Error when install check_mk free edition

**CMK version:2.1
**OS version:Ubuntu 20

**Error message:Temporary filesystem already mounted
Starting agent-receiver…Already running.
Starting mkeventd…Already running.
Starting liveproxyd…Already running.
Starting mknotifyd…OK
Starting rrdcached…Already running.
Starting cmc…Already running.
Starting apache…(already running: 17965)…OK
Starting dcd…Already running.
Starting redis…/omd/sites/monitoring/etc/rc.d/85-redis: line 10: 18137 Killed init-redis
OK

after starting the check_mk site login page not opening. it is showing

Proxy Error

The proxy server received an invalid response from an upstream server.
The proxy server could not handle the request

Reason: Error reading from remote server


Apache/2.4.41 (Ubuntu) Server