MQTT user password.txt, Error: Address in use

Installing and Using OpenWrt
1

I am trying to set up MQTT and I receive several errors that partially seem to be very common.

The first one is that when I start mosquitto with the configuration file, then mosquitto seems to have no file access to the password.txt.
how do I add user mosquitto to the password.txt and is it enough to give it only read rights or how to proceed?

The second one is that I can't start mosquitto because port 1883 is in use.
the command lsof -i TCP:1883 doesn't work.

EDIT:

root@OpenWrt:/etc/mosquitto# netstat -t 1883
Active Internet connections (w/o servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State
tcp        0    304 OpenWrt.lan:ssh         xxx.lan:7057          ESTABLISHED
tcp        0      0 OpenWrt.lan:ssh           xxx.lan:7494          ESTABLISHED
tcp        0      0 OpenWrt.lan:ssh           xxx.lan:7020          ESTABLISHED