Moxa Technologies IA262 Manual do Utilizador descarregar pdf (Página 27)

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

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