Using php5-memcached to store sessions on distributed servers

This article is an extension of the previous article about storing sessions in Memcached with PHP.

Using Memcached for sessions storage is generally a matter of speed (storing them in memory is faster than on disk) and of scalability (using a Memcached server allows you to have several web servers serving the same PHP application in a seamless way).

In the previous article, we mentioned (3 years ago) that the php5-memcached extension did not seem to manage the storage of sessions quite well, or at least that the configuration of such setup was not well documented. This time, we’ve been able to do it with php5-memcached. This time also, we’re talking about distributing Memcached on several servers. Typically, in a cloud environment with several web servers and no dedicated memcached server, or a need for some kind of fail-over solution for the memcached server. We’re setting this up on 3 Ubuntu 14.04 servers in 64bit that act as load-balanced web servers behind a load balancer managed by Nginx. If you use another distribution or operating system, you might need to adapt the commands we’re showing here.

Installing Memcached + PHP

So the few commands you need to launch first are to install the required software, on the 3 web servers (you can either do that on one of them then replicate the image if you are using Cloud instances, or you can install simultaneously on your 3 web servers using ClusterSSH, for example, with the cssh server1 server2 server3 command) :

sudo apt-get install memcached php5-memcached
sudo service apache2 restart

The second command is to make sure Apache understands the php5-memcached extension is there.

In order to enable the connection to Memcached from the different load-balanced servers, we need to change the Memcached configuration to listen on the external IP address. Check the IP address with /sbin/ifconfig. The Memcached configuration file is located in /etc/memcached.conf. Locate the “-l” option and change “127.0.0.1” for your external IP, then save and close the file. Note that this might introduce a security flaw, where you are possibly opening the connection to your Memcached server to the outside world. You can prevent that using a firewall (iptables is a big classic, available on Ubuntu)

Next, restart the Memcached daemon:

sudo service memcached restart

Now you have a Memcached server running on each of your web servers, accessible from the other web servers. To test this, connect to any of your web servers and try a telnet connection on the default Memcached port: 11211, like so:

user@server1$ telnet ip-server2 11211

To get out of there, just type “quit” and Enter.

OK, so now we have 3 Memcached servers, we only need to wrap up configuring PHP to use these Memcached servers to store sessions.

Configuring PHP to use Memcached as session storage

This is done by editing your Apache VirtualHost files (on each web server) and adding (before the closing </VirtualHost> tag) the following PHP settings:

 php_admin_value session.save_handler memcached
 php_admin_value session.save_path "ip-server1:11211,ip-server2:11211,ip-server3:11211"

Now reload your web server:

 sudo service apache2 reload

You should now be able to connect to your web application using the distributed Memcached server as a session storage (you usually don’t need to change anything in your application itself, but some might exceptionally define their own session storage policy).

The dangers of using a distributed Memcached server

Apart from the possible open access to your Memcached server previously mentioned, which is particularly security-related, you have to take another danger, mostly high-availability related, into account.

When using a distributed Memcached server configuration, it is important to understand that it works as sharded spaces configuration. That is, it doesn’t store the same sessions over on the various available Memcached server. It only stores each single session in one single server. The decision of where it will store the session is out of the context of this article, but it means that, if you have 300 users with active sessions on your system at any one time, and one of your web servers goes down, you still have 2 web servers and 2 Memcached servers, but ultimately around 100 users will loose their session (that was stored on the web server that went down).

Worst: the PHP configuration will not understand this, and still try to send sessions to the server that was considered to hold these 100 sessions, making it impossible for the users to login again until the corresponding Memcached server is back up (unless you change the configuration in your PHP configuration).

This is why you have to consider 2 things, and why this article is just one step in the right direction:

• you should configure the Memcached servers from inside your application for the sessions management (as such, you should have a save_handler defined inside it and check for the availability of each server *before* you store the session in it)
• if your sessions are critical, you should always have some kind of data persistence mechanism, whereby (for example), you store the session in the database once every ten times it is modified

We hope this was of some use to you in understanding how to use Memcached for sessions storage in PHP. Please don’t hesitate to leave questions or comments below.

Howto connect OpenMeetings 2 or 3 with Chamilo LMS 1.9.8

Chamilo LMS 1.9.8 comes with an OpenMeetings plugin. This means that you can organize OpenMeetings videoconference rooms directly from your Chamilo courses.

Now this setup requires a few essential things. The 2 most important are: a working installation of Chamilo (referenced as [C] below) and a working installation of OpenMeetings (referenced as [OM] below), then you need to have:

• [CH] php5-curl extension installed and running
• [OM] a user with web services privileges
• [CH] to configure host, user and password (or salt) inside the “plugins” section, button “Configure” of the OpenMeetings plugin

This is pretty much it, but if you are missing one of these, that won’t work!

Using Chamilo juju charm to setup a dev environment on Digital Ocean

If you’re in a hurry/on speed, know this:

• this procedure is slightly more difficult (so longer) than installing the charm on Amazon
• you can skip directly to “Installing Juju”
• if you already have juju installed, you can skip to the last 2 lines of the “Installing juju” section
• if you already have juju-docean installed and configured, you can skip directly to “Provisioning VMs”
• otherwise, just continue reading, it’s worth a few minutes…

This tutorial regroups a lot of advanced notions, so if you want to know more about one of the following elements, please follow these links:

• Juju
• Ubuntu
• Juju Charm
• Juju Charm for Chamilo
• Digital Ocean
• Juju for Digital Ocean

Before anything else, please note that the following is highly experimental. There are still a series of issues that should be worked out in order to make this process failproof.

Basic setup

Before we start using commands and stuff, you’ll have to note the following:

• We are using a Chamilo Charm developed by José Antonio Rey (kudos to him) as a voluntary contribution to the project
• Charms are configurations to install applications (and stuff) inside the Juju framework
• The Juju framework is developed by the Ubuntu team, so we’re using an Ubuntu (14.04) desktop (or in this case laptop) to launch all the following
• Digital Ocean is one cloud hosting provider, which is particularly cheap and good for development purposes. The “default” environment for Juju is Amazon, so we’ll have a few additional steps because of this choice. The Digital Ocean plugin to Juju is developed by geekmush on Github, and as far as I know he is not related to either Ubuntu nor Digital Ocean, so he is also worth praising for his contribution
• Chamilo requires a web server and a database server. In this Charm, it is assumed that we want both of these on separate virtual machines, so you will need two of them (unless you change the parameters a little)
• Juju is written in Go but relies on several Python libraries. As such, you’ll have to have python installed on your system and maybe Juju will shout because it is missing a few dependencies. Notably, I installed python3-yaml to avoid a few warnings (it is required for the following, although the installer for Juju says it’s optional)

Installing Juju

On a default Ubuntu desktop installation, you’ll have to install Juju first. Because we are going to use Juju connected to Digital Ocean, we need a recent version of Juju, so let’s add it the unconventional way (with the ppa), launching the following on the command line:

sudo add-apt-repository ppa:juju/devel
sudo apt-get update && apt-get install juju
juju version

For some reason, in my case, this created my home directory’s .juju/ folder with root permissions, which then prevented me to reconfigure my environment (requirement for the Digital Ocean Juju plugin), so I changed permissions (my user is “ywarnier”, so change that to your user):

sudo chown -R ywarnier:ywarnier .juju

Then we need to install the juju-docean plugin:

sudo apt-get install python3-yaml
sudo pip install -U juju-docean

Setting up Digital Ocean access

Now we need to configure our Digital Ocean (D.O.) API so the system will be able to call D.O. in our place and create instances (and stuff).

You first need to grab your API key, client ID and SSH key ID from the Digital Ocean interface. You can do that from the Digital Ocean API page. Obviously, you need a Digital Ocean account to do this and a few bucks of credit (although you can get $10 free credit from several places). If your API key says “Hidden”, that’s because you must have it stored somewhere already (for other services?). If you don’t, you’ll have to re-generate one. Your SSH key ID is the name you gave to the SSH key you use from your computer to connect to your new instances. If you don’t have it, that’s probably because you haven’t configured any. Please do in the “SSH Keys” menu item on the left side of your D.O. panel.

 export DO_CLIENT_ID=aseriesof21alphanumericalcharacters
 export DO_SSH_KEY="user@computer"
 export DO_API_KEY=aseriesof32characters

Setting up the Digital Ocean Juju environment

Now we need a bit of manual config to be able to use Digital Ocean (last bit, promised). Edit the ~/.juju/environments.yaml file and paste the following:

environments:
 digitalocean:
 type: manual
 bootstrap-host: null
 bootstrap-user: root

Just a note: the “type: manual” line implies it is a bit more complicated than on amazon later on, and we will have to launch a few more commands to provision new machines *before* we deploy Chamilo.

Generating the Juju environment

Now we’re going to create our Juju controller. The Juju controller can be an independent Virtual Machine (VM), or it can be the same as the one on which you will deploy Chamilo. It all depends on your budget and your requirements.

juju docean bootstrap --constraints="mem=1g, region=nyc1"
  2014/06/22 11:50.24:INFO Launching bootstrap host
  2014/06/22 11:51.29:INFO Bootstrapping environmen

Note that we took a decision to use a 1GB (RAM) VM here (mem=1g), in a datacenter in New York (region=nyc1). For the record, I tried creating them in nyc2, which is also a valid D.O. datacenter, but it failed miserably (sometimes not creating the VM, sometimes creating it without IP, sometimes creating it fully, but in the end never returning with a proper success response for my environment to be created), so sticking to nyc1 is probably a reasonable time-saver.

Provisioning VMs

To be able to deploy Chamilo, we’ll use two VMs: one for the web server and one for the database

juju docean add-machine -n 2 --constraints="mem=1g, region=nyc1"
2014/06/22 12:44.59:INFO Launching 2 instances
2014/06/22 12:46.42:INFO Registered id:1908893 name:digitalocean-8d14c9bc671555ff872d8d6731f84d68 ip:198.199.82.172 as juju machine
2014/06/22 12:49.08:INFO Registered id:1908894 name:digitalocean-a9ba29cfe55549f58e5f7e365199c5ed ip:208.68.39.19 as juju machine

Now, the “-n 2” above allows you to create these 2 instances, but you could also launch 2 different instances of different properties, doing it one by one. In our case, I suggest you use version Trusty of Ubuntu for the MySQL machine, to avoid a little bug in the Precise version of the charm:

juju docean add-machine --constraints="mem=2g, region=nyc1"
juju docean add-machine --series=trusty --constraints="mem=1g, region=nyc1"

The important thing here being that you can later identify the machine itself by a simple ID, using juju status:

juju status
environment: digitalocean
machines:
 "0":
  agent-state: started
  agent-version: 1.19.3
  dns-name: 192.241.142.154
  instance-id: 'manual:'
  series: precise
  hardware: arch=amd64 cpu-cores=1 mem=994M
  state-server-member-status: has-vote
 "1":
  agent-state: started
  agent-version: 1.19.3
  dns-name: 198.199.82.172
  instance-id: manual:198.199.82.172
  series: precise
  hardware: arch=amd64 cpu-cores=1 mem=994M
 "2":
  agent-state: started
  agent-version: 1.19.3
  dns-name: 208.68.39.19
  instance-id: manual:208.68.39.19
  series: trusty
  hardware: arch=amd64 cpu-cores=1 mem=994M

If you made a mistake at some point or just wanna try things out, you can destroy these instances with

juju docean terminate-machine 1

where “1” is the ID of the machine, as shown above before each of them.

Deploying Chamilo

Now we’ve got our machines, we just need to deploy the Chamilo Charm and the MySQL Charm (you need MySQL to run Chamilo):

juju deploy cs:~jose/chamilo --to 1
juju deploy mysql --to 2

Please note that the “–to n” option is to specify on which machine you want to deploy the selected service.

Now, we need to configure Chamilo a little. We’re going to give it a domain name (you’ll have to redirect this domain name to the IP of the first machine – the one with the Chamilo service – in order to use it when ready) and a password for the “admin” user (the user created by default):

juju set chamilo domain=test.chamilo.net pass=blabla

Now we still need to tell Juju to link the Chamilo service with the MySQL service:

juju add-relation chamilo mysql

And finally, apply all the above and expose the chamilo service to the public:

juju expose chamilo

If something goes wrong with a service, you can always remove it with:

juju destroy-service chamilo

You can replace “chamilo” by the service with which you are having the issue, of course. If that doesn’t work out, you can always remove (terminate) the machine itself (see above).

Useful tricks

You can connect at any time to any of your virtual machines through the command

juju ssh chamilo/0

where “chamilo/0” is the name appearing below “units” in your services.

You can check the status of all your instances with

juju status

Note that, sometimes, you might end up with dozens or hundreds of instances. In this case, it won’t be as practical to show the status of all instances (I have no solution for that now, but I’m sure there is a way to filter the results of a juju status).

You can launch a command on the virtual machines’ command line like this:

juju run --service chamilo "tail /var/log/juju/unit-chamilo-0.log"

This way, you are actually executing the command remotely and getting the results locally.

You can also see the error log locally, connecting in SSH (first) and then launching:

 tail /var/log/juju/unit-chamilo-0.log

Obviously, that gives you a little more flexibility.

Notes about unexpected errors

One of the “silent” things is that Juju considers the default machine to be Ubuntu Precise. In the case of MySQL, the default Charm is configured for Trusty. This means that if you want to install this package, you need to install a virtual machine in Trusty. Otherwise, you might get some other issues. In my case, the Precise Charm didn’t really work (missing yaml), so I decided to go for Trusty.

You can choose the distribution of your machine with –series=trusty, for example:

juju docean add-machine --series=trusty --constraints="mem=2g, region=nyc1"

We tested the chamilo charm relatively extensively.

Unmounting the whole thing

If this was just a test, and you’re happy, maybe you want to remove everything. If so, the quickest way to do that is to launch a destroy-environment command, but you will first need to destroy each machine and, before that, each services that :

juju destroy service chamilo mysql
juju destroy machine 1 2
juju destroy-environment digitalocean

This should reasonnably quickly remove the whole setup.

You should still check your Digital Ocean’s dashboard, though, as apparently it doesn’t always delete the nodes you created with Juju…

Quick commands list for the impatient

Assuming you’re running Ubuntu 14.04 and that you know which values to change in the commands below:

sudo add-apt-repository ppa:juju/devel
sudo apt-get update && apt-get install juju
sudo chmod -R 0700 .juju
sudo apt-get install python3-yaml
sudo pip install -U juju-docean
export DO_CLIENT_ID=aseriesof21alphanumericalcharacters 
export DO_SSH_KEY="user@computer" 
export DO_API_KEY=aseriesof32characters
juju docean bootstrap --constraints="mem=1g, region=nyc1"
juju docean add-machine --constraints="mem=2g, region=nyc1"
juju docean add-machine --series=trusty --constraints="mem=1g, region=nyc1"
juju deploy cs:~jose/chamilo --to 1
juju deploy mysql --to 2
juju set chamilo domain=test.chamilo.net pass=blabla
juju add-relation chamilo mysql
juju expose chamilo

And connect your browser to test.chamilo.net (that you must have redirected to the corresponding IP first) and login with admin/blabla.

Embedding webcam with SimpleScreenRecorder

In case, like me, you use SimpleScreenRecorder on Ubuntu to do screencasts, you might be missing something: the ability to embed your webcam’s feed *inside* the screencast (like this little capture on the right side which shows how amazed I am).

Well, there’s a simple, command-line based solution to that, as explained by Maarten Baert, developer of SimpleScreenRecorder: just use one of the 3 following commands (for me, the last one is the only one that works and I haven’t searched *at all* for why the others don’t. I just copy-pasted it.

ffplay -f v4l2 /dev/video0
avplay -f v4l2 /dev/video0

mplayer tv:// -tv driver=v4l2:width=640:height=480 -vo xv

Obviously, for the last one, you can change the resolution just by changing the number there.

You can check the details here: https://github.com/MaartenBaert/ssr/issues/64#issuecomment-27766079

SimpleScreenRecorder is not inside the default Ubuntu packages, so you’ll have to add it to your sources following the procedure in the “Download” paragraph here: http://www.maartenbaert.be/simplescreenrecorder/#features

gem install mysql2 on Debian Wheezy with MariaDB 10

Just in case you would be in this situation (and given the fact I couldn’t find online information about it), if you are ever installing the mysql2 gem on a Debian Wheezy system with MariaDB 10 (I would guess a rather rare situation), you might get this error:

# gem install mysql2 -v=0.3.11
Building native extensions. This could take a while...
ERROR: Error installing mysql2:
 ERROR: Failed to build gem native extension.

 /usr/bin/ruby1.9.1 extconf.rb
checking for rb_thread_blocking_region()... yes
checking for rb_wait_for_single_fd()... yes
checking for mysql_query() in -lmysqlclient... no
checking for main() in -lm... yes
checking for mysql_query() in -lmysqlclient... no
checking for main() in -lz... yes
checking for mysql_query() in -lmysqlclient... no
checking for main() in -lsocket... no
checking for mysql_query() in -lmysqlclient... no
checking for main() in -lnsl... yes
checking for mysql_query() in -lmysqlclient... no
checking for main() in -lmygcc... no
checking for mysql_query() in -lmysqlclient... no
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of
necessary libraries and/or headers. Check the mkmf.log file for more
details. You may need configuration options.

Provided configuration options:
 --with-opt-dir
 --without-opt-dir
 --with-opt-include
 --without-opt-include=${opt-dir}/include
 --with-opt-lib
 --without-opt-lib=${opt-dir}/lib
 --with-make-prog
 --without-make-prog
 --srcdir=.
 --curdir
 --ruby=/usr/bin/ruby1.9.1
 --with-mysql-config
 --without-mysql-config
 --with-mysql-dir
 --without-mysql-dir
 --with-mysql-include
 --without-mysql-include=${mysql-dir}/include
 --with-mysql-lib
 --without-mysql-lib=${mysql-dir}/lib
 --with-mysqlclientlib
 --without-mysqlclientlib
 --with-mlib
 --without-mlib
 --with-mysqlclientlib
 --without-mysqlclientlib
 --with-zlib
 --without-zlib
 --with-mysqlclientlib
 --without-mysqlclientlib
 --with-socketlib
 --without-socketlib
 --with-mysqlclientlib
 --without-mysqlclientlib
 --with-nsllib
 --without-nsllib
 --with-mysqlclientlib
 --without-mysqlclientlib
 --with-mygcclib
 --without-mygcclib
 --with-mysqlclientlib
 --without-mysqlclientlib


Gem files will remain installed in /var/lib/gems/1.9.1/gems/mysql2-0.3.11 for inspection.
Results logged to /var/lib/gems/1.9.1/gems/mysql2-0.3.11/ext/mysql2/gem_make.out

 

If you find yourself in that situation, the solution is apparently to first issue an

apt-get install libmariadbd-dev

And then repeat the gem install mysql2 command. Done.

Howto install OpenMeetings 2.2 server on a Debian Wheezy box

This guide is written specifically to cover a lack of quality documentation for the installation procedure of an OpenMeetings 2.2 server on a Debian Wheezy box.

It will be based on the manual available already for this procedure (but relatively badly structured and written in a rather improvable English), by Alvaro Bustos with the help of Federico Christian Tomasczik. Thanks to both of them. My manual is mostly a rewrite of the information in their guide, hopefully with enough precision to allow someone to script it. Also the fact that the guide is only available publicly as PDF is not ideal. Finally, there is a lot of space for interpretation in the dynamic links provided which, in my case, made me mistakenly go for 3.0 instead of my intended 2.2, which had considerable consequences in the particular task I was trying to achieve: write an OpenMeetings plugin for Chamilo.

Because that’s probably the easiest way to do it for anyone reading this manual, I will be explaining on the basis of a Digital Ocean virtual machine (or “Droplet”). I found that the $40/month (4GB of RAM) image works fine, but you can try with a 2GB one, maybe that works out too.
If you never tried Digital Ocean before, you have two options:

You create an account, pay $20 in advance with PayPal, create a new Droplet, choose Debian Wheezy 64bit (I picked New York 2 Data Center, but it *really* shouldn’t matter where it is) and jump to the beginning of this tutorial or
Find a machine where you can install Debian Wheezy (either virtual or physical), make sure it’s got an internet connection and start working

And of course, any Debian Wheezy machine would do.

For the sake of simplicity, I’ll assume you got root access to it.
I’ll also pass the OpenMeetings “client” install. If you don’t know how to install Flash, you should look for that information somewhere else.

I usually use VIM as an editor, so if the Debian box is new, I install vim:

apt-get update
apt-get install vim


Finally, I’ll assume that your server is available through a simple IP address or a domain name. Below, I will assume a ficticious URL of “video.openmeetings.net”. Replace that string with yours however you see fit.

Without further ado, let’s begin.

For some reason, Red5 seems to be failing to start when it cannot find a fully qualified domain name (FQDN) for the server on which it runs. To avoid this, simply put the right (or a fake) domain name in /etc/hosts, at the end of the first line. Following the logic above, I’m calling it video.openmeetings.net. Feel free to call it whatever you like, but try to use something that isn’t used by anyone else:


127.0.0.1 localhost video.openmeetings.net


Create an /etc/apt/sources.list.d/openmeetings.list with the following contents:

deb-src http://http.debian.net/debian/ wheezy main
deb http://http.debian.net/debian/ wheezy contrib non-free
deb http://http.debian.net/debian/ wheezy-updates main contrib
deb-src http://http.debian.net/debian/ wheezy-updates main contrib
deb http://www.deb-multimedia.org wheezy main non-free


Create an /etc/apt/sources.list.d/oracle-java.list with the following contents (because OpenMeetings does not officially support OpenJDK yet):

deb http://ppa.launchpad.net/webupd8team/java/ubuntu precise main
deb-src http://ppa.launchpad.net/webupd8team/java/ubuntu precise main


Then do the following (on the command line):

apt-key adv --keyserver keyserver.ubuntu.com --recv-keys EEA14886
apt-get update && apt-get install -y --force-yes deb-multimedia-keyring oracle-java6-installer


You’ll have to agree to the Oracle Binary Code license terms with the last command (in the oracle-java6-installer). This is manual (as far as I know, there is no way to automate it).

Now, we want to make sure this installed version of Java will be the one used for the rest of the processes on this server, by updating the alternatives and picking the one that says java-6-oracle and “jre” in the same path:

update-alternatives --config java


If this is a new, clean, server, the command will only mention that there is only one alternative, so that there is nothing to select.

You may want to also automatically set the environment variable, feature which is provided by the following package in WebUpd8’s repository:

apt-get install oracle-java6-set-default

Now we want to install Libreoffice, as it will be used by JODconverter (installed below) to convert documents:

apt-get install -y --force-yes libreoffice


On Digital Ocean’s machines, the download is super-fast (around 10 seconds for 450MB) and the whole installation should take about 30 seconds max.

We also need to install a few conversion libraries:

apt-get install -y --force-yes imagemagick libgif4 libjpeg62 libmp3lame0


…and the SWFtools (this is one of the trickiest parts for Debian/Ubuntu installations, but luckily someone packaged it)


cd
wget http://assiste.serpro.gov.br/libs/swftools_0.9.1-1_amd64.deb
dpkg -i swftools_0.9.1-1_amd64.deb

Note: for 32bit, you’ll have to download http://assiste.serpro.gov.br/libs/swftools_0.9.1-1_i386.deb

Now the ffmpeg library needs to be installed by hand in order to get access to a more recent version of the lib. In effect, Debian Wheezy “deb-multimedia” repository’s version is 1.0.8 and we’d like to get 1.1.2. Note that, during the “make” process (which might take more than 10 minutes), you can continue the installation with the other steps in a parallel terminal. Just don’t forget, at the end, to launch the checkinstall process.


apt-get install -y --force-yes libart-2.0-2 libt1-5 zip unzip bzip2 subversion git-core checkinstall yasm texi2html libfaac-dev libfaad-dev libmp3lame-dev libsdl1.2-dev libx11-dev libxfixes-dev libxvidcore4 libxvidcore-dev zlib1g-dev libogg-dev sox libvorbis0a libvorbis-dev libgsm1 libgsm1-dev libfaad2 flvtool2 lame
cd /opt
wget http://ffmpeg.org/releases/ffmpeg-1.1.2.tar.gz
tar zxf ffmpeg-1.1.2.tar.gz
cd ffmpeg-1.1.2
./configure --enable-libmp3lame --enable-libxvid --enable-libvorbis --enable-libgsm --enable-gpl --enable-nonfree
make
mkdir /usr/local/share/ffmpeg /usr/local/share/man /usr/local/include
checkinstall


The “make” command is probably the step that will take the most time of the whole installation (around 12 minutes, just by itself).

Press “Enter” 3 times to select the default options suggested by the installer.
This will (slowly) make a Debian package (ffmpeg_1.1.2-1_amd64.deb) and install it (as I mentioned, this might take more than 12 minutes on the suggested virtual machine).

It is suggested you “hold” this package version, to prevent Debian from trying to update it during the next apt-get upgrade. To do this:

apt-mark hold ffmpeg


At this point, feel free to delete everything you want from the /opt directory where we downloaded and built the ffmpeg package:

rm -rf /opt/ffmpeg*


Install the MySQL server (there is a default database used by OpenMeetings but it’s not meant for production).

apt-get install mysql-server


Give it a root password (twice). Note that it’s considered *really bad practice* to leave a blank password, so please think about something simple and safe instead of avoiding your responsibility. It also has nothing to do with system’s root password.

Connect to MySQL to prepare the openmeetings database:

mysql -uroot -p
mysql> CREATE DATABASE openmeetings DEFAULT CHARACTER SET 'utf8';
mysql> GRANT ALL PRIVILEGES ON openmeetings.* TO 'openmeetings'@'localhost' IDENTIFIED BY 'some-password-here' WITH GRANT OPTION;
mysql> quit


Now we’re ready to install OpenMeetings. You should get the latest stable version from here: http://openmeetings.apache.org/downloads.html
Other sources are likely to be less stable and I certainly did loose a lot of time on this, so I definitely recommend the stable. The following code is based on the stable that was downloadable at the time of writing, so you might want to check the link above. Beware that the link above does not provide a direct link for the download: it sends you to a mirrors page, from which you’ll have to pick a mirror. The command below downloads it directly from one of the mirrors.

mkdir /opt/red5
cd /opt/red5
wget http://www.webhostingjams.com/mirror/apache/openmeetings/2.2.0/bin/apache-openmeetings-2.2.0.tar.gz
tar zxf apache-openmeetings-2.2.0.tar.gz
rm apache-openmeetings-2.2.0.tar.gz
cd webapps/openmeetings/WEB-INF/classes/META-INF/
mv persistence.xml persistence.xml-ori
mv mysql_persistence.xml persistence.xml
vim persistence.xml


For the sake of copy-paste speed, you can launch all but the last command in one go with:


mkdir /opt/red5 && cd /opt/red5 && wget http://www.webhostingjams.com/mirror/apache/openmeetings/2.2.0/bin/apache-openmeetings-2.2.0.tar.gz && tar zxf apache-openmeetings-2.2.0.tar.gz && rm apache-openmeetings-2.2.0.tar.gz && cd webapps/openmeetings/WEB-INF/classes/META-INF/ && mv persistence.xml persistence.xml-ori && mv mysql_persistence.xml persistence.xml

vim persistence.xml

Here is where you’ll have to configure the XML file to set the db name, username and password for the openmeetings database we created above.
Find the “Url=” part. A few lines below, you’ll find a Username and a Password fields. Place the right ones there and save (with :wq if using VIM).


, Username=openmeetings
, Password=some-password-here" />


Now we’ll install the Java to MySQL connector (MySQL Connector/J aka MySQL JDBC).

cd /opt
wget http://ftp.sunet.se/pub/databases/relational/mysql/Downloads/Connector-J/mysql-connector-java-5.1.28.tar.gz
tar zxf mysql-connector-java-5.1.28.tar.gz
cp mysql-connector-java-5.1.28/mysql-connector-java-5.1.28-bin.jar /opt/red5/webapps/openmeetings/WEB-INF/lib/mysql-connector-java.jar
rm -rf mysql-connector*


Download the JOD converter to be able to convert files uploaded to OpenMeetings. Note that we’ll leave it into /opt for now, as OpenMeetings allows us to select the source for this converter. Also note that the version we download is version 3, while the one available in Wheezy is version 2.2.2 (I have no idea if this is relevant, but considering it is not to be installed or anything, the effort is not really worth the question in this case).


cd /opt
wget http://jodconverter.googlecode.com/files/jodconverter-core-3.0-beta-4-dist.zip
unzip jodconverter-core-3.0-beta-4-dist.zip

Newer versions might come in the future, so make sure you check http://code.google.com/p/jodconverter/downloads/list for any other version.

Now our red5 folder is ready to be put online, so we’ll move it to somewhere more permanent.

mv red5 /usr/lib
chown -R nobody /usr/lib/red5


Starting and stopping OpenMeetings is kind of complex, because there are several services involved. Luckily, someone wrote a script for us which, although not perfect, will help us solve this problem quickly:

wget https://cwiki.apache.org/confluence/download/attachments/27838216/OpenMeetings+2.x+run+script+Squeeze.zip?version=1
unzip OpenMeetings+2.x+run+script+Squeeze.zip\?version\=1



mv OpenMeetings\ 2.x\ run\ script\ Squeeze/red5 /etc/init.d/
chmod +x /etc/init.d/red5


And then we can finally start OpenMeetings (or should I say the Red5 server, which serves OpenMeetings):

/etc/init.d/red5 start


Now load it from your browser on http://video.openmeetings.net:5080/openmeetings/install and follow the information carefully.
Please note that the database doesn’t have to be configured through the web interface: it’s already been done in the XML file (remember?).

You will have to indicate the paths to the different conversion services, though.
To do this, you only need to know the following:
FFMPEG Path = /usr/local/bin
JOD Path = /opt/jodconverter-core-3.0-beta-4/lib

This should be enough for you to complete the installation and be able to use OpenMeetings! Have fun!

Bonus: if you want your server to be able to send e-mails, do the following:

apt-get install exim4
dpkg-reconfigure exim4-config

And then type “Enter” for every question except the one with 5 options beginning with “Internet sites”. There, you should select the first option “Internet sites” if you don’t know better, of course. Then go on with just “Enter” through it until you’re back on the command line.

Creating multiple git forks using upstream branches

Working with Git is… complex. It’s not that it’s from another world, and the complexity is probably worth it considering the crazy things it allows you to do, but sometimes it’s just mind-bloggingly complex to understand how to do things right.

Recently, we’ve had to manage a series of projects with changes that cannot be applied directly to our original Git repository on Github, so we decided, after giving it some thought, to make several forks of the project (instead of branches), to manage more clearly permissions and the real intentions behind each of the forks.

This would allow us a few important things:

• define precisely permissions based on the repository
• use the repository to pull changes directly on our servers
• have some level of local customization on each server, using local commits (and subsequent merges)
• keep easy track of the changes that have been made on requests from some of our “customers” (they’re not necessarily commercial customers – sometimes they’re just users who decided to go crazy and show us what they can do, and we want to show that in public)

To do that, we need to fork our project (chamilo/chamilo-lms) several times over.

So the first problem is: you cannot fork the same project twice with the same user.
Adrian Short (@adrianshort) kind of solved that issue in his blog article, saying that you can just do the fork manually, creating an empty repo on Github and filling it with a copy of the main repo, then adding the origin remote manually.

Even though that works, the Github page (starting from the second fork with the same user) will *not* indicate it has been forked from chamilo/chamilo-lms: you’ll have to issue the
git remote -v
command to see that the upstream is correct.

The second problem is that the article doesn’t dive into the details of branch-level forks, so this article intends to solve that particular missing detail, and in that respect, the Github help is definitely useful. Check Syncing a fork help page if you want the crunchy details.

To make it short, there are 3 issues here:

• fetching the branches from the original repo (upstream)
• getting the desired branch to be checked out into your local repo
• defining that, from now on, you want to work on your repo as a fork of that specific branch in upstream (to be able to sync with it later on)

The complete procedure then, considering my personal account (ywarnier) and the original chamilo/chamilo-lms project on Github, with the intention to work on branch 1.9.x, would look like this:


git clone git@github.com:chamilo/chamilo-lms
git remote -v
git remote rename origin upstream

(here you have to create the “chamilo-lms-fork1” repo by hand in your Git account)

git remote add origin git@github.com:ywarnier/chamilo-lms-fork1.git
git remote -v
git push -u origin master
git branch -va
git fetch upstream
git branch -va
git checkout --track remotes/upstream/1.9.x


This should get you up and kicking with your multiple forks in a relatively short time, hopefully!

On PHP and cache slams and solutions

While reading about Doctrine’s cache mechanism (which applies to other stuff than database queries, by the way), my eye was caught by a little message at the end (last section) about cache slams.

I have used cache mechanisms extensively over the last few years, but (maybe luckily) never happened to witness a “cache slam”.
There’s a link to a blog (by an unnamed author) that explains that.

To make it short, you can have race conditions in APC (and probably in other caching mechanisms in PHP) when you assign a specific time for expiry of cache data, and a user gets to that expiry time at the same time (or very very very closely) as other users. This provokes a chain reaction (a little bit like an atomic bomb, but not with the same effect – unless some crazy military scientist binds a high-traffic website to the initiation process of an atomic bomb) which makes your website eat all memory and freeze (or something like that).

In reply to me mentioning it on Twitter, @PierreJoye (from the PHP development team) kindly pointed me to APCu, which is a user-land caching mechanism (or so to speak an APC without the opcode, and simplified).

Apparently, this one doesn’t have the cache slam issue (although I haven’t checked it myself, I have faith in Pierre here) and it’s already in PECL (still in beta though), so if you want to try it out on Debian/Ubuntu, you will probably be able to sort it out with a simple:

sudo apt-get install php5-dev php5-pear make
sudo pecl install APCu

(and then configure your PHP to include it).

Don’t forget that it is a PECL library, meaning it’s most likely you’ll have to recompile your PHP to enable it, but PECL should handle that just fine (in our case it’s a bit more complicated if we want to avoid asking our users – of Chamilo, that is – for more dependencies).

Anyway, just so you know, there are people like that who like to make the world a better place for us, PHP developers, so that we can make the world a better place developing professional-grade, super-efficient free software in PHP! Don’t miss out on contributing to that!

PHP’s @ hurts performance

Did you know…?

As a “take away” information taken from this post https://gist.github.com/nikic/6699370 (by famous PHP core developer @nikita_ppv), it appears like the @ sign in PHP (used to “hide” errors, as the “error-suppression operator” it is) also disables the “compiled variables” optimization (OpCode caching).

Great VIM regexp tutorial

Just a (great) reference: http://vimregex.com/

Read it = love it!