Adjust the CentOS system time and time zone to synchronize with the Internet

The procedure is as follows: 1. change the time zone # cp/usr/share/zoneinfo/Asia/Shanghai/etc/localtime to Dongba district of China # vi/etc/sysconfig/clockZONE = & quot; asia/Shanghai & quot; UTC = falseARC = false 2,

The procedure is as follows:

1. modify the time zone
# Cp/usr/share/zoneinfo/Asia/Shanghai/etc/localtime
Change to UTC + 8 in China
# Vi/etc/sysconfig/clock
ZONE = "Asia/Shanghai"
UTC = false

ARC = false

 

2. configure a new time
Date setting:
# Date-s 2013/09/26

Time setting:

# Date-s 11:47:06

# Date-s "12:00:00"

# Date-s "12:00:00 20131206"

# Date-s "12:00:00"

# Date-s "20131206 12:00:00"

Date indicates the OS time displayed.

Clock is the time when the Bios is displayed.

View hardware Time (BIOS ):
Hwclock [-rw]
-R: view the current BIOS time. the default value is-r.

-W: write the current linux system time to the BIOS

-S (systohc): adjust the hardware time to be the same as the current system time

# Hwclock-s:

# Hwclock-w: update linux internal time to bios/cmos

When we finish the Linux time, we also need to use hwclock-w to update the BIOS time, because every time the system is started, the BIOS will read the time again, therefore, BIOS is an important time basis.
# Hwclock

Thursday, September 26, 2013 10 seconds-1.002805 seconds

After the system time (date) is modified, the BIOS clock must be synchronized to force the system time to be written to CMOS:

# Clock-w or # hwclock-w

 

3. implement Internet time synchronization (skip the above two steps here)
Method 1. automatic network calibration at startup:
Vi/etc/rc. d/rc. local

/Usr/sbin/ntpdate-u 192.168.0.2 192.168.0.3 192.168.0.4;/sbin/hwclock-w

The following ip addresses correspond to hosts that require the same time synchronization in the LAN.

 

Method 2. set the scheduled task
The crontab format is as follows:
SHELL =/bin/bash
PATH =/sbin:/bin:/usr/sbin:/usr/bin
MAILTO = root
HOME =/

# For details see man 4 crontabs

# Example of job definition:
#. ---------------- Minute (0-59)
# |. ----------- Hour (0-23)
# |. ---------- Day of month (1-31)
# |. ------- Month (1-12) OR jan, feb, mar, apr...
# |. ---- Day of week (0-6) (Sunday = 0 or 7) OR sun, mon, tue, wed, thu, fri, sat
# |

# ***** User-name command to be executed

 

You can also set crontab to schedule a task in either of the following ways:

1. write it in/etc/crontab
Code:
0 12 *** root ntpdate 210.72.145.44
Synchronize time with China National Time Service Center at every day
Of course, the premise is that
# Yum-y install ntpdate

The code is
0 12 *** root ntpdate asia.pool.ntp.org
2. run the crontab-e command.
Crontab-e
0 12 *** root ntpdate asia.pool.ntp.org; hwclock-w

 

Manual and time server calibration time:

1. first disable the ntpd service:

# Service ntpd stop

2. then calibrate with the time server:

# Ntpdate asia.pool.ntp.org

3. BIOS synchronization time:

# Hwclock-w

4. After calibration, enable ntpd service

# Service ntpd start