mosquitto_sub fails with "Error: Problem setting TLS options: File not found." when using certificate files on xubuntu 20.02

Question

I have a weird problem with mosquitto_sub 1.6.14 running on xubuntu 20.02. Everything works fine as long as I don't use certificate files. When using certificate files, I am getting "Error: Problem setting TLS options: File not found." every time. I am using the following commandline:

mosquitto_sub -h test.mosquitto.org -p 8884 -t tengo/bravo --cafile ~/test/mosquitto.org.crt --cert ~/test/returned.crt --key ~/test/client.key

When using the same command line with the same files on a fedora33 machine, everything works fine.

Can anybody help me? Please!

Answer 1

You should manually connect the mosquitto:home plug to snapd home slot, using below command.

sudo snap connect mosquitto:home snapd:home

Answer 2

For me when this error shows up, the problem usually is that I do not have read access to any one of the --cafile, --cert or --key files. Sometimes I have scripts that generate these files in a docker container, with a mounted drive and permissions don't align.

This error is returned when any of these files couldn't be opened. Have a look at the source code here:

https://github.com/eclipse/mosquitto/blob/master/apps/mosquitto_ctrl/options.c#L599 https://github.com/eclipse/mosquitto/blob/master/lib/options.c#L128

Answer 3

The root-cause of the problem seems to be the installation via snap. I followed the primary suggestion on https://mosquitto.org/download/ to install via snap, having the mentioned problems.

I found a post in ask-ubuntu where someone had a similar problem, where mosquito worked initially after installing with apt, but did not work anymore when reinstalling with snap.

So I tried to remove the snap installation and followed the secondary installation hints on https://mosquitto.org/download/ to install via apt.

Surprise surprise ... now it works.