LinuxNetMag
Just on time: VCron, Kcrontab
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LinuxNetMag #3

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printer-version


 
Uhr
Cron and at make it possible to start any command at a given time. 
However, many users touch them as little as possible since the configuration is terrifying, even by Linux standards, although the programs are very useful. Two programs may help.



 
The Crontab

At and Crontab start programs at a given time. At is designed to start something once at the time desired while cron handles calls which you want to be executed on a regular basis. For example if you want to have your artificial web server statistics delivered every 30 minutes, cron is the right program for you. To configure cron, a text file in the directory /var/cron/tabs is used where every user gets his/her own file. In this file the command that you want to execute and the starting time are saved. You should not edit this file on your own but rather use the program crontab. This one is started with the command

>> crontab -e
A text editor enables you to edit the file. Especially older distributions use vi as the standard editor and the cryptic commands are often a mystery to many users. Use the variable EDITOR to choose your favorite editor (e.g. export EDITOR="/path/xedit"). However, without your reading the man pages as well, the configuration still should be impossible.
It was obvious that under these circumstances some user would develop a graphical frontend for cron. 
 
 
VCron

Although using TCL/TK8.0, the frontend looks a little bit old but it is still quite useful. The program offers the configuration of cron jobs and also the call of at commands. 
Screenshot
You are able to choose the time, the months and the days by clicking on the appropriate check-boxes. This way no mistakes can be made, but it may be tough if you want to start something every two minutes. In this case you have to click 30 times to get through the different menues. If you configured it via crontab -e a simple 0-59/2 in the text editor would be enough. This is not very obvious but much faster. A button with the command "every X minutes" might have made some sense.
In addition, this program supports a lot of languages and an online help (although this one is rather spartan).
The commands which have to be executed can be entered via keyboard or by selecting them with a file browser if it is just one call.
We feel that a function for variables might have been of some use. The default setting makes cron send a mail to the owner of crontab if the command has not correctly been executed. To suppress this you have to add 

MAILTO=""
into crontab but with Vcron this is not possible.
This program convinces nevertheless especially all those users who do not have KDE running on their computer and therefore cannot use Kcrontab. The few times I normally use crontab in a year I do not want to read the crontab-manpages every time. Furthermore, with a size of only 32kB Vcron is a small program.
 
 
Kcrontab

The second candidate for the configuration of crontab is Kcrontab. The name already tells us that it is a program for KDE. You can use it with other windowmanagers but the KDE basis packages have to be installed to use e.g. the online help. The frontend looks much better and also the help is bigger than for Vcron. The program does not support the configuration of at jobs, just cron. 

Screenshot: kcrontab
A big advantage is the possible configuration of variables. A button exists to execute a command every day or month but we miss the ability to execute something every X minutes. The time is entered by keyboard but an entry like 0-59/2 is not supported because the text field does not support special characters just numbers smaller than 60.
To every entry a comment can be added but the command cannot be chosen with a file browser.
Kcrontab does not have a homepage but you can find it at the KDE homepage.
 

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