Archive for January, 2008

Friends… Many of you might have heard about the Cron Job. Specially those with some knowledge of Linux must have heard about it.
We will discuss about this CRON Funda today-

Linux O.S.

First of all, What is a Cron Job?

On Unix systems, cron is used for automating tasks. Instead of getting out of bed at 3 A.M. to run a command that can be anything from backing up a drive, or a command that deletes old files, you can use cron to schedule those tasks.

There is no actually program called “cron”. There are however, the program “crontab” and the daemon “crond”. By running the “crontab” program, you can enter commands in a text file, and they will automatically be saved in the /var/spool/cron/ directory. For example my entries (for user shruti) would be in /var/spool/cron/shruti. The crond daemon reads the files regularly and executes the commands at the time they are scheduled for.

Say for some reason, you want to check the output of the command ‘w’ every hour to see who’s on.

How to use Cron?

The setup of a crontab file is as follows:
There are six fields:

1. minute (0-59)
2. hour (0-23)
3. day of month (1-31)
4. month (1-12, or name such as jan, feb, etc)
5. day of week ( 0-6(6 = Sunday) or name such as mon, tue,etc)
6. command to run

So an example could be this:

0 1 24 5 0 w

That will run a command at 1:00AM on Monday, May 24th. Now that gets a bit cyptic. To make it a little better, this would also work:

0 1 24 may mon w

But what if you want it to run every hour, regardless of date? An “*” means that that field doesn’t matter, or do the command no matter what is in those fields. So to run our ‘w’ command every hour, the command would be this:

0 * * * * w

Which means that it runs everyday, every hour at the 0 minute mark, meaning the beginning of the hour.

A bunch of different variations of fields can be generated like this. For instance, say you wanted a command to run every 2 hours. You could specify the “hour” field as this:
*/2 Which would run at 2,4,6,8, etc…

You can also use commas to specify more than one time. For instance, say you want to run it at half past the hour, and a quarter of. You could specify the minute field as this: 30,45

If you use a dash between two values, it will include everything in between them. An example of this would be to run a command everyday for the first week of a month. The day of the month field would be this: 1-7

So to have the commmand run every 2 hours, at half past and a quarter of, and run for the first 7 days of a month. We would have this:

30,45 */2 1-7 * * w

To save the output to a text file, such as ‘wholog’ you could write the command like this:

0 * * * * w >> /home/shruti/wholog

Now by default, you will be emailed the output as well, so to avoid this, add this to the command:

0 * * * * w >> /home/shruti/wholog 2>&1

Note: root can edit other users crontabs like this: ‘crontab -e -u username’
A nice little trick is to setup a directory with a bunch of scripts you want run at a certain time, such as every hour, then make this entry in your crontab:

0 * * * * run-parts /home/shruti/hour.cron/

Or something to that effect. That command will run everything in the /home/shruti/hour.cron/ directory. /etc/crontab shows an example of this so you can check that out to see it in action.

Hope this helps you to understand a brief concept of Cron Job.
Your suggestions and comments will be gratefuly acknowledged.

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A young man was getting ready to graduate college. For many months he had admired a beautiful sports car in a dealer’s showroom, and knowing his father could well afford it, he told him that was all he wanted.

As Graduation Day approached, the young man awaited signs that his father had purchased the car. Finally, on the morning of his graduation his father called him into his private study. His father told him how proud he was to have such a fine son, and told him how much he loved him. He handed his son
a beautiful wrapped gift box.

Curious, but somewhat disappointed the young man opened the box and found a lovely, leather-bound Bible. Angrily, he raised his voice at his father and said, “With all your money you give me a Bible?” and stormed out of the house, leaving the holy book.

Many years passed and the young man was very successful in business.He had a beautiful home and wonderful family, but realized his father was very old, and thought perhaps he should go to him. He had not seen him since that graduation day. Before he could make arrangements, He received a telegram telling him his father had passed away, and willed all of his possessions to his son. He needed to come home immediately and take care things.

When he arrived at his father’s house, sudden sadness and regret filled his heart.
He began to search his father’s important papers and saw the still new Bible, just as he had left it years ago. With tears, he opened the Bible and began to turn the pages. As he read those words, a car key dropped from an envelope taped behind the Bible.

It had a tag with the dealer’s name, the same dealer who had the sports car he had desired. On the tag was the date of his graduation, and the words…PAID IN FULL.

How many times do we miss God’s blessings because they are not packaged as we expected?

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Your resume is not only a piece of paper having your educational qualification, your interests and hobbies.
It’s the medium which delivers information about you before you can elaborate on them.
A well formatted resume can make a big difference in a Fresher’s career. As for the recruiter
“First impression is the last impression”. The resume showcases our expertise, skills & Project Experience
we are possessing and a right resume will reflect the right kind of job profile the person is handling.

Gone are the days of typical oldie format resume where we used to just copy n paste our contents in it 🙂
Managing all your information in a resume is a Pain !!!
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Friends… today I am going to write about some axioms of the Software Testing.
First of all the word “axiom” – It means a self evident or universally recognized truth.
An established rule/principle or law.

We should always keep in mind one thing as NEVER say that “The Software (Product) is tested completely!” Followed by it as “There are no BUGS in it!” These kind of statements will definitely result in many harsh issues. See “To err is human!” No entity in this world will be without defects or bugs!
So avoid using the above mentioned 2 terms for the S/W Product.

Following are some Software Testing Axioms –

  • It is impossible to test the program completely.
  • Software Testing is Risk based exercise.
  • Testing can’t show the bugs that doesn’t exist.
  • The more bugs you find, the more bugs are there.
  • Not all the bugs you find will be fixed.
  • Product specifications are never fixed.

Kindly let me know your views about these articles.

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“Software Testing” is a process used to measure the quality of the developed software.

The recent revolution in how the S/W is created comes not from Programming language or Code organisation but from how Testing & QA (Quality Assurance) are accomplished.

Usually quality is constrained in such topics as Correctness, Completeness, Security.
There are some other factors too such as, Capability, Relibility, Compability, Efficiancy, Portability, Maintainability and Usability as specified by ISO Standard under ISO 9126.

In my view, Software Testing is not merely finding the bugs or defects in the Software, but it is completely dedicated to the descipline of evaluating the quality of Software.
Software can not be shipped to the customer, unless it is verified by QA Team.

I found many people confused with Validation & Verification. There is a bias of Views between the order of Validation & Verification. Some say that Validation comes before Verification & viceversa.

In my view, Verification comes before Validation.

Verification – In Verification, we first verify that “Have we built the Software right?” It also can be called as the Specification about the S/W.

Validation – In Validation, we can check “Have we built the right Software?” We can call it like whether our developed product is upto the level to fulfil Customer requirements.

So these were some of the Basic Fundas just to clearify the curiosity about what exactly Software Testing & Quality Assurance is!

I will get back to you soon with some more stuff about the “Software Testing” 🙂

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