php-amqplib: Uncaught exception ‘Exception’ with message ‘Error reading data. Recevived 0 instead of expected 1 bytes’

I’ve been playing around with RabbitMQ recently, but trying to find out what caused the above error included a trip through wireshark and an attempt to dig through the source code of php-amqplib. It seems that it’s (usually) caused by a permission problem: either the wrong username / password combination as reported by some on the wide internet, or by my own issue: the authenticated user didn’t have access to the vhost I tried to associate my connection with.

You can see the active permissions for a vhost path by using rabbitmqctl:

sudo rabbitmqctl list_permissions -p /vhostname

.. or you if you’ve installed the web management plugin for rabbitmq: select Virtual Hosts in the menu, then select the vhost you want to see permissions for.

You can give a user (all out) access to the vhost by using rabbitmqctl:

sudo rabbitmqctl set_permissions -p /vhostname guest ".*" ".*" ".*"

.. or by adding the permissions through the web management interface, where you can select the user and the permission regexes for the user/vhost combination.

Writing a Munin Plugin

I have to admit something. I’ve become addicted.

One of the things I finally got around to doing while living the quiet life over the christmas holiday was to dive a bit further into Munin – a simple framework for collecting information from your computers and servers and making nice graphs that you can watch while you’re bored.

I’m not going to write a lot about how you can create your own Munin plugin to create your own graphs, as they have a very simple tutorial giving you all the basics about writing Munin plugins themselves. The only thing you need to remember are these two tidbits:

  1. When Munin first registers your plugin, it runs your script with config as the only argument. This provides Munin with the name of the graph, the labels and names (keys) of the graphs you’re providing values for, information about the axis, etc.
  2. When Munin runs your script without the config argument, it expects you to give it values for the keys you provided it in the configuration.

You enable and disable plugins by creating symlinks in /etc/munin/plugins (at least under debian / ubuntu), and plugins are usually stored in /usr/share/munin/plugins.

I keep my plugins archived together with the rest of the repository for my web projects, and then either symlink the content into the plugins-directory or create a simple wrapper script that changes the current directory to the location of the script and then invokes it (to make the current working directory be correct).

A very simple bash script that does this – and passes through any parameters given to the script:

cd  && php ./