CentOS7 中使用NTP进行时间同步

雨点打透心脏的1/2处 2022-08-09 20:30 320阅读 0赞

### 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][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：**

<table> 
 <thead> 
  <tr> 
   <th>IP</th> 
   <th>用途</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>192.168.11.212</td> 
   <td>ntpd服务器，用于与外部公共ntpd同步标准时间</td> 
  </tr> 
  <tr> 
   <td>172.16.248.129</td> 
   <td>ntpd客户端，用于与ntpd同步时间</td> 
  </tr> 
  <tr> 
   <td>172.16.248.130</td> 
   <td>ntpd客户端，用于与ntpd同步时间</td> 
  </tr> 
  <tr> 
   <td>172,16,248.131</td> 
   <td>ntpd客户端，用于与ntpd同步时间</td> 
  </tr> 
 </tbody> 
</table>

### 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。

[http_www.pool.ntp.org_zone_cn]: http://www.pool.ntp.org/zone/cn