How I am Trying To Keep My Eyes Safe On Computer

Lately I've been on computer a lot and with this, the usual problem with most computer users has started to bother me. Going through some of the blogs online for keeping eyes safe while using computer, I came through few suggestions and in this post, I'm writing how I'm trying to keep my eyes safe. Though not tremendously helpful for everybody, I thought I would share this and you could also use my technique.

The problem with computer addicts is not getting their eyes off the computer for much longer period and though I've been trying to remember to keep my eyes off the computer in regular interval, I usually never implement this.

My two principles based on my readings on different websites are:

• 20-20-20: In the 20 minutes interval, keep your eyes away for 20 seconds (& view other objects which are around 20 feet away)
• 2 hrs rule: In the 2 hours interval, stay away from computers for at least 2 minutes.

But, you can not really follow the rules so easily and I had to find some other alternative to do so. This is how I am doing it now.

Create two cron jobs for each of the above mentioned methods such that notify-send is triggered in each 20 minutes and each 2 hours informing you to keep yourself safe from computers. So my /etc/crontab looked like this:

*/20 * * * * techgaun export DISPLAY=:0.0 && /usr/bin/notify-send -i /home/techgaun/Samar/scripts/eye_inv.ico "20 - 20 - 20" "Time to take rest. Keep your eye safe :)"
01 */2 * * * techgaun export DISPLAY=:0.0 && /usr/bin/notify-send -i /home/techgaun/Samar/scripts/eye_inv.ico "2 hrs eye rest" "Time to take rest for 2 minutes. Keep your eye safe :)"

You need to replace techgaun with your username and need to give correct path to the ico file if you like to use icon like me. Otherwise, you could just omit the icon in notify-send command. I hope this proves useful for some of you :)


Read more...

Two Ways To Print Lines From File Reversely

Ever tried to print lines in files in the reverse order? You will know two simple methods to print lines from file in the reverse order.

Imagine a file somefile.txt with content something like this:

a
b
c
d
e

Method 1:

$ tac somefile.txt
e
d
c
b
a

Method 2:

$ sort -r somefile.txt
e
d
c
b
a

You can achieve the same effect through other techniques as well but I'll stick to these simple ones :)


Read more...

Compile 32 Bit Binaries On 64 Bit Machine

Well I had this special need if you recall my previous blog post since my friend had 64 bit machine. Sometimes, there might be this necessity to compile 32 bit binaries on your 64 bit machine. This post describes how to do so.

First make sure the necessary x86 libraries are installed. We require 32-bit shared libraries for AMD64 to compile binaries in 32 bit format. The command below installs the i386 version of libc6-dev:

$ sudo apt-get install libc6-dev-i386

Now you can compile your code in 32 bit binary format using the -m32 flag where 32 represents the x86 processor (-m64 would mean x64 processor).

$ gcc -m32 -o test test.c

I hope this helps :)


Read more...

Pointers Without Pointer Variables

Since a pointer variable is nothing but a variable holding 4 bytes memory address (at least on 32-bit addressing), I had a thought that non-pointer variables which can hold 4-bytes of data can be used in place of pointer variables. This post shows how this can be achieved.
The code example below uses an unsigned integer variable in order to store memory addresses to point the integer array.

#include 

int main(int argc, char **argv)
{
        int num[] = {1, 2, 3, 4, 5};
        unsigned int ptr;
        int i;
        ptr = (unsigned int) num;
        for (i = 0; i < 5; i++)
        {
                printf("%p - %d\n\n", (void *) ptr, *(int *)(ptr));
                ptr = ptr + 4;
        }
        return 0;
}

The same concept can be used to use non-pointer variable for pointing other datatypes. After all, its about correct type-casting and since 4 bytes datatype can hold memory addresses, pointer is not always necessary. It must be noted that the increment would be different for different datatypes. Since integer requires 4 bytes, ptr is incremented in this example. If we had character array, then ptr would have to be increased by 1 since char type requires 1 byte.

However, pointers are there to make our life easy. It was just for fun :)


Read more...

Rename MySQL root User [How To]

MySQL ships with the default user 'root' who has all kind of access to the MySQL database. We often wish to rename this user to something else because of maybe security issues or any other reason. While renaming 'root' to something else is not going to alleviate all sorts of security problems that may arise, it is good idea to rename 'root' to some other name.

Login to the MySQL console and then type the following SQL statements:

mysql> use mysql;
mysql> update user set user="some_other_user" where user="root";
mysql> flush privileges;

It is often good idea to drop anonymous users and the test database because of security reasons. I bet you are never going to use that test database so why keep it? Run the SQL statements as below to do so:

mysql> drop user "";
mysql> drop database test;

Also, make sure you use strong passwords. You can use mysqladmin to change passwords.

$ mysqladmin -u my_new_user -p password 's0m3_r4nd0m_$|r0ng_p455' $ history -c $ rm ~/.mysql_history

The later two commands are to ensure that no log of any of your MySQL queries or admin level commands have been stored in the history.

I hope this helps :)


Read more...

Manual Sun Java Installation In Linux

Be it be multiple installations of java or be it be custom server, you might run into the necessity of manually installing java. This tutorial will provide step by step commands for installing java manually in linux.

Though the process was done on CentOS, it should work for most linux systems with or without slightest modifications. The process below installs Sun Java and configures Sun Java to be the default java to be used. Below are the steps I took to install and configure java in my system:

$ cd /opt/java
$ wget http://download.oracle.com/otn-pub/java/jdk/6u45-b15/jdk-6u45-linux-i586.tar.gz
$ tar xvfz jdk-6u45-linux-i586.tar.gz
$ echo 'export JAVA_HOME=/opt/java/jdk1.6.0_45' > /etc/profile.d/sun-jdk.sh
$ echo 'export PATH=$JAVA_HOME/bin:$PATH' >> /etc/profile.d/sun-jdk.sh
$ alternatives --install /usr/bin/java java /opt/java/jdk1.6.0_45/bin/java 2
$ java -version

java version "1.6.0_45"
Java(TM) SE Runtime Environment (build 1.6.0_45-b06)
Java HotSpot(TM) 64-Bit Server VM (build 20.45-b01, mixed mode)

If you wish to reconfigure the default java, you can run alternatives as below & choose the appropriate option:

$ alternatives --config java

I hope this helps :)


Read more...

Share Local Directory With Remote Server During RDP Session

Well I have to constantly rdesktop to the remote servers at my workstation and sometimes I have to copy files and folders from my local machine. This post will provide you the steps on how to share files and folders with remote server during rdp session. Normally, your RDP session would start with the following command:

$ rdesktop -g90% your_server

But we wish to do something extra i.e. we need to share our directory with the remote server. The good news is that the rdesktop command supports device redirection using a -r flag which can be repeated.

Your command would look something like below:

$ rdesktop -g90% -r disk:share=/home/samar/scripts myserver

You can then access your share as a drive or media. I hope this helps :)


Read more...

Customizing Jenkins Layout

We use jenkins as our continuous integration server at our workplace and without any doubt, its the best CI tool I've used. We had been thinking of customizing jenkins layout to fit our company and thanks to the plugins developed by people who make jenkins not just another random tool on the internet, but the software WITH awesome community. There are particularly two plugins that seemed to fit our scenario. The first one is Simple Theme Plugin and the second one is Page Markup Plugin.

The later one does allow to add markups to the page but didn't best fit for our scenario. So we decided to use the Simple Theme Plugin. Installing the plugin is straightforward in jenkins. Once the Simple Theme Plugin is installed, a new content box will appear in your Manage Jenkins -> Configure System which will look something like below:

This plugin requires you to specify your own custom .css and .js file. The good thing about jenkins is you can place your own content at the JENKINS_INSTALL_DIR/userContent/ directory and then access it via http://yourbuildserver.tld/jenkins_path/userConent/yourfile.ext. I was working on the windows system where my jenkins install was at C:\.jenkins\ and hence I placed my CSS and image files inside the userContent directory of jenkins install folder. This should not be very difficult on any other systems if you are familiar with jenkins and your OS.

You can grab the jenkins css files from the webapp root directory (I was using tomcat so I grabbed it from inside there) and then edit the css as per your necessity. In my case, I had to change the header style only so my CSS looked something like below:

#top-panel {
  background-size:100% 100%;
  height: 43px;
  }
  
#top-panel td#login-field span a {
    background: none; }
 
#top-panel a {
    background: url("title.png") 0 0 no-repeat;
    display: block;
    width: 107px;
    height: 27px;
    margin: 10px 0 -5px 0px; }
#top-panel td > a img {
      display: none; }

This is all you have to do. Btw, don't fall for the readme.txt inside userContent directory which says: "Files in this directory will be served under your http://server/jenkins/userContent/". Make sure you specify the URL according to your server configuration not according to this specification thus appending "/jenkins" in your URL.


Read more...