Mosquitto is an open source implementation of a server for version 5.0, 3.1.1, and 3.1 of the MQTT protocol. It also includes a C and C++ client library, and the mosquitto_pub and mosquitto_sub utilities for publishing and subscribing.

See the following links for more information on MQTT:

• Community page: https://mqtt.org/
• MQTT v3.1.1 standard: https://docs.oasis-open.org/mqtt/mqtt/v3.1.1/mqtt-v3.1.1.html
• MQTT v5.0 standard: https://docs.oasis-open.org/mqtt/mqtt/v5.0/mqtt-v5.0.html

Mosquitto project information is available at the following locations:

• Main homepage: https://mosquitto.org/
• Find existing bugs or submit a new bug: https://github.com/eclipse/mosquitto/issues
• Source code repository: https://github.com/eclipse/mosquitto

There is also a public test server available at https://test.mosquitto.org/

See https://mosquitto.org/download/ for details on installing binaries for various platforms.

If you have installed a binary package the broker should have been started automatically. If not, it can be started with a very basic configuration:

mosquitto

Then use mosquitto_sub to subscribe to a topic:

mosquitto_sub -t 'test/topic' -v

And to publish a message:

mosquitto_pub -t 'test/topic' -m 'hello world'

Note that starting the broker like this allows anonymous/unauthenticated access but only from the local computer, so it's only really useful for initial testing.

If you want to have clients from another computer connect, you will need to provide a configuration file. If you have installed from a binary package, you will probably already have a configuration file at somewhere like /etc/mosquitto/mosquitto.conf. If you've compiled from source, you can write your config file then run as mosquitto -c /path/to/mosquitto.conf.

To start your config file you define a listener and you will need to think about what authentication you require. It is not advised to run your broker with anonymous access when it is publically available.

For details on how to do this, look at the authentication methods available and the dynamic security plugin.

Documentation for the broker, clients and client library API can be found in the man pages, which are available online at https://mosquitto.org/man/. There are also pages with an introduction to the features of MQTT, the mosquitto_passwd utility for dealing with username/passwords, and a description of the configuration file options available for the broker.

Detailed client library API documentation can be found at https://mosquitto.org/api/

To build from source the recommended route for end users is to download the archive from https://mosquitto.org/download/.

On Windows and Mac, use cmake to build. On other platforms, just run make to build. For Windows, see also README-windows.md.

If you are building from the git repository then the documentation will not already be built. Use make binary to skip building the man pages, or install docbook-xsl on Debian/Ubuntu systems.

• c-ares (libc-ares-dev on Debian based systems) - only when compiled with make WITH_SRV=yes
• cJSON - for client JSON output support. Disable with make WITH_CJSON=no Auto detected with CMake.
• libwebsockets (libwebsockets-dev) - enable with make WITH_WEBSOCKETS=yes
• openssl (libssl-dev on Debian based systems) - disable with make WITH_TLS=no
• pthreads - for client library thread support. This is required to support the mosquitto_loop_start() and mosquitto_loop_stop() functions. If compiled without pthread support, the library isn't guaranteed to be thread safe.
• uthash / utlist - bundled versions of these headers are provided, disable their use with make WITH_BUNDLED_DEPS=no
• xsltproc (xsltproc and docbook-xsl on Debian based systems) - only needed when building from git sources - disable with make WITH_DOCS=no

Equivalent options for enabling/disabling features are available when using the CMake build.

Mosquitto was written by Roger Light roger@atchoo.org