Solving Package 'xyz' has no installation candidate !!

During installing any package in ubuntu, if we encounter "no installation candidate" error, we first have to run the following two commands.

sudo apt-get clean
sudo apt-get update

Then you can try re installing the package.

However there are at times when we come across an error "A error occured during the signature verification". In such cases the installation of the package cannot be proceeded.

I followed this link and could solve the problem. Following are the list of commands mentioned in the link to solve the problem.
           

sudo apt-get clean
sudo mv /var/lib/apt/lists /tmp
sudo mkdir -p /var/lib/apt/lists/partial
sudo apt-get clean
sudo apt-get update

After running the above commands, the signature verification error will be gone. we can resume the installation of the original package.

Passionately,
Achutha

NS2 Installation and Running in Ubuntu 12.04

Network Simulation(NS) is very useful in simulating network and analysing various parameters of a wireless network or wired network. The simulator allows you to test the working of various protocols.
Preferable OS is Linux. If you want to run through windows, then help of cygwin can be taken.
I have ubuntu 12.04 with me.

Step1:
Download ns-2allione from here .A zip file will be downloaded.

Step2:
Go to corresponding directory of download and run the following command for unpacking.
tar -zxvf ns-allinone-2.35.tar.gz

Step3:
Install few of the prerequisite libraries

sudo apt-get install tcl8.5-dev tk8.5-dev --fix-missing
sudo apt-get install build-essential autoconf automake --fix-missing
sudo apt-get install perl xgraph xorg-dev libxt-dev libx11-dev libxmu-dev --fix-missing

Step4: Run the installation set up file
cd your_path_to_directory_of_download/ns-allinone-2.35
./install


Step5: Couple of library paths has to be added to the PATH,LD_LIBRARY_PATH & TCL_LIBRARY_PATH env variables.
libray paths will be given if its installed properly in the step4.
and run the following commands by filling appropriate library paths

export PATH=$PATH:/home/user/achuth/WirelessSensorNetworks/ns-allinone-2.35/bin:/home/user/achuth/WirelessSensorNetworks/ns-allinone-2.35/tcl8.5.10/unix:/home/user/achuth/WirelessSensorNetworks/ns-allinone-2.35/tk8.5.10/unix

export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/home/user/achuth/WirelessSensorNetworks/ns-allinone-2.35/otcl-1.14:/home/user/achuth/WirelessSensorNetworks/ns-allinone-2.35/lib

export TCL_LIBRARY=$TCL_LIBRARY:/home/user/achuth/WirelessSensorNetworks/ns-allinone-2.35/tcl8.5.10/library


Your Installation is done !!!

Step5:Execute the following commands to validate the simulation.
cd ns-2.35
./validate


Step6: Download Network Animator and ns.
sudo apt-get install nam
sudo apt-get install ns

Step7: Download the code from internet of any protocol with extension .tcl and run
    ns eg1.tcl
Now, three files will be generated,
with extensions like, testeg.nam, testeg.tr,win.tr

After this run,
nam testeg.nam

Now simulator will be launched, and you are good to explore !!


Thanks
Achutha

Not Able to set proxy and port in Android SDK Manager in Linux???

For some reasons,SDK Manager in ubuntu doesnt show the options of setting http-proxy and port. Because of this reason,if you are behind proxy,then SDK Manager will not be able to fetch any updates.. After googling a bit, i found the solution..

Step 1:
           Go to ~/.android folder
Step 2:
           If androidtool.cfg file is present,then update the proxy and port like below

                         sdkman.force.http=true
                         http.proxyPort=8080
                         http.proxyHost=144.16.192.247

         else if the file is not found, create a file called androidtool.cfg(vi androidtool.cfg) and copy the following
                       sdkman.force.http=true
                       http.proxyPort=8080
                        http.proxyHost=144.16.192.247

Note: Please update your respective proxy and port.

Step3 :Now go to android/sdk/tools folder and run the following command
sudo ./android update sdk

You should be able to see the options to update the proxy and port for android sdk manager.