Set the path to an access control list file. If defined, the contents of the file are used to control client access to topics on the broker.

If this parameter is defined then only the topics listed will have access. Topic access is added with lines of the format:

topic [read|write|readwrite] <topic>

The access type is controlled using "read", "write" or "readwrite". This parameter is optional (unless <topic> includes a space character) - if not given then the access is read/write. <topic> can contain the + or # wildcards as in subscriptions.

The first set of topics are applied to anonymous clients, assuming allow_anonymous is true. User specific topic ACLs are added after a user line as follows:

user <username>

The username referred to here is the same as in password_file. It is not the clientid.

It is also possible to define ACLs based on pattern substitution within the topic. The form is the same as for the topic keyword, but using pattern as the keyword.

pattern [read|write|readwrite] <topic>

The patterns available for substition are:

The substitution pattern must be the only text for that level of hierarchy. Pattern ACLs apply to all users even if the "user" keyword has previously been given.

Example:

pattern write sensor/%u/data

Allow access for bridge connection messages:

pattern write $SYS/broker/connection/%c/state

If the first character of a line of the ACL file is a # it is treated as a comment.

Reloaded on reload signal. The currently loaded ACLs will be freed and reloaded. Existing subscriptions will be affected after the reload.

Boolean value that determines whether clients that connect without providing a username are allowed to connect. If set to false then another means of connection should be created to control authenticated client access. Defaults to true.

Reloaded on reload signal.

If a client is subscribed to multiple subscriptions that overlap, e.g. foo/# and foo/+/baz , then MQTT expects that when the broker receives a message on a topic that matches both subscriptions, such as foo/bar/baz, then the client should only receive the message once.

Mosquitto keeps track of which clients a message has been sent to in order to meet this requirement. This option allows this behaviour to be disabled, which may be useful if you have a large number of clients subscribed to the same set of topics and want to minimise memory usage.

It can be safely set to true if you know in advance that your clients will never have overlapping subscriptions, otherwise your clients must be able to correctly deal with duplicate messages even when then have QoS=2.

Defaults to true.

Reloaded on reload signal.

Options to be passed to the auth plugin. See the specific plugin instructions.

Specify an external module to use for authentication and access control. This allows custom username/password and access control functions to be created.

Not currently reloaded on reload signal.

If true then before an ACL check is made, the username/client id of the client needing the check is searched for the presence of either a '+' or '#' character. If either of these characters is found in either the username or client id, then the ACL check is denied before it is sent to the plugin.

This check prevents the case where a malicious user could circumvent an ACL check by using one of these characters as their username or client id. This is the same issue as was reported with mosquitto itself as CVE-2017-7650.

If you are entirely sure that the plugin you are using is not vulnerable to this attack (i.e. if you never use usernames or client ids in topics) then you can disable this extra check and hence have all ACL checks delivered to your plugin by setting this option to false.

Defaults to true.

Not currently reloaded on reload signal.

The number of seconds that mosquitto will wait between each time it saves the in-memory database to disk. If set to 0, the in-memory database will only be saved when mosquitto exits or when receiving the SIGUSR1 signal. Note that this setting only has an effect if persistence is enabled. Defaults to 1800 seconds (30 minutes).

Reloaded on reload signal.

If true, mosquitto will count the number of subscription changes, retained messages received and queued messages and if the total exceeds autosave_interval then the in-memory database will be saved to disk. If false, mosquitto will save the in-memory database to disk by treating autosave_interval as a time in seconds.

Reloaded on reload signal.

If defined, only clients that have a clientid with a prefix that matches clientid_prefixes will be allowed to connect to the broker. For example, setting "secure-" here would mean a client "secure-client" could connect but another with clientid "mqtt" couldn't. By default, all client ids are valid.

Reloaded on reload signal. Note that currently connected clients will be unaffected by any changes.

If set to true, the log will include entries when clients connect and disconnect. If set to false, these entries will not appear.

Reloaded on reload signal.

External configuration files may be included by using the include_dir option. This defines a directory that will be searched for config files. All files that end in '.conf' will be loaded as a configuration file. It is best to have this as the last option in the main file. This option will only be processed from the main configuration file. The directory specified must not contain the main configuration file.

Send log messages to a particular destination. Possible destinations are: stdout stderr syslog topic.

stdout and stderr log to the console on the named output.

syslog uses the userspace syslog facility which usually ends up in /var/log/messages or similar and topic logs to the broker topic '$SYS/broker/log/<severity>', where severity is one of D, E, W, N, I, M which are debug, error, warning, notice, information and message. Message type severity is used by the subscribe and unsubscribe log_type options and publishes log messages at $SYS/broker/log/M/subscribe and $SYS/broker/log/M/unsubscribe.

The file destination requires an additional parameter which is the file to be logged to, e.g. "log_dest file /var/log/mosquitto.log". The file will be closed and reopened when the broker receives a HUP signal. Only a single file destination may be configured.

Use "log_dest none" if you wish to disable logging. Defaults to stderr. This option may be specified multiple times.

Note that if the broker is running as a Windows service it will default to "log_dest none" and neither stdout nor stderr logging is available.

Reloaded on reload signal.

If using syslog logging (not on Windows), messages will be logged to the "daemon" facility by default. Use the log_facility option to choose which of local0 to local7 to log to instead. The option value should be an integer value, e.g. "log_facility 5" to use local5.

Boolean value, if set to true a timestamp value will be added to each log entry. The default is true.

Reloaded on reload signal.

Choose types of messages to log. Possible types are: debug, error, warning, notice, information, subscribe, unsubscribe, websockets, none, all.

Defaults to error, warning, notice and information. This option may be specified multiple times. Note that the debug type (used for decoding incoming/outgoing network packets) is never logged in topics.

Reloaded on reload signal.

The maximum number of QoS 1 or 2 messages that can be in the process of being transmitted simultaneously. This includes messages currently going through handshakes and messages that are being retried. Defaults to 20. Set to 0 for no maximum. If set to 1, this will guarantee in-order delivery of messages.

Reloaded on reload signal.

The maximum number of QoS 1 or 2 messages to hold in the queue above those messages that are currently in flight. Defaults to 100. Set to 0 for no maximum (not recommended). See also the queue_qos0_messages option.

Reloaded on reload signal.

This option sets the maximum publish payload size that the broker will allow. Received messages that exceed this size will not be accepted by the broker. The default value is 0, which means that all valid MQTT messages are accepted. MQTT imposes a maximum payload size of 268435455 bytes.

Set the path to a password file. If defined, the contents of the file are used to control client access to the broker. The file can be created using the mosquitto_passwd(1) utility. If mosquitto is compiled without TLS support (it is recommended that TLS support is included), then the password file should be a text file with each line in the format "username:password", where the colon and password are optional but recommended. If allow_anonymous is set to false, only users defined in this file will be able to connect. Setting allow_anonymous to true when password_fileis defined is valid and could be used with acl_file to have e.g. read only guest/anonymous accounts and defined users that can publish.

Reloaded on reload signal. The currently loaded username and password data will be freed and reloaded. Clients that are already connected will not be affected.

See also mosquitto_passwd(1).

If true, connection, subscription and message data will be written to the disk in mosquitto.db at the location dictated by persistence_location. When mosquitto is restarted, it will reload the information stored in mosquitto.db. The data will be written to disk when mosquitto closes and also at periodic intervals as defined by autosave_interval. Writing of the persistence database may also be forced by sending mosquitto the SIGUSR1 signal. If false, the data will be stored in memory only. Defaults to false.

Reloaded on reload signal.

The filename to use for the persistent database. Defaults to mosquitto.db.

Reloaded on reload signal.

The path where the persistence database should be stored. Must end in a trailing slash. If not given, then the current directory is used.

Reloaded on reload signal.

This option allows persistent clients (those with clean session set to false) to be removed if they do not reconnect within a certain time frame. This is a non-standard option. As far as the MQTT spec is concerned, persistent clients persist forever.

Badly designed clients may set clean session to false whilst using a randomly generated client id. This leads to persistent clients that will never reconnect. This option allows these clients to be removed.

The expiration period should be an integer followed by one of h d w m y for hour, day, week, month and year respectively. For example:

As this is a non-standard option, the default if not set is to never expire persistent clients.

Reloaded on reload signal.

Write a pid file to the file specified. If not given (the default), no pid file will be written. If the pid file cannot be written, mosquitto will exit. This option only has an effect is mosquitto is run in daemon mode.

If mosquitto is being automatically started by an init script it will usually be required to write a pid file. This should then be configured as e.g. /var/run/mosquitto.pid

Not reloaded on reload signal.

Set the path to a pre-shared-key file. This option requires a listener to be have PSK support enabled. If defined, the contents of the file are used to control client access to the broker. Each line should be in the format "identity:key", where the key is a hexadecimal string with no leading "0x". A client connecting to a listener that has PSK support enabled must provide a matching identity and PSK to allow the encrypted connection to proceed.

Reloaded on reload signal. The currently loaded identity and key data will be freed and reloaded. Clients that are already connected will not be affected.

Set to true to queue messages with QoS 0 when a persistent client is disconnected. These messages are included in the limit imposed by max_queued_messages. Defaults to false.

Note that the MQTT v3.1 spec states that only QoS 1 and 2 messages should be saved in this situation so this is a non-standard option.

Reloaded on reload signal.

This is a synonym of the persistence option.

Reloaded on reload signal.

The integer number of seconds after a QoS=1 or QoS=2 message has been sent that mosquitto will wait before retrying when no response is received. If unset, defaults to 20 seconds.

Reloaded on reload signal.

The integer number of seconds between the internal message store being cleaned of messages that are no longer referenced. Lower values will result in lower memory usage but more processor time, higher values will have the opposite effect. Setting a value of 0 means the unreferenced messages will be disposed of as quickly as possible. Defaults to 10 seconds.

Reloaded on reload signal.

The integer number of seconds between updates of the $SYS subscription hierarchy, which provides status information about the broker. If unset, defaults to 10 seconds.

Set to 0 to disable publishing the $SYS hierarchy completely.

Reloaded on reload signal.

The MQTT specification requires that the QoS of a message delivered to a subscriber is never upgraded to match the QoS of the subscription. Enabling this option changes this behaviour. If upgrade_outgoing_qos is set true, messages sent to a subscriber will always match the QoS of its subscription. This is a non-standard option not provided for by the spec. Defaults to false.

Reloaded on reload signal.

When run as root, change to this user and its primary group on startup. If mosquitto is unable to change to this user and group, it will exit with an error. The user specified must have read/write access to the persistence database if it is to be written. If run as a non-root user, this setting has no effect. Defaults to mosquitto.

This setting has no effect on Windows and so you should run mosquitto as the user you wish it to run as.

Not reloaded on reload signal.

Specify the address and optionally the port of the bridge to connect to. This must be given for each bridge connection. If the port is not specified, the default of 1883 is used.

Multiple host addresses can be specified on the address config. See the round_robin option for more details on the behaviour of bridges with multiple addresses.

If a bridge has topics that have "out" direction, the default behaviour is to send an unsubscribe request to the remote broker on that topic. This means that changing a topic direction from "in" to "out" will not keep receiving incoming messages. Sending these unsubscribe requests is not always desirable, setting bridge_attempt_unsubscribe to false will disable sending the unsubscribe request. Defaults to true.

Set the version of the MQTT protocol to use with for this bridge. Can be one of mqttv31 or mqttv311. Defaults to mqttv31.

Set the clean session option for this bridge. Setting to false (the default), means that all subscriptions on the remote broker are kept in case of the network connection dropping. If set to true, all subscriptions and messages on the remote broker will be cleaned up if the connection drops. Note that setting to true may cause a large amount of retained messages to be sent each time the bridge reconnects.

If you are using bridges with cleansession set to false (the default), then you may get unexpected behaviour from incoming topics if you change what topics you are subscribing to. This is because the remote broker keeps the subscription for the old topic. If you have this problem, connect your bridge with cleansession set to true, then reconnect with cleansession set to false as normal.

This variable marks the start of a new bridge connection. It is also used to give the bridge a name which is used as the client id on the remote broker.

Set the number of seconds after which the bridge should send a ping if no other traffic has occurred. Defaults to 60. A minimum value of 5 seconds is allowed.

Set the amount of time a bridge using the lazy start type must be idle before it will be stopped. Defaults to 60 seconds.

Set the clientid to use on the local broker. If not defined, this defaults to local.<clientid>. If you are bridging a broker to itself, it is important that local_clientid and clientid do not match.

Configure the password to be used when connecting this bridge to the local broker. This may be important when authentication and ACLs are being used.

Configure the username to be used when connecting this bridge to the local broker. This may be important when authentication and ACLs are being used.

If set to true, publish notification messages to the local and remote brokers giving information about the state of the bridge connection. Retained messages are published to the topic $SYS/broker/connection/<clientid>/state unless otherwise set with notification_topics. If the message is 1 then the connection is active, or 0 if the connection has failed. Defaults to true.

Choose the topic on which notifications will be published for this bridge. If not set the messages will be sent on the topic $SYS/broker/connection/<clientid>/state.

Set the client id for this bridge connection. If not defined, this defaults to 'name.hostname', where name is the connection name and hostname is the hostname of this computer.

This replaces the old "clientid" option to avoid confusion with local/remote sides of the bridge. "clientid" remains valid for the time being.

Configure a password for the bridge. This is used for authentication purposes when connecting to a broker that supports MQTT v3.1 and up and requires a username and/or password to connect. This option is only valid if a remote_username is also supplied.

This replaces the old "password" option to avoid confusion with local/remote sides of the bridge. "password" remains valid for the time being.

Configure a username for the bridge. This is used for authentication purposes when connecting to a broker that supports MQTT v3.1 and up and requires a username and/or password to connect. See also the remote_password option.

This replaces the old "username" option to avoid confusion with local/remote sides of the bridge. "username" remains valid for the time being.

Set the amount of time a bridge using the automatic start type will wait until attempting to reconnect. Defaults to 30 seconds.

If the bridge has more than one address given in the address/addresses configuration, the round_robin option defines the behaviour of the bridge on a failure of the bridge connection. If round_robin is false, the default value, then the first address is treated as the main bridge connection. If the connection fails, the other secondary addresses will be attempted in turn. Whilst connected to a secondary bridge, the bridge will periodically attempt to reconnect to the main bridge until successful.

If round_robin is true, then all addresses are treated as equals. If a connection fails, the next address will be tried and if successful will remain connected until it fails.

Set the start type of the bridge. This controls how the bridge starts and can be one of three types: automatic, lazy and once. Note that RSMB provides a fourth start type "manual" which isn't currently supported by mosquitto.

automatic is the default start type and means that the bridge connection will be started automatically when the broker starts and also restarted after a short delay (30 seconds) if the connection fails.

Bridges using the lazy start type will be started automatically when the number of queued messages exceeds the number set with the threshold option. It will be stopped automatically after the time set by the idle_timeout parameter. Use this start type if you wish the connection to only be active when it is needed.

A bridge using the once start type will be started automatically when the broker starts but will not be restarted if the connection fails.

Set the number of messages that need to be queued for a bridge with lazy start type to be restarted. Defaults to 10 messages.

Define a topic pattern to be shared between the two brokers. Any topics matching the pattern (which may include wildcards) are shared. The second parameter defines the direction that the messages will be shared in, so it is possible to import messages from a remote broker using in, export messages to a remote broker using out or share messages in both directions. If this parameter is not defined, the default of out is used. The QoS level defines the publish/subscribe QoS level used for this topic and defaults to 0.

The local-prefix and remote-prefix options allow topics to be remapped when publishing to and receiving from remote brokers. This allows a topic tree from the local broker to be inserted into the topic tree of the remote broker at an appropriate place.

For incoming topics, the bridge will prepend the pattern with the remote prefix and subscribe to the resulting topic on the remote broker. When a matching incoming message is received, the remote prefix will be removed from the topic and then the local prefix added.

For outgoing topics, the bridge will prepend the pattern with the local prefix and subscribe to the resulting topic on the local broker. When an outgoing message is processed, the local prefix will be removed from the topic then the remote prefix added.

When using topic mapping, an empty prefix can be defined using the place marker "". Using the empty marker for the topic itself is also valid. The table below defines what combination of empty or value is valid.

To remap an entire topic tree, use e.g.:

topic # both 2 local/topic/ remote/topic/

This option can be specified multiple times per bridge.

Care must be taken to ensure that loops are not created with this option. If you are experiencing high CPU load from a broker, it is possible that you have a loop where each broker is forever forwarding each other the same messages.

See also the cleansession option if you have messages arriving on unexpected topics when using incoming topics.

connection test-mosquitto-org
address test.mosquitto.org
cleansession true
topic clients/total in 0 test/mosquitto/org $SYS/broker/

If try_private is set to true, the bridge will attempt to indicate to the remote broker that it is a bridge not an ordinary client. If successful, this means that loop detection will be more effective and that retained messages will be propagated correctly. Not all brokers support this feature so it may be necessary to set try_private to false if your bridge does not connect properly.

Defaults to true.