Working with cron
From Oxxus Wiki
Cron is a daemon which executes commands and scripts automatically at a precise time.
You can modify the crontab with the following command:
crontab -e
-e is a switch for editing crontab
Some other switches are:
- -l for listing active crontabs
- -r for removing a crontab
By default, crontab is modified for a username you are logged in as. You can modify another user's crontab with -u [user] option.
When you have started editing crontab, you need to type in each line cron job you want to be executed.
Sample of the line would be:
0 0 * * * /usr/scripts/checkProcesses
First five characters stand for:
- - minutes
- - hours
- - day in a month
- - day in a week
- - month in a year
The rest of the line contains the command to be executed or the path to the shell script.
In the example above, the script /usr/scripts/checkProcesses is set to be executed every day at 00:00
To set the script to execute every five minutes, you could use the following line:
*/5 * * * * /usr/scripts/checkProcesses
In this example the minute character is extended with /5 which means every fifth minute literally.
Please note that editing crontab will open vi editor and some basic usage of vi editor is: press i to get into insert mode and write the line, and press esc to exit from insert mode when finished.
To record a file, type:
:wq
With : all vi commands start, and wq is for write and quit.
Vi is a very old editor but it's present across all Unix and Linux distributions and it's a default editor used by many applications.
