node-red-nodes/utility/daemon

node-red-node-daemon

A Node-RED node that runs and monitors a long running system command.

Similar to the exec node - but this calls the command at start time and then pipes any input to the node to the STDIN of the running command, and feeds any STDOUT to the first output.

Useful for monitoring command line based processes.

Install

Either use the Editor - Menu - Manage Palette - Install option or run the following command in your Node-RED user directory - typically ~/.node-red

npm i node-red-node-daemon

Usage

Calls out to a long running system command. Sends msg.payload to stdin of the process.

Note Only the command itself should be placed in the command field. All parameters must be placed in the arguments field.

The command provides 3 outputs... stdout, stderr, and return code, from the running command.

If the called program stops (i.e. a return code is produced), this node can attempt to restart the command automatically.

Setting msg.kill to a signal name (e.g. SIGINT, SIGHUP) will stop the process - but if the restart flag is set it will then auto restart.

Sending msg.start will also re-start the process.

Note: Some applications will automatically buffer lines of output. It is advisable to turn off this behaviour. For example, if running a Python app, the -u parameter will stop the output being buffered.

For example it can be used to run and then monitor the dump1090 plane spotter, and also to interact with various python apps that everyone seem to write these days :-)