mosquitto_sub — an MQTT version 3.1 client for subscribing to topics
client id prefix] [
keepalive time] [
port number] [
message QoS] [
] | [
mosquitto_sub is a simple MQTT version 3.1 client that will subscribe to a topic and print the messages that it receives.
The options below may be given on the command line, but may also
be placed in a config file located at
$HOME/.config/mosquitto_sub with one pair of
per line. The values in the config file will be used as defaults
and can be overridden by using the command line. The exceptions to
-T, which if
given in the config file will not be overridden. Note also that
currently some options cannot be negated, e.g.
-S. Config file lines that have a
# as the first character are treated as comments
and not processed any further.
Disconnect and exit the program immediately after the first message is received. This may be useful in shell scripts where on a single status value is required, for example.
-R to print only the
first fresh message (i.e. that does not have the
retained flag set), or with
filter which topics are processed.
Bind the outgoing connection to a local ip address/hostname. Use this argument if you need to restrict network communication to a particular interface.
Disable the 'clean session' flag. This means that all of the subscriptions for the client will be maintained after it disconnects, along with subsequent QoS 1 and QoS 2 messages that arrive. When the client reconnects, it will receive all of the queued messages.
If using this option, it is recommended that the
client id is set manually with
Define the path to a file containing PEM encoded CA certificates that are trusted. Used to enable SSL communication.
Define the path to a directory containing PEM encoded CA certificates that are trusted. Used to enable SSL communication.
--capath to work correctly, the
certificate files must have ".crt" as the file ending
and you must run "c_rehash <path to capath>" each
time you add/remove a certificate.
Define the path to a file containing a PEM encoded certificate for this client, if required by the server.
An openssl compatible list of TLS ciphers to support in the client. See ciphers(1) for more information.
Enable debug messages.
Display usage information.
Specify the host to connect to. Defaults to localhost.
The id to use for this client. If not given, defaults
to mosquitto_sub_ appended with the process id of the
client. Cannot be used at the same time as the
Provide a prefix that the client id will be built
from by appending the process id of the client. This is
useful where the broker is using the clientid_prefixes
option. Cannot be used at the same time as the
When using certificate based encryption, this option disables verification of the server hostname in the server certificate. This can be useful when testing initial server configurations but makes it possible for a malicious third party to impersonate your server through DNS spoofing, for example. Use this option in testing only. If you need to resort to using this option in a production environment, your setup is at fault and there is no point using encryption.
The number of seconds between sending PING commands to the broker for the purposes of informing it we are still connected and functioning. Defaults to 60 seconds.
Define the path to a file containing a PEM encoded private key for this client, if required by the server.
Do not append an end of line character to the payload
when printing. This allows streaming of payload data
from multiple messages directly to another application
unmodified. Only really makes sense when not using
Connect to the port specified instead of the default 1883.
Provide a password to be used for authenticating with
the broker. Using this argument without also specifying a
username is invalid. This requires a broker that supports
MQTT v3.1. See also the
Provide the hexadecimal (no leading 0x)
pre-shared-key matching the one used on the broker to
use TLS-PSK encryption support.
--psk-identity must also be provided
to enable TLS-PSK.
The client identity to use with TLS-PSK support. This may be used instead of a username if the broker is configured to do so.
Specify the quality of service desired for the incoming messages, from 0, 1 and 2. Defaults to 0. See mqtt(7) for more information on QoS.
The QoS is identical for all topics subscribed to in a single instance of mosquitto_sub.
If this argument is given, no runtime errors will be
printed. This excludes any error messages given in case of
invalid user input (e.g. using
--port without a
If this argument is given, messages that are received that have the retain bit set will not be printed. Messages with retain set are "stale", in that it is not known when they were originally published. When subscribing to a wildcard topic there may be a large number of retained messages. This argument suppresses their display.
Use SRV lookups to determine which host to connect
to. Performs lookups to
_mqtt._tcp.<host> when used in
-h, otherwise uses
The MQTT topic to subscribe to. See mqtt(7) for more information on MQTT topics.
This option may be repeated to subscribe to multiple topics.
Suppress printing of topics that match the filter. This allows subscribing to a wildcard topic and only printing a partial set of the wildcard hierarchy.
For example, subscribe to the BBC tree, but suppress output from Radio 3:
This option may be repeated to filter out multiple topics or topic trees.
Choose which TLS protocol version to use when
communicating with the broker. Valid options are
tlsv1. The default value is
tlsv1.2. If the installed version of
openssl is too old, only
tlsv1 will be
available. Must match the protocol version used by the
Provide a username to be used for authenticating with
the broker. This requires a broker that supports MQTT v3.1.
See also the
Print received messages verbosely. With this argument, messages will be printed as "topic payload". When this argument is not given, the messages are printed as "payload".
Specify a message that will be stored by the broker
and sent out if this client disconnects unexpectedly. This
must be used in conjunction with
The QoS to use for the Will. Defaults to 0. This must
be used in conjunction with
If given, if the client disconnects unexpectedly the
message sent out will be treated as a retained message.
This must be used in conjunction with
The topic on which to send a Will, in the event that the client disconnects unexpectedly.
mosquitto_sub can register a message with the broker that will be sent out if it disconnects unexpectedly. See mqtt(7) for more information.
The minimum requirement for this is to use
specify which topic the will should be sent out on. This will result in
a non-retained, zero length message with QoS 0.
--will-qos arguments to
modify the other will parameters.
Note that these really are examples - the subscriptions will work if you run them as shown, but there must be something publishing messages on those topics for you to receive anything.
Subscribe to temperature information on localhost with QoS 1:
Subscribe to hard drive temperature updates on multiple machines/hard drives. This expects each machine to be publishing its hard drive temperature to sensors/machines/HOSTNAME/temperature/HD_NAME.
Subscribe to all broker status messages:
Configuration file for default options.