Tag: shell scripts

Running WordPress cron on a multisite instance

For a long time I used the WP Cron Control plugin and an associated cron job to make sure that scheduled actions on my WordPress multisite instance were executed properly. (You should never rely on event execution that is triggered by visits to your website, the WordPress default, IMHO.) But after the upgrade to WordPress 5.4 I noticed that some of my scheduled events in WordPress were not firing on time, sometimes delayed by 10-20 minutes. I did some troubleshooting and got as far as suspecting a weird interaction between that plugin and WordPress 5.4, but never got to the bottom of it.

When I reluctantly went in search of a new solution, I decided to try using WP CLI cron commands, executed via my server’s own cron service. Ryan Hellyer provided most of what I needed in this helpful post, and I extended it a bit for my own purposes.

Here’s the resulting script that I use:

#!/bin/bash

# This script runs all due events on every WordPress site in a Multisite install, using WP CLI.
# To be run by the "www-data" user every minute or so.
#
# Thanks https://geek.hellyer.kiwi/2017/01/29/using-wp-cli-run-cron-jobs-multisite-networks/

PATH_TO_WORDPRESS="/path/to/wordpress"
DEBUG=false
DEBUG_LOG=/var/log/wp-cron

if [ "$DEBUG" = true ]; then
        echo $(date -u) "Running WP Cron for all sites." >> $DEBUG_LOG
fi

for URL in = $(wp site list --field=url --path="/path/to/wordpress" --deleted=0 --archived=0)
do
        if [[ $URL == "http"* ]]; then
                if [ "$DEBUG" = true ]; then
                        echo $(date -u) "Running WP Cron for $URL:" >> $DEBUG_LOG
                        wp cron event run --due-now --url="$URL" --path="$PATH_TO_WORDPRESS" >> $DEBUG_LOG
                else
                        wp cron event run --quiet --due-now --url="$URL" --path="$PATH_TO_WORDPRESS"
                fi
        fi
done

Then, in my system crontab:

# Run WordPress Cron For All Sites
*/2 * * * * www-data /bin/bash /path/to/bin/run-wp-cli-cron-for-sites.bash

Yes, I run cron every 2 minutes; there are some sites I operate that require very precise execution times in order to be useful. One implication is that this solution does not scale up very well; if the total execution time of all cron jobs across all sites exceeds 2 minutes, I could quickly run into situations where duplicate jobs are running trying to do the same thing, and that could be bad for performance or worse.

Generic ‘send to Slack’ shell script

On any given server I maintain, I like to set up a generic “send a message to Slack” shell script that can be called from any other tool or service running on that machine. With it I can log information of interest to a Slack channel for reading or maybe action.

Here’s what send-to-slack.sh usually looks like:

#!/bin/bash -e

message=$1

[ ! -z "$message" ] && curl -X POST -H 'Content-type: application/json' --data "{
              \"text\": \"${message}\"
      }" https://hooks.slack.com/services/12345/67890/abcdefghijklmnop

That last line has the “incoming webhook URL” provided by Slack when you set Slack up to receive messages via incoming webhooks, something that is included in even their most basic/free tier.

Running the script and sending a message to the channel is as simple as $ sh send-to-slack.sh 'My message goes here' and the result is what you would expect:

Once that’s in place and tested, I can call the script from wherever I want on that server. Other shell scripts. Custom WordPress functions. Cron jobs. And so on.

There are many other ways this could be customized or extended. It’s worth noting that this is not necessarily a fully secure way to do things if you have untrusted users who can control the input to the script and the message that gets output…please remember to sanitize your inputs and escape your outputs!