DA-660-8/16-LX User’s Manual
Managing Embedded Linux
3-9
Copy the example shell script
fixtime
to directory
/etc/init.d
, and then use
chmod 755 fixtime
to
make the shell script executable. Next, use the vi editor to edit the file
/etc/inittab
. Add the
following line to the bottom of the file:
ntp : 2345 : respawn : /etc/init.d/fixtime
Use the command
#init q
to re-init the kernel.
Cron—Daemon to Execute Scheduled Commands
Start Cron from the directory /
etc/rc.d/rc. local
. The cron process will return immediately, so you
do not 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:
mm h dom
mon dow
user
command
month 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 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/init.d/rc.local
#/etc/init.d/cron start
