Moxa UC-8410A-LX [42/86] Execute scheduled commands with cron

Moxa UC-8410A-T-LX [42/86] Execute scheduled commands with cron

UC-8410A Series Linux Software General Debian Package Usage

5-2

NTP Client

The UC-8410A-LX has a built-in NTP (Network Time Protocol) client that is used to initialize a time request to

a remote NTP server. Use

#ntpdate <this client utility> to update the system time.

ntpdate 192.168.1.97

hwclock –w

Visit http://www.ntp.org

for more information about NTP and NTP server addresses.

192.168.4.127 – PuTTY

moxa@Moxa:~$ sudo ntpdate 192.168.50.33

6 May 03:55:10 ntpdate[4511]: step time server 192.168.50.33 offset 78338115.278119

sec

moxa@Moxa:~$ sudo hwclock -w

moxa@Moxa:~$ sudo hwclock

Tue 06 May 2014 03:56:14 AM UTC -0.846314 seconds

NOTE

Before using the NTP client utility, check your IP and DNS settings to make sure that an Internet connection is

available. Refer to Chapter 2 for instructions on how to configure the Ethernet interface, and see Chapter 4 for

DNS setting information.

Execute Scheduled Commands with cron

The cron daemon reads /etc/crontab to retrieve scripts and other commands to be run at regularly

scheduled times.

The cron daemon wakes up every minute and checks each command listed in the crontab file to see if it should

be run at that time. Whenever cron executes a command, a report is automatically mailed to the owner of the

crontab (or to the user named in the MAILTO environment variable in the crontab, if such a user exists).

Modify the file /etc/crontab to schedule an application. Crontab entries follow the format below:

mm h dom mon dow user command

minute hour date month week user Command

0-59 0-23 1-31 1-12 0-6 (0 is Sunday)

For example, issue the following command if you want to launch a program at 8:00 every day:

#minute hour date month dow user command

* 8 * * * root /path/to/your/program

Every column in a crontab entry must be marked with a character. The asterisk indicates “every possible unit,”

so that setting an asterisk in the day-of-week column will configure cron to run the command on every day of

the week. If you wish to run a command “every X minutes” or “every X hours”, then use the format */X.

Updating System Time and RTC

Take the following steps to use cron to update the system time and RTC:

1. Write a shell script named fixtime.sh and save it to the /home directory.

#!/bin/sh

ntpdate time.stdtime.gov.tw

hwclock –w

exit 0

2. Reset the access permissions for fixtime.sh

moxa@Moxa:~# chmod 755 fixtime.sh

Moxa UC-8410A-LX [42/86] Execute scheduled commands with cron

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