Pattern Based Database GRANT In MySQL

At our workplace, we need to manage database access for different teams and rather than adding another grant on the addition of new database, I've been following a pattern based database access grants in MySQL.

We let different teams work on replicas of same database and hence append the terms such as _dev and _qa as the database prefix. And, we define GRANTS based on these patterns. An example would be something like below:

GRANT ALL ON `%\_dev`.* TO 'user'@'%' IDENTIFIED BY 'password' WITH GRANT OPTION;

I hope this proves useful for some of you guys :)


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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 :)


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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 :)


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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 :)


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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 :)


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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 :)


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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 :)


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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 :)


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