Provided by: mosquitto_1.4.8-1build1_amd64 bug

NAME

       mosquitto.conf - the configuration file for mosquitto

SYNOPSIS

       mosquitto.conf

DESCRIPTION

       mosquitto.conf is the configuration file for mosquitto. This file can reside anywhere as
       long as mosquitto can read it. By default, mosquitto does not need a configuration file
       and will use the default values listed below. See mosquitto(8) for information on how to
       load a configuration file.

FILE FORMAT

       All lines with a # as the very first character are treated as a comment.

       Configuration lines start with a variable name. The variable value is separated from the
       name by a single space.

AUTHENTICATION

       The authentication options described below allow a wide range of possibilities in
       conjunction with the listener options. This section aims to clarify the possibilities.

       The simplest option is to have no authentication at all. This is the default if no other
       options are given. Unauthenticated encrypted support is provided by using the certificate
       based SSL/TLS based options cafile/capath, certfile and keyfile.

       MQTT provides username/password authentication as part of the protocol. Use the
       password_file option to define the valid usernames and passwords. Be sure to use network
       encryption if you are using this option otherwise the username and password will be
       vulnerable to interception.

       When using certificate based encryption there are two options that affect authentication.
       The first is require_certificate, which may be set to true or false. If false, the SSL/TLS
       component of the client will verify the server but there is no requirement for the client
       to provide anything for the server: authentication is limited to the MQTT built in
       username/password. If require_certificate is true, the client must provide a valid
       certificate in order to connect successfully. In this case, the second option,
       use_identity_as_username, becomes relevant. If set to true, the Common Name (CN) from the
       client certificate is used instead of the MQTT username for access control purposes. The
       password is not replaced because it is assumed that only authenticated clients have valid
       certificates. If use_identity_as_username is false, the client must authenticate as normal
       (if required by password_file) through the MQTT options.

       When using pre-shared-key based encryption through the psk_hint and psk_file options, the
       client must provide a valid identity and key in order to connect to the broker before any
       MQTT communication takes place. If use_identity_as_username is true, the PSK identity is
       used instead of the MQTT username for access control purposes. If use_identity_as_username
       is false, the client may still authenticate using the MQTT username/password if using the
       password_file option.

       Both certificate and PSK based encryption are configured on a per-listener basis.

       Authentication plugins can be created to replace the password_file and psk_file options
       (as well as the ACL options) with e.g. SQL based lookups.

       It is possible to support multiple authentication schemes at once. A config could be
       created that had a listener for all of the different encryption options described above
       and hence a large number of ways of authenticating.

GENERAL OPTIONS

       acl_file file path
           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:

           ·   %c to match the client id of the client

           ·   %u to match the username of the client

           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.

       allow_anonymous [ true | false ]
           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.

       allow_duplicate_messages [ true | false ]
           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.

       auth_opt_* value
           Options to be passed to the auth plugin. See the specific plugin instructions.

       auth_plugin file path
           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.

       autosave_interval seconds
           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.

       autosave_on_changes [ true | false ]
           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.

       clientid_prefixes prefix
           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.

       connection_messages [ true | false ]
           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.

       include_dir dir
           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.

       log_dest destinations
           Send log messages to a particular destination. Possible destinations are:
           stdoutstderrsyslogtopic.

           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.

       log_facility local facility
           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.

       log_timestamp [ true | false ]
           Boolean value, if set to true a timestamp value will be added to each log entry. The
           default is true.

           Reloaded on reload signal.

       log_type types
           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.

       max_inflight_messages count
           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.

       max_queued_messages count
           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.

       message_size_limit limit
           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.

       password_file file path
           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).

       persistence [ true | false ]
           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.

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

           Reloaded on reload signal.

       persistence_location path
           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.

       persistent_client_expiration duration
           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:

           ·   persistent_client_expiration 2m

           ·   persistent_client_expiration 14d

           ·   persistent_client_expiration 1y

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

           Reloaded on reload signal.

       pid_file file path
           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.

       psk_file file path
           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.

       queue_qos0_messages [ true | false ]
           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.

       retained_persistence [ true | false ]
           This is a synonym of the persistence option.

           Reloaded on reload signal.

       retry_interval seconds
           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.

       store_clean_interval seconds
           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.

       sys_interval seconds
           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.

       upgrade_outgoing_qos [ true | false ]
           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.

       user username
           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.

LISTENERS

       The network ports that mosquitto listens on can be controlled using listeners. The default
       listener options can be overridden and further listeners can be created.

   General Options
       bind_address address
           Listen for incoming network connections on the specified IP address/hostname only.
           This is useful to restrict access to certain network interfaces. To restrict access to
           mosquitto to the local host only, use "bind_address localhost". This only applies to
           the default listener. Use the listener variable to control other listeners.

           Not reloaded on reload signal.

       http_dir directory
           When a listener is using the websockets protocol, it is possible to serve http data as
           well. Set http_dir to a directory which contains the files you wish to serve. If this
           option is not specified, then no normal http connections will be possible.

           Not reloaded on reload signal.

       listener port
           Listen for incoming network connection on the specified port. A second optional
           argument allows the listener to be bound to a specific ip address/hostname. If this
           variable is used and neither bind_address nor port are used then the default listener
           will not be started. This option may be specified multiple times. See also the
           mount_point option.

           Not reloaded on reload signal.

       max_connections count
           Limit the total number of clients connected for the current listener. Set to -1 to
           have "unlimited" connections. Note that other limits may be imposed that are outside
           the control of mosquitto. See e.g.  limits.conf(5).

           Not reloaded on reload signal.

       mount_point topic prefix
           This option is used with the listener option to isolate groups of clients. When a
           client connects to a listener which uses this option, the string argument is attached
           to the start of all topics for this client. This prefix is removed when any messages
           are sent to the client. This means a client connected to a listener with mount point
           example can only see messages that are published in the topic hierarchy example and
           above.

           Not reloaded on reload signal.

       port port number
           Set the network port for the default listener to listen on. Defaults to 1883.

           Not reloaded on reload signal.

       protocol value
           Set the protocol to accept for this listener. Can be mqtt, the default, or websockets
           if available.

           Websockets support is currently disabled by default at compile time. Certificate based
           TLS may be used with websockets, except that only the cafile, certfile, keyfile and
           ciphers options are supported.

           Not reloaded on reload signal.

       use_username_as_clientid [ true | false ]
           Set use_username_as_clientid to true to replace the clientid that a client connected
           with with its username. This allows authentication to be tied to the clientid, which
           means that it is possible to prevent one client disconnecting another by using the
           same clientid. Defaults to false.

           If a client connects with no username it will be disconnected as not authorised when
           this option is set to true. Do not use in conjunction with clientid_prefixes.

           See also use_identity_as_username.

           Not reloaded on reload signal.

       websockets_log_level level
           Change the websockets logging level. This is a global option, it is not possible to
           set per listener. This is an integer that is interpreted by libwebsockets as a bit
           mask for its lws_log_levels enum. See the libwebsockets documentation for more
           details.

           To use this option, log_type websockets must also be enabled. Defaults to 0.

   Certificate based SSL/TLS Support
       The following options are available for all listeners to configure certificate based SSL
       support. See also "Pre-shared-key based SSL/TLS support".

       cafile file path
           At least one of cafile or capath must be provided to allow SSL support.

           cafile is used to define the path to a file containing the PEM encoded CA certificates
           that are trusted.

       capath directory path
           At least one of cafile or capath must be provided to allow SSL support.

           capath is used to define a directory that contains PEM encoded CA certificates that
           are trusted. For capath to work correctly, the certificates files must have ".pem" as
           the file ending and you must run "c_rehash <path to capath>" each time you add/remove
           a certificate.

       certfile file path
           Path to the PEM encoded server certificate.

       ciphers cipher:list
           The list of allowed ciphers, each separated with a colon. Available ciphers can be
           obtained using the "openssl ciphers" command.

       crlfile file path
           If you have require_certificate set to true, you can create a certificate revocation
           list file to revoke access to particular client certificates. If you have done this,
           use crlfile to point to the PEM encoded revocation file.

       keyfile file path
           Path to the PEM encoded keyfile.

       require_certificate [ true | false ]
           By default an SSL/TLS enabled listener will operate in a similar fashion to a https
           enabled web server, in that the server has a certificate signed by a CA and the client
           will verify that it is a trusted certificate. The overall aim is encryption of the
           network traffic. By setting require_certificate to true, the client must provide a
           valid certificate in order for the network connection to proceed. This allows access
           to the broker to be controlled outside of the mechanisms provided by MQTT.

       tls_version version
           Configure the version of the TLS protocol to be used for this listener. Possible
           values are tlsv1.2, tlsv1.1 and tlsv1. If left unset, the default of allowing all of
           TLS v1.2, v1.1 and v1.0 is used.

       use_identity_as_username [ true | false ]
           If require_certificate is true, you may set use_identity_as_username to true to use
           the CN value from the client certificate as a username. If this is true, the
           password_file option will not be used for this listener.

   Pre-shared-key based SSL/TLS Support
       The following options are available for all listeners to configure pre-shared-key based
       SSL support. See also "Certificate based SSL/TLS support".

       ciphers cipher:list
           When using PSK, the encryption ciphers used will be chosen from the list of available
           PSK ciphers. If you want to control which ciphers are available, use this option. The
           list of available ciphers can be optained using the "openssl ciphers" command and
           should be provided in the same format as the output of that command.

       psk_hint hint
           The psk_hint option enables pre-shared-key support for this listener and also acts as
           an identifier for this listener. The hint is sent to clients and may be used locally
           to aid authentication. The hint is a free form string that doesn't have much meaning
           in itself, so feel free to be creative.

           If this option is provided, see psk_file to define the pre-shared keys to be used or
           create a security plugin to handle them.

       tls_version version
           Configure the version of the TLS protocol to be used for this listener. Possible
           values are tlsv1.2, tlsv1.1 and tlsv1. If left unset, the default of allowing all of
           TLS v1.2, v1.1 and v1.0 is used.

       use_identity_as_username [ true | false ]
           Set use_identity_as_username to have the psk identity sent by the client used as its
           username. The username will be checked as normal, so password_file or another means of
           authentication checking must be used. No password will be used.

CONFIGURING BRIDGES

       Multiple bridges (connections to other brokers) can be configured using the following
       variables.

       Bridges cannot currently be reloaded on reload signal.

       address address[:port] [address[:port]], addresses address[:port] [address[:port]]
           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.

       bridge_attempt_unsubscribe [ true | false ]
           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.

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

       cleansession [ true | false ]
           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.

       connection name
           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.

       keepalive_interval seconds
           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.

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

       local_clientid id
           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.

       local_password password
           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.

       local_username username
           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.

       notifications [ true | false ]
           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.

       notification_topic topic
           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.

       remote_clientid id
           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.

       remote_password value
           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.

       remote_username name
           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.

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

       round_robin [ true | false ]
           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.

       start_type [ automatic | lazy | once ]
           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.

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

       topic pattern [[[ out | in | both ] qos-level] local-prefix remote-prefix]
           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.

           ┌──┬───────┬──────────────┬───────────────┬──────────────────┐
           │  │ TopicLocal PrefixRemote PrefixValidity         │
           ├──┼───────┼──────────────┼───────────────┼──────────────────┤
           │1 │ value │ value        │ value         │ valid            │
           ├──┼───────┼──────────────┼───────────────┼──────────────────┤
           │2 │ value │ value        │ ""            │ valid            │
           ├──┼───────┼──────────────┼───────────────┼──────────────────┤
           │3 │ value │ ""           │ value         │ valid            │
           ├──┼───────┼──────────────┼───────────────┼──────────────────┤
           │4 │ value │ ""           │ ""            │ valid (no        │
           │  │       │              │               │ remapping)       │
           ├──┼───────┼──────────────┼───────────────┼──────────────────┤
           │5 │ ""    │ value        │ value         │ valid (remap     │
           │  │       │              │               │ single local     │
           │  │       │              │               │ topic to remote) │
           ├──┼───────┼──────────────┼───────────────┼──────────────────┤
           │6 │ ""    │ value        │ ""            │ invalid          │
           ├──┼───────┼──────────────┼───────────────┼──────────────────┤
           │7 │ ""    │ ""           │ value         │ invalid          │
           ├──┼───────┼──────────────┼───────────────┼──────────────────┤
           │8 │ ""    │ ""           │ ""            │ invalid          │
           └──┴───────┴──────────────┴───────────────┴──────────────────┘
           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.

           Example Bridge Topic Remapping.  The configuration below connects a bridge to the
           broker at test.mosquitto.org. It subscribes to the remote topic
           $SYS/broker/clients/total and republishes the messages received to the local topic
           test/mosquitto/org/clients/total

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

       try_private [ true | false ]
           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.

   SSL/TLS Support
       The following options are available for all bridges to configure SSL/TLS support.

       bridge_attempt_unsubscribe [ true | false ]
           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.

       bridge_cafile file path
           One of bridge_cafile or bridge_capath must be provided to allow SSL/TLS support.

           bridge_cafile is used to define the path to a file containing the PEM encoded CA
           certificates that have signed the certificate for the remote broker.

       bridge_capath file path
           One of bridge_capath or bridge_capath must be provided to allow SSL/TLS support.

           bridge_capath is used to define the path to a directory containing the PEM encoded CA
           certificates that have signed the certificate for the remote broker. For bridge_capath
           to work correctly, the certificate files must have ".crt" as the file ending and you
           must run "c_rehash <path to bridge_capath>" each time you add/remove a certificate.

       bridge_certfile file path
           Path to the PEM encoded client certificate for this bridge, if required by the remote
           broker.

       bridge_identity identity
           Pre-shared-key encryption provides an alternative to certificate based encryption. A
           bridge can be configured to use PSK with the bridge_identity and bridge_psk options.
           This is the client identity used with PSK encryption. Only one of certificate and PSK
           based encryption can be used on one bridge at once.

       bridge_insecure [ true | false ]
           When using certificate based TLS, the bridge will attempt to verify the hostname
           provided in the remote certificate matches the host/address being connected to. This
           may cause problems in testing scenarios, so bridge_insecure may be set to false to
           disable the hostname verification.

           Setting this option to true means that a malicious third party could potentially
           inpersonate your server, so it should always be set to false in production
           environments.

       bridge_keyfile file path
           Path to the PEM encoded private key for this bridge, if required by the remote broker.

       bridge_psk key
           Pre-shared-key encryption provides an alternative to certificate based encryption. A
           bridge can be configured to use PSK with the bridge_identity and bridge_psk options.
           This is the pre-shared-key in hexadecimal format with no "0x". Only one of certificate
           and PSK based encryption can be used on one bridge at once.

       bridge_tls_version version
           Configure the version of the TLS protocol to be used for this bridge. Possible values
           are tlsv1.2, tlsv1.1 and tlsv1. Defaults to tlsv1.2. The remote broker must support
           the same version of TLS for the connection to succeed.

FILES

       mosquitto.conf

BUGS

       mosquitto bug information can be found at
       https://bugs.eclipse.org/bugs/describecomponents.cgi?product=Mosquitto

SEE ALSO

       mosquitto(8), mosquitto_passwd(1), mosquitto-tls(7), mqtt(7), limits.conf(5)

AUTHOR

       Roger Light <roger@atchoo.org>