User`s manual

IA260-261-262 EM-2260 LX User’s Manual Managing Embedded Linux
3-10
Cron—Daemon to Execute Scheduled Commands
Start Cron from the directory /etc/rc.d/rc.local . It will return immediately, so you don’t need to
start it with ‘&’ to run in the background.
The Cron daemon will search
/etc/cron.d/crontab for crontab files, which are named after
accounts in /etc/passwd.
Cron wakes up every minute, and checks each command to see if it should be run in the current
minute. Modify the file
/etc/cron.d/crontab to set up your scheduled applications. Crontab files
have the following format:
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 mode of fixtime.sh
#chmod 755 fixtime.sh
STEP3: Modify /etc/cron.d/crontab file to run fixtime.sh at 8:00 every day.
Add the following line to the end of the 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 in the file /etc/rc.d/rc.local
#/etc/init.d/cron start