SHELL

how to start cron job

#Red Hat / CentOs:

service crond start

#or

/etc/init.d/crond start

#Ubuntu:

sudo service cron start

#or

sudo /etc/init.d/cron start

create cron job from command line

#write out current crontab
crontab -l > mycron
#echo new cron into cron file
echo "00 09 * * 1-5 echo hello" >> mycron
#install new cron file
crontab mycron
rm mycron

setup cron job

# to list all crontab content (including scheduled jobs)
crontab -l

# to edit crontab file
crontab -e

# once you have finished adding tasks, save the file and exit
# the cron daemon will read and execute the instructions provided

How CRON jobs works

# Use the hash sign to prefix a comment
# +---------------- minute (0 - 59)
# |  +------------- hour (0 - 23)
# |  |  +---------- day of month (1 - 31)
# |  |  |  +------- month (1 - 12)
# |  |  |  |  +---- day of week (0 - 7) (Sunday=0 or 7)
# |  |  |  |  |
# *  *  *  *  *  command to be executed
#-----------------------------------------------------------