CentOS 7 中使用NTP进行时间同步

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

巴特西

CentOS 7 中使用NTP进行时间同步

3. 检查服务是否安装

4. 设置ntp服务器: 192.168.11.212

5. 设置ntp客户端: 172.16.248.129|130|131

最新文章

热门文章