Add Cron Job on Linux

Edit the cron file

Cron jobs are stored in a file.
Edit that file as

crontab -e

No restart of cron service required after making changes to the cron file.

Cron Syntax

1 2 3 4 5 /path/to/command arg1 arg2

or

1 2 3 4 5 /root/backup.sh

Where

1: Minute (0-59)
2: Hours (0-23)
3: Day (0-31)
4: Month (0-12 [12 == December])
5: Day of the week(0-7 [7 or 0 == sunday])
/path/to/command – Script or command name to schedule

Examples

Use crontab.guru website.

“At minute 30 of the day.”

30 * * * *

“At every 30th minute.”

*/30 * * * *

“At 04:05 on Sunday.”

5 4 * * sun

“At 22:00 on every day-of-week from Monday through Friday.”

0 22 * * 1-5

Operators

Operator	Meaning	Example
*	Every possible value.	* in hour means every hour of the day
,	Comma separated list of values	2,4 in hour field means 2nd and 4th hour of the day
-	Range of values	9-11 days is equivalent to 9,10,11 with comma operator
/	Step value, used to skip by the step value	Usage with range: 0-10/3 means every third hour in that range. Can be used with * like */2 means every second hour of the day

Check Service

sudo service cron status

Output to file

Update the cron job as below:

* * * * * /path/to/script.sh >> /path/to/logfile/output.log 2>&1

2>&1 in the end also redirects error stream to the file. For more info read this.

Cron logs

cat /var/log/syslog | grep cron