Sunday, June 26, 2016

Car Driving Tips

My title


1.Gear Shifting Tips 
Press clutch pedal fully down and engage the gears slowly .To shift into Reverse gear, stop the car and rest the lever in neutral for 3 seconds

2. A/c Cooling Tips
If the interior is hot open the window  for few minutes, Blower on in fresh air mode, close the window Switch A/c on ,Set to minimum temperature  using recirculation mode

3. Fuel saving Tips Maintain recommended tire pressure,  Avoid frequent gear change, sudden acceleration  and braking , Avoid half clutch ride.

4.Windows Defog Tips
Change air intake to fresh air mode from recirculation, set air flow to defrost, turn on A/c, set the fan speed and temperature as required

Tuesday, June 7, 2016

6 Stages of Linux Boot Process (Startup Sequence)





Press the power button on your system, and after few moments you see the Linux login prompt.

Have you ever wondered what happens behind the scenes from the time you press the power button until the Linux login prompt appears?
The following are the 6 high level stages of a typical Linux boot process.

1. BIOS

  • BIOS stands for Basic Input/Output System
  • Performs some system integrity checks, booting Linux begins in the BIOS at address 0xFFFF0. The first step of the BIOS is the power-on self test (POST).
  • Searches, loads, and executes the boot loader program.
  • It looks for boot loader in floppy, cd-rom, or hard drive. You can press a key (typically F12 of F2, but it depends on your system) during the BIOS startup to change the boot sequence.
  • Once the boot loader program is detected and loaded into the memory, BIOS gives the control to it.
  • So, in simple terms BIOS loads and executes the MBR boot loader.

2. MBR

  • MBR stands for Master Boot Record.
  • It is located in the 1st sector of the bootable disk. Typically /dev/hda, or /dev/sda
  • MBR is less than 512 bytes in size. This has three components 1) primary boot loader info in 1st 446 bytes 2) partition table info in next 64 bytes 3) mbr validation check in last 2 bytes.
  • It contains information about GRUB (or LILO in old systems).
  • So, in simple terms MBR loads and executes the GRUB boot loader.

3. GRUB

  • GRUB stands for Grand Unified Bootloader.
  • If you have multiple kernel images installed on your system, you can choose which one to be executed.
  • GRUB displays a splash screen, waits for few seconds, if you don’t enter anything, it loads the default kernel image as specified in the grub configuration file.
  • GRUB has the knowledge of the filesystem (the older Linux loader LILO didn’t understand filesystem).
  • Grub configuration file is /boot/grub/grub.conf (/etc/grub.conf is a link to this). The following is sample grub.conf of CentOS.
  • #boot=/dev/sda default=0 timeout=5 splashimage=(hd0,0)/boot/grub/splash.xpm.gz hiddenmenu title CentOS (2.6.18-194.el5PAE) root (hd0,0) kernel /boot/vmlinuz-2.6.18-194.el5PAE ro root=LABEL=/ initrd /boot/initrd-2.6.18-194.el5PAE.img
  • As you notice from the above info, it contains kernel and initrd image.
  • So, in simple terms GRUB just loads and executes Kernel and initrd images.

4. Kernel

  • Mounts the root file system as specified in the “root=” in grub.conf
  • Kernel executes the /sbin/init program
  • Since init was the 1st program to be executed by Linux Kernel, it has the process id (PID) of 1. Do a ‘ps -ef | grep init’ and check the pid.
  • initrd stands for Initial RAM Disk.
  • initrd is used by kernel as temporary root file system until kernel is booted and the real root file system is mounted. It also contains necessary drivers compiled inside, which helps it to access the hard drive partitions, and other hardware.

5. Init

  • Looks at the /etc/inittab file to decide the Linux run level.
  • Following are the available run levels
    • 0 – halt
    • 1 – Single user mode
    • 2 – Multiuser, without NFS
    • 3 – Full multiuser mode
    • 4 – unused
    • 5 – X11
    • 6 – reboot
  • Init identifies the default initlevel from /etc/inittab and uses that to load all appropriate program.
  • Execute ‘grep initdefault /etc/inittab’ on your system to identify the default run level
  • If you want to get into trouble, you can set the default run level to 0 or 6. Since you know what 0 and 6 means, probably you might not do that.
  • Typically you would set the default run level to either 3 or 5.

6. Runlevel programs

  • When the Linux system is booting up, you might see various services getting started. For example, it might say “starting sendmail …. OK”. Those are the runlevel programs, executed from the run level directory as defined by your run level.
  • Depending on your default init level setting, the system will execute the programs from one of the following directories.
    • Run level 0 – /etc/rc.d/rc0.d/
    • Run level 1 – /etc/rc.d/rc1.d/
    • Run level 2 – /etc/rc.d/rc2.d/
    • Run level 3 – /etc/rc.d/rc3.d/
    • Run level 4 – /etc/rc.d/rc4.d/
    • Run level 5 – /etc/rc.d/rc5.d/
    • Run level 6 – /etc/rc.d/rc6.d/
  • Please note that there are also symbolic links available for these directory under /etc directly. So, /etc/rc0.d is linked to /etc/rc.d/rc0.d.
  • Under the /etc/rc.d/rc*.d/ directories, you would see programs that start with S and K.
  • Programs starts with S are used during startup. S for startup.
  • Programs starts with K are used during shutdown. K for kill.
  • There are numbers right next to S and K in the program names. Those are the sequence number in which the programs should be started or killed.
  • For example, S12syslog is to start the syslog deamon, which has the sequence number of 12. S80sendmail is to start the sendmail daemon, which has the sequence number of 80. So, syslog program will be started before sendmail.

There you have it. That is what happens during the Linux boot process.

Monday, June 6, 2016

Tennyson: 10 quotes

1. "Theirs not to reason why, theirs but to do and die."
From The Charge of the Light Brigade, the poem tells of the famous and brutal military disaster in the Crimean war. Nowadays, the saying is often used in the workplace and encourages one to press on no matter what the task.

2. "Tis better to have loved and lost than never to have loved at all."
The saying, which is most commonly used to console someone after a break-up, tugs at the heartstrings and serves as a comfort for those with tumultuous love lives.

3. "If I had a flower for every time I thought of you... I could walk through my garden forever."
This romantic sentiment may sound like the message on a greeting card, but it now makes its way into wedding speeches and toasts.

4."Knowledge comes, but wisdom lingers."
This simple phrase insinuates that knowledge is pieces of information that aren't always retained, but wisdom is a deeper understanding based on life experiences.

5. "A lie that is half-truth is the darkest of all lies."
"His poems are full of concentrated lines and phrases that linger in the mind because of their shape, their sound, their mouthability. They ask to be read and then re-read," explains Douglas-Fairhurst.

6. "I am a part of all that I have met."
In Ulysses, a dramatic monologue detailing the Greek hero's escapades, Tennyson succinctly offers his view that humans are shaped by a combination of all life's experiences.

7. "Better not be at all than not be noble."
In The Princess, Tennyson tells the story of a heroine who refuses to marry, and instead ends up founding a women's university. After a long pursuit and a series of trials, the princess eventually falls in love with a prince.
Tennyson's musing on nobility suggests that there is nothing worse than poor character.

8. "No man ever got very high by pulling other people down. The intelligent merchant does not knock his competitors. The sensible worker does not knock those who work with him. Don't knock your friends. Don't knock your enemies. Don't knock yourself."
This is the kind of maxim that The Office's David Brent might consider framing.
"Often he composed individual lines before working out where to fit them into a poem, and just as he sometimes treated these lines like pieces of lego he could build up into bigger blocks of writing," according to Douglas-Fairhurst.

9. "Who are wise in love, love most, say least."
In Merlin and Viviene, Tennyson tells the passionate love story of a woman seducing a man.
In this particular line of the poem, Tennyson suggests that someone who is in love should show love, not just vocalise their admiration.

10. "Nor is it wiser to weep a true occasion lost, but trim our sails, and let old bygones be."

"Many of Tennyson's poems are concerned with memory - what we should hold onto from the past, and what we should abandon," says Douglas-Fairhurst. "His best poems don't just describe the workings of memory - they also enable it by making themselves so memorable.