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mosquitto/man/mosquitto.conf.5.xml
Bart Desplanques 105e30ff5b Fix engine support. 
Do not try to open keyfile when keyform is "engine": this is not necessarily a real file.
Dynamic engines require init with OPENSSL_INIT_ENGINE_DYNAMIC before they can be loaded.

Signed-off-by: Bart Desplanques <bart.desplanques@gmail.com>
2023-06-02 19:11:50 +02:00

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<?xml version='1.0' encoding='UTF-8'?>
<?xml-stylesheet type="text/xsl" href="manpage.xsl"?>
<refentry xml:id="mosquitto.conf" xmlns:xlink="http://www.w3.org/1999/xlink">
<refmeta>
<refentrytitle>mosquitto.conf</refentrytitle>
<manvolnum>5</manvolnum>
<refmiscinfo class="source">Mosquitto Project</refmiscinfo>
<refmiscinfo class="manual">File formats and conventions</refmiscinfo>
</refmeta>
<refnamediv>
<refname>mosquitto.conf</refname>
<refpurpose>the configuration file for mosquitto</refpurpose>
</refnamediv>
<refsynopsisdiv>
<cmdsynopsis>
<command>mosquitto.conf</command>
</cmdsynopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para><command>mosquitto.conf</command> 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
<citerefentry><refentrytitle><link xlink:href="mosquitto-8.html">mosquitto</link></refentrytitle><manvolnum>8</manvolnum></citerefentry>
for information on how to load a configuration file.</para>
<para>
Mosquitto can be instructed to reload the configuration file by sending
a SIGHUP signal as described in the Signals section of
<citerefentry><refentrytitle><link xlink:href="mosquitto-8.html">mosquitto</link></refentrytitle><manvolnum>8</manvolnum></citerefentry>.
Not all configuration options can be reloaded, as detailed in the options below.
</para>
</refsect1>
<refsect1>
<title>File Format</title>
<para>All lines with a # as the very first character are treated as a
comment.</para>
<para>Configuration lines start with a variable name. The variable
value is separated from the name by a single space.</para>
</refsect1>
<refsect1>
<title>Authentication</title>
<para>The authentication options described below allow a wide range of
possibilities in conjunction with the listener options. This
section aims to clarify the possibilities. An overview is also available at
<ulink url="https://mosquitto.org/documentation/authentication-methods/"/></para>
<para>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 certfile and keyfile.</para>
<para>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. Use the
<option>per_listener_settings</option> to control whether passwords
are required globally or on a per-listener basis.</para>
<para>Mosquitto provides the Dynamic Security plugin which handles
username/password authentication and access control in a much
more flexible way than a password file. See
<ulink url="https://mosquitto.org/documentation/dynamic-security/"/>
</para>
<para>When using certificate based encryption there are three 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 and third options, use_identity_as_username and
use_subject_as_username, become relevant. If set to true,
use_identity_as_username causes the Common Name (CN) from the
client certificate to be used instead of the MQTT username for
access control purposes. The password is not used because it is
assumed that only authenticated clients have valid certificates.
This means that any CA certificates you include in cafile or capath
will be able to issue client certificates that are valid for
connecting to your broker. If use_identity_as_username is false,
the client must authenticate as normal (if required by
password_file) through the MQTT options. The same principle applies
for the use_subject_as_username option, but the entire certificate
subject is used as the username instead of just the CN.</para>
<para>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.</para>
<para>Both certificate and PSK based encryption are configured on a
per-listener basis.</para>
<para>Authentication plugins can be created to augment the
password_file, acl_file and psk_file options with e.g. SQL based
lookups.</para>
<para>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.</para>
</refsect1>
<refsect1>
<title>General Options</title>
<variablelist>
<varlistentry>
<term><option>acl_file</option> <replaceable>file path</replaceable></term>
<listitem>
<para>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.</para>
<para>If this parameter is defined then only the topics
listed will have access. Topic access is added with
lines of the format:</para>
<para><code>topic [read|write|readwrite|deny] &lt;topic&gt;</code></para>
<para>The access type is controlled using "read", "write",
"readwrite" or "deny". This parameter is optional (unless
&lt;topic&gt; includes a space character) - if not
given then the access is read/write. &lt;topic&gt; can
contain the + or # wildcards as in
subscriptions. The "deny" option can used to explicitly
deny access to a topic that would otherwise be granted
by a broader read/write/readwrite statement. Any "deny"
topics are handled before topics that grant read/write access.</para>
<para>The first set of topics are applied to anonymous
clients, assuming <option>allow_anonymous</option> is
true. User specific topic ACLs are added after a user
line as follows:</para>
<para><code>user &lt;username&gt;</code></para>
<para>The username referred to here is the same as in
<option>password_file</option>. It is not the
clientid.</para>
<para>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.</para>
<para><code>pattern [read|write|readwrite|deny] &lt;topic&gt;</code></para>
<para>The patterns available for substition are:</para>
<itemizedlist mark="circle">
<listitem><para>%c to match the client id of the client</para></listitem>
<listitem><para>%u to match the username of the client</para></listitem>
</itemizedlist>
<para>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.</para>
<para>Example:</para>
<para><code>pattern write sensor/%u/data</code></para>
<para>Allow access for bridge connection messages:</para>
<para><code>pattern write $SYS/broker/connection/%c/state</code></para>
<para>If the first character of a line of the ACL file is a
# it is treated as a comment.</para>
<para>If <option>per_listener_settings</option> is
<replaceable>true</replaceable>, this option applies to
the current listener being configured only. If
<option>per_listener_settings</option> is
<replaceable>false</replaceable>, this option applies
to all listeners.</para>
<para>Reloaded on reload signal. The currently loaded ACLs
will be freed and reloaded. Existing subscriptions will
be affected after the reload.</para>
<para>See also
<ulink url="https://mosquitto.org/documentation/dynamic-security/"/>
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>allow_anonymous</option> [ true | false ]</term>
<listitem>
<para>Boolean value that determines whether clients that
connect without providing a username are allowed to
connect. If set to <replaceable>false</replaceable>
then another means of connection should be created to
control authenticated client access.</para>
<para>Defaults to <replaceable>false</replaceable>,
unless no listeners are defined in the configuration
file, in which case it set to <replaceable>true</replaceable>,
but connections are only allowed from the local machine.</para>
<para>If <option>per_listener_settings</option> is
<replaceable>true</replaceable>, this option applies to
the current listener being configured only. If
<option>per_listener_settings</option> is
<replaceable>false</replaceable>, this option applies
to all listeners.</para>
<important><para>In version 1.6.x and earlier, this option defaulted
to <replaceable>true</replaceable> unless there was another security
option set.</para></important>
<para>Reloaded on reload signal.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>allow_duplicate_messages</option> [ true | false ]</term>
<listitem>
<para>This option is deprecated and will be removed in a
future version. The behaviour will default to true.
</para>
<para>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.</para>
<para>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.</para>
<para>It can be safely set to
<replaceable>true</replaceable> 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.</para>
<para>Defaults to <replaceable>true</replaceable>.</para>
<para>This option applies globally.</para>
<para>Reloaded on reload signal.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>allow_zero_length_clientid</option> [ true | false ]</term>
<listitem>
<para>MQTT 3.1.1 and MQTT 5 allow clients to connect with a zero
length client id and have the broker generate a client
id for them. Use this option to allow/disallow this
behaviour. Defaults to true.</para>
<para>See also the <option>auto_id_prefix</option> option.</para>
<para>If <option>per_listener_settings</option> is
<replaceable>true</replaceable>, this option applies to
the current listener being configured only. If
<option>per_listener_settings</option> is
<replaceable>false</replaceable>, this option applies
to all listeners.</para>
<para>Reloaded on reload signal.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>auth_plugin_deny_special_chars</option> [ true | false ]</term>
<listitem>
<para>If <replaceable>true</replaceable> 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.</para>
<para>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.</para>
<para>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 <replaceable>false</replaceable>.</para>
<para>Defaults to <replaceable>true</replaceable>.</para>
<para>Applies to the current authentication plugin being configured.</para>
<para>Not currently reloaded on reload signal.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>auto_id_prefix</option> <replaceable>prefix</replaceable></term>
<listitem>
<para>If <option>allow_zero_length_clientid</option> is
<replaceable>true</replaceable>, this option allows you
to set a string that will be prefixed to the
automatically generated client ids to aid visibility in
logs. Defaults to <option>auto-</option>.</para>
<para>If <option>per_listener_settings</option> is
<replaceable>true</replaceable>, this option applies to
the current listener being configured only. If
<option>per_listener_settings</option> is
<replaceable>false</replaceable>, this option applies
to all listeners.</para>
<para>Reloaded on reload signal.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>autosave_interval</option> <replaceable>seconds</replaceable></term>
<listitem>
<para>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).</para>
<para>This option applies globally.</para>
<para>Reloaded on reload signal.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>autosave_on_changes</option> [ true | false ]</term>
<listitem>
<para>If <replaceable>true</replaceable>, mosquitto will
count the number of subscription changes, retained
messages received and queued messages and if the total
exceeds <option>autosave_interval</option> then the
in-memory database will be saved to disk. If
<replaceable>false</replaceable>, mosquitto will save
the in-memory database to disk by treating
<option>autosave_interval</option> as a time in
seconds.</para>
<para>This option applies globally.</para>
<para>Reloaded on reload signal.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>check_retain_source</option> [ true | false ]</term>
<listitem>
<para>This option affects the scenario when a client
subscribes to a topic that has retained messages. It is
possible that the client that published the retained
message to the topic had access at the time they
published, but that access has been subsequently
removed. If <option>check_retain_source</option> is set
to true, the default, the source of a retained message
will be checked for access rights before it is
republished. When set to false, no check will be made
and the retained message will always be
published.</para>
<para>This option applies globally, regardless of the
<option>per_listener_settings</option> option.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>clientid_prefixes</option> <replaceable>prefix</replaceable></term>
<listitem>
<para>This option is deprecated and will be removed in a
future version.</para>
<para>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.</para>
<para>This option applies globally.</para>
<para>Reloaded on reload signal. Note that currently
connected clients will be unaffected by any
changes.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>connection_messages</option> [ true | false ]</term>
<listitem>
<para>If set to <replaceable>true</replaceable>, the log
will include entries when clients connect and
disconnect. If set to <replaceable>false</replaceable>,
these entries will not appear.</para>
<para>This option applies globally.</para>
<para>Reloaded on reload signal.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>include_dir</option> <replaceable>dir</replaceable></term>
<listitem>
<para>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.</para>
<para>The configuration files in
<option>include_dir</option> are loaded in case
sensitive alphabetical order, with the upper case of
each letter ordered before the lower case of the same
letter.</para>
<example title="Load Order for include_dir" label="Load Order for include_dir">
<para>Given the files
<replaceable>b.conf</replaceable>,
<replaceable>A.conf</replaceable>,
<replaceable>01.conf</replaceable>,
<replaceable>a.conf</replaceable>,
<replaceable>B.conf</replaceable>, and
<replaceable>00.conf</replaceable> inside
<option>include_dir</option>, the config files
would be loaded in this order:</para>
<programlisting language="config">
00.conf
01.conf
A.conf
a.conf
B.conf
b.conf
</programlisting></example>
<para>If this option is used multiple times, then each
<option>include_dir</option> option is processed
completely in the order that they are written in the
main configuration file.</para>
<example title="Load Order for Multiple include_dir" label="Load Order for Multiple include_dir">
<para>Assuming a directory
<replaceable>one.d</replaceable> containing
files <replaceable>B.conf</replaceable> and
<replaceable>C.conf</replaceable>, and a second
directory <replaceable>two.d</replaceable>
containing files
<replaceable>A.conf</replaceable> and
<replaceable>D.conf</replaceable>, and a
config:</para>
<programlisting language="config">
include_dir one.d
include_dir two.d
</programlisting><para>Then the config files would be loaded in this order:</para>
<programlisting language="config">
# files from one.d
B.conf
C.conf
# files from two.d
A.conf
D.conf
</programlisting></example>
</listitem>
</varlistentry>
<varlistentry>
<term><option>log_dest</option> <replaceable>destinations</replaceable></term>
<listitem>
<para>Send log messages to a particular destination.
Possible destinations are: <option>stdout</option>
<option>stderr</option> <option>syslog</option>
<option>topic</option> <option>file</option>
<option>dlt</option>.</para>
<para><option>stdout</option> and
<option>stderr</option> log to the console on the
named output.</para>
<para><option>syslog</option> uses the userspace syslog
facility which usually ends up in /var/log/messages or
similar.</para>
<para><option>topic</option> logs to the broker topic
'$SYS/broker/log/&lt;severity&gt;', where severity is
one of E, W, N, I, M which are 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. Debug messages are never
logged on topics.</para>
<para>The <option>file</option> 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.</para>
<para>The <option>dlt</option> destination is for the
automotive `Diagnostic Log and Trace` tool. This
requires that Mosquitto has been compiled with DLT
support.</para>
<para>Use "log_dest none" if you wish to disable logging.
Defaults to stderr. This option may be specified
multiple times.</para>
<para>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.</para>
<para>Reloaded on reload signal.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>log_facility</option> <replaceable>local facility</replaceable></term>
<listitem>
<para>If using syslog logging (not on Windows), messages
will be logged to the "daemon" facility by default. Use
the <option>log_facility</option> 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.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>log_timestamp</option> [ true | false ]</term>
<listitem>
<para>Boolean value, if set to
<replaceable>true</replaceable> a timestamp value will
be added to each log entry. The default is
<replaceable>true</replaceable>.</para>
<para>Reloaded on reload signal.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>log_timestamp_format</option> <replaceable>format</replaceable></term>
<listitem>
<para>Set the format of the log timestamp. If left unset,
this is the number of seconds since the Unix epoch.
This option is a free text string which will be passed
to the strftime function as the format specifier. To
get an ISO 8601 datetime, for example:</para>
<programlisting language="config">
log_timestamp_format %Y-%m-%dT%H:%M:%S
</programlisting>
<para>Reloaded on reload signal.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>log_type</option> <replaceable>types</replaceable></term>
<listitem>
<para>Choose types of messages to log. Possible types are:
<replaceable>debug</replaceable>,
<replaceable>error</replaceable>,
<replaceable>warning</replaceable>,
<replaceable>notice</replaceable>,
<replaceable>information</replaceable>,
<replaceable>subscribe</replaceable>,
<replaceable>unsubscribe</replaceable>,
<replaceable>websockets</replaceable>,
<replaceable>none</replaceable>,
<replaceable>all</replaceable>.</para>
<para>Defaults to <replaceable>error</replaceable>,
<replaceable>warning</replaceable>, <replaceable>notice
</replaceable>and
<replaceable>information</replaceable>. This option
may be specified multiple times. Note that the
<replaceable>debug </replaceable>type (used for
decoding incoming/outgoing network packets) is never
logged in topics.</para>
<para>Reloaded on reload signal.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>max_inflight_bytes</option> <replaceable>count</replaceable></term>
<listitem>
<para>Outgoing QoS 1 and 2 messages will be allowed in flight until this byte
limit is reached. This allows control of outgoing message rate based on
message size rather than message count. If the limit is set to 100,
messages of over 100 bytes are still allowed, but only a single message
can be in flight at once. Defaults to 0. (No limit).</para>
<para>See also the <option>max_inflight_messages</option> option.</para>
<para>This option applies globally.</para>
<para>Reloaded on reload signal.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>max_inflight_messages</option> <replaceable>count</replaceable></term>
<listitem>
<para>The maximum number of outgoing 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.</para>
<para>This option applies globally.</para>
<para>Reloaded on reload signal.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>max_keepalive</option> <replaceable>value</replaceable></term>
<listitem>
<para>For MQTT v5 clients, it is possible to have the
server send a "server keepalive" value that will
override the keepalive value set by the client. This
is intended to be used as a mechanism to say that the
server will disconnect the client earlier than it
anticipated, and that the client should use the new
keepalive value. The max_keepalive option allows you to
specify that clients may only connect with keepalive
less than or equal to this value, otherwise they will
be sent a server keepalive telling them to use
max_keepalive. This only applies to MQTT v5 clients.
The maximum value allowable, and default value, is
65535.</para>
<para>
Set to 0 to allow clients to set keepalive = 0, which
means no keepalive checks are made and the client will
never be disconnected by the broker if no messages are
received. You should be very sure this is the behaviour
that you want.
</para>
<para>
For MQTT v3.1.1 and v3.1 clients, there is no mechanism
to tell the client what keepalive value they should use.
If an MQTT v3.1.1 or v3.1 client specifies a keepalive
time greater than max_keepalive they will be sent a
CONNACK message with the "identifier rejected" reason
code, and disconnected.
</para>
<para>This option applies globally.</para>
<para>Reloaded on reload signal.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>max_packet_size</option> <replaceable>value</replaceable></term>
<listitem>
<para>For MQTT v5 clients, it is possible to have the
server send a "maximum packet size" value that will
instruct the client it will not accept MQTT packets
with size greater than <option>value</option> bytes.
This applies to the full MQTT packet, not just the
payload. Setting this option to a positive value will
set the maximum packet size to that number of bytes. If
a client sends a packet which is larger than this
value, it will be disconnected. This applies to all
clients regardless of the protocol version they are
using, but v3.1.1 and earlier clients will of course
not have received the maximum packet size information.
Defaults to no limit.</para>
<para>This option applies to all clients, not just those
using MQTT v5, but it is not possible to notify clients
using MQTT v3.1.1 or MQTT v3.1 of the limit.</para>
<para>Setting below 20 bytes is forbidden because it is
likely to interfere with normal client operation even
with small payloads.</para>
<para>This option applies globally.</para>
<para>Reloaded on reload signal.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>max_queued_bytes</option> <replaceable>count</replaceable></term>
<listitem>
<para>The number of outgoing QoS 1 and 2 messages above those currently in-flight will be
queued (per client) by the broker. Once this limit has been reached, subsequent
messages will be silently dropped. This is an important option if you are sending
messages at a high rate and/or have clients who are slow to respond or may be offline
for extended periods of time. Defaults to 0. (No maximum).</para>
<para>See also the
<option>max_queued_messages</option> option.
If both max_queued_messages and max_queued_bytes are specified,
packets will be queued until the first limit is reached.
</para>
<para>This option applies globally.</para>
<para>Reloaded on reload signal.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>max_queued_messages</option> <replaceable>count</replaceable></term>
<listitem>
<para>The maximum number of QoS 1 or 2 messages to hold in the
queue (per client) above those messages that are currently
in flight. Defaults to 1000. Set to 0 for no maximum (not
recommended). See also the
<option>queue_qos0_messages</option> and
<option>max_queued_bytes</option> options.</para>
<para>This option applies globally.</para>
<para>Reloaded on reload signal.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>memory_limit</option> <replaceable>limit</replaceable></term>
<listitem>
<para>
This option sets the maximum number of heap memory bytes that the broker
will allocate, and hence sets a hard limit on memory use by the broker.
Memory requests that exceed this value will be denied. The effect will
vary depending on what has been denied. If an incoming message is being
processed, then the message will be dropped and the publishing client
will be disconnected. If an outgoing message is being sent, then the
individual message will be dropped and the receiving client will be
disconnected. Defaults to no limit.</para>
<para>This option is only available if memory tracking support is compiled
in.</para>
<para>Reloaded on reload signal. Setting to a lower value and reloading will
not result in memory being freed.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>message_size_limit</option> <replaceable>limit</replaceable></term>
<listitem>
<para>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. This means that the
message will not be forwarded on to subscribing clients, but the QoS flow
will be completed for QoS 1 or QoS 2 messages. MQTT v5 clients using QoS 1
or QoS 2 will receive a PUBACK or PUBREC with the "implementation specific
error" reason code.</para>
<para>The default value is 0, which means that all valid MQTT
messages are accepted. MQTT imposes a maximum payload
size of 268435455 bytes.</para>
<para>This option applies globally.</para>
<para>Reloaded on reload signal.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>password_file</option> <replaceable>file path</replaceable></term>
<listitem>
<para>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
<citerefentry><refentrytitle><link xlink:href="mosquitto_passwd-1.html">mosquitto_passwd</link></refentrytitle><manvolnum>1</manvolnum></citerefentry>
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
<option>allow_anonymous</option> is set to
<replaceable>false</replaceable>, only users defined in
this file will be able to connect. Setting
<option>allow_anonymous</option> to
<replaceable>true</replaceable> when
<replaceable>password_file</replaceable>is 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.</para>
<para>If <option>per_listener_settings</option> is
<replaceable>true</replaceable>, this option applies to
the current listener being configured only. If
<option>per_listener_settings</option> is
<replaceable>false</replaceable>, this option applies
to all listeners.</para>
<para>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.</para>
<para>See also
<citerefentry><refentrytitle><link xlink:href="mosquitto_passwd-1.html">mosquitto_passwd</link></refentrytitle><manvolnum>1</manvolnum></citerefentry> and
<ulink url="https://mosquitto.org/documentation/dynamic-security/"/>
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>per_listener_settings</option> [ true | false ]</term>
<listitem>
<para>If <replaceable>true</replaceable>, then
authentication and access control settings will be
controlled on a per-listener basis. The following
options are affected:</para>
<para><option>password_file</option>,
<option>acl_file</option>, <option>psk_file</option>,
<option>allow_anonymous</option>,
<option>allow_zero_length_clientid</option>,
<option>auto_id_prefix</option>.</para>
<option>plugin</option>,
<option>plugin_opt_*</option>,
<para>Note that if set to true, then a durable client (i.e.
with clean session set to false) that has disconnected
will use the ACL settings defined for the listener that
it was most recently connected to.</para>
<para>The default behaviour is for this to be set to
<replaceable>false</replaceable>, which maintains the
settings behaviour from previous versions of
mosquitto.</para>
<para>Reloaded on reload signal.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>persistence</option> [ true | false ]</term>
<listitem>
<para>If <replaceable>true</replaceable>, 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 <replaceable>false</replaceable>, the data
will be stored in memory only. Defaults to
<replaceable>false</replaceable>.</para>
<para>The persistence file may change its format in a new
version. The broker can currently read all old formats,
but will only save in the latest format. It should always
be safe to upgrade, but cautious users may wish to take a
copy of the persistence file before installing a new
version so that they can roll back to an earlier version
if necessary.</para>
<para>This option applies globally.</para>
<para>Reloaded on reload signal.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>persistence_file</option> <replaceable>file name</replaceable></term>
<listitem>
<para>The filename to use for the persistent database.
Defaults to mosquitto.db.</para>
<para>This option applies globally.</para>
<para>Reloaded on reload signal.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>persistence_location</option> <replaceable>path</replaceable></term>
<listitem>
<para>The path where the persistence database should be
stored. If not given, then the current directory is used.</para>
<para>This option applies globally.</para>
<para>Reloaded on reload signal.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>persistent_client_expiration</option> <replaceable>duration</replaceable></term>
<listitem>
<para>
This option allows the session of persistent clients (those with clean
session set to false) <emphasis>that are not currently connected</emphasis> to be removed if they
do not reconnect within a certain time frame. This is a non-standard option
in MQTT v3.1. MQTT v3.1.1 and v5.0 allow brokers to remove client sessions.
</para>
<para>
Badly designed clients may set clean session to false whilst using a randomly
generated client id. This leads to persistent clients that connect once and
never reconnect. This option allows these clients to be removed. 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.
</para>
<para>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:</para>
<itemizedlist mark="circle">
<listitem><para>persistent_client_expiration 2m</para></listitem>
<listitem><para>persistent_client_expiration 14d</para></listitem>
<listitem><para>persistent_client_expiration 1y</para></listitem>
</itemizedlist>
<para>As this is a non-standard option, the default if not
set is to never expire persistent clients.</para>
<para>This option applies globally.</para>
<para>Reloaded on reload signal.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>pid_file</option> <replaceable>file path</replaceable></term>
<listitem>
<para>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.</para>
<para>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/mosquitto.pid</para>
<para>Not reloaded on reload signal.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>plugin_opt_*</option> <replaceable>value</replaceable></term>
<listitem>
<para>
Options to be passed to the most recent
<option>plugin</option> defined in the
configuration file. See the specific
plugin instructions for details of what
options are available.
</para>
<para>Applies to the current plugin being configured.</para>
<para>
This is also available as the <option>auth_opt_*</option>
option, but this use is deprecated and will be removed
in a future version.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>plugin</option> <replaceable>file path</replaceable></term>
<listitem>
<para>Specify an external module to use for authentication
and access control. This allows custom
username/password and access control functions to be
created.</para>
<para>Can be specified multiple times to load multiple
plugins. The plugins will be processed in the order
that they are specified.</para>
<para>If <option>password_file</option>, or
<option>acl_file</option> are used in the config file
alongsize <option>plugin</option>, the plugin
checks will run after the built in checks.</para>
<para>Not currently reloaded on reload signal.</para>
<para>See also
<ulink url="https://mosquitto.org/documentation/dynamic-security/"/>
</para>
<para>
This is also available as the <option>auth_plugin</option>
option, but this use is deprecated and will be removed
in a future version.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>psk_file</option> <replaceable>file path</replaceable></term>
<listitem>
<para>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.</para>
<para>If <option>per_listener_settings</option> is
<replaceable>true</replaceable>, this option applies to
the current listener being configured only. If
<option>per_listener_settings</option> is
<replaceable>false</replaceable>, this option applies
to all listeners.</para>
<para>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.</para>
</listitem> </varlistentry>
<varlistentry>
<term><option>queue_qos0_messages</option> [ true | false ]</term>
<listitem>
<para>Set to <replaceable>true</replaceable> to queue
messages with QoS 0 when a persistent client is
disconnected. When bridges topics are configured with QoS level 1 or 2 incoming
QoS 0 messages for these topics are also queued.
These messages are included in the limit
imposed by max_queued_messages. Defaults to
<replaceable>false</replaceable>.</para>
<para>Note that the MQTT v3.1.1 spec states that only QoS 1
and 2 messages should be saved in this situation so
this is a non-standard option.</para>
<para>This option applies globally.</para>
<para>Reloaded on reload signal.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>retain_available</option> [ true | false ]</term>
<listitem>
<para>If set to false, then retained messages are not
supported. Clients that send a message with the retain
bit will be disconnected if this option is set to
false. Defaults to true.</para>
<para>This option applies globally.</para>
<para>Reloaded on reload signal.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>set_tcp_nodelay</option> [ true | false ]</term>
<listitem>
<para>If set to true, the TCP_NODELAY option will be set on
client sockets to disable Nagle's algorithm. This
has the effect of reducing latency of some messages
at potentially increasing the number of TCP packets
being sent. Defaults to false.</para>
<para>This option applies globally.</para>
<para>Reloaded on reload signal.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>sys_interval</option> <replaceable>seconds</replaceable></term>
<listitem>
<para>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.</para>
<para>Set to 0 to disable publishing the $SYS hierarchy
completely.</para>
<para>This option applies globally.</para>
<para>Reloaded on reload signal.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>upgrade_outgoing_qos</option> [ true | false ]</term>
<listitem>
<para>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
<option>upgrade_outgoing_qos</option> is set
<replaceable>true</replaceable>, 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
<replaceable>false</replaceable>.</para>
<para>This option applies globally.</para>
<para>Reloaded on reload signal.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>user</option> <replaceable>username</replaceable></term>
<listitem>
<para>When run as root, change to this user and its primary
group on startup. If set to "mosquitto" or left unset,
and if the "mosquitto" user does not exist, then
mosquitto will change to the "nobody" user instead.
If this is set to another value and 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.</para>
<para>This setting has no effect on Windows and so you
should run mosquitto as the user you wish it to run
as.</para>
<para>Not reloaded on reload signal.</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Listeners</title>
<para>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.</para>
<refsect2>
<title>General Options</title>
<variablelist>
<varlistentry>
<term><option>bind_address</option> <replaceable>address</replaceable></term>
<listitem>
<para>This option is deprecated and will be removed in a
future version. Use the <option>listener</option> instead.
</para>
<para>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
<option>listener</option> option to control other
listeners.</para>
<para>It is recommended to use an explicit
<option>listener</option> rather than rely on the
implicit default listener options like this.</para>
<para>Not reloaded on reload signal.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>bind_interface</option> <replaceable>device</replaceable></term>
<listitem>
<para>Listen for incoming network connections only on
the specified interface. This is similar to the
<option>bind_address</option> option but is useful
when an interface has multiple addresses or the
address may change.</para>
<para>If used at the same time as the
<option>bind_address</option> for the default
listener, or the <replaceable>bind
address/host</replaceable> part of the
<option>listener</option>, then <option>bind_interface</option>
will take priority.</para>
<para>This option is not available on Windows.</para>
<para>Not reloaded on reload signal.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>http_dir</option> <replaceable>directory</replaceable></term>
<listitem>
<para>When a listener is using the websockets protocol,
it is possible to serve http data as well. Set
<option>http_dir</option> 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.</para>
<para>Not reloaded on reload signal.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>listener</option> <replaceable>port</replaceable> <replaceable><optional>bind address/host/unix socket path</optional></replaceable></term>
<listitem>
<para>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 the global <option>bind_address</option>
nor <option>port</option> options are used then the
default listener will not be started.</para>
<para>The <option>bind address/host</option> option
allows this listener to be bound to a specific IP
address by passing an IP address or hostname. For
websockets listeners, it is only possible to pass
an IP address here.</para>
<para>On systems that support Unix Domain Sockets, this
option can also be used to create a Unix socket rather
than opening a TCP socket. In this case, the port must
be set to 0, and the unix socket path must be given.</para>
<para>This option may be specified multiple times. See
also the <option>mount_point</option>
option.</para>
<para>Not reloaded on reload signal.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>max_connections</option> <replaceable>count</replaceable></term>
<listitem>
<para>Limit the total number of clients connected for
the current listener. Set to <literal>-1</literal>
to have "unlimited" connections. Note that other
limits may be imposed that are outside the control
of mosquitto. See e.g.
<citerefentry><refentrytitle><link xlink:href="http://linux.die.net/man/5/limits.conf">limits.conf</link></refentrytitle></citerefentry>.</para>
<para>Not reloaded on reload signal.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>max_qos</option> <replaceable>value</replaceable></term>
<listitem>
<para>Limit the QoS value allowed for clients connecting to this
listener. Defaults to 2, which means any QoS can be
used. Set to 0 or 1 to limit to those QoS values.
This makes use of an MQTT v5 feature to notify
clients of the limitation. MQTT v3.1.1 clients will
not be aware of the limitation. Clients publishing
to this listener with a too-high QoS will be
disconnected.</para>
<para>Not reloaded on reload signal.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>max_topic_alias</option> <replaceable>number</replaceable></term>
<listitem>
<para>This option sets the maximum number topic aliases
that an MQTT v5 client is allowed to create. This option
applies per listener. Defaults to 10. Set to 0 to
disallow topic aliases. The maximum value possible is 65535.</para>
<para>Not reloaded on reload signal.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>mount_point</option> <replaceable>topic prefix</replaceable></term>
<listitem>
<para>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
<replaceable>example</replaceable> can only see
messages that are published in the topic hierarchy
<replaceable>example</replaceable> and below.</para>
<para>Not reloaded on reload signal.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>port</option> <replaceable>port number</replaceable></term>
<listitem>
<para>This option is deprecated and will be removed in a
future version. Use the <option>listener</option> instead.
</para>
<para>Set the network port for the default listener to
listen on. Defaults to 1883.</para>
<para>Not reloaded on reload signal.</para>
<para>It is recommended to use an explicit
<option>listener</option> rather than rely on the
implicit default listener options like this.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>protocol</option> <replaceable>value</replaceable></term>
<listitem>
<para>Set the protocol to accept for the current listener. Can
be <option>mqtt</option>, the default, or
<option>websockets</option> if available.</para>
<para>Websockets support is currently disabled by
default at compile time. Certificate based TLS may be used
with websockets, except that only the
<option>cafile</option>, <option>certfile</option>,
<option>keyfile</option>, <option>ciphers</option>, and
<option>ciphers_tls1.3</option> options are
supported.</para>
<para>Not reloaded on reload signal.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>socket_domain</option> [ ipv4 | ipv6 ]</term>
<listitem>
<para>By default, a listener will attempt to listen on
all supported IP protocol versions. If you do not
have an IPv4 or IPv6 interface you may wish to
disable support for either of those protocol
versions. In particular, note that due to the
limitations of the websockets library, it will only
ever attempt to open IPv6 sockets if IPv6 support
is compiled in, and so will fail if IPv6 is not
available.</para>
<para>Set to <option>ipv4</option> to force the
listener to only use IPv4, or set to
<option>ipv6</option> to force the listener to only
use IPv6. If you want support for both IPv4 and
IPv6, then do not use the
<option>socket_domain</option> option.</para>
<para>Not reloaded on reload signal.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>use_username_as_clientid</option> [ true | false ]</term>
<listitem>
<para>Set <option>use_username_as_clientid</option> to
true to replace the clientid that a client
connected 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.</para>
<para>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
<option>clientid_prefixes</option>.</para>
<para>This does not apply globally, but on a per-listener basis.</para>
<para>See also
<option>use_identity_as_username</option>.</para>
<para>Not reloaded on reload signal.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>websockets_log_level</option> <replaceable>level</replaceable></term>
<listitem>
<para>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.</para>
<para>To use this option, <option>log_type
websockets</option> must also be enabled.
Defaults to 0.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>websockets_headers_size</option> <replaceable>size</replaceable></term>
<listitem>
<para>Change the websockets headers size. This is a
global option, it is not possible to set per
listener. This option sets the size of the buffer
used in the libwebsockets library when reading HTTP
headers. If you are passing large header data such
as cookies then you may need to increase this
value. If left unset, or set to 0, then the default
of 1024 bytes will be used.</para>
</listitem>
</varlistentry>
</variablelist>
</refsect2>
<refsect2>
<title>Certificate based SSL/TLS Support</title>
<para>The following options are available for all listeners to
configure certificate based SSL support. See also
"Pre-shared-key based SSL/TLS support".</para>
<variablelist>
<varlistentry>
<term><option>cafile</option> <replaceable>file path</replaceable></term>
<listitem>
<para><option>cafile</option> is used to define the
path to a file containing the PEM encoded CA
certificates that are trusted when checking incoming
client certificates.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>capath</option> <replaceable>directory path</replaceable></term>
<listitem>
<para><option>capath</option> is used to define a
directory that contains PEM encoded CA certificates
that are trusted when checking incoming client
certificates. For <option>capath</option> to
work correctly, the certificates files must have
".pem" as the file ending and you must run
"openssl rehash &lt;path to capath&gt;" each time
you add/remove a certificate.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>certfile</option> <replaceable>file path</replaceable></term>
<listitem>
<para>
Path to the PEM encoded server certificate. This
option and <option>keyfile</option> must be present
to enable certificate based TLS encryption.
</para>
<para>
The certificate pointed to by this option will be
reloaded when Mosquitto receives a SIGHUP signal.
This can be used to load new certificates prior to
the existing ones expiring.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>ciphers</option> <replaceable>cipher:list</replaceable></term>
<listitem>
<para>
The list of allowed ciphers for this listener, for
TLS v1.2 and earlier only, each separated with
a colon. Available ciphers can be obtained using
the "openssl ciphers" command.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>ciphers_tls1.3</option> <replaceable>cipher:list</replaceable></term>
<listitem>
<para>
The list of allowed ciphersuites for this listener,
for TLS v1.3, each separated with a colon.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>crlfile</option> <replaceable>file path</replaceable></term>
<listitem>
<para>If you have <option>require_certificate</option>
set to <replaceable>true</replaceable>, 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.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>dhparamfile</option> <replaceable>file path</replaceable></term>
<listitem>
<para>To allow the use of ephemeral DH key exchange,
which provides forward security, the listener must
load DH parameters. This can be specified with the
dhparamfile option. The dhparamfile can be
generated with the command e.g.</para>
<programlisting>
openssl dhparam -out dhparam.pem 2048</programlisting>
</listitem>
</varlistentry>
<varlistentry>
<term><option>keyfile</option> <replaceable>file path</replaceable></term>
<listitem>
<para>
If <option>tls_keyform</option> equals "pem" this is the
path to the PEM encoded server key. This option
and <option>certfile</option> must be present
to enable certificate based TLS encryption. If
<option>tls_keyform</option> is "engine" this represents
the engine handle of the private key.
</para>
<para>
The private key pointed to by this option will be
reloaded when Mosquitto receives a SIGHUP signal.
This can be used to load new keys prior to
the existing ones expiring.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>require_certificate</option> [ true | false ]</term>
<listitem>
<para>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
<option>require_certificate</option> to
<replaceable>true</replaceable>, a client connecting
to this listener 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.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>tls_engine</option> <replaceable>engine</replaceable></term>
<listitem>
<para>A valid openssl engine id. These can be listed with
openssl engine command.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>tls_engine_kpass_sha1</option> <replaceable>engine_kpass_sha1</replaceable></term>
<listitem>
<para>SHA1 of the private key password when using an
TLS engine. Some TLS engines such as the TPM
engine may require the use of a password in order
to be accessed. This option allows a hex encoded
SHA1 hash of the password to the engine directly,
instead of the user being prompted for the
password.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>tls_keyform</option> [ pem | engine ]</term>
<listitem>
<para>Specifies the type of private key in use when
making TLS connections.. This can be "pem" or
"engine". This parameter is useful when a TPM
module is being used and the private key has been
created with it. Defaults to "pem", which means
normal private key files are used.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>tls_version</option> <replaceable>version</replaceable></term>
<listitem>
<para>Configure the minimum version of the TLS protocol to be
used for this listener. Possible values are
<replaceable>tlsv1.3</replaceable>,
<replaceable>tlsv1.2</replaceable> and
<replaceable>tlsv1.1</replaceable>. If left unset,
the default allows TLS v1.3 and v1.2.</para>
<para>In Mosquitto version 1.6.x and earlier, this
option set the only TLS protocol version that
was allowed, rather than the minimum.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>use_identity_as_username</option> [ true | false ]</term>
<listitem>
<para>If <option>require_certificate</option> is
<replaceable>true</replaceable>, you may set
<option>use_identity_as_username</option> to
<replaceable>true</replaceable> to use the CN value
from the client certificate as a username. If this
is <replaceable>true</replaceable>, the
<option>password_file</option> option will not be
used for this listener.</para>
<para>This takes priority over
<option>use_subject_as_username</option> if both
are set to <replaceable>true</replaceable>.</para>
<para>See also
<option>use_subject_as_username</option></para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>use_subject_as_username</option> [ true | false ]</term>
<listitem>
<para>If <option>require_certificate</option> is
<replaceable>true</replaceable>, you may set
<option>use_subject_as_username</option> to
<replaceable>true</replaceable> to use the complete subject value
from the client certificate as a username. If this
is <replaceable>true</replaceable>, the
<option>password_file</option> option will not be
used for this listener.</para>
<para>The subject will be generated in a form similar
to <option>CN=test client,OU=Production,O=Server,L=Nottingham,ST=Nottinghamshire,C=GB</option>.</para>
<para>See also
<option>use_identity_as_username</option></para>
</listitem>
</varlistentry>
</variablelist>
</refsect2>
<refsect2>
<title>Pre-shared-key based SSL/TLS Support</title>
<para>The following options are available for all listeners to
configure pre-shared-key based SSL support. See also
"Certificate based SSL/TLS support".</para>
<variablelist>
<varlistentry>
<term><option>ciphers</option> <replaceable>cipher:list</replaceable></term>
<listitem>
<para>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.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>psk_hint</option> <replaceable>hint</replaceable></term>
<listitem>
<para>The <option>psk_hint</option> 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.</para>
<para>If this option is provided, see
<option>psk_file</option> to define the pre-shared
keys to be used or create a security plugin to
handle them.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>tls_version</option> <replaceable>version</replaceable></term>
<listitem>
<para>Configure the minimum version of the TLS protocol to be
used for this listener. Possible values are
<replaceable>tlsv1.3</replaceable>,
<replaceable>tlsv1.2</replaceable> and
<replaceable>tlsv1.1</replaceable>. If left unset,
the default of allowing TLS v1.3 and v1.2.</para>
<para>In Mosquitto version 1.6.x and earlier, this
option set the only TLS protocol version that
was allowed, rather than the minimum.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>use_identity_as_username</option> [ true | false ]</term>
<listitem>
<para>Set <option>use_identity_as_username</option> to
have the psk identity sent by the client used as
its username. The username will be checked as
normal, so <option>password_file</option> or
another means of authentication checking must be
used. No password will be used.</para>
</listitem>
</varlistentry>
</variablelist>
</refsect2>
</refsect1>
<refsect1>
<title>Configuring Bridges</title>
<para>Multiple bridges (connections to other brokers) can be configured
using the following variables.</para>
<para>Bridges cannot currently be reloaded on reload signal.</para>
<variablelist>
<varlistentry>
<term><option>address</option> <replaceable>address[:port]</replaceable> <replaceable>[address[:port]]</replaceable></term>
<term><option>addresses</option> <replaceable>address[:port]</replaceable> <replaceable>[address[:port]]</replaceable></term>
<listitem>
<para>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.</para>
<para>If you use an IPv6 address, then the port is not
optional.</para>
<para>Multiple host addresses can be specified on the
address config. See the <option>round_robin</option>
option for more details on the behaviour of bridges
with multiple addresses.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>bridge_attempt_unsubscribe</option> [ true | false ]</term>
<listitem>
<para>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
<option>bridge_attempt_unsubscribe</option> to
<replaceable>false</replaceable> will disable sending
the unsubscribe request. Defaults to
<replaceable>true</replaceable>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>bridge_bind_address</option> <replaceable>ip address</replaceable></term>
<listitem>
<para>
If you need to have the bridge connect over a particular
network interface, use bridge_bind_address to tell the
bridge which local IP address the socket should bind to,
e.g. <option>bridge_bind_address 192.168.1.10</option>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>bridge_max_packet_size</option> <replaceable>value</replaceable></term>
<listitem>
<para>
If you wish to restrict the size of messages sent to a
remote bridge, use this option. This sets the maximum
number of bytes for the total message, including headers
and payload. Note that MQTT v5 brokers may provide their
own maximum-packet-size property. In this case, the
smaller of the two limits will be used. Set to 0 for
"unlimited".
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>bridge_outgoing_retain</option> [ true | false ]</term>
<listitem>
<para>Some MQTT brokers do not allow retained messages. MQTT v5 gives
a mechanism for brokers to tell clients that they do not support
retained messages, but this is not possible for MQTT v3.1.1 or v3.1.
If you need to bridge to a v3.1.1 or v3.1 broker that does not support
retained messages, set the <option>bridge_outgoing_retain</option>
option to <replaceable>false</replaceable>. This will remove the
retain bit on all outgoing messages to that bridge, regardless of any
other setting. Defaults to <replaceable>true</replaceable>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>bridge_protocol_version</option> <replaceable>version</replaceable></term>
<listitem>
<para>Set the version of the MQTT protocol to use with for
this bridge. Can be one of
<replaceable>mqttv50</replaceable>,
<replaceable>mqttv311</replaceable> or
<replaceable>mqttv31</replaceable>. Defaults to
<replaceable>mqttv311</replaceable>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>cleansession</option> [ true | false ]</term>
<listitem>
<para>Set the clean session option for this bridge. Setting
to <replaceable>false</replaceable> (the default),
means that all subscriptions on the remote broker are
kept in case of the network connection dropping. If set
to <replaceable>true</replaceable>, all subscriptions
and messages on the remote broker will be cleaned up if
the connection drops. Note that setting to
<replaceable>true</replaceable> may cause a large
amount of retained messages to be sent each time the
bridge reconnects.</para>
<para>If you are using bridges with
<option>cleansession</option> set to
<replaceable>false</replaceable> (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 <option>cleansession</option> set to
<replaceable>true</replaceable>, then reconnect with
cleansession set to <replaceable>false</replaceable> as
normal.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>local_cleansession</option> [ true | false]</term>
<listitem>
<para>The regular <option>cleansession</option> covers both the local subscriptions
and the remote subscriptions. local_cleansession allows splitting this.
Setting <replaceable>false</replaceable> will mean that the local connection
will preserve subscription, independent of the remote connection.
</para>
<para>Defaults to the value of bridge.cleansession unless explicitly specified.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>connection</option> <replaceable>name</replaceable></term>
<listitem>
<para>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.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>keepalive_interval</option> <replaceable>seconds</replaceable></term>
<listitem>
<para>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.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>idle_timeout</option> <replaceable>seconds</replaceable></term>
<listitem>
<para>Set the amount of time a bridge using the lazy start
type must be idle before it will be stopped. Defaults
to 60 seconds.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>local_clientid</option> <replaceable>id</replaceable></term>
<listitem>
<para>Set the clientid to use on the local broker. If not
defined, this defaults to
<option>local.&lt;remote_clientid&gt;</option>. If you are
bridging a broker to itself, it is important that
local_clientid and remote_clientid do not match.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>local_password</option> <replaceable>password</replaceable></term>
<listitem>
<para>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.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>local_username</option> <replaceable>username</replaceable></term>
<listitem>
<para>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.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>notifications</option> [ true | false ]</term>
<listitem>
<para>If set to <replaceable>true</replaceable>, 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/&lt;remote_clientid&gt;/state
unless otherwise set with
<option>notification_topic</option>s. If the message
is 1 then the connection is active, or 0 if the
connection has failed. Defaults to
<replaceable>true</replaceable>.</para>
<para>This uses the Last Will and Testament (LWT) feature.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>notifications_local_only</option> [ true | false ]</term>
<listitem>
<para>If set to <replaceable>true</replaceable>, only publish
notification messages to the local broker giving
information about the state of the bridge connection.
Defaults to <replaceable>false</replaceable>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>notification_topic</option> <replaceable>topic</replaceable></term>
<listitem>
<para>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/&lt;remote_clientid&gt;/state.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>remote_clientid</option> <replaceable>id</replaceable></term>
<listitem>
<para>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.</para>
<para>This replaces the old "clientid" option to avoid
confusion with local/remote sides of the bridge.
"clientid" remains valid for the time being.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>remote_password</option> <replaceable>value</replaceable></term>
<listitem>
<para>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.</para>
<para>This replaces the old "password" option to avoid
confusion with local/remote sides of the bridge.
"password" remains valid for the time being.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>remote_username</option> <replaceable>name</replaceable></term>
<listitem>
<para>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
<option>remote_password</option> option.</para>
<para>This replaces the old "username" option to avoid
confusion with local/remote sides of the bridge.
"username" remains valid for the time being.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>restart_timeout</option> <replaceable>base cap</replaceable></term>
<term><option>restart_timeout</option> <replaceable>constant</replaceable></term>
<listitem>
<para>Set the amount of time a bridge using the automatic
start type will wait until attempting to reconnect.</para>
<para>This option can be configured to use a constant delay
time in seconds, or to use a backoff mechanism based on
"Decorrelated Jitter", which adds a degree of
randomness to when the restart occurs, starting at the
base and increasing up to the cap. Set a constant
timeout of 20 seconds:</para>
<programlisting language="config">
restart_timeout 20</programlisting>
<para>Set backoff with a base (start value) of 10 seconds and a cap (upper
limit) of 60 seconds:</para>
<programlisting language="config">
restart_timeout 10 30</programlisting>
<para>Defaults to jitter with a base of 5 seconds and cap
of 30 seconds.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>round_robin</option> [ true | false ]</term>
<listitem>
<para>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
<replaceable>false</replaceable>, 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.</para>
<para>If round_robin is <replaceable>true</replaceable>,
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.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>start_type</option> [ automatic | lazy | once ]</term>
<listitem>
<para>Set the start type of the bridge. This controls how
the bridge starts and can be one of three types:
<replaceable>automatic</replaceable>, <replaceable>lazy
</replaceable>and <replaceable>once</replaceable>. Note
that RSMB provides a fourth start type "manual" which
isn't currently supported by mosquitto.</para>
<para><replaceable>automatic</replaceable> 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.</para>
<para>Bridges using the <replaceable>lazy</replaceable>
start type will be started automatically when the
number of queued messages exceeds the number set with
the <option>threshold</option> option. It will be
stopped automatically after the time set by the
<option>idle_timeout</option> parameter. Use this start
type if you wish the connection to only be active when
it is needed.</para>
<para>A bridge using the <replaceable>once</replaceable>
start type will be started automatically when the
broker starts but will not be restarted if the
connection fails.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>threshold</option> <replaceable>count</replaceable></term>
<listitem>
<para>Set the number of messages that need to be queued for
a bridge with lazy start type to be restarted.
Defaults to 10 messages.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>topic</option> <replaceable>pattern</replaceable> [[[ out | in | both ] qos-level] local-prefix remote-prefix]</term>
<listitem>
<para>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 <replaceable>in</replaceable>, export
messages to a remote broker using
<replaceable>out</replaceable> or share messages in
both directions. If this parameter is not defined, the
default of <replaceable>out</replaceable> is used. The
QoS level defines the publish/subscribe QoS level used
for this topic and defaults to 0.</para>
<para>The <replaceable>local-prefix</replaceable> and
<replaceable>remote-prefix</replaceable> 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.</para>
<para>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.</para>
<para>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.</para>
<para>When using topic mapping, an empty prefix can be
defined using the place marker
<replaceable>""</replaceable>. Using the empty marker
for the topic itself is also valid. The table below
defines what combination of empty or value is
valid. The <option>Full Local Topic</option> and
<option>Full Remote Topic</option> show the resulting
topics that would be used on the local and remote ends
of the bridge. For example, for the first table row if
you publish to <option>L/topic</option> on the local
broker, then the remote broker will receive a message
on the topic <option>R/topic</option>.</para>
<informaltable>
<tgroup cols="6">
<thead>
<row>
<entry><emphasis>Pattern</emphasis></entry>
<entry><emphasis>Local Prefix</emphasis></entry>
<entry><emphasis>Remote Prefix</emphasis></entry>
<entry><emphasis>Validity</emphasis></entry>
<entry><emphasis>Full Local Topic</emphasis></entry>
<entry><emphasis>Full Remote Topic</emphasis></entry>
</row>
</thead>
<tbody>
<row><entry>pattern</entry><entry>L/</entry><entry>R/</entry><entry>valid</entry><entry>L/pattern</entry><entry>R/pattern</entry></row>
<row><entry>pattern</entry><entry>L/</entry><entry>""</entry><entry>valid</entry><entry>L/pattern</entry><entry>pattern</entry></row>
<row><entry>pattern</entry><entry>""</entry><entry>R/</entry><entry>valid</entry><entry>pattern</entry><entry>R/pattern</entry></row>
<row><entry>pattern</entry><entry>""</entry><entry>""</entry><entry>valid (no remapping)</entry><entry>pattern</entry><entry>pattern</entry></row>
<row><entry>""</entry><entry>local</entry><entry>remote</entry><entry>valid (remap single local topic to remote)</entry><entry>local</entry><entry>remote</entry></row>
<row><entry>""</entry><entry>local</entry><entry>""</entry><entry>invalid</entry><entry></entry><entry></entry></row>
<row><entry>""</entry><entry>""</entry><entry>remote</entry><entry>invalid</entry><entry></entry><entry></entry></row>
<row><entry>""</entry><entry>""</entry><entry>""</entry><entry>invalid</entry><entry></entry><entry></entry></row>
</tbody>
</tgroup>
</informaltable>
<para>To remap an entire topic tree, use e.g.:</para>
<programlisting language="config">
topic # both 2 local/topic/ remote/topic/</programlisting>
<para>This option can be specified multiple times per
bridge.</para>
<para>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.</para>
<para>See also the <option>cleansession</option> option if
you have messages arriving on unexpected topics when
using incoming topics.</para>
<example title="Bridge Topic Remapping" label="Bridge Topic Remapping">
<para>The configuration below connects a bridge to the
broker at <option>test.mosquitto.org</option>. It
subscribes to the remote topic
<option>$SYS/broker/clients/total</option> and
republishes the messages received to the local topic
<option>test/mosquitto/org/clients/total</option></para>
<programlisting language="config">
connection test-mosquitto-org
address test.mosquitto.org
cleansession true
topic clients/total in 0 test/mosquitto/org/ $SYS/broker/
</programlisting></example>
</listitem>
</varlistentry>
<varlistentry>
<term><option>try_private</option> [ true | false ]</term>
<listitem>
<para>If try_private is set to
<replaceable>true</replaceable>, 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 <option>try_private</option> to
<replaceable>false</replaceable> if your bridge does
not connect properly.</para>
<para>Defaults to <replaceable>true</replaceable>.</para>
</listitem>
</varlistentry>
</variablelist>
<refsect2>
<title>SSL/TLS Support</title>
<para>The following options are available for all bridges to
configure SSL/TLS support.</para>
<variablelist>
<varlistentry>
<term><option>bridge_alpn</option> <replaceable>alpn</replaceable></term>
<listitem>
<para>Configure the application layer protocol negotiation
option for the TLS session. Useful for brokers that support
both websockets and MQTT on the same port.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>bridge_cafile</option> <replaceable>file path</replaceable></term>
<listitem>
<para>One of <option>bridge_cafile</option> or
<option>bridge_capath</option> must be provided to
allow SSL/TLS support.</para>
<para>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.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>bridge_capath</option> <replaceable>file path</replaceable></term>
<listitem>
<para>One of <option>bridge_capath</option> or
<option>bridge_cafile</option> must be provided to
allow SSL/TLS support.</para>
<para>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 "openssl rehash
&lt;path to bridge_capath&gt;" each time you
add/remove a certificate.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>bridge_certfile</option> <replaceable>file path</replaceable></term>
<listitem>
<para>Path to the PEM encoded client certificate for
this bridge, if required by the remote
broker.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>bridge_identity</option> <replaceable>identity</replaceable></term>
<listitem>
<para>Pre-shared-key encryption provides an alternative
to certificate based encryption. A bridge can be
configured to use PSK with the
<option>bridge_identity</option> and
<option>bridge_psk</option> 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.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>bridge_insecure</option> [ true | false ]</term>
<listitem>
<para>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 <option>bridge_insecure</option> may
be set to <replaceable>true</replaceable> to
disable the hostname verification.</para>
<para>Setting this option to
<replaceable>true</replaceable> means that a
malicious third party could potentially impersonate
your server, so it should always be set to
<replaceable>false</replaceable> in production
environments.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>bridge_keyfile</option> <replaceable>file path</replaceable></term>
<listitem>
<para>Path to the PEM encoded private key for this
bridge, if required by the remote broker.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>bridge_psk</option> <replaceable>key</replaceable></term>
<listitem>
<para>Pre-shared-key encryption provides an alternative
to certificate based encryption. A bridge can be
configured to use PSK with the
<option>bridge_identity</option> and
<option>bridge_psk</option> 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.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>bridge_require_ocsp</option> [ true | false ]</term>
<listitem>
<para>When set to true, the bridge requires OCSP on the TLS
connection it opens as client.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>bridge_tls_version</option> <replaceable>version</replaceable></term>
<listitem>
<para>Configure the version of the TLS protocol to be
used for this bridge. Possible values are
<replaceable>tlsv1.3</replaceable>,
<replaceable>tlsv1.2</replaceable> and
<replaceable>tlsv1.1</replaceable>. Defaults to
<replaceable>tlsv1.2</replaceable>. The remote
broker must support the same version of TLS for the
connection to succeed.</para>
</listitem>
</varlistentry>
</variablelist>
</refsect2>
</refsect1>
<refsect1>
<title>Files</title>
<para>mosquitto.conf</para>
</refsect1>
<refsect1>
<title>Bugs</title>
<para><command>mosquitto</command> bug information can be found at
<ulink url="https://github.com/eclipse/mosquitto/issues"/></para>
</refsect1>
<refsect1>
<title>See Also</title>
<simplelist type="inline">
<member>
<citerefentry>
<refentrytitle><link xlink:href="mosquitto-8.html">mosquitto</link></refentrytitle>
<manvolnum>8</manvolnum>
</citerefentry>
</member>
<member>
<citerefentry>
<refentrytitle><link xlink:href="mosquitto_passwd-1.html">mosquitto_passwd</link></refentrytitle>
<manvolnum>1</manvolnum>
</citerefentry>
</member>
<member>
<citerefentry>
<refentrytitle><link xlink:href="mosquitto-tls-7.html">mosquitto-tls</link></refentrytitle>
<manvolnum>7</manvolnum>
</citerefentry>
</member>
<member>
<citerefentry>
<refentrytitle><link xlink:href="mqtt-7.html">mqtt</link></refentrytitle>
<manvolnum>7</manvolnum>
</citerefentry>
</member>
<member>
<citerefentry>
<refentrytitle><link xlink:href="http://linux.die.net/man/5/limits.conf">limits.conf</link></refentrytitle>
<manvolnum>5</manvolnum>
</citerefentry>
</member>
</simplelist>
</refsect1>
<refsect1>
<title>Author</title>
<para>Roger Light <email>roger@atchoo.org</email></para>
</refsect1>
</refentry>
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