This article will teach you on, how to schedule a corn job for executing a script or command or shell script at a particular time every day. As a system administrator, we know the importance of running the routine maintenance jobs in the background automatically. The Linux corn utility will help us to maintain these jobs to run in the background.
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 Any Linux command or script
To see a list of cron jobs which exists on the machine, run the below command –
# crontab -l no crontab for root
To add the new cron job run the below command –
#crontab -e no crontab for root - using an empty one Select an editor. To change later, run 'select-editor'. 1. /bin/ed 2. /bin/nano <---- easiest 3. /usr/bin/vim.basic 4. /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 Specific Time
Add the below example to execute the specified log backup shell script at 11:00 on every day. We can specify the comma-separated value in a field specifies that the script needs to be executed in all the mentioned time.
00 11 * * * /home/backups/scripts/log_backup.sh
Conclusion: At the end of the configuration you are able to run a script or command at a specific time every day, like this we can specify the time for multiple execution with comma separated values.