Setup Tips

Setup Wordpress Multisite Cron

2013-08-03T01:55:00+10:00

I run a multisite wordpress installation, and I have been a bit concerned about the amount of load caused by the inbuilt cron managed by wordpress. Given I have a three node cluster, I also only wanted one node to be running cron.

Yoast had good things to say about the WP cron control plugin ¹. Unfortunately, this plugin is all well and good for normal wordpress sites but will not work for multisite installations. For multisite installations you will need to call the cron job for every domain you host. This is very tedious and prone to error if you host lots of domains.

I found a workable solution ² for multi sites using the wp-cron control plugin and another plugin called wp-multisite-cron that iterates through the domains nicely calling cron for each of them. It’s not an official wordpress plugin ³ but the code looks good and is hosted on github.

The steps are

Download the wp-cron-control plugin and network activate it
Download the wp-multisite-cron plugin and network activate it
Add the following lines to wp-config.php

define('DISABLE_WP_CRON', true);  
define('WP_CRON_CONTROL_SECRET', your-secret-key-goes-here);

I had to edit wp_multisite_cron.php to include the secret key. Just edit line 194

$cron_url = site_url().'/wp-cron.php?doing_wp_cron&'.WP_CRON_CONTROL_SECRET;

Add a crontab entry on your master server.

* */15 * * * *
/usr/bin/wget -q -O /tmp/test.html  http://yourdomain/wp-admin/admin-ajax.php?action=wp_multisite_cron_call

If you have a multi-node cluster make sure your crontab entry only goes on the master server. Also, if you use round-robin DNS ensure that the /etc/hosts file on the master servers includes only the IP address of only the master server for the yourdomain entry, where yourdomain is the main domain of your multi-site wordpress intallation. This ensures that the wget call will always be made to your master server and not the other nodes in your cluster.
Under Settings->WP multisite cron, I set Concurrent crons to 5. The default setting is way too high.

Gotchas

If you get the following error messages when calling the multisite cron command

another cron process running or previous not older than 60 secs

then you probably forgot to add define(‘DISABLE_WP_CRON’, true); to wp-config.php

Screen Error | Cannot Open Your Terminal

2013-05-14T19:28:00+10:00

A user had the following problem when trying to re-open a previous screen session they had initiated and then detached from.

user@host: screen -r 8814.pts-0.host  
Cannot open your terminal '/dev/pts/41' - please check.

After some research there were two suggestions. One solution suggested changing the permissions of /dev/pts/41 - clearly a very bad idea.

The solution that worked was to run script /dev/null first.

user@host: script /dev/null  
Script started, file is /dev/null

user@host: screen -ls  
There is a screen on:  
8814.pts-0.host (Detached)

user@host: screen -r 8814.pts-0.host

The user had probably ran a sudosu to themselves.

Reference: http://serverfault.com/questions/116775/sudo-as-different-user-and-running-screen/116830#116830

Most Useful Chrome Extensions

2013-04-26T01:11:00+10:00

These are the Chrome extensions that I find most useful for increasing my productivity at my desktop.

Buffer

Buffer is the best way to share great content to Twitter, Facebook and LinkedIn from anywhere on the web, with just one click.

Clearly

Clearly makes blog posts, articles and webpages clean and easy to read. Save them to Evernote to read anywhere. You can also create advertisement free PDF print
outs of blog posts. There is also a text to speech translator built in, but it only works for relatively small documents.

Evernote Web Clipper

Use the Evernote extension to save things you see on the web into your Evernote account. It even lets you search through your notes. Permissions Visit website

Feedly - Your News, RSS, Google Reader

Feedly is a news reader for creative minds. Seamless migration from Google Reader. This is my indended replacement for Googe Reader.

HootSuite Hootlet

Quickly share web pages to all of your social networks using the HootSuite Hootlet.

LastPass

LastPass is a free password manager and form filler. LastPass is also available for Firefox, Internet Explorer, Opera and Safari. Permissions Visit website

Pocket (formerly Read It Later)

Pocket Extension for Google Chrome - The best way to save articles, videos and more

ScribeFire

An easy-to-use blog editor lets you post to all of your blogs.

Weather

This application geolocates you and displays in one click your favorite location. Its great for Ubuntu desktops where there is no currently functioning weather application available.

Sending and reading web content such as news articles and blog posts to your Kindle device. This works well in conjunction with Clearly. I use Clearly to get rid of all the ads and then forward the cleaned page to my Kindle.

Image Attribution Gumundur Bjarni Alafsson ↩