"; */ ?>

tutorials

hardware / howto / linux / network / tutorials / ubuntu — 9 Comments
29
Sep 08

Sure Way to Restart a Wireless Network

linux penguin is watching windows fly

While wireless signal is good, the network is dead – why is that? Many reasons, of course. You can spend time to figure out the reason and then try to fix, which is a good approach, but requires some time. Or you can restart the network to see if it resolves the issue, and if it does – forget that the problem ever existed.

However the way to restart a wireless network is not always “black and white”. Sometimes it is possible using GUI, and sometimes by typing something that means “network service restart”. And yes these ways are “clean”, but have a drawback – they rely on operating system to do what it suppose to do and restart the network.

However, OS does not always behave (yes, Linux does not always behave, along with Mac, and Windows, and “any” OS.. ). But here is a sure way to restart it – you would need to get down to the driver level though – to be less OS (or distribution) specific. But I’ll guide you through, don’t worry..

So, the signal is full/good/strong:

wireless signal is good
but there is no network:

$ ping -c 4 google.com
ping: unknown host google.com

First thing to do is to see what wireless card you are using:

$ lspci | grep -i network
08:00.0 Network controller: Intel Corporation PRO/Wireless 3945ABG Network Connection (rev 02)

In my case it is Intel 3945ABG. Next, check what driver is used for this card. I did a simple google search, and saw that the driver is “ipw”something.

Let’s see what ipw-like modules/drivers are currently running/loaded:

$ modprobe -l | grep ipw
/lib/modules/2.6.20-17-generic/kernel/ubuntu/wireless/ipw3945/ipw3945.ko
/lib/modules/2.6.20-17-generic/kernel/drivers/usb/serial/ipw.ko
/lib/modules/2.6.20-17-generic/kernel/drivers/net/wireless/ipw2200.ko
/lib/modules/2.6.20-17-generic/kernel/drivers/net/wireless/ipw2100.ko

Here it is “ipw3945”. Let’s kill it (-r stands for “remove”):

$ sudo modprobe -r ipw3945

Let’s start it back up:

$ sudo modprobe ipw3945

Checking connectivity:

$ ping -c 4 google.com
 
PING google.com (64.233.187.99) 56(84) bytes of data.
64 bytes from jc-in-f99.google.com (64.233.187.99): icmp_seq=1 ttl=238 time=43.3 ms
64 bytes from jc-in-f99.google.com (64.233.187.99): icmp_seq=2 ttl=238 time=28.9 ms
64 bytes from jc-in-f99.google.com (64.233.187.99): icmp_seq=3 ttl=238 time=27.7 ms
64 bytes from jc-in-f99.google.com (64.233.187.99): icmp_seq=4 ttl=238 time=34.7 ms
 
--- google.com ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 3005ms
rtt min/avg/max/mdev = 27.742/33.685/43.323/6.165 ms

Perfect!

howto / mysql / rails / tutorials — 7 Comments
14
Sep 08

Configure Rails and MySQL to Support UTF-8

Rails on MySql

The fact that there are so many different countries, people and languages makes it very interesting to watch all them to use a single tool. Besides the different cultures of programming, there is a definite difference in languages that the tool needs to support in order to become widely used.

Luckily, if the tool is written to support UTF-8 encoding it is guaranteed to support all the modern spoken languages. Since UTF-8 is able to represent any character in the Unicode standard, yet the initial encoding of byte codes and character assignments for UTF-8 is backwards compatible with ASCII, and for these reasons, it is steadily becoming the preferred encoding for e-mail, web pages, and other places where characters are stored or streamed – in our case it is a mySql database.

When working with Rails on mySql, it is most of the time, a good practice to make sure the UTF-8 support is enabled, since even if there is no immediate need, in the future, clients of the Rails application could come from different points of Earth – due to the Earthy nature of the Internet.

Here are 3 simple steps on how to configure a Rails application and mySql database to support UTF-8 encoding:

Step 1. From the Rails side, due to the “convention over configuration” principle, there is only one thing to make sure of. Open the Rails database configuration file:

  vi config/database.yml

(here I used “vi” text editor, but any editor of choice can be used: notepad/textmate/emacs/aptana.. etc)

Notice the “encoding” option, and make sure it is set to “utf-8”:

  ...
        development:
        adapter: mysql
>>>  encoding: utf8
        database: my_international_db
        username: user
        password: password
        socket: /var/run/mysqld/mysqld.sock
  ...

That will conclude this step, since everything from Rails side is configured. Simple? Well, yes – Rails is well designed to keep it simple stupid.

Above is the sample for the Rails development environment, make sure that testing and production environments have the same configuration.

Step 2. Now it is time to configure MySql server. This will be done by editing “my.cnf” – mySQL configuration file:

  vi /etc/mysql/my.cnf

There are several sections in the file. Modify two of them – “client” and “mysqld” as shown below to configure mySql for UTF-8 support:

...
[client]
 
default-character-set=utf8
 
...
[mysqld]
 
default-character-set=utf8
character-set-server=utf8
default-collation=utf8_unicode_ci
...

Step 3. The very last action would be to restart MySql server. Here is an example on how to do it in Linux (Ubuntu):

  sudo /etc/init.d/mysql restart

NOTE: Only databases that are created after the above change will support UTF-8 encoding.

After these three steps Rails application and MySql server are configured, and ready to serve the whole planet!

cool places / howto / java / linux / software / technology / tutorials / ubuntu — 5 Comments
11
Sep 08

Install Sun Application Server on Ubuntu

Sun Microsystems

On the client site when working on Java (or should I say JEE) projects, the application servers are most of the time “rotate” between these four: JBoss, Websphere, Weblogic, and someties Geronimo. However there are some clients who have pretty tight contracts with Sun, and in these cases the Sun Application Server is used.

I think now days in development world in general, well except maybe .NET part of it, Ubuntu and/or Mac OS slowly become OSs of choice for developers. Sun app server however is not the most used app server out there, and since its installation could be a bit non-straightforward, here are four simple steps on how to install it on Ubuntu box:

Step 1. Download the “.bin” form sun:

“Sun Java System Application Server”

http://java.sun.com/j2ee/1.4/download.html (I needed 8.2, but there are more recent ones)

Step 2. Change permissions, to make it runnable:

chmod 744 sjsas_pe-8_2-linux.bin

Step 3. If you just run it:

./sjsas_pe-8_2-linux.bin

It is going to complaint that it is missing a standard c++ library:

./sjsas_pe-8_2-linux.bin: error while loading shared libraries: libstdc++-libc6.2-2.so.3: cannot open shared object file: No such file or directory

Having done some “apt-cache” searches ( apt-cache search libstdc++ ), found that Ubuntu has “libstdc++.so.6” in /usr/lib.
From /usr/lib run:

 sudo ln -s libstdc++.so.6 libstdc++-libc6.2-2.so.3

Step 4. Run it now, it will install Sun App Server successfully! * **

* Do not run installation as root – it will fail (for most sun app servers versions)

** If you use any form of Beryl (or some Compiz’es), disable it, or reload window manager as a “Gnome Manager”. This is due to the fact the the installer is written in Swing, and Swing does not get along too well with some display managers.

howto / linux / rails / ruby / software / technology / tutorials / ubuntu — 12 Comments
2
Aug 08

Make rails.vim Work: Compile VIM From Sources

rails.vimEver heard about rails.vim project? “Accept no imitations: rails.vim is the one true Vim plugin for syntax highlighing, easy navigation, and script invocation for all your Ruby on Rails applications, transparently and unobtrusively” says creator Tim Pope.

The very good “rails.vim” guide can be found here or just by reading project’s vimdoc here.

PROBLEM:

There is however one gotcha for Ubuntu Hardy Heron lovers (or other modern Linux distros). Using rails.vim would result in VIM “segmentation fault”crashes similar to:

Vim: Caught deadly signal ABRT
Vim: Finished.
Aborted

REASON:

This is due to the fact that a packaged VIM that comes from some Linux distros repositories has old patches.

SOLUTION:

One of possible solutions would be to download most current VIM sources from http://www.vim.org/sources.php and compile/install it manually. Below is how it is done on Ubuntu (but should be pretty similar on any Linux distro):

1. Get vim sources:

wget ftp://ftp.vim.org/pub/vim/unix/vim-7.1.tar.bz2

(where ‘7.1’ is the current VIM version at the moment of writing)

2. Unpack it

tar -xvjf vim-7.1.tar.bz2

3. Install terminal libraries (vim needs them to compile correctly)

sudo apt-get install libncurses5-dev

4. Configure / Compile / Install

./configure --with-features=huge
make
sudo make install

5. Point your system to newly compiled VIM:

sudo rm /etc/alternatives/vi
sudo rm /etc/alternatives/vim
sudo rm /etc/alternatives/vimdiff
 
sudo ln -s /usr/local/bin/vim /etc/alternatives/vi
sudo ln -s /usr/local/bin/vim /etc/alternatives/vim
sudo ln -s /usr/local/bin/vimdiff /etc/alternatives/vimdiff

DONE

hardware / howto / interesting / linux / linuxmce / software / technology / tutorials / ubuntu — 5 Comments
15
Jul 08

Forward VNC through SSH

linuxmce screenshotFrequently I need to access my LinuxMCE machine over VNC, due to different reasons (when I am not home, when my Wii Remote batteries died, etc..). Usually SSH solves most of my needs, but sometimes it is very nice to control my linuxMCE box over VNC.

Here I will show you several very easy steps on how to configure your server/client to be able to tunnel VNC traffic through SSH, and be able to control your server in the GUI way :) This approach will work on most systems (not LinuxMCE specific) although here I chose Ubuntu as an “example OS”.

Before we begin, I would assume that:

  • The server already has ssh server installed, if not: 
    sudo apt-get install openssh-server
  • If connecting from the outside (like from work to home box), your router’s firewall forwards port 22 to your server’s IP

Here is how it is done:

Server Side Configuration

1. Installing VNC server, here I chose to install x11vnc, but it could be pretty much any VNC server of your choice (TightVNC, etc..):

sudo apt-get install x11vnc

2. Now let’s finish :) our server configuration by running the VNC server:

x11vnc

by default it is going to run without a password, and on port 5900

Client Side Configuration

1. In order to connect to the VNC server, we need to have a VNC viewer installed:

sudo apt-get install xvncviewer

* again, it can be pretty much any VNC viewer of your choice

2. Now the most interesting part of this whole process – enter this command:

ssh -L 5900:127.0.0.1:5900 yourusername@yourserver.com

this tells your system to tunnel all the traffic from the port 5900 on “yourserver.com” to the local (client’s) port 5900 via SSH. Simple, and yet very powerful – a “magic one-liner” :)

3. Fire up another shell on the client side and enter:

xvncviewer 127.0.0.1

do you see a cute colorful square screen? Do you recognize your server’s Desktop?

Done :)

P.S. For LinuxMCE specifically, you should also add a couple firewall rules:

– Go to the LinuxMCE web admin
– From the upper menu, go to “Advanced -> Network -> Firewall rules”

add this three rules:

tcp  	5900 to 5900  	5900  	192.168.80.1             port_forward
tcp 	5900 to 5900 	0 	0                        core_input
tcp  	22 to 22  	0  	0                        core_input

– The first rule allows external network (Internet) to access the VNC server on the Core (LinuxMCE server)
– The second rule allows anybody inside the home network ( since it is not wise to open 5900 port on your router to the whole world ) to have their 5900 port to be forwarded to the Core.
– The third rule (I think you already have it) allows anybody to access LinuxMCE server via port 22 (SSH)

Be careful about the rules above, as I assume that your LinuxMCE server is behind another firewall, cause you really do not want to open 5900 port to the public

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