AH00161: server reached MaxRequestWorkers setting Nginx / Apache Origin: Edge & web server Last updated 5 Nov 2026

Apache: [mpm_event:error] AH00484: server reached MaxRequestWorkers setting, consider raising the MaxRequestWorkers setting

Apache used all its worker slots, so new requests queue or time out.

Exact message you may see server reached MaxRequestWorkers setting, consider raising the MaxRequestWorkers settingAH00161: server reached MaxRequestWorkers setting[mpm_event:error] AH00484: server reached MaxRequestWorkers setting[mpm_prefork:error] AH00161: server reached MaxRequestWorkers setting[mpm_worker:error] AH00286: server reached MaxClients setting
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Seen on: Apache Linux

Meaning

Raise MaxRequestWorkers (and ServerLimit/ThreadsPerChild for event/worker MPM) to fit available RAM (workers ≈ free RAM / avg process size). Also fix slow requests holding workers, enable KeepAlive tuning (KeepAliveTimeout 2-5), and consider PHP-FPM + event MPM instead of prefork+mod_php.

Common causes

  • Traffic spike or slow backend holding workers
  • Default limit (150/256) too low
  • Long KeepAlive timeouts
  • Prefork MPM with mod_php (memory heavy)
  • Slow client attacks

⚡ Quick fix

  1. Tune MaxRequestWorkers to your RAM
  2. Lower KeepAliveTimeout, enable mod_reqtimeout
  3. Switch to event MPM + PHP-FPM

Detailed fix by platform

Linux

  1. apachectl -V | grep -i mpm; ps -ylC apache2 --sort:rss | awk '{sum+=$8} END {print sum/NR/1024 " MB avg"}'

How to diagnose

  1. Limit — MaxRequestWorkers?
  2. RAM — Per-process memory?
  3. Slow — Long requests?

🔧 Still not fixed?

Many errors look alike. If the steps above didn’t solve it, one of these is probably what you’re facing:

Where this error sits

Origin: Edge & web server. Errors that are often confused with or caused by this one (click to open):

103 — HTTP 103 Early Hints (HTTP)1031200 — Cloudflare Error 1200: Cache connection limit (Cloudflare)1200304 — HTTP 304 Not Modified (HTTP)304503 — HTTP 503 Service Unavailable (HTTP)503504 — HTTP 504 Gateway Timeout (HTTP)504524 — Cloudflare Error 524: A Timeout Occurred (Cloudflare)524AH00015: Unable to open logs — Apache: AH00091: apache2: could not open error log file /var/log/apache2/error.log. AH00015: Unable to open logs (Permission denied) (Nginx / Apache)AH00015: Unable to op…AH00037: Symbolic link not allowed or link target not accessible — Apache: [core:error] AH00037: Symbolic link not allowed or link target not accessible: /var/www/html/current (Nginx / Apache)AH00037: Symbolic lin…AH00161: …

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