Linux的时间设置与同步(NTP)
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在oracle10g做rac的时候，尽量要保持2个节点的时间一样，liunx的NTP服务是可以满足这个需求的。今天我就用一个非系统工程师的理解来说明下如何配置NTP同步。原理我就不说了，我也是一知半解的，就是懂点配置。
客户端的配置文件
说道配置文件，NTP的配置文件就在/etc/ntp.conf
(如果看客您只想看怎么配置 搜索crontab 在本页面，即进入正文)
[root@xuexi1 ~]# cat /etc/ntp.conf
# 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.
restrict 127.0.0.1
restrict -6 ::1
# 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.rhel.pool.ntp.org
server 1.rhel.pool.ntp.org
server 2.rhel.pool.ntp.org
#broadcast 192.168.1.255 key 42 # broadcast server
#broadcastclient # broadcast client
#broadcast 224.0.1.1 key 42 # multicast server
#multicastclient 224.0.1.1 # multicast client
#manycastserver 239.255.254.254 # manycast server
#manycastclient 239.255.254.254 key 42 # 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
# Drift file. Put this in a directory which the daemon can write to.
# No symbolic links allowed, either, since the daemon updates the file
# by creating a temporary in the same directory and then rename()'ing
# it to the file.
driftfile /var/lib/ntp/drift
# 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这个文件常用的没有几个属性,我们把注释的部分都去掉看看
[root@xuexi1 ~]# cat /etc/ntp.conf |grep -v ^#
#权限部分限制
restrict default kod nomodify notrap nopeer noquery <==拒絕 IPv4 的用戶
restrict -6 default kod nomodify notrap nopeer noquery <==拒絕 IPv6 的用戶
restrict 127.0.0.1 <==底下兩個是預設值，放行本機來源
restrict -6 ::1
#設定服务器地址
server 0.rhel.pool.ntp.org
server 1.rhel.pool.ntp.org
server 2.rhel.pool.ntp.org
server 127.127.1.0 # local clock
fudge 127.127.1.0 stratum 10
#时间差异设置和KEY 不需要改动一般情况下
driftfile /var/lib/ntp/drift
keys /etc/ntp/keys
常用的查看ntp的命令如下：
[root@xuexi1 ~]# /etc/init.d/ntpd start #启动ntp服务
Starting ntpd: [ OK ]
[root@xuexi1 ~]#
[root@xuexi1 ~]# chkconfig ntpd on #开机启动
[root@xuexi1 ~]#
[root@xuexi1 ~]# netstat -tlunp | grep ntp #查看端口占用
udp 0 0 10.10.27.11:123 0.0.0.0:* 4996/ntpd
udp 0 0 127.0.0.1:123 0.0.0.0:* 4996/ntpd
udp 0 0 0.0.0.0:123 0.0.0.0:* 4996/ntpd
udp 0 0 ::1:123 :::* 4996/ntpd
udp 0 0 fe80::20c:29ff:fe90:123 :::* 4996/ntpd
udp 0 0 :::123 :::* 4996/ntpd
[root@xuexi1 ~]#
[root@xuexi1 ~]#
[root@xuexi1 ~]#
[root@xuexi1 ~]#
[root@xuexi1 ~]# ntpstat #查看同步情况
unsynchronised
time server re-starting
polling server every 64 s
[root@xuexi1 ~]#
[root@xuexi1 ~]# ntpq -p
remote refid st t when poll reach delay offset jitter
==============================================================================
*LOCAL(0) .LOCL. 10 l 24 64 37 0.000 0.000 0.001
说了这么多原理，还是给大家一个例子吧，下面是一个服务端的配置，
[root@xuexi1 etc]# cat ntp.conf
restrict default kod nomodify notrap nopeer noquery
restrict -6 default kod nomodify notrap nopeer noquery
restrict 127.0.0.1
restrict -6 ::1
restrict 10.10.27.13 #可以访问的主机IP，也可以设置整个网段，看最上面的全文件内容
server 0.rhel.pool.ntp.org
server 1.rhel.pool.ntp.org
server 2.rhel.pool.ntp.org
server 127.127.1.0 # local clock
fudge 127.127.1.0 stratum 10
driftfile /var/lib/ntp/drift
keys /etc/ntp/keys
Broadcastdelay 0.008
[root@xuexi1 etc]# 客户端的配置文件
[root@localhost ~]# cat /etc/ntp.conf |grep -v ^#
restrict default kod nomodify notrap nopeer noquery
restrict -6 default kod nomodify notrap nopeer noquery
restrict 127.0.0.1
restrict -6 ::1
server 10.10.27.11 prefer
driftfile /var/lib/ntp/drift
keys /etc/ntp/keys
Broadcastdelay 0.008 #从字面意思来看 是 广播延时时间。不明白干吗用的，原文件没有说明有这个参数
[root@localhost ~]# 这样配置以后，大家就可以启动服务了，在两个节点服务器（由于ntpd的server/client之间的时间误差不允许超过1000秒，因此你得先手动进行时间同步，然后再设定与启动服务。）
[root@xuexi1 ~]# /etc/init.d/ntpd start #启动ntp服务
Starting ntpd: [ OK ]
[root@xuexi1 ~]#
[root@xuexi1 ~]# chkconfig ntpd on #开机启动
[root@xuexi1 ~]#
[root@xuexi1 ~]# netstat -tlunp | grep ntp #查看端口占用下面给大家也演示下crontab的方式，这个很简单，我推荐这个方法
服务器端：直接添加下面的最后一行 对了10.10.27.11是服务端IP
[root@xuexi1 ~]# cat /etc/ntp.conf |grep -v ^#
restrict default kod nomodify notrap nopeer noquery
restrict -6 default kod nomodify notrap nopeer noquery
restrict 127.0.0.1
restrict -6 ::1
server 0.rhel.pool.ntp.org
server 1.rhel.pool.ntp.org
server 2.rhel.pool.ntp.org
server 127.127.1.0 # local clock
fudge 127.127.1.0 stratum 10
driftfile /var/lib/ntp/drift
keys /etc/ntp/keys
restrict 10.10.27.0 mask 255.255.255.0 nomodify #直接编辑文件 添加这行 没事闲着不要加 notrap
[root@xuexi1 ~]# 服务端配置好了以后，记得启动
[root@xuexi1 ~]# /etc/init.d/ntpd start #启动ntp服务
Starting ntpd: [ OK ]
[root@xuexi1 ~]# 客户端就有点麻烦了
[root@localhost ~]# ll ntpdate_to_11.sh #新建一个sh文件
-rwxrwxrwx 1 root root 47 Jun 12 11:47 ntpdate_to_11.sh
[root@localhost ~]#
[root@localhost ~]# cat ntpdate_to_11.sh #文件内容如下
while :; do ntpdate 10.10.27.11; sleep 1; done
[root@localhost ~]#
[root@localhost ~]# pwd
/root
[root@localhost ~]#
[root@localhost ~]# crontab -e
在VI界面输入“* * * * * /usr/sbin/ntpdate 10.10.27.11 >> /root/ntpdate_to_rac1.log 2>&1” #记得保存啊
[root@localhost ~]# crontab -l #查看下是否添加成功
* * * * * /usr/sbin/ntpdate 10.10.27.11 >> /root/ntpdate_to_rac1.log 2>&1一开始的时候会报
ntpdate_to_11.sh ntpdate_to_rac1.log
[root@localhost ~]# cat ntpdate_to_rac1.log
12 Jun 11:51:05 ntpdate[4520]: no server suitable for synchronization found
12 Jun 11:52:05 ntpdate[4532]: no server suitable for synchronization found
12 Jun 11:53:01 ntpdate[4547]: no server suitable for synchronization found
12 Jun 11:54:01 ntpdate[4559]: no server suitable for synchronization found
12 Jun 11:55:02 ntpdate[4570]: no server suitable for synchronization found
12 Jun 11:56:01 ntpdate[4583]: no server suitable for synchronization found
12 Jun 11:57:01 ntpdate[4595]: no server suitable for synchronization found
12 Jun 11:58:01 ntpdate[4607]: no server suitable for synchronization found
12 Jun 11:59:01 ntpdate[4620]: no server suitable for synchronization found
12 Jun 12:00:01 ntpdate[4631]: no server suitable for synchronization found
12 Jun 12:01:01 ntpdate[4642]: no server suitable for synchronization found
12 Jun 12:02:01 ntpdate[4654]: adjust time server 10.10.27.11 offset 0.077524 sec
12 Jun 12:03:01 ntpdate[4662]: adjust time server 10.10.27.11 offset 0.017492 sec
12 Jun 12:04:01 ntpdate[4670]: adjust time server 10.10.27.11 offset -0.008772 sec
12 Jun 12:05:01 ntpdate[4679]: adjust time server 10.10.27.11 offset 0.004367 sec
12 Jun 12:06:01 ntpdate[4688]: adjust time server 10.10.27.11 offset -0.002139 sec
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