Add troubleshooting/nginx-port-80-conflict.md

troubleshooting/nginx-port-80-conflict.md

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+# Nginx Port 80 Conflict
+
+## Problem
+
+Docker nginx container would not start.
+
+### Error
+
+```bash
+failed to bind host port 0.0.0.0:80
+```
+
+## Cause
+
+Ubuntu nginx service was already using port 80.
+
+## Fix
+
+Check what is using port 80:
+
+```bash
+ss -tulpn | grep :80
+```
+
+Stop nginx:
+
+```bash
+systemctl stop nginx
+```
+
+Disable nginx:
+
+```bash
+systemctl disable nginx
+```
+
+Remove nginx:
+
+```bash
+apt remove nginx nginx-common -y
+```
+
+Try the Docker container again.
+
+```bash
+docker run -d --name nginx -p 80:80 nginx
+```
+
+## Result
+
+The Docker nginx container started successfully and was able to bind to port 80.