can you tell me how to run it every 3o minutes please?

will a script run hourly if i put the script in the /etc/cron.hourly/ folder?

It should do, if there's an entry in your crontab to run all scripts in that directory. For example, in root's crontab under Slackware:

# Run hourly cron jobs at 47 minutes after the hour:
47 * * * * /usr/bin/run-parts /etc/cron.hourly 1> /dev/null

As for running a script every half hour, can you not just change the minute field to */30? I run getmail every minute in this way.

Crontab syntax :
A crontab file has five fields for specifying day , date and time followed by the command to be run at that interval.

* * * * * command to be executed
- - - - -
| | | | |
| | | | +----- day of week (0 - 6) (Sunday=0)
| | | +------- month (1 - 12)
| | +--------- day of month (1 - 31)
| +----------- hour (0 - 23)
+------------- min (0 - 59)

* in the value field above means all legal values as in braces for that column.
The value column can have a * or a list of elements separated by commas. An element is either a number in the ranges shown above or two numbers in the range separated by a hyphen (meaning an inclusive range).
Notes
A. ) Repeat pattern like /2 for every 2 minutes or /10 for every 10 minutes is not supported by all operating systems. If you try to use it and crontab complains it is probably not supported.

B.) The specification of days can be made in two fields: month day and weekday. If both are specified in an entry, they are cumulative meaning both of the entries will get executed .

4. Crontab Example
A line in crontab file like below removes the tmp files from /home/someuser/tmp each day at 6:30 PM.

where can i see the root's crontab?

login as root

and run

from any normal user

thanks. finally see it.

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