Hello smuseby,
I think the issue is due to the mosquitto.conf file being missing in the specified path.
Here is a example mosquitto.conf you could use for testing purposes:
listener 1883
allow_anonymous true
persistence true
persistence_location /mosquitto/data/
log_dest file /mosquitto/log/mosquitto.log
Paste the config file into /etc/mosquitto/config/mosquitto.conf and then run:
docker run -it -d --name mos1 -p 1883:1883 -v /etc/mosquitto/config/mosquitto.conf:/mosquitto/config/mosquitto.conf eclipse-mosquitto:2
You can afterwards use the command line clients for subscribe/publish on MQTT topics.
Examples:
mosquitto_sub -h localhost -p 1883 -t "test"
mosquitto_pub -h localhost -p 1883 -t "test" -m "MQTT is great!"