Crontab

·        The cron system is managed by the crondaemon. It gets information about which programs and when they should run from the system's and users' crontab entries. Only the root user has access to the system crontabs, while each user should only have access to his own crontabs.

·        At system startup the cron daemon searches /var/spool/cron/ for crontab entries which are named after accounts in /etc/passwd, it searches /etc/cron.d/ and it searches /etc/crontab, then uses this information every minute to check if there is something to be done. It executes commands as the user who owns the crontab file and mails any output of commands to the owner.

·        You could also use the crontab-l command to display crontabs.

·        Some variables are set, and after that there's the actual scheduling, one line per job, starting with 5 time and date fields. The first field contains the minutes (from 0 to 59), the second defines the hour of execution (0-23), the third is day of the month (1-31), then the number of the month (1-12), the last is day of the week (0-7, both 0 and 7 are Sunday). An asterisk in these fields represents the total acceptable range for the field.

·        Lists are allowed; to execute a job from Monday to Friday enter 1-5 in the last field, to execute a job on Monday, Wednesday and Friday enter 1,3,5.

·        Keep in mind that output of commands, if any, is mailed to the owner of the crontab file. If no mail service is configured, you might find the output of your commands in your local mailbox, /var/spool/mail/<your_username>, a plain text file.

·        $ crontab -e

nocrontab for flash - using an empty one

##This script is to delete files and will run every 55th minute ##

55 * * * * /home/ flash /scripting/delete