | What it does |
|---|---|
| lsof | Lists open files and the processes holding them |
| -i :53 | Limits output to port 53, the standard DNS port |
| -S | Caps the time spent on slow kernel calls |
If systemd-resolved appears in the output, that service handles name resolution and the resolvectl method below applies. Nothing on port 53 means no local cache exists, so there is nothing to clear. Sorting out address ranges on the same box is quicker with an IP subnet calculator.
Four Ways To Linux Flush DNS
| Method | Command | Works on |
|---|---|---|
| resolvectl | sudo resolvectl flush-caches | Any systemd build |
| USR2 signal | sudo killall -USR2 systemd-resolved | Ubuntu 20.04 and newer |
| Service restart | sudo systemctl restart systemd-resolved | Any systemd build |
| nscd | sudo /etc/init.d/nscd restart | Older distributions |
Clear the DNS Cache With resolvectl
Press Ctrl + Alt + T for a terminal, then run:
sudo resolvectl flush-cachesThe sudo prefix grants root rights. resolvectl talks to systemd-resolved, and flush-caches tells it to drop every stored entry. The command prints nothing when it succeeds. Systems on systemd 238 or older need sudo systemd-resolve --flush-caches instead, since the tool was renamed at version 239.
Flush systemd-resolved With a USR2 Signal
You can also poke the daemon directly:
sudo killall -USR2 systemd-resolvedkillall matches processes by name, and USR2 is the signal systemd-resolved treats as an order to empty its cache. The service never stops, so open connections survive. Check the result in the journal:
sudo journalctl -r -u systemd-resolvedHere -r puts the newest entries first and -u narrows output to that single unit.
Restart systemd-resolved to Clear the Cache
A restart wipes the cache too, because the service rebuilds its store on startup:
sudo systemctl restart systemd-resolvedUse this when the resolver itself misbehaves, not just its stored data. Anyone writing or fixing unit files around it can save time with a systemd unit file generator. A full machine reboot clears the cache as well, though that is heavier than the job needs.
Flush DNS on Older Distributions With nscd
Legacy builds ship the Name Service Cache Daemon rather than systemd-resolved. Restart it:
sudo /etc/init.d/nscd restartThe daemon comes back with an empty store. On setups running dnsmasq, send it a hangup signal with sudo killall -HUP dnsmasq. This dnsmasq configuration guide covers how that resolver caches and forwards queries.
Verify the Linux Flush DNS Worked
Two checks confirm the result. Start with the cache counter:
resolvectl statisticsCurrent Cache Size should read 0 straight after a flush. Then confirm the service is healthy and run a live query:
sudo systemctl status systemd-resolved
nslookup google.comA fresh answer means your machine pulled the record again rather than reading it from memory.
Common Linux Flush DNS Errors and Fixes
| Problem | Fix |
|---|---|
| command not found | Confirm the box actually uses systemd-resolved |
| Lookups still fail | Check /etc/resolv.conf, restart networking, verify server addresses |
| No systemd present | Use nscd or dnsmasq, whichever the distribution ships |
| Old IP keeps returning | The stale record sits upstream, not on your machine |
A “command not found” error on resolvectl usually points to a release older than systemd 239, or a distribution that never enabled the service. Confirming the release settles it fast, and this walkthrough on identifying your Ubuntu release shows three ways to read it.
When queries keep failing after a flush, open /etc/resolv.conf and read the nameserver lines. If you are new to the editor, the shortcuts for saving and quitting nano save some guessing. Restart networking afterwards with sudo systemctl restart network-manager.
Still stuck on an old address? Your router or public resolver holds it until the TTL expires, and no local command shortens that wait. Clear it from the router admin panel instead. Firewall rules can also swallow port 53 traffic, which nftables rule handling explains in detail.
FAQs
How do I flush DNS in Linux quickly?
Run sudo resolvectl flush-caches in a terminal. It clears the systemd-resolved cache on Ubuntu, Debian, Fedora and most current distributions, and returns no output when it succeeds.
Does every Linux system cache DNS records?
No. Plain glibc keeps no cache. Caching happens only when systemd-resolved, nscd, dnsmasq or a local BIND resolver runs, so many minimal servers have nothing to flush.
Why does resolvectl say command not found?
Your distribution either predates systemd 239 or does not use systemd-resolved. Try sudo systemd-resolve –flush-caches, or switch to the nscd or dnsmasq command for your setup.
How can I confirm the DNS cache is empty?
Run resolvectl statistics and read Current Cache Size. A value of 0 confirms the flush worked. Follow it with nslookup or dig to test a live lookup.
Do I need to restart my computer after flushing DNS?
No. The flush takes effect at once. A reboot clears the cache as a side effect, but it is never required for the change to apply.
