Setting up a cronjob on shared web space: no SSH, no crontab

Setup

Step by step

1. Check whether your system already has an address

   Many systems ship a ready-made file that works through their scheduled tasks, such as wp-cron.php in WordPress or cron.php in Nextcloud. In that case you do not need a script of your own and can go straight to the step "Test in the browser". The addresses of common systems are listed in the guide overview.

2. Put your own script into a file

   For tasks of your own, upload a PHP file to your web space via FTP, for example cron.php. Its first line checks a secret key so that not every visitor can trigger the work. Your actual code follows after that.

   <?php
   // cron.php - called on a schedule by Cronjob.de
   if (!isset($_GET['key']) || !hash_equals('A-LONG-SECRET', (string) $_GET['key'])) {
       http_response_code(403);
       exit;
   }
   ignore_user_abort(true);   // keep working even if the caller hangs up
   set_time_limit(300);
   
   // ... the actual work goes here: sync data, send mails, clean up ...
   
   echo 'OK';

3. Choose a long key

   Replace A-LONG-SECRET with a random string of at least 30 characters, for example from your password manager. Letters and digits only, so there is nothing to encode in the address. The finished address looks like this:

   https://your-domain.com/cron.php?key=k8Qz3vN1pR7wXc2mT9bL5sHf4gJd6aYe

4. Test in the browser

   Open the address once with the key: the correct answer is OK. Then once without the key: now you must get an empty page with error 403. If the browser asks for a password or your host shows an error page, directory protection or a firewall is in the way.

5. Create an account at Cronjob.de

   Registration takes a minute and is free. Five cronjobs stay free forever, the first 14 days run on the Unlimited plan.

6. Create a cronjob with that address

   Enter the address including the key and choose the interval. If your script sits behind directory protection, store user name and password in the cronjob's advanced settings.

   */5 * * * *

   You can enter this expression at Cronjob.de exactly as it is – the schedule field understands crontab notation. But you do not have to know it: simply click the schedule together instead.

What the five fields of an expression like */5 * * * * mean is explained in the crontab reference – with examples and the most common pitfalls. You can build the expression in the crontab generator. Whether you need an outside service at all is shown in the comparison of the three ways.

Verification

Is it actually running?

In the Cronjob.de call log you will see every call within a few minutes, with status, runtime and the start of the response, which for this script is OK. If a call fails, you can get an email. For the very first test you can also have the script write date and time into a file.

FAQ

Common questions about Webspace

My host has a cron manager. Do I need this anyway?

Not necessarily. If its intervals and runtimes are enough for you, use it. A call from outside pays off when you need a tighter interval, your package has no cron manager, or you want a log and a notification on errors. Which way fits when is covered in the comparison of the three ways.

Is it not dangerous for the script to be publicly reachable?

With the key check in the first line only someone who knows the key can trigger it. Use https so the address cannot be read in transit, and do not print confidential data in the script. If you want more, add directory protection with user name and password in front. Cronjob.de then signs in on every call.

What happens if my script takes longer?

We wait 45 seconds on the free plan and 60 seconds on the paid ones. After that we hang up. With ignore_user_abort(true) your script keeps working at most hosts anyway, until their own time limit kicks in. It is safer to split large jobs into chunks: for example 100 records per call, but more often.

Does this only work with PHP?

No. We call an address, and what runs behind it does not matter to us. It can be a PHP script, a route in your application, a webhook or a Python script your host runs through the web.

Can I run several tasks with different intervals?

Yes. Create a separate file or parameter per task and one cronjob with its own schedule for each. That way the log also shows separately which task ran.