Sunday, April 25, 2010

Automating Your Job, The CRON Way!

Often you require to do some stuff periodically like backups or maintenance work. It might be a bit difficult if you have to do it manually every time. You have to have a working net connection if you are doing it remotely or you need to be physically present in front of your computer system. Then you have to repeat certain tasks which you do every day. Won't it be nice if you could just put everything in a simple script that could run automatically every time. CRON comes to your rescue here. CRON is nothing but a text file consisting of the path of scripts to be executed and the time according to which it'll be executed. First of all let me tell you some of the most general commands for setting up a cron table.

crontab -e --> Edit your crontab file.
crontab -l --> Show your crontab file.
crontab -r --> Remove your crontab file.
crontab -v --> Display the last time you edited your crontab file

There is a fixed format for the way an entry has to be made in a cron file. I found an interesting way of showing it here which I am replicating.

* * * * * command to be executed
- - - - -
| | | | |
| | | | +----- day of week (0 - 6) (Sunday=0)
| | | +------- month (1 - 12)
| | +--------- day of month (1 - 31)
| +----------- hour (0 - 23)
+------------- min (0 - 59)

You can also use special entries. Below is a list for them:

Entry          Description             Equivalent To

@reboot  Run once, at startup.  None

@yearly  Run once a year  0 0 1 1 *

@annually  (same as @yearly)  0 0 1 1 *

@monthly  Run once a month  0 0 1 * *

@weekly  Run once a week  0 0 * * 0

@daily          Run once a day          0 0 * * *

@midnight  (same as @daily)  0 0 * * *

@hourly  Run once an hour  0 * * * *

A sample cron file looks like this.

Monday, April 5, 2010

Git For Newbies

Note: This is not a complete guide for git. It will just help you getting started and using smoothly.


Git is a versioning system. It is an ideal tool for managing projects, revisions and stuff like that. Anyone who wants to contribute can clone the code repository, make the changes or add some code and request for merge. This way bug fixes can be done and new features can be added. Gitorious provides open source infrastructure for hosting open source projects that use Git. The central entity in Gitorious is the project, which contains one or more top-level repositories and any repositories managed by the project's contributors.

Cloning A Repository on

We will use's hosted git for example. First of all you need to register yourself with which is a straight forward step. We are going to use ownCloud, a KDE project, for illustration. Next, go to and click on "Clone this repository on Gitorious" from the right sidebar. Congrats! you have created a clone for yourself.

Cloning A Repository On Your Local Machine

We have to do this the hard way. I am considering the Ubuntu Linux in my mind. First of all we need to install git. For that fire the following command
sudo apt-get install git-core

Once you get the git on your system, let us now create the clone. For that fire:
git clone git://

Now that you have the code, you can start with the bug-fixes and contribute code.

Commit To Local Git

After you make the changes to the code or add some file, you'll need to commit that to your local git repo. If you have added some files then you have to tell git to track the new files by using the following command:
git add file-name.

Once the files are added then you can commit to the git repo by firing the following command:
git commit -a

You'll be presented with a file where you have to describe the changes you made. Keep it short and to the point.

Pushing To Gitorious

Now you can push the changed repository to the repo by:
git push master

This will push the repo from your system to Now request a merge from the right sidebar. Someone will look at your request and your work will be added to the main repo if found fit.