Proxmox Ubuntu Appliance /tmp/dlt cannot be opened

[borpin]

Just installed mosquitto on a Proxmox Ubuntu 20.04 appliance.

On startup the following error is seen

* mosquitto.service - Mosquitto MQTT v3.1/v3.1.1 Broker
     Loaded: loaded (/lib/systemd/system/mosquitto.service; enabled; vendor preset: enabled)
     Active: active (running) since Sun 2020-06-28 10:40:31 UTC; 10min ago
       Docs: man:mosquitto.conf(5)
             man:mosquitto(8)
   Main PID: 9184 (mosquitto)
      Tasks: 3 (limit: 4915)
     Memory: 1.9M
     CGroup: /system.slice/mosquitto.service
             `-9184 /usr/sbin/mosquitto -c /etc/mosquitto/mosquitto.conf

Jun 28 10:40:31 mosquitto systemd[1]: Starting Mosquitto MQTT v3.1/v3.1.1 Broker...
Jun 28 10:40:31 mosquitto mosquitto[9184]: 1593340831: Loading config file /etc/mosquitto/conf.d/bridge.conf
Jun 28 10:40:31 mosquitto mosquitto[9184]: [72979.790296]~DLT~ 9184~INFO     ~FIFO /tmp/dlt cannot be opened. Retrying later...
Jun 28 10:40:31 mosquitto systemd[1]: Started Mosquitto MQTT v3.1/v3.1.1 Broker.

In the Minimal container, DLT is not running.

I see that #993 implemented DLT.

Is it possible to disable it?

[ralight]

Alas not at the moment, but it really really should be. I've just added support to the develop branch, which you could use. Alternatively, compiling without DLT support would do the job.

[colinl]

On a PC running Ubuntu 20.04 with Mosquitto installed from the standard Ubuntu repo (version 1.6.9-1) I see this message, and on shutting down mosquitto I see
~DLT~ 2361~WARNING ~Lost log messages in user buffer when exiting: 11
and there is about a 10 second delay when stopping, which is annoying. Is the delay caused by this problem? If so is there any workaround to stop it delaying the shutdown?

[ralight]

It is the DLT logging that is causing the delay, which is annoying. I've just pushed another change to the fixes branch which checks when DLT is available before trying to initialise DLT, which then avoids this delay.

[colinl]

OK, thanks. That doesn't really help in the short term when installing from the Ubuntu repo, but that is not anything that can be fixed here I know. I had hoped there might be some workaround but there may not be.

[ralight]

You could emulate the dlt fifo being available.

The below would work for a once off very very simple case, there are plenty of ways you could automate it depending on what you would prefer.

mkfifo /tmp/dlt
cat /tmp/dlt

[colinl]

OK, Many thanks.

[sreeharshar84]

You can suppress the message "]DLT141085~INFO ~FIFO /tmp/dlt cannot be opened. Retrying later..." by adding this line to your code before calling "dlt_register_app()" :

dlt_log_init(DLT_LOG_DROPPED);

This will avoid printing out the warning that it is unable to connect dlt-daemon when only console mode is chosen. There is no
way in dlt currently to avoid this issue.

More info: https://pfefferz.github.io/dlt-daemon-doxygen-built/dlt__common_8c_source.html#l02029

[ralight]

@sreeharshar84 Thanks for the hint. The problem here isn't really about the message, but about the big delay on shutdown. This has been fixed in 1.6.11 anyway.

[joshuakoh1]

How do I get the 1.6.11 fix? I've installed mosquitto with sudo apt install mosquitto mosquitto-clients

[colinl]

@joshakoh1 you can install from https://launchpad.net/~mosquitto-dev/+archive/ubuntu/mosquitto-ppa

[abhinav0927]

@colinl Can you please explain the steps to install the mosquitto from https://launchpad.net/~mosquitto-dev/+archive/ubuntu/mosquitto-ppa

What version of mosquitto it has? Is it the latest version

[ralight]

@abhinav0927 It has the latest version, yes.

The steps are:

sudo add-apt-repository ppa:mosquitto-dev/mosquitto-ppa
sudo apt-get update
sudo apt install mosquitto