On Linux servers, cron can be used to schedule jobs that run commands and shell scripts at fixed times, dates or intervals. It's great for repetitive tasks like backups, downloads and deleting log files.
Set the default editor
Here's how to use the Vi text editor in a one-time session or as the default crontab editor.
Run the export command to set the default editor for the session
Change to user's home directory and edit the user's environment PATH settings (CentOS) to permanently set the user's default editor
Append the following
# User specific aliases and functions export VISUAL=vi export EDITOR=$VISUAL
Activate the change in settings
Each line in a crontab file represents a scheduled job. Each job begins with time parameters in the following sequence:
minute: between 0 and 59.
hour: between 0 and 23.
day: day of month, depends on month.
month: between 1 and 12.
day of week: between 0 and 7, where Sunday can be both 0 or 7.
command: the command to execute.
* any value (placeholder or unused date parameter)
/ step values.
- range of values.
, value list separator.
Run a shell script at 11:00am every day
0 11 * * * sh /home/user/script.sh
Run a shell script every two hours, on the hour
0 */2 * * * sh /home/user/script.sh
Run a shell script every fifteen minutes
*/15 * * * * sh /home/user/script.sh
Run a shell at 11:00am every Tuesday
0 11 * * 2 sh /home/user/script.sh
Make sure the crontab file ends with an empty line
sudo setenforce 0
sudo systemctl status crond check service status
crontab -l list jobs
crontab -e edit jobs
Clear log files
This example has three jobs. Each job runs a different shell script, silences cron error messages and then appends any remaining output to a specific log file.
01 01 * * * /home/ontology.sh > /dev/null 2 >> /home/saf/logs/cron.log
01 01 * * * /home/webapps.sh > /dev/null 2 >> /home/saf/logs/cron.log
01 01 * * * /home/logs.sh > /dev/null 2 >> /home/saf/logs/cron.log
> is for redirect
/dev/null is a black hole for data
2 is the file descriptor for Standard Error (STDERR)
>> append to file