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I will use this article to collect interesting tips and tricks about using the Linux cron. This is not so much about setting up a cron, but about little things I use or discovered!

What is a cron ?

The cron daemon is a long-running process that executes commands at specific dates and times. You can use this to schedule activities, either as one-time events or as recurring tasks.

What is the crontab?

For commands that need to be executed repeatedly (e.g., hourly, daily, or weekly), you can use the crontab command. The crontab command creates a crontab file containing commands and instructions for the cron daemon to execute.

Format is: MIN HOUR DOM MON DOW CMD
Minute field
Hour field
Day of month
Day of week
Command

Run every 5 minutes

Run yearly, monthly, weekly, daily or on reboot.
@yearly will run at 00:00 on Jan 1st for every year.
@monthly will run at 00:00 on 1st of every month.
@weekly will run at 00:00 on starting of every week.
@daily will run at 00:00 on every day.
@reboot  will run after the server has been rebooted


TIPS

1. Send cron output via email

2. Use a real cron for WordPress

A real cron does not rely on website activity and executes independently.

Do not forget to disable the virtual WordPress Cron in the wp-config.php!

3. Prevent Emails being sent, when cron executes > /dev/null 2>&1

4. Set Standard Variables

5. Output Redirection

TOOLS

  1. Crontab UI (NodeJS) – Easy way to edit your crontab visually. @Github
  2. Chronis ( >= PHP 7) – Chronis will help you define cron jobs using natural language / YAML and will generate the crontab files for you. @Github
  3. PHP Cron Expression Parser – Standard (V7) compliant crontab expression parser/validator with support for time zones. @Github
  4. PhpGt/Cron (PHP) – Define background jobs in standard crontab format and the Cron Runner will execute them when they are due. Jobs can be either normal scripts, or calls to static functions with automatic autoloading taken care of. @Github
  5. Cronicle (NodeJS) – A simple, distributed task scheduler and runner with a web based UI. @GitHub / Website

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Structure opened its doors a couple of days ago.

Structure offers a simple and powerful IoT cloud platform for developing the next generation of connected experiences. They offer device management with robust data visualization that reacts in real-time.

They have a nice drag & drop workflow interface that allows you to forward data coming in, combine data or just store it.

I will be testing a builder kit with the platform, that includes the Adafruit Feather Huzzah, which offers native Wifi connectivity. My Raspberry Pi’s will also find their way into the system. The platform allows to consume REST Apis as well,  that will make it even more fun to build something unique.

If you are interested in IoT, you should really check it out. Its free :)

Structure / Adafruit Feather Huzzah

Enjoy coding …

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“Home automation with Raspberry PI and Arduino using Node.js, MongoDB, HTML5 and Websockets”

  • Full access to the GPIO of the Raspberry Pi
  • Communication with an attached Arduino
  • Wake-on-LAN (not really hardware, but at least it wakes up hardware)
  • Stream your webcam via socket.io
  • Node.js, Socket.io, Expressjs, Requirejs
  • HTML5, CSS3 and Websockets
  • Jade templating
  • Responsive design

GitHub

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