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CentOS 7 中使用NTP进行时间同步

[日期:2015-11-07] 来源:Linux社区  作者:scorpio3k [字体: ]

1. NTP时钟同步方式说明
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

2. 环境情况
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

3. 检查服务是否安装

  • 使用rpm检查ntp包是否安装
[root@localhost kevin]# rpm -q ntp
ntp-4.2.6p5-19.el7.CentOS.3.x86_64
  • 如果已经安装则略过此步,否则使用yum进行安装,并设置系统开机自动启动并启动服务
[root@localhost kevin]# yum -y install ntp
[root@localhost kevin]# systemctl enable ntpd
[root@localhost kevin]# systemctl start ntpd

4. 设置ntp服务器: 192.168.11.212

配置前先使用命令:ntpdate -u cn.pool.ntp.org,同步服务器

  • 修改/etc/ntp.conf文件,红色字体是修改的内容
# 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
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

5. 设置ntp客户端: 172.16.248.129|130|131

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。

CentOS NTP服务器安装与配置 http://www.linuxidc.com/Linux/2014-01/95258.htm

Linux实战部署系列之NTP服务器 http://www.linuxidc.com/Linux/2013-11/92275.htm

多种操作系统NTP客户端配置 http://www.linuxidc.com/Linux/2013-10/91928.htm

搭建企业级NTP时间服务器 http://www.linuxidc.com/Linux/2014-02/97205.htm

Linux下快速搭建ntp时间同步服务器 http://www.linuxidc.com/Linux/2014-07/104371.htm

CentOS 6.3 下实现NTP时间服务器 http://www.linuxidc.com/Linux/2014-08/105414.htm

本文永久更新链接地址http://www.linuxidc.com/Linux/2015-11/124911.htm

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