Advertise SFTP on Network using Avahi

I just realized that I can broadcast / advertise my SFTP server to other computers connected to the network.

Go to /etc/avahi/services
and create a file named sftp.service, which contains:





   %h SFTP
 
   
      _sftp-ssh._tcp
      22
 

Now, you can see your SFTP server in Nautilus.

This guy has more complete list on what can be broadcast using avah i

Django Login and Sign-Up Page Together

It is very common to combine login and sign-up form in one page, so I implemented it in django. Here's how I do it.

First, create UserForm class which contains whatever information you need, such as: username, password, full name, address, email, gender, etc.

Second, add login url to your urls.py, something like the following:

(r'^/login/$', 'django.contrib.auth.views.login', { 'template_name': 'myapp/login.html', 'reg_form': UserForm() }),

Third, create in your template folder myapp/login.html which content is like shown in docs.djangoproject.com/en/dev/topics/auth/ (search for sample registration/login.html)

Make sure you use the exact same variable name (form, next, etc), unless you know what you are doing.

Also, in this template, add another html form and render your UserForm object (in my case the variable name is reg_form.

Fourth, create sign_up view, which perform whatever it is necessary in order to save the new user. Make sure you add { 'form': django.contrib.auth.forms.AuthenticationForm() } to the context data.

Sixth, add sign_up url to your urls.py, something like the following:

(r'^/sign-up/$', myapp.views.sign_up ),

Notes:

I created my own User class with additional information that django user (auth_user) does not provide. In order to do that, I create (custom) User with a OneToOne relationship with django user which is also the primary_key.

That's how I do it. Hopefully, give you some ideas if you want to implement something similar.

Consuming Django Tastypie RESTful WS with Apache HTTPClient and GSON

Creating RESTful Web Service is so simple using Django Tastypie. It's pretty much just about registering which model you want to expose. Even more amazing is that filtering feature. Read here to get more info about it.

I decided to create Java frontend to replace the existing, which uses Python Gtk. To keep with the existing look and feel I use java-gnome binding. The transition from python gtk to java-gnome is quite smooth. Java-gnome has such a good design, so the only thing that I need to for the transition is just adapting to the java paradigm, which is wonderful.

To get the JSON object from the web service, I chose Apache HTPClient, just to make things simple. I know that there are a lot of java REST client, such as restlet, jersey, etc. I stick with the simplest one.
The next thing is to figure out how to transform JSON result from the RESTful web service to POJO.  Here comes GSON to the rescue. I did not want to use python attribute name convention in my java codes. So, this one I need to solve. Fortunately, GSON comes with clever and handy feature named FieldNamingPolicy. Obviously they have really good experience in different programming language hence this feature available.

To give example on how to use it, taken from the site:


SomeObject someObject = new SomeObject("first", "second");
Gson gson = new GsonBuilder().setFieldNamingPolicy(FieldNamingPolicy.LOWER_CASE_WITH_UNDERSCORES).create();
String jsonRepresentation = gson.toJson(someObject);
System.out.println(jsonRepresentation);


Awesome! That simple and you can keep the java attribute naming convention and make your java codes look good.

Debian with Ubuntu Fonts

Here is how I configure my Debian system to use the same font config as Ubuntu.
Simply download, fontconfig-config_2.8.0-3ubuntu9_all.deb. The link will take you to Ubuntu 12.04 fontconfig-config deb package.
After you saved that deb file, extract it to get its contents:
$ dpkg-deb -x fontconfig-config_2.8.0-3ubuntu9_all.deb /tmp/extract/

then replace the content of Debian's /etc/fonts/* with data from /tmp/extract/etc/fonts/*

$ sudo cp -r /tmp/extract/etc/fonts/* /etc/fonts/

Logout and log back in to see the change.

Using CSS to Make Your HTML Page Printer Friendly

Besides for styling for regular media (such as screen / pc monitor), css can also be used to make the web layout suitable for printing.
Perhaps you have a web page which has logo, menu, navigation, videos, and other things on it. Also there is a table or other information which you actually need. You would not want those irrelevant elements cluttering all over when you print it, right?

To solve it, simple use specific stylesheet for printing purpose and define it for "print" media. Here is an example of using external stylesheet for "print" media:


Next step is to eliminate those unnecessary elements using display: none. Here's an example:
div#menu {
display: none;
}

Now, as a bonus, I found out a way to make the default printing orientation as landscape. Here's it is:

@page {
size: landscape;
}

Another interesting thing that I found during my work is that !important rule defined in other css for any other media other than "print" will also effects the "print" media layout. I did not expect that, since I assume that !important rules defined for "screen" media, for example, would only effect that particular media. So, make sure you override the !important rule in the "print" css.

Django Blog Zinnia Limit User to Own Entry/Post

I just need a simple yet flexible django based blog application, and found django-blog-zinnia. I really admire how simple it is. The only major adjustment that I need is to limit user to his/her own blog entry/post.

Combining basic django (admin) knowledge with soome info from django-blog-zinnia documentation, I found a simple solution. Of course this is related with django-blog-zinnia's admin interface, and there is a documentation about how to make some modification to the EntryAdmin. Read more from here.

The idea is to create a django application and create admin.py on that app's top level directory (the same location with models.py).

Here is how my admin.py codes look like:
############# admin.py #################

from django.contrib import admin
from zinnia.models import Entry
from zinnia.admin.entry import EntryAdmin

class FilteredEntryAdmin(EntryAdmin):
    def queryset(self, request):
        qs = super(FilteredEntryAdmin, self).queryset(request)
        if request.user.is_superuser:
            return qs
        return qs.filter(authors=request.user)

admin.site.unregister(Entry)
admin.site.register(Entry, FilteredEntryAdmin)

############# end of admin.py #################

Remember to add the newly created app in settings.py INSTALLED_APPS, and make sure you put it below zinnia.

Django's documentation is quite complete and comprehensive. To get more information about ModelAdmin, queryset, etc, go to this link. From there I got the idea of overriding the queryset and use filter to limit the entry based on user.

(pip) Install Python Imaging Library (PIL)

I had a problem when I tried installing Python Imaging Library (PIL) version 1.1.7, within virtualenv, using pip. Actually, there was not any errors raised during installation, but when I used it in Django for the ImageField, I kept getting 'Upload a valid image. The file you uploaded was either not an image or a corrupted image' error message.
I figured out that the problem is due to the manual installation of PIL using pip, instead of using Debian/Ubuntu's apt-get.
So, the simplest solution would be using the
$ sudo apt-get install python-imaging

The thing is, I need PIL installed in my virtualenv environment. Getting some info from this link, I figured out a way to install PIL within virtualenv. In order to do that, some changes need to be done inside the PIL's setup.py script.
Step 0: sudo apt-get install libjpeg62 libjpeg62-dev
Step 1: get PIL source kit (here).
Step 2: untar, unzip the file
Step 3: locate setup.py from Step 2, and open that file for editing
Step 4: around line 200 (you should see other paths around there), add the following
add_directory(library_dirs, "/usr/lib/i386-linux-gnu")  # for 64 bit replace with /usr/lib/x86_64-linux-gnu
Step 5: tar and gzip the modified PIL source.
Step 6: activate your virtualenv, should you need it
Step 7: pip install

I made some test with my django-blog-zinnia project, by uploading some pictures and no more error messages.

Disable Network Manager and Use Script to Connect to WPA2 Wireless Connection

I would like some of the computers at my work to be able to connect to a specific wireless access point with WPA2 encryption and keep trying to connect (indefinitely) if the Access Point (AP) is not on yet. When the AP is up and running, those computers should be able to connect without any human interaction. There is a possibility that the AP is turned off for a while or restarted, due to some reason, and those computers should be able to reconnect automatically when the AP is back online again.

The default behavior on Ubuntu and Fedora is a little bit different (but far from my need). When a computer is already connected to AP, and the AP suddenly becomes unavailable for a while, there will be a WEP/WPA password dialog. User has to click the connect button again and if the AP is not available yet it will keep showing password dialog. When the user click cancel button, it will stop trying to connect to that particular AP.

Finally I figured out how to set the computer to keep trying to connect indefinitely and no matter how many times the AP becomes unavailable, it will keep doing it until it is (re)connected.

Here is how I did it:
The main issue is with the default behavior of the NetworkManager. I have not found any NetworkManager configuration so I could set it the way I explained earlier. Please let me know if someone knows how to do the exact thing that I need using NetworkManager.

The first step is to disable NetworkManager:
To disable it temporarily, use the following command:
$ sudo service network-manager stop

To permanently disable NetworkManager, do the following:
edit /etc/init/network-manager.conf
comment "start on...", so it would be like the following:
# start on

Next step is to create a wpa supplicant configuration file, do the following:
Create "/etc/wpa_supplicant/wpa_supplicant.conf" file and make it executable.
Put the following configurations inside it:
########### wpa_supplicant.conf ############


ctrl_interface=/var/run/wpa_supplicant

network={
    ssid="your_wlan_essid"
    scan_ssid=1
    key_mgmt=WPA-PSK
    psk="your_wpa2_passphrase"
}


########### end of wpa_supplicant.conf ############

Now, I am not really comfortable to put my plain text wpa2 passphrase inside the config file. So, I use the following method:
$ wpa_passphrase your_wlan_essid your_plain_text_passphrase

Use the output of the command above for your encrypted passphrase

Third step is to edit the /etc/network/interfaces configuration file.
Here is how my config file looks:
############# /etc/network/interfaces ###########

auto lo
iface lo inet loopback

auto wlan0
iface wlan0 inet dhcp
   wpa-conf /etc/wpa_supplicant/wpa_supplicant.conf
   wpa-action /etc/wpa_supplicant/action_wpa.sh

############# end of /etc/network/interfaces ###########

Notice that /etc/wpa_supplicant/wpa_supplicant.conf is the configuration file we just created previously, and /etc/wpa_supplicant/action_wpa.sh should exist from the default ubuntu (11.10) installation.

Now for the test:
Test #1
Make sure your AP is on.
Restart your computer, and after you logged in, you should be connected to AP.

Test #2

Make sure your AP is off.
Restart your computer, and after you logged in, you should not be connected to AP.

Turn on your AP.
Not long after that your computer should be connected to AP.

Test #2
Make sure your AP is on and your computer is connected to AP.
Turn off your AP.
Your computer should be disconnected from AP.
Wait for a while to be sure that your computer is not connected and the retry connection attempt failed.

Turn back your AP on.
Not long after that your computer should be reconnected to AP.


Now, this is exactly what I want for my setting at work.

Python SimpleHTTPServer

I needed to do some test and share a file on different machine. Fortunately there is a very simple solution for what I need, which is using Python's SimpleHTTPServer.
What I needed to do is simply go to the directory where the file is and then execute the following command:

$ python -m SimpleHTTPServer

Executing above command without arguments will run the webserver on 0.0.0.0:8000.

For more information just click here.

Disable Google Chrome Developer Tools

Finally, I found a way to disable google chrome developer tools. I need it because I have some browser based application that I need to deploy, and google chrome is really suitable for my need. The only thing that prevented me doing so is the dev tools. I don't want user to play around with the dev tools, do some hacking and stuff. No way!
Now, here is how to disable devtools:
Edit ~/.config/google-chrome/Default/Preferences
On Mac OSX: ~/Library/Application Support/Google/Chrome/Default
Add "disabled": true to the "devtools" key, so it becomes like the following:
"devtools": { "disabled": true, "split_location": 256 }
Save it, and restart browser. Done!
Here is where I originally found the solution.

Ubuntu 11.10 Virtual NIC IP Workaround

The normal way of adding virtual nic ip is by setting it in /etc/network/interfaces, like the following:

auto eth0:0
iface eth0:0 inet static
address 192.168.0.111
netmask 255.255.255.0
broadcast 192.168.0.255
gateway 192.168.0.1

Unfortunately, there is a known bug which prevent such configuration to work. Take a look here.

The first workaround that I figured out is by using /etc/rc.local script.

Add the following lines before exit(0) inside that script:

#################################

sleep 4  # This due to concurrency, set some delay in order for the networking to be set up properly first

ifconfig eth0:0 192.168.0.111 netmask 255.255.255.0 broadcast 192.168.0.255

# or use below command to replace above ifconfig command

# ip addr add 192.168.0.111 dev eth0

#################################

The second workaround is, IMHO, better. No sleep hack necessary, since upstart script is used instead of rc.local script.

Create /etc/init/network-interface-virtual.conf (or use different name as you like), with the following lines inside:

#################################

description "configure virtual network device"

respawn

console none

start on (net-device-up IFACE=eth0)

stop on runlevel [!12345]

script

exec ip addr add 192.168.0.111 dev eth0

# or use ifconfig command below

# ifconfig eth0:0 192.168.0.111 netmask 255.255.255.0 broadcast 192.168.0.255

end script

#################################

Reboot your system if necessary and everything is set and the virtual nic ip is ready to use. Oh, one more thing. There is also a bug (I think), which makes the virtual nic ip not showing with the ifconfig -a command. Just ping the virtual ip address to test whether it's up or not. 

Ubuntu 11.10 and Realtek (RTL8111/RTL8168) NIC driver problem

Finally, I figured out the problem that I had with network connection. The problem was with Realtek (RTL8111/RTL8168) NIC, which somehow detected differently by ubuntu 11.10 and uses r8169 kernel module driver.
To be sure, do check your NIC using:
$ sudo lscpi

You should see something like ...Realtek (RTL8111/RTL8168)...
Next step is to remove the r8169 module using:
$ rmmod r8169

If necessary install build-essential, etc:
$ sudo apt-get install build-essential linux-headers-$(uname -r) linux-source

Then, download the proper driver for that particular NIC from here. The file name should be something like r8168-8.027.00.tar.bz2.
Uncompress the file, and run the shell script file, as root:
# ./autorun.sh

Check the newly compiled driver:

$ sudo lsmod | grep r8168
$ ifconfig -a


Blacklist the r8169 module driver, by editing /etc/modprobe.d/blacklist.conf, add:
#blacklist r8169 driver
blacklist r8169

Reboot your system if necessary.