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automatically spawn implicit background services


First, the command line interface wires up actions for each command and loads the auto-daemon module:

#!/usr/bin/env node
var autod = require('auto-daemon');
var opts = {
    rpcfile: __dirname + '/iface.js',
    sockfile: '/tmp/whatever.sock',
    methods: [ 'add', 'get', 'close' ]
var cmd = process.argv[2];
autod(opts, function (err, r, c) {
    if (err) {
    else if (cmd === 'add') {
        var n = Number(process.argv[3]);
        r.add(n, function (res) {
    else if (cmd === 'get') {
        r.get(function (res) {
    else if (cmd === 'close') {

Next, the iface.js provides the interfaces and stores the state:

var n = 0;
module.exports = function (server, stream) {
    return {
        add: function (m, cb) { cb(+= m) },
        get: function (cb) { cb(n) },
        close: function () { server.close(); stream.destroy() }

Now the first time the command is run, a daemon is implicitly launched in the background. When the server is shutdown with close, the state is reset as a new server is implicitly created on the next action:

$ node cmd.js add 2
$ node cmd.js add 3
$ node cmd.js add 4
$ node cmd.js close
$ node cmd.js add 5


var autod = require('auto-daemon')
var createServer = require('auto-daemon/server')
var listen = require('auto-daemon/listen')

var d = autod(opts, cb)

Connect to a daemon instance, spawning the daemon first if it isn't already running.

cb(err, rpc, connection) fires with the rpc interface to call methods on and the unix socket connection instance.

  • opts.rpcfile - file that exports an rpc interface (required)
  • opts.methods - an array of methods to expose (required)
  • opts.sockfile - file to use as the unix socket (required)
  • opts.autoclose - if true, close the server when the refcount drops to 0
  • opts.debug - when true, forward stdout and stderr in the daemonized process to the local stdout and stderr
  • opts.args - an array of extra arguments to pass as the third argument to the interface. Must serialize as process arguments.
  • opts.execPath - a string path to spawn. Default: process.execPath
  • opts.cwd - working directory to pass through to spawn()
  • opts.env - environment to pass through the spawn()
  • opts.exit - when autoclosing, call process.exit() to force a process exit

The daemon refcount goes up by 1 for each connection and drops by 1 when a client disconnects. If the object returned by the rpc interface is an event emitter, it can emit 'ref' events to increment the refcount and 'unref' events to decrement the refcount.

The method format is the same as multiplex-rpc: methods that end in :s are interpreted as stream methods.

d.on('process', ps)

Get a handle to spawned processes.

var server = createServer(createIface, opts)

Use this method if you'd rather create the server yourself. This is useful if you want the server to listen in the foreground.

Pass in the createIface function, which should be the same value as requiring an rpc file.

opts.autoclose behaves the same as with autod().

var server = listen(createIface, opts)

Create and listen on a unix socket opts.sockfile. The process id is written to opts.pidfile.

The server emits a ready event when the pidfile has been written.

rpc interface

The rpc file should export a function that returns an object.

The function will be called like so:

var createIface = require(rpcfile);
var iface = createIface(server, stream, args)

and should return the rpc methods in iface for that connection.

  • server is the daemon server instance
  • stream is the stream for the current session
  • args is an array of extra arguments provided by opts.args

If the method is a stream method, it should return a stream. Otherwise methods can accept a callback as their last argument.