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mosquitto.conf.5.xml
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mosquitto.conf.5.xml
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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:https://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>mosquitto</refentrytitle><manvolnum>8</manvolnum></citerefentry>
for information on how to load a configuration file.</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.</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 cafile/capath, 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>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] <topic></code></para>
<para>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.</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 <username></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] <topic></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>Reloaded on reload signal. The currently loaded ACLs
will be freed and reloaded. Existing subscriptions will
be affected after the reload.</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>true</replaceable> if no
other security options are set. If <option>password_file</option>
or <option>psk_file</option> is set, or if an
authentication plugin is loaded which implements
username/password or TLS-PSK checks, then
<option>allow_anonymous</option> defaults to
<replaceable>false</replaceable>.</para>
<para>Reloaded on reload signal.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>allow_duplicate_messages</option> [ true | false ]</term>
<listitem>
<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>Reloaded on reload signal.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>allow_zero_length_clientid</option> [ true | false ]</term>
<listitem>
<para>MQTT 3.1.1 allows 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>Reloaded on reload signal.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>auth_opt_*</option> <replaceable>value</replaceable></term>
<listitem>
<para>Options to be passed to the auth plugin. See the
specific plugin instructions. </para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>auth_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>auth_plugin</option>, the plugin
checks will run after the built in checks.</para>
<para>Not currently 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>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>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>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>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>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>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>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>.</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 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.</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>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>QoS 1 and 2 messages will be allowed in flight until this byte
limit is reached. Defaults to 0. (No limit)
See also the <option>max_inflight_messages</option> option.
</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 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>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. Do not set below 10 seconds.</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>Setting below 20 bytes is forbidden because it is
likely to interfere with normal client operation even
with small payloads.</para>
<para>Reloaded on reload signal.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>max_queued_bytes</option> <replaceable>count</replaceable></term>
<listitem>
<para>QoS 1 and 2 messages above those currently in-flight will be
queued (per client) until this limit is exceeded.
Defaults to 0. (No maximum) 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>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 100. 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>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.
The default value is 0, which means that all valid MQTT
messages are accepted. MQTT imposes a maximum payload
size of 268435455 bytes.</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>mosquitto_passwd</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>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>mosquitto_passwd</refentrytitle><manvolnum>1</manvolnum></citerefentry>.</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>auth_plugin</option>,
<option>auth_opt_*</option>,
<option>auto_id_prefix</option>.</para>
<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>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>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. Must end in a trailing slash. If not given,
then the current directory is used.</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 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.</para>
<para>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.</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>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. This
option only has an effect is mosquitto is run in daemon
mode.</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.pid</para>
<para>Not reloaded on reload signal.</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>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. 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>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>Reloaded on reload signal.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>retained_persistence</option> [ true | false ]</term>
<listitem>
<para>This is a synonym of the <option>persistence</option>
option.</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>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>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>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 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>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.</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>It is valid to use this option together with
<option>bind_address</option> for the default
listener, or the <replaceable>bind
address/host</replaceable> part of the
<option>listener</option> definition. Care should
be taken to ensure that the address being bound to
is on the interface being bound to. If you set the
<option>bind_interface</option> to be
<replaceable>eth0</replaceable>, and
<option>bind_address</option> to
<replaceable>127.0.0.1</replaceable>, then the
broker will start correctly but you will be unable
to connect.</para>
<para>This option is currently only available on
Linux, and requires elevated privileges.</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</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>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>limits.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
<para>Not reloaded on reload signal.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>maximum_qos</option> <replaceable>count</replaceable></term>
<listitem>
<para>Limit the QoS value allowed when using 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 publshing
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. It
applies per listener. Defaults to 10. Set to 0 to
disallow topic aliases.</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>Set the network port for the default listener to
listen on. Defaults to 1883.</para>
<para>Not reloaded on reload signal.</para>