I followed the excellent LVM Tutorial, and was surprised how easy everything goes. Here is a short cheat sheet of the important commands (take care to exchange the partition/volume names if you use this):

Installation

I use Ubuntu, so this is a piece of cake:

sudo apt-get install lvm2

There is also a GUI available, but I found the command line tools are very easy to use so there is no real need. I wouldn’t use EVMS as it is not supported in Ubuntu 7.10 and may cause problems.

Create a New Filesystem

First I create the physical volume on the partition sdg1, create a new volume group ext_vg that contains this physical volume, and create a new logical volume of size 450GB within the volume group. Finally create the filesystem (disabled reservation space, see Get More Space Out of Your ext3 Partition).

sudo pvcreate /dev/sdg1
sudo vgcreate ext_vg /dev/sdg1
sudo lvcreate -L 450G -n ext ext_vg
sudo mkfs.ext3 -m 0 /dev/ext_vg/ext

Show Status

Each LVM layer has its corresponding command to get information about the metadata:

sudo pvdisplay
sudo vgdisplay
sudo lvdisplay
sudo pvs
sudo vgs
sudo lvs

Mount via fstab

I use the filesystem mainly for data, so allowing just rw is enough (no executables allowed). noatime allows quicker access.

sudo mkdir /media/mega
/dev/ext_vg/ext /media/mega     ext3    rw,noatime,user 0       2
mount /media/mega

Resize

It is even possible to do an online resize of the system, wohoo This extends the logical volume by 200MB.

sudo lvextend -L +200 /dev/ext_vg/ext
sudo resize2fs -p /dev/ext_vg/ext

You can watch the resize process going on with df -h.

Add Another Partition to the Logical Volume

To add another partition and use up all the available space in the logical volume, first add the physical volume to the volume group, then use pvdisplay to find out the total available number of free PE (add the numbers from the physical volumes), then use lvextend to use up all this available space.

sudo pvcreate /dev/sdb1
sudo vgextend ext_vg /dev/sdb1
sudo pvdisplay
sudo lvextend -l +63602 /dev/ext_vg/ext
sudo resize2fs /dev/ext_vg/ext

That’s it! Any questions? please post.

I am a long-term StumbleUpon user, which means that I don’t get much sleep. Now, after almost 4 years of stumbling, I have decided to get my life back. Well, at least some sleep!

What does this do?

Every night when I have to work on the next day (Sunday night to Thursday night ), at 23:25 my computer shows me this little warning message:

I use this little trick with Ubuntu, but it should work anywhere where Gnome is installed.

How?

Thanks to the power of Linux, this is not difficult to do for yourself, and configure it however you want it to behave:

1. Open /etc/crontab with your favourite text editor (no need for crontab -e since this is the system wide crontab), e.g.

   sudo gedit /etc/crontab

2. Add the following lines (replace manker with your username!)

   25 23 * * 0-4   manker  /usr/bin/zenity --display :0 --warning --text="Shutdown in 5 minutes. Go to bed."
   25 23 * * 0-4   root    shutdown -h +5

3. The first part of both lines 25 23 * * 0-4 means that the commands are executed at 23:25, but only Sunday (day 0) to Thursday (day 4). Read man 5 crontab for a detailed description of that format.
4. The first command uses zenity to show a warning message. You have to execute this as the same user that you use for working, or you will not see the message, so change manker to your username (root does not work either).
5. The second command shutdown -h +5 means that the computer will halt in 5 minutes. This has to be run as root, and it also shows nice warning messages in all your open terminals so you can’t really miss it.
6. Save the file, and stumble until it is 23:25.

Sweet dreams!

tune2fs -m 0 /dev/sdf1

Replace sdf1 with your partition name. You don’t even have to unmount your disk. Voilá, 11.5 GB more space for free Here is the output of df -h as proof:

Before:

Filesystem            Size  Used Avail Use% Mounted on
/dev/sdf1             230G  193G   26G  89% /media/disk

After:

Filesystem            Size  Used Avail Use% Mounted on
/dev/sdf1             230G  193G   38G  84% /media/disk

If you like this, you might also be interested in How to change Ubuntu forced fsck.

Update: The free space limitation is also used to prevent fragmentation. So if you set the limit to zero and operate on a very full harddisk for a while, your filesystem might slow down.

sudo tune2fs -c 0 -i 1m /dev/sda3

This disables maximum mount time for forced check, but instead uses timed check. Every month the harddisk is forced to get checked. I can live with that.

Markus Holzmann, an intern at Profactor of my fellow colleague Philipp Hartl, had the opportunity to experiment with Ajax during his job. He wrote a tutorial about how to push events from the server to the client. For example, display popup messages on all browsers at the same time (see screencast in full resolution here):

Cometd Hello World

I’ve read Chris Bucchere’s Say Hello World to Comet and built an application based on this using a more current version of Jetty (version 6.1.5) which I embedded into a Tomcat v5.5 Server. For the developing I used Eclipse 3.2.

Start your Engines

At first you have to get the server running. As I mentioned I embedded Jetty into a Tomcat server. Therefore you have configure the libraries:

1. Add the packages org.mortbay.cometd and dojox.cometd to your source folder and delete the client package in the org.mortbay.cometd package.
2. Add jetty-util-6.1.5.jar, jetty-6.1.5.jar and servlet-api-2.5-6.1.5.jar to your build path.
3. Copy the jetty-util-6.1.5.jar file into the /lib folder in the WEB-INF directory.

Replace the existing servlets in your web.xml – file in the WEB-INF – folder with the following servlets:

<servlet>
  <servlet-name>cometd</servlet-name>
  <servlet-class>org.mortbay.cometd.continuation.ContinuationCometdServlet</servlet-class>
  <load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
  <servlet-name>cometd</servlet-name>
  <url-pattern>/cometd/*</url-pattern>
 </servlet-mapping>

For the project I used the dojo toolkit (version 0.4.3) which has an integrated COMETd class that makes it easy to build comet projects. Download it and add it to your WebContent folder.

When you’ve done all this, the hardest piece of work for this program is already done.

Hack the Code

Now you can implement the code for the client side: You need a HTML file with a button on it. The code for this looks like this (download):

<html>
  <head>
    <script type="text/javascript" src="../dojo.js"></script>
    <script type="text/javascript">
      dojo.require("dojo.io.cometd");

      cometd.init({}, "cometd");

      cometd.subscribe("/hello/world", false, "publishHandler");

      publishHandler = function(msg) {
        alert(msg.data.test);
      }
    </script>
  </head>
  <body>
    <input type="button"
       onclick="<b>cometd.publish('/hello/world', { test: 'hello world' } )</b>"
       value="Click Me!">
  </body>
</html>

Line by line, the above bold code works like this:

1. In the line

   <script type="text/javascript" src="../dojo.js"></script>

   you integrate the dojo toolkit into the project.

2. To activate the cometd class of dojo:

   dojo.require("dojo.io.cometd");

3. Connect the server with the client:

   cometd.init({}, "cometd");

4. Here we say what to do when there is a subscribe event:

   cometd.subscribe("/hello/world", false, "publishHandler");

5. Last but not least, the publishHandler function serves as the callback function, which uses alert to show a simple message box:

   publishHandler = function(msg) {
     alert(msg.data.test);
   }

Give it a Try

When you load the HTML file now, you can click on the button and an alert box saying hello world will appear:

The reason for this is that when you click the code

cometd.publish('/hello/world', { test: 'hello world' } )

is executed which publishes a text on the channel with the id /hello/world.

The funny thing is that this is able to run on any number of browsers. Everytime when a client clicks the button, on all browsers that view this page the alert box is shown. (See screencast above).

Pushing Data from Server to Client

You can also add serverside code to trigger an event. I wrote a JSP file with the following code:

<%@page import="java.util.*"%>
<%@page import="dojox.cometd.*" %>
<%
Bayeux b = (Bayeux)getServletContext().getAttribute(Bayeux.DOJOX_COMETD_BAYEUX);
Channel c = b.getChannel("/hello/world",false);

Map<String,Object> message = new HashMap<String,Object>();
message.put("test", "jsp: hello world");

c.publish(b.newClient("server_user",null),message, "new server message");
%>

When this page is loaded, an alert popup appears at the page saying jsp: hello world.

Remember pushing too much data from server to client can slow the performance of your site specially is you have a huge amount of traffic. Getting one of the best wordpress hosting will solve this kind of problem.

That’s it. Happy hacking!

Search, install, remove available packages (preferred method)

sudo aptitude search ABC
sudo aptitude install ABC
sudo aptitude remove ABC

.deb (you have to take care of dependencies on your own)

sudo dpkg -i ABC.deb

.rpm (requires sudo aptitude install alien)

sudo alien -i *.rpm

.tar.gz (requires sudo aptitude install checkinstall)

tar xzvf ABC.tar.gz
cd ABC
./configure
make
sudo checkinstall

.package, .sh, .bin (Just download and execute)

chmod +x ABC
./ABC

.exe (requires sudo aptitude install wine)

wine ABC.exe