Crontabs - Job scheduler explained

Open crontab using below command:

 

crontab -e 

 

Its syntax is like below 

* * * * * command/script to be executed/

# Example of job definition:

 

# .---------------- minute (0 - 59)
# |  .------------- hour (0 - 23)
# |  |  .---------- day of month (1 - 31)
# |  |  |  .------- month (1 - 12) OR jan,feb,mar,apr ...
# |  |  |  |  .---- day of week (0 - 6) (Sunday=0 or 7) OR sun,mon,tue,wed,thu,fri,sat
# |  |  |  |  |
# *  *  *  *  * user-name  command to be executed

Listing of Cronjobs can be done using below command: 

 

crontab -l 

 

 Examples:  

 

1. Take backup every day midnight.

0 0 * * * /my/path/to/script/backup.sh

2. Start mongo server @reboot

@reboot /usr/bin/mongod

3.  Mysql database backup every sunday

* * * * 0 /usr/bin/mysqldump -u root -p{root123} userdb2 &gt; /home/nagaraju/myfile_$(date +\%Y-\%m-\%d).sql&nbsp;&nbsp; #every week on Sunday<br />