503 Service Unavailable means the server is reachable but is refusing to handle requests at the moment. Usually it is in maintenance mode, overloaded, or a resource limit has been hit.
If you are visiting the site
A 503 is meant to be temporary. Wait a few minutes and reload.
If you run the site
1. Stuck WordPress maintenance mode
During updates, WordPress creates a file called .maintenance in the site folder. If an update is interrupted, the file stays and every visitor sees Briefly unavailable for scheduled maintenance. Delete it:
rm /var/www/example.com/public/.maintenanceThen rerun the update that was interrupted.
2. PHP-FPM has no free workers
When every PHP worker is busy, new requests queue and eventually fail. Look for this warning:
sudo grep 'max_children' /var/log/php*-fpm.log /var/log/php-fpm/*.log 2>/dev/nullserver reached pm.max_children setting means you need more workers (if there is memory to spare), faster pages, or page caching.
3. Hosting account limits
On shared hosting, a 503 or 508 often means the account hit its CPU, memory or process cap. The control panel’s resource usage page shows when. Traffic spikes, bots or a heavy plugin are the usual reasons.
4. Traffic floods and bots
Check the access log for one address or one URL being hit thousands of times:
sudo awk '{print $1}' /var/log/nginx/access.log | sort | uniq -c | sort -rn | headBlock abusive addresses at the firewall, or put the site behind a CDN that filters bots.
5. A service is deliberately stopped
Load balancers return 503 when no healthy backend is left, and some setups show it while an app restarts. Check the backend services are running.
Related
- 429 Too Many Requests, when a limit targets one visitor.
- 500 Internal Server Error.
Something out of date? Software changes. If a step no longer works, tell us and we will check it and update the page.
