This article we will teach you to schedule a cron job to be executed at a specific time in a day.
General Syntax of a Cron Job
MIN HOUR Day of month Month Day of Week Command 0-59 0-23 1-31 1-12 0-6 linux command or script
To see the list of cron jobs which exists on the machine, run the below command
# crontab -u test1 -l no crontab for test1
To Add the New Cron Job to Test1 User, run the below Command –
#crontab -u test1 -e no crontab for test1 - using an empty one Select an editor. To change later, run 'select-editor'. /bin/ed /bin/nano <---- easiest /usr/bin/vim.basic /usr/bin/vim.tiny Choose 1-4 :2 # Edit this file to introduce tasks to be run by cron. # # Each task to run has to be defined through a single line # indicating with different fields when the task will be run # and what command to run for the task # # To define the time you can provide concrete values for # minute (m), hour (h), day of month (dom), month (mon), # and day of week (dow) or use '*' in these fields (for 'any').# # Notice that tasks will be started based on the cron's system # daemon's notion of time and timezones. # # Output of the crontab jobs (including errors) is sent through # email to the user the crontab file belongs to (unless redirected). # # For example, you can run a backup of all your user accounts # at 5 a.m every week with: # 0 5 * * 1 tar -zcf /var/backups/home.tgz /home/ # # For more information see the manual pages of crontab(5) and cron(8) # # m h dom mon dow command
Scheduling a Job for a different user
The basic usage of cron is to execute a job in a specific time as shown below. This will execute the Full backup shell script (backup_files.sh) on Every day at 9 AM and 6 PM
00 09-18 * * * /home/test1/backup_files.sh
00 – 00th Minute 09-18 – 09 AM & 06:00PM * --Every day of the Month * -- Every Month. * --Every day of the week
At the end of the configuration, you should be able to run a script or command at a specific time every day from a particular user. Like this, we can specify Cron jobs to any user. These type of Crons are generally used to take a backup of the users data such as Desktop, Downloads etc.