mosquitto

Section: (8)
Updated: 15 August 2010
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NAME

mosquitto - an mqtt broker

SYNOPSIS

mosquitto [-c config file] [-d | --daemon] [-i interface[:port]] [-p port number]

DESCRIPTION

mosquitto is a broker for the mqtt protocol version 3.

It is intended to be a drop in replacement for rsmb, but it's a long way off yet.

OPTIONS

-c, --config-file: Load configuration from a file. If not given, the default values as described in mosquitto.conf(5) are used.
-d, --daemon: Run mosquitto in the background as a daemon. All other behaviour remains the same.
-i, --interface: Listen for incoming network connections on the specified interface only. The port to listen to can be changed from the default by appending it to the interface name, e.g. eth0:1884. This is useful to restrict access to certain network interfaces. To restrict access to mosquitto to the local host only, use "--interface lo". This option may be specified multiple times.
-p, --port: Listen on the port specified instead of the default 1883. This acts in addition to the port setting in the config file. May be specified multiple times to open multiple sockets listening on different ports. This socket will be bound to all network interfaces.

LIMITATIONS

mosquitto implements all of the mqtt protocol version 3, but there are some significant limitations compared to rsmb.

*: There is only basic bridge support.
*: There are vastly fewer configuration options.
*: There is less logging information.
*: The $SYS hierarchy is smaller.
*: 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.

BROKER STATUS

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 sent.

$SYS/broker/bytes/received: The total number of bytes received since the broker started.
$SYS/broker/bytes/sent: The total number of bytes sent since the broker started.
$SYS/broker/changeset: The repository changeset (revision) associated with this build.
$SYS/broker/clients/total: The total number of clients currently either connected to the broker or disconnected but with clean session not set.
$SYS/broker/heap/current size: The current size of the heap memory in use by mosquitto. Note that this topic may be unavailable depending on compile time options.
$SYS/broker/messages/inflight: The number of messages currently in flight.
$SYS/broker/messages/received: The total number of messages received since the broker started.
$SYS/broker/messages/sent: The total number of messages sent since the broker started.
$SYS/broker/timestamp: The timestamp at which this particular build of the broker was made. Static.
$SYS/broker/uptime: The amount of time in seconds the broker has been online.
$SYS/broker/version: 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:

*: a/b/c/d
*: +/b/c/d
*: a/+/c/d
*: a/+/+/d
*: +/+/+/+

The following subscriptions will not match:

*: a/b/c
*: b/+/c/d
*: +/+/+

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 subscriptions will match:

*: a/b/c/d
*: #
*: a/#
*: a/b/#
*: a/b/c/#
*: +/b/c/#

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.

BRIDGES

Multiple brokers can be connected together with the bridging functionality. This is useful where it is desirable to share information between 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).

SIGNALS

SIGUSR1: Upon receiving the SIGUSR1 signal, mosquitto will write the persistence database to disk. This signal is only acted upon if persistence is enabled.
SIGUSR2: The SIGUSR2 signal causes mosquitto to run VACUUM on the in-memory database. This frees currently unused memory associated with the database.

FILES

/etc/mosquitto.conf: Configuration file. See mosquitto.conf(5).
/var/lib/mosquitto/mosquitto.db: Persistent message data storage location if persist enabled.
/etc/hosts.allow, /etc/hosts.deny: Host access control via tcp-wrappers as described in hosts_access(5).

BUGS

mosquitto bug information can be found at http://launchpad.net/mosquitto.

THANKS

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 protocol.

Thanks also to everybody at the Ubuntu UK Podcast and Linux Outlaws for organising OggCamp, where Andy gave a talk that inspired mosquitto.

AUTHOR

Roger Light <roger@atchoo.org>

This document was created by man2html, using the manual pages.
Time: 17:13:08 GMT, August 15, 2010