Cron Scheduling

Cron Scheduling

Schedule recurring work in device scripts using cron expressions

Device scripts can define named cron schedules to run recurring tasks — polling a sensor, sending a heartbeat, or clearing a buffer — without any external scheduler.

How It Works

Cron schedules are initialized when a device connects. The platform evaluates each expression and schedules the next fire time. When a cron fires, onCron is called with the schedule’s name. After each firing, the next occurrence is computed and scheduled automatically.

Crons are scoped to the device connection: they start when the device connects and stop when it disconnects.

Defining Schedules

Add a crons property to your device class. Keys are arbitrary schedule names; values are standard 5-field cron expressions in UTC.

import { DeviceEntrypoint } from "@devicesdk/core";

export default class TemperatureSensor extends DeviceEntrypoint {
  crons = {
    heartbeat: "*/5 * * * *",   // every 5 minutes
    dailyReport: "0 8 * * *",   // daily at 08:00 UTC
  };

  async onCron(name: string) {
    if (name === "heartbeat") {
      // read sensor, post to webhook, etc.
    }
    if (name === "dailyReport") {
      // send daily summary
    }
  }
}

Cron Expression Format

Expressions use the standard 5-field format (all times in UTC):

minute  hour  day-of-month  month  day-of-week
0-59    0-23  1-31          1-12   0-6 (0=Sunday)

Field Syntax

Syntax Example Meaning
* * Any value
N 5 Specific value
*/N */15 Every N units
N-M 1-5 Range (inclusive)
N,M 0,30 List of values
N-M/S 0-30/10 Range with step

Common Examples

Expression Schedule
* * * * * Every minute
*/5 * * * * Every 5 minutes
0 * * * * Every hour (on the hour)
0 8 * * * Daily at 08:00 UTC
0 8 * * 1-5 Weekdays at 08:00 UTC
0 0 1 * * First day of every month

When Are Schedules Updated?

Cron definitions are read from your script once, when the device connects. If you change the crons property and redeploy, the new schedule takes effect on the next device connection (i.e., after the device reboots or reconnects). Running devicesdk deploy sends a reboot command to connected devices, so new crons take effect automatically after a deploy.

Cron Expressions and Day-of-Week / Day-of-Month

When both day-of-month and day-of-week are restricted (not *), the cron fires on days that match either condition (OR semantics). For example, 0 8 1 * 1 fires at 08:00 UTC on the 1st of the month and every Monday.

Limitations

  • All cron times are in UTC — there is no timezone support in cron expressions.
  • The minimum granularity is 1 minute — sub-minute intervals are not supported.
  • Crons only fire while the device is connected. If the device is offline when a cron was due, the missed fire is skipped; it does not catch up.