---
name: "mqtt-publisher"
section: "1"
platform: "linux"
package: "linuxcnc-uspace"
version: "1:2.9.4-2+deb13u1"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/mqtt-publisher"
---

# mqtt-publisher(1)

send HAL pin data to MQTT broker periodically

## NAME

mqtt-publisher - send HAL pin data to MQTT broker periodically

## SYNOPSIS

**loadusr -W mqtt-publisher \[options\] keys**=pin1\[,pin2...\]

## DESCRIPTION

**mqtt-publisher** is a non-realtime program that reads HAL values periodically and passes the values to a MQTT broker.

When specifying the MQTT settings in the INI file, this is the recommended setup:

HAL file:

```
loadusr -W mqtt-publisher [MQTT]DRYRUN --mqtt-broker=[MQTT]BROKER \
  --mqtt-user=[MQTT]USERNAME --mqtt-password=[MQTT]PASSWORD keys=halui.estop.is-activated
```

INI file:

```
[MQTT]
DRYRUN = --dryrun
BROKER = broker.local
USERNAME = username
PASSWORD = password
```

This component need the Paho python library installed to function. On debian this is available from the python3-paho-mqtt package.

## OPTIONS

**keys**=*pin1\[,pin2,...\]*

The name of HAL pins, signals and other values to publish using MQTT. The names are also used as the JSON keys in the MQTT message published with the broker. If multiple "keys=" options are specified, the lists are merged.

- **--dryrun**

  Do not set up MQTT connection, only print message to stdout. Useful for debugging and testing.

- **--mqtt-broker**=*FQDN*

  The fully qualified DNS name of the MQTT broker. The default broker name is "localhost".

- **--mqtt-port**=*PORTNUMBER*

  The port to use of the MQTT broker. The default port is 1883.

- **--mqtt-user**=*USERNAME*

  The user name to use when connecting to the MQTT broker.

- **--mqtt-password**=*PASSWORD*

  The password to use when connecting to the MQTT broker.

- **--mqtt-prefix**=*PREFIX*

  The MQTT prefix/topic to use when publishing to the MQTT broker. The default prefix is "devices/linuxcnc/machine".

## FUNCTIONS

**mqtt-publisher**

The loop reading HAL values and publishing MQTT messages.

## PINS

**mqtt-publisher**.**enable** bit input

When TRUE, publish messages to MQTT broker. When FALSE, do not publish messages. Default is TRUE.

**mqtt-publisher**.**period** u32 input

The number of seconds to sleep between publishing MQTT messages to the broker. Default is 10 seconds.

**mqtt-publisher**.**lastpublish** u32 output

When the last MQTT publication was published in number of seconds since EPOC. If no publication has taken place, the value is zero.

## EXAMPLES

Any set of HAL pins and signals can be published. This setup might be a useful starting point:

```
loadusr -W mqtt-publisher \
  [MQTT]DRYRUN \
  --mqtt-broker=[MQTT]BROKER
  --mqtt-user=[MQTT]USERNAME \
  --mqtt-password=[MQTT]PASSWORD \
  keys=halui.axis.a.pos-feedback,halui.axis.b.pos-feedback,\
halui.axis.c.pos-feedback,halui.axis.u.pos-feedback,\
halui.axis.v.pos-feedback,halui.axis.w.pos-feedback,\
halui.axis.x.pos-feedback,halui.axis.y.pos-feedback,\
halui.axis.z.pos-feedback \
  keys=halui.estop.is-activated, halui.joint.0.is-homed,\
halui.joint.1.is-homed,halui.joint.2.is-homed,halui.joint.3.is-homed,\
halui.joint.4.is-homed,halui.joint.5.is-homed,halui.joint.6.is-homed,\
halui.joint.7.is-homed,halui.joint.8.is-homed \
  keys=halui.machine.is-on,halui.max-velocity.value,halui.mode.is-auto,
halui.mode.is-manual,halui.mode.is-mdi,halui.mode.is-teleop,
halui.program.is-running
```

Note: It is recommended to use the line continuation character "\\" as shown here to improve readability. But note that spaces must be left in to delimit options, and must not be included (including at the beginning of a line) inside a single option.

HAL limits a single option/token (for example "keys=") to 255 characters. To work around this issue use multiple "keys=" entries as shown.

## SEE ALSO

**hal**(3hal)

## AUTHOR

Component and documentation created by Petter Reinholdtsen, as part of the LinuxCNC project.

## COPYRIGHT

Copyright © 2023 Petter Reinholdtsen. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.