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

1. 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

1. 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
   

1. 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`"