Scheduling Cronjobs with Multiple Examples(Automation)

cronjob scheduling is possible using crontab command and each and every user crontab is separate

# crontab -e   = To edit cronjob schedule
# crontab -l = To list scheduled cronjobs
# crontab -r = To remove all cronjobs in single attempt

whenever you schedule a cronjob with particular user the same cronjob will run using same user, ensure user is having execution permission to the user.

Know crontab fields and its values

[root@server ~]# cat /etc/crontab
SHELL=/bin/bash
PATH=/sbin:/bin:/usr/sbin:/usr/bin
MAILTO=root

# For details see man 4 crontabs
# 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

Scheduling cronjobs to run @every minute

To run cronjob yet every one minute first field is minutes, first field we can right with separated by comma. below three examples we can use to schedule a cronjob to run every minute.

# crontab -e

* * * * * sh /scripts/everyminute.sh
1,2,3,4,5,6,7,8,9,10......60 * * * * sh /scripts/everyminute.sh
*/1 * * * * sh /scripts/everyoneminute.sh

Scheduling cronjobs to run @every 5 minutes

below two examples to schedule cronjob for every 5 minutes, again we have to make use of first field to run script @every 5 minutes because first field is minutes
```
 */5 * * * * sh /scripts/testscript.sh
 5,10,15,20,25,30,35,40,45,50,55,0 * * * * sh /scripts/testscript.sh
```

Scheduling cronjobs to run @every 30 minutes if we want monitoring our file system @every 30 minutes using shell script you can do using below
```
 * /30   * sh /scripts/FS-Monitoring.sh
 or
 0,30 * * * * sh /scripts/FS-Monitoring.sh
```
1. Scheduling cronjobs to run @every hour
```
 0 */3 * * * sh /scripts/cronjob-every-3hours.sh
 or
 * 0,3,6,9,12,15,18,21 * * * sh /scripts/cronjob-every-3hours.sh
```
  1. Scheduling cronjobs to run @every day Or once in a day
```
 59 23 * * * sh /scripts/daily-report.sh
 or
 @daily sh /scripts/daily-report.sh
```
    1. Schedule cronjobs to run every alternate day
```
 0 * * * 0,2,4,6 sh /scripts/every-alternate-day.sh
```
      Run cronjob first and Second Saturday of the month
    2. ```
     0 1 1-7,15-21 6 /scripts/every-first-second-sat.sh
```
  9. Cronjob for every week
  
  to schedule a cronjob to run @every week we can make use of week of the day 5th field in crontab
```
     0 0 * * 0 sh /scripts/every-week.sh
```
  OR
  
  we can also make use of special schedule
```
     @weekly sh /scripts/every-week.sh
```
  10. Run cronjob @every month 1st date
  
  Here we have to use day of the month, field 3
```
     0 0 1 * * sh /scripts/every-mont-1st.sh
```
  OR
```
     @monthly sh /scripts/every-month.sh
```
  11. Schedule cronjob to run once in a year
  
  I would like to schedule an cronjob to say happy new year to all the employees on midnight of every year 31st Dec.
```
     59 23 31 12 *  echo "Happy New Year to All"
```
  OR
```
     @yearly echo "Happy New Year"
```
  12. I want to run a cronjob @every server reboot
  
  every time whenever server is rebooted i would like to get notification. We can make use of special schedule
```
     @reboot echo Server Rebooted | mail -s "Server Rebooted `hostname`"
```

Scheduling Cronjobs with Multiple Examples(Automation)

Know crontab fields and its values

Scheduling cronjobs to run @every minute

Run cronjob first and Second Saturday of the month

9. Cronjob for every week

10. Run cronjob @every month 1st date

11. Schedule cronjob to run once in a year

12. I want to run a cronjob @every server reboot