User`s manual

UC-7400-LX Plus User’s Manual Managing Embedded Linux
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Crontab is located in the /etc/cron.d directory. Modify the file /etc/cron.d/crontab to set up your
scheduled applications. Crontab has the following format:
mm h dom mon dow user command
min hour date month week user command
0-59 0-23 1-31 1-12 0-6 (0 is Sunday)
The following example demonstrates how to use Cron.
How to use cron to update the system time and RTC time every day at 8:00.
STEP1: Write a shell script named fixtime.sh and save it to /home/.
#!/bin/sh
ntpdate time.nist.gov
hwclock –-systohc
exit 0
STEP2: Change the mode of fixtime.sh
#chmod 755 fixtime.sh
STEP3: Modify the file /etc/cron.d/crontab to run fixtime.sh at 8:00 every day.
Add the following line to the end of crontab:
* 8 * * * root/home/fixtime.sh
STEP4: Enable the cron daemon manually.
#/etc/init.d/cron start
STEP5: Enable cron when the system boots up.
Add the following line to the file /etc/init.d/rc.local
#/etc/init.d/cron start
By default, cron service is disabled on boot. To enable cron service, please refer to the section
“Enabling and Disabling Daemons” in this chapter.