最近虚拟化服务器出现时钟同步异常:定时同步,但发现时间比个人电脑时间相差10几个小 时。看了下鸟哥的私房菜,觉得没太大问题,于是决定测试NTP服务以排查问题。因网络限 制,无法连接到互联网,就采用其中的一台虚拟机作为NTP服务器,并以本机时间为准。测 试后才知道原来是系统安装时没有选择时区(默认为美国纽约),而使用的NTP服务器时区 为中国,所以导致虚拟化服务器时间相差13个小时。

从这次经历,再次得到一些经验教训:

  • 安装Linux时注意选择合适的时区;
  • 仔细阅读官方文档,这些才是最权威的文档;
  • 结合理论进行测试,绝知此事要躬行;
  • 要掌握一个理论,不是一朝一夕之事;

搭建NTP服务器

主要配置

启用本机时钟作为NTP基准时间,主要需取消注释server 127.127.1.0 # local clockfudge 127.127.1.0 stratum 10

完整配置如下:

[[email protected] ~]# cat /etc/ntp.conf
# For more information about this file, see the man pages
# ntp.conf(5), ntp_acc(5), ntp_auth(5), ntp_clock(5), ntp_misc(5), ntp_mon(5).

driftfile /var/lib/ntp/drift

# Permit time synchronization with our time source, but do not
# permit the source to query or modify the service on this system.
#restrict default kod nomodify notrap nopeer noquery
#restrict -6 default kod nomodify notrap nopeer noquery

# Permit all access over the loopback interface.  This could
# be tightened as well, but to do so would effect some of
# the administrative functions.

# Hosts on local network are less restricted.
restrict 192.168.1.0 mask 255.255.255.0 nomodify notrap

# Use public servers from the pool.ntp.org project.
# Please consider joining the pool (http://www.pool.ntp.org/join.html).
#server 0.centos.pool.ntp.org
#server 1.centos.pool.ntp.org
#server 2.centos.pool.ntp.org

#broadcast 192.168.1.255 autokey	# broadcast server
#broadcastclient			# broadcast client
#broadcast 224.0.1.1 autokey		# multicast server
#multicastclient 224.0.1.1		# multicast client
#manycastserver 239.255.254.254		# manycast server
#manycastclient 239.255.254.254 autokey # manycast client

# Undisciplined Local Clock. This is a fake driver intended for backup
# and when no outside source of synchronized time is available. 
server	127.127.1.0	# local clock
fudge	127.127.1.0 stratum 10	

# Enable public key cryptography.
#crypto

includefile /etc/ntp/crypto/pw

# Key file containing the keys and key identifiers used when operating
# with symmetric key cryptography. 
keys /etc/ntp/keys

# Specify the key identifiers which are trusted.
#trustedkey 4 8 42

# Specify the key identifier to use with the ntpdc utility.
#requestkey 8

# Specify the key identifier to use with the ntpq utility.
#controlkey 8

# Enable writing of statistics records.
#statistics clockstats cryptostats loopstats peerstats

开启服务

开启ntp服务

[[email protected] ~]# service ntpd restart
Shutting down ntpd:                                        [  OK  ]
Starting ntpd:                                             [  OK  ]

注意:

每次重启NTP服务之后大约要5分钟客户端才能建立正常的NTP通讯连接,否则在执行ntpdate时候将返回:

[[email protected] ~]# ntpdate -d 192.168.1.162
... ...
192.168.1.162: Server dropped: strata too high
server 192.168.1.162, port 123
stratum 16, precision -23, leap 11, trust 000
... ...
8 Jan 19:28:07 ntpdate[17795]: no server suitable for synchronization found

在ntp客户端用ntpdate –d查看,发现有“Server dropped: strata too high”的错误,并且显示“stratum 16”。而正常情况下stratum这个值得范围是“0~15”。

这是因为NTP server还没有和其自身或者它的server同步上。详见NTP常见错误

同步测试

1. NTP服务器(192.168.1.162)

当前时间:

[[email protected] ~]# date
Tue Jan  8 19:32:42 EST 2013

2. NTP客户端时间(192.168.1.163):

当前时间:

[[email protected] ~]# date
Tue Jan  8 19:33:37 EST 2013

与192.168.1.162同步:

[[email protected] ~]# ntpdate 192.168.1.162
 8 Jan 19:33:51 ntpdate[24174]: adjust time server 192.168.1.162 offset -0.000002 sec

与172.31.1.1同步,时间滞后,大概是13个小时:

[[email protected] ~]# ntpdate 172.31.1.1
 8 Jan 06:34:10 ntpdate[24270]: step time server 172.31.1.1 offset -46801.549132 sec

在与172.31.1.1同步时,出现时钟同步异常,因与192.168.1.162同步的时钟相差太大。导致这种情况大致推测有两个原因:1)172.31.1.1上时间不对;2)192.168.1.162、163时间不对。不过这两点很快都被排除了,经过同事提点,查看鸟哥的私房菜,对比世界时差表,才知道是192.168.1.162、163系统的时区不正确。由于系统安装时没有选择时区(默认为美国纽约),与中国上海大概相差13个小时。

3.调整时区

系统当前时区

[[email protected] ~]# cat /etc/sysconfig/clock.20130109 
# The time zone of the system is defined by the contents of /etc/localtime.
# This file is only for evaluation by system-config-date, do not rely on its
# contents elsewhere.
ZONE="America/New York"

调整后系统时区

[[email protected] ~]# cat /etc/sysconfig/clock
# The time zone of the system is defined by the contents of /etc/localtime.
# This file is only for evaluation by system-config-date, do not rely on its
# contents elsewhere.
ZONE="Asia/Shanghai"

调整后时,再次与172.31.1.1同步:

[[email protected] ~]# date
Wed Jan  9 21:59:23 CST 2013
[[email protected] ~]# cp /usr/share/zoneinfo/Asia/Shanghai /etc/localtime 
cp: overwrite `/etc/localtime'? y
[[email protected] ~]# clock -w
[[email protected] ~]# date
Wed Jan  9 21:59:53 CST 2013
[[email protected] ~]# ntpdate 172.31.1.1
 9 Jan 09:04:46 ntpdate[5898]: step time server 172.31.1.1 offset -46801.989143 sec

设置定时同步

[[email protected] ~]# crontab -l
00 07 * * *  /usr/sbin/ntpdate 172.31.1.1 && /sbin/hwclock -w

鸟哥的讲解

例題:

假設你的筆記型電腦安裝 CentOS 這套系統,而且選擇的時區為台灣。現在,你將有一個月的時間要出差到美國的紐約去, 你會帶著這個筆電,那麼到了美國之後,時間會不一致啊!你該如何手動的調整時間參數呢?

答:

因為時區資料檔在 /usr/share/zoneinfo 內,在該目錄內會找到 /usr/share/zoneinfo/America/New_York 這個時區檔。 而時區設定檔在 /etc/sysconfig/clock ,且目前的時間格式在 /etc/localtime ,所以你應該這樣做:

[[email protected] ~]# date
Thu Jul 28 15:08:39 CST 2011  <==重點是 CST 這個時區喔!

[[email protected] ~]# vim /etc/sysconfig/clock
ZONE="America/New_York"       <==改的是這裡啦!

[[email protected] ~]# cp /usr/share/zoneinfo/America/New_York /etc/localtime
[[email protected] ~]# date
Thu Jul 28 03:09:21 EDT 2011  <==時區與時間都改變了!

這個範例做完之後,記得將這兩個檔案改回來!不然以後你的時間都是美國時間啦!

参考



blog comments powered by Disqus

Published

16 January 2013

Categories

Tags

Github