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Remote Logging

ESP32 Manager contains a tiny logger module that is able to send output to multiple independent appenders. esp32m library contains, among others, 2 appenders able to send log messages to remote servers for storage and analysis. This feature may be extremely helpful when debugging applications, especially when no physical access to the ESP32 chip or its UART0 is available.

Logging to rsyslog​

Server setup​

RSYSLOG daemon is included by default in the majority of modern Linux distributions. Is capable of collecting remote log messages over the TCP or UDP protocol. Many distributions have this feature disabled by default, so we need a little tweak to enable it. Open /etc/rsyslog.conf and make sure that the following lines are un-commented:

module(load="imudp")
input(type="imudp" port="514")

Now restart the rsyslog daemon and check that it is listening on UDP port 514::

$ sudo systemctl restart rsyslog
$ sudo netstat -nlp | grep rsyslogd

if everything is right, you should see something like this:

udp        0      0 0.0.0.0:514             0.0.0.0:*                           9335/rsyslogd
udp6       0      0 :::514                  :::*                                9335/rsyslogd

Appender setup​

Add CONFIG_ESP32M_LOG_UDP=y to your sdkconfig to enable UDP logging to rsyslog. Alternatively, add the following code to your main.cpp:

#include <esp32m/log/udp.hpp>

...

log::addBufferedAppender(new log::Udp());

By default, UDP appender looks for syslog.lan name on your local network. You can just add this name to the /etc/hosts file on the machine with the rsyslog server, or add static name to your local DNS. Alternatively, you can pass IP or DNS name of your rsyslog server to the new log::Udp() statement.

Checking output​

If everything is set up correctly, you should start seeing log messages from your ESP32 in the /var/log/syslog. It is also possible to redirect these messages to separate file or files. Refer to RSYSLOG documentation for details.

Logging to MQTT​

If you need remote logging, rsyslog option is generally the best due to low footprint and the best possible performance. However, if you don't have access to a Linux machine with rsyslog, or if you want to capture log messages in your own MQTT-enabled application, MQTT logging may be useful.

Client and server setup​

Refer to MQTT setup tutorial page for details.

Appender setup​

Add the following code to your main.cpp to enable UDP logging to mqtt:

#include <esp32m/log/mqtt.hpp>

...

log::addBufferedAppender(&log::Mqtt::instance());

Checking output​

Run this command on the computer with MQTT server to see log messages:

$ mosquitto_sub -t 'esp32m/log/#'