mosquitto - an mqtt broker
mosquitto [-c config file] [-d | --daemon] [-p port number]
mosquitto is a broker for the mqtt protocol version 3.1.
Load configuration from a file. If not given, the default values as described in mosquitto.conf(5) are used.
Run mosquitto in the background as a daemon. All other behaviour remains the same.
Listen on the port specified instead of the default 1883. This acts in addition to the port setting in the config file. May be spec-
ified multiple times to open multiple sockets listening on different ports. This socket will be bound to all network interfaces.
mosquitto implements all of the mqtt protocol version 3.1, but there are some limitations compared to rsmb.
o There are fewer configuration options.
o There is less logging information.
o It isn't as well tested or documented...
It should be noted that all of the above limitations should have "currently" included in them. They will all be fixed at some point.
Clients can find information about the broker by subscribing to topics in the $SYS hierarchy as follows. Topics marked as static are only
sent once per client on subscription. All other topics are updated every sys_interval seconds. If sys_interval is 0, then updates are not
The average number of bytes received per second since the broker started.
The average number of bytes sent per second since the broker started.
The total number of bytes received since the broker started.
The total number of bytes sent since the broker started.
The repository changeset (revision) associated with this build. Static.
The number of currently connected clients
The total number of persistent clients (with clean session disabled) that are registered at the broker but are currently disconnect-
The maximum number of active clients that have been connected to the broker. This is only calculated when the $SYS topic tree is up-
dated, so short lived client connections may not be counted.
The total number of active clients currently connected to the broker.
The current size of the heap memory in use by mosquitto. Note that this topic may be unavailable depending on compile time options.
The largest amount of heap memory used by mosquitto. Note that this topic may be unavailable depending on compile time options.
The number of messages with QoS>0 that are awaiting acknowledgments.
The average number of messages received per second since the broker started.
The average number of messages sent per second since the broker started.
The total number of messages received since the broker started.
The total number of messages sent since the broker started.
The number of messages currently held in the message store.
The timestamp at which this particular build of the broker was made. Static.
The amount of time in seconds the broker has been online.
The version of the broker. Static.
WILDCARD TOPIC SUBSCRIPTIONS
In addition to allowing clients to subscribe to specific topics, mosquitto also allows the use of two wildcards in subscriptions. + is the
wildcard used to match a single level of hierarchy. For example, for a topic of "a/b/c/d", the following example subscriptions will match:
The following subscriptions will not match:
The second wildcard is # and is used to match all subsequent levels of hierarchy. With a topic of "a/b/c/d", the following example sub-
scriptions will match:
The $SYS hierarchy does not match a subscription of "#". If you want to observe the entire $SYS hierarchy, subscribe to $SYS/#.
Note that the wildcards must be only ever used on their own, so a subscription of "a/b+/c" is not valid use of a wildcard. The # wildcard
must only ever be used as the final character of a subscription.
Multiple brokers can be connected together with the bridging functionality. This is useful where it is desirable to share information be-
tween locations, but where not all of the information needs to be shared. An example could be where a number of users are running a broker
to help record power usage and for a number of other reasons. The power usage could be shared through bridging all of the user brokers to a
common broker, allowing the power usage of all users to be collected and compared. The other information would remain local to each broker.
For information on configuring bridges, see mosquitto.conf(5).
SIGHUP Upon receiving the SIGHUP signal, mosquitto will attempt to reload configuration file data, assuming that the -c argument was pro-
vided when mosquitto was started. Not all configuration parameters can be reloaded without restarting. See mosquitto.conf(5) for de-
Upon receiving the SIGUSR1 signal, mosquitto will write the persistence database to disk. This signal is only acted upon if persis-
tence is enabled.
SIGHUP Upon receiving the SIGHUP signal, mosquitto will attempt to reload its configuration. Not all configuration parameters can be
reloaded without a restart. See mosquitto.conf(5) for details.
The SIGUSR2 signal causes mosquitto to print out the current subscription tree, along with information about where retained messages
exist. This is intended as a testing feature only and may be removed at any time.
Configuration file. See mosquitto.conf(5).
Persistent message data storage location if persist enabled.
Host access control via tcp-wrappers as described in hosts_access(5).
mosquitto bug information can be found at http://launchpad.net/mosquitto
mqtt(7) mosquitto.conf(5) hosts_access(5) mosquitto_pub(1) mosquitto_sub(1) libmosquitto(3)
Thanks to Andy Stanford-Clark for being one of the people who came up with MQTT in the first place and providing clarifications of the pro-
Thanks also to everybody at the Ubuntu UK Podcast and Linux Outlaws for organising OggCamp, where Andy gave a talk that inspired mosquitto.
Roger Light <email@example.com>
5 February 2012 mosquitto(8)