- Wordpress Cron Manager
- Wordpress Cronjob
- Wordpress Cron Manager
- Wordpress Coronavirus
- Wordpress Cron Not Working
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- WP-cron is first loaded by WordPress when a page is requested on the front or backend of a site at which point WP-cron displays the necessary page to the site visitor. Though convenient, it is known to fail for a variety of reasons, including but not limited to the following.
- Actions are one of the two types of Hooks.They provide a way for running a function at a specific point in the execution of WordPress Core, plugins, and themes. They are the counterpart to Filters.
If you schedule a post or a backup, for example, WordPress cron will check for them, and then launch them. The thing is that WordPress cron is executed when someone visits your website – every single time someone visits your website, that is. So, if you have a lot of traffic, then having WordPress cron triggering every time someone visits your website will create a lot of calls to the wp.
Executing certain commands at given intervals or times is a very typical task for system administrators. In the past it was common to use cron or some variation for this, in some way or the other.
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Background
Cron does the job it was written for. But this was years ago, and these days Kernels offer neat things like CPU quotas and memory limits. Cron has no means to use those – but other tools have.
Additionally, newer tools provide dependencies, a proper configuration language (instead of hard-to-maintain bash lines), multiple triggers, randomized delays and real logging.
Especially the last bit, real logging, is essential: Cron can forward log messages it thinks needs to be forwarded. But without real kernel backed process management (cgroups) there is no real way for Cron to see if a job is running or has finished, and what log lines belong to it.
Systemd has all this – and thus it makes sense to create new recurrent jobs in Systemd and even migrate old ones sometimes.
Setting up the timer
What is needed are two things: a service file describing WHAT should be done, and a timer file describing WHEN to do it.
Let’s start with the WHAT: we create a typical service file named
backupjob.service
executing a backup bash script:Note that we do not enable the service here! We can start it for quick and easy debugging – which is also way easier than with Cron.
Keep in mind that this is a typical systemd service. You can also add requirements, dependencies, performance options and so on in a standardized fashion. With Cron this is not possible, would have to be done in the bash script itself and thus would be messy, hard to maintain, and most likely duplicate work between multiple Cron jobs. And btw.: that way not at all following the UNIX philosophy!
Next, the WHEN. We need a timer file, something which describes when to execute the service,
backupjob.timer
.As you can see, this job is scheduled to run daily, with an accuracy of 1 hour. The accuracy is an interesting bit: systemd tries to avoid starting all services at the exact same time, to avoid massive system load at
:00
. Just recently a technician at a large cloud provider mentioned that data centers could be designed way more efficient if not everyone would put their Cron jobs to the full minute.Speaking about, besides
OnCalendar
there is also a way to start jobs relative to the boot up time, or relative to when the timer was run last. For example, to run something every 15 minutes, set OnActiveSec=15min
. More information can be found in the timer documentation.Starting and stopping the timer
As mentioned above, the service unit files are not activated, instead the timers are:
sudo systemctl enable --now backupjob.timer
Stopping a timer is equally simple:
systemctl stop backupjob.timer
. If you want to avoid that it is started again during the next boot, also disable it: systemctl disable backupjob.timer
.Additional tooling
One of the great things of using the systemd ecosystem is that it is very easy to work with timers: with
systemctl list-timers
a nice and clear overview of the current state and time of next execution is given:At the same time, you can get the detailed status with
systemctl status logrotate.timer
– or of all of them via systemctl status *timer
.Logs are simply available via
journalctl -u logrotate.timer
– and the logs for the executed service can be read via journalctl -u logrotate.service
.And if you just don’t want to deal with systemd files right now – but nevertheless want all the goods from it, you can also launch systemd services or general commands with a one-time execution:
Final words
Writing systemd timers instead of traditional Cron jobs makes operating, maintaining and even writing of recurrent jobs much easier.
The only thing you might be missing is easily sending out stuff via mail.
Image by Ryan McGuire from Pixabay
Let's talk about robbing a bank
Imagine a team of thieves who are set to rob a bank. They've hired a driver to pick them up at an appointed time. The exact time that they'll walk out of the bank.
They then enter the bank and have set their stopwatch. Install linux on virtualbox mac. They have 180 seconds to get everything they can and walk back out – in order to beat the cops to the bank. And in 180 seconds (three minutes), their driver will drive up and pick them up.
In a situation like that, if you're one of the bank robbers, you want to make sure that everything goes according to plan, right?
But what if I told you that the driver's watch worked differently than other watches? What if I told you that his second hand moved only when he was on his cell phone? Or only when he moved his arm? Or only when he smoked a cigar?
Wordpress Cron Manager
Not a very reliable watch, right? And if that's not reliable, could you count on him to come get you at the right time?
I didn't think so.
Let's talk about WP-Cron
We'll get back to our bank robbers in a just a second. But first let's cover what Cron is.
It's actually the name of a command from the old Unix days where you could schedule a future event to happen at a specific time. That's pretty handy, right? Imagine you wrote some logic but you only wanted it to happen at midnight. Then you'd put that code in a spot and only call it every night at midnight, using Cron.
So you can then imagine that WP-Cron is like that. And it is. Except where it's different.
WP-Cron is Cron for WordPress. And here's the thing – every server that runs WordPress is different. So that means that implementing a low-level set of commands that will work on any and every environment is pretty darn tough.
So WP-Cron doesn't work that way. It's not based on the server, or the server's clock.
Instead, there's a check every time a person calls one of your pages or posts. Every time WordPress goes to work, it checks to see if there are any jobs that need to leverage WP-Cron.
But that's a bit precarious, as you might imagine. Especially for sites that don't get hit very often.
In other worlds, WP-Cron works fine for sites that get a decent amount of attention, but not necessarily as great for those sites with little to no traffic.
In this way, WP-Cron is like having a driver with a watch whose time is dependent on something other than the normal second passing. Instead, it's tied to a variable (like arm movement). In your case, the variable is a request (as in a call to a post or page).
So is WP-Cron great for large sites?
Since I told you it wasn't great for small sites, you're likely thinking that it's awesome for large sites because they're always getting traffic. And that would mean that processes would get called any and all the time.
That is true. But that is also its potential issue on highly trafficked sites. Because every request can spawn a process that goes to work and takes up server resources. Imagine spinning up several (a lot) of server processes all concurrently. That might easily bring your server down if you don't have adequate resources.
So in the end, I don't like WP-Cron for small sites. And I don't like it very much for large sites.
I prefer a regular cron job. Something that's scheduled using a normal clock.
Wordpress Cronjob
![Wordpress Cron Wordpress Cron](/uploads/1/3/7/4/137424169/457729540.png)
Here's what I use instead of WP-Cron
A few years ago we decided to make some nightly routines in our real estate solutions that use WordPress. And that's when we decided to move from WP-Cron to something else. Our something else is called SetCronJob – and it's an online service.
Wordpress Cron Manager
The service works regardless of what kind of server I'm hosting with, which is helpful for us. It also is really easy to schedule and control. And lastly, it's inexpensive (and free for some folks).
We've been using an externalized cron service now for 30 months and have absolutely loved the simplicity and consistency of the service.
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Because, if you're going to rob a bank, or do anything even more important, you want the guy who's helping you to have a watch that works – all the time, every time.
Wordpress Cron Not Working
And that means I need an external cron service like SetCronJob. Check it out!