How to configure Mosquitto in Docker to have read/write access

Question

I have the issue that my Mosquitto broker on my Synology cannot open or access a log file in a directory the docker container is mapped to. The structure it is aiming for exists, I even created the 'mosquitto.log' for it in the attempt to overcome the problem.

I installed Mosquitto in Docker through:

sudo docker run --name="mqtt" --restart=always --net=host -p 1883:1883 -p 9001:9001 -v /volume1/docker/mqtt/config:/mosquitto/config -v /volume1/docker/mqtt/log:/mosquitto/log -v /volume1/docker/mqtt/data:/mosquitto/data -tid eclipse-mosquitto

The container runs, but the log shows

Error: Unable to open log file /mqtt/log/mosquitto.log for writing.
Error: No such file or directory.

Looking for a solution I found this thread -> GitHub but changing ownership or rights does not change a thing.

The container I created goes by the name mqtt and, within my docker directory there is a structure with the following rights:

docker
|_ drwxrwxrwx  1     1883  1883  26 Jan  8 14:33 mqtt
|  |_ drwxrwxrwx 1 1883 1883 28 Jan 14 16:57 config
|  |  |_ -rwxrwxrwx 1 1883 1883 280 Jan 14 17:02 mosquitto.conf
|  |_ drwxrwxrwx 1 1883 1883  0 Jan  8 14:33 data
|  |_ drwxrwxrwx 1 1883 1883 26 Jan 14 17:09 log

and mosquitto.conf looks like this

persistence true
persistence_location /mqtt/data/

log_dest stdout
log_dest file /mqtt/log/mosquitto.log
log_type warning
log_timestamp true
connection_messages true

and I did not create a user or a group that goes by 1883

Answer 1

-v /volume1/docker/mqtt/log:/mosquitto/log

This makes the folder available as /mosquitto/log in the container. But in your config you are telling mosquitto to log to /mqtt/log/mosquitto.log which does not match the above.

Either use -v /volume1/docker/mqtt/log:/mqtt/log or change the mosquitto.conf to use /mosquitto/log (I'd suggest the second option as this matches the defaults used in the docker image; you should also update persistence_location ).