NTP在linux下有两种时钟同步方式,分别为直接同步和平滑同步:
直接同步
使用ntpdate命令进行同步,直接进行时间变更。如果服务器上存在一个12点运行的任务,当前服务器时间是13点,但标准时间时11点,使用此命令可能会造成任务重复执行。因此使用ntpdate同步可能会引发风险,因此该命令也多用于配置时钟同步服务时第一次同步时间时使用。
平滑同步
使用ntpd进行时钟同步,可以保证一个时间不经历两次,它每次同步时间的偏移量不会太陡,是慢慢来的,这正因为这样,ntpd平滑同步可能耗费的时间比较长。标准时钟同步服务
http://www.pool.ntp.org/zone/cn网站包含全球的标准时间同步服务,也包括对中国时间的同步,对应的URL为cn.pool.ntp.org
,在其中也描述了ntp配置文件中的建议写法:
server 1.cn.pool.ntp.org
server 3.asia.pool.ntp.org
server 2.asia.pool.ntp.org
准备四台电脑,分别为:
IP | 用途 |
---|---|
192.168.11.212 | ntpd服务器,用于与外部公共ntpd同步标准时间 |
172.16.248.129 | ntpd客户端,用于与ntpd同步时间 |
172.16.248.130 | ntpd客户端,用于与ntpd同步时间 |
172,16,248.131 | ntpd客户端,用于与ntpd同步时间 |
[root@localhost kevin]# rpm -q ntp
ntp-4.2.6p5-19.el7.centos.3.x86_64
[root@localhost kevin]# yum -y install ntp
[root@localhost kevin]# systemctl enable ntpd
[root@localhost kevin]# systemctl start ntpd
配置前先使用命令:
ntpdate -u cn.pool.ntp.org
,同步服务器
# 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 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 ::1
# Hosts on local network are less restricted.
#restrict 192.168.1.0 mask 255.255.255.0 nomodify notrap
restrict 172.16.248.0 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 iburst
server 2.cn.pool.ntp.org
server 1.asia.pool.ntp.org
server 2.asia.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
# 允许上层时间服务器主动修改本机时间
restrict 2.cn.pool.ntp.org nomodify notrap noquery
restrict 1.asia.pool.ntp.org nomodify notrap noquery
restrict 2.asia.pool.ntp.org nomodify notrap noquery
server 127.0.0.1 # local clock
fudge 127.0.0.1 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
# Disable the monitoring facility to prevent amplification attacks using ntpdc
# monlist command when default restrict does not include the noquery flag. See
# CVE-2013-5211 for more details.
# Note: Monitoring will not be disabled with the limited restriction flag.
disable monitor
修改完成后重启ntpd服务
systemctl restart ntpd
使用ntpq -p 查看网络中的NTP服务器,同时显示客户端和每个服务器的关系
使用ntpstat 命令查看时间同步状态,这个一般需要5-10分钟后才能成功连接和同步。所以,服务器启动后需要稍等下:
刚启动的时候,一般是:
# ntpstat
unsynchronised
time server re-starting
polling server every 64 s
连接并同步后:
# ntpstat
synchronised to NTP server (202.112.10.36) at stratum 3
time correct to within 275 ms
polling server every 256 s
安装ntp服务并设置为自动启动,和前面的设置方式相同。然后编辑/etc/ntp.conf文件,红色字体为变化的内容。
# 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 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 ::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.centos.pool.ntp.org iburst
server 172.16.248.1
restrict 172.16.248.1 nomodify notrap noquery
server 127.0.0.1
fudge 127.0.0.1 stratum 10
#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
# 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
# Disable the monitoring facility to prevent amplification attacks using ntpdc
# monlist command when default restrict does not include the noquery flag. See
# CVE-2013-5211 for more details.
# Note: Monitoring will not be disabled with the limited restriction flag.
disable monitor
重启ntpd服务
#systemctl restart ntpd
启动后,查看同步情况
# ntpq -p
# ntpstat
因为是内网,一般ntpstat很快就可以同步上。
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原文地址:http://blog.csdn.net/scorpio3k/article/details/49645219