Linux下NTPD服务器构建实践（linux下ntp服务器）

随着科技的发展，NTPD（Network Time Protocol Daemon）网络时间协议守护进程已经被广泛用于时间同步。NTPD的相关服务可以帮助我们更方便的控制各类系统服务。本文主要介绍NTPD服务在Linux 平台下的搭建和配置实践。

## 一、Linux 平台的NTPD安装

首先我们可以使用命令`yum install ntp`来安装NTPD服务：

“`shell

[root@localhost ~]# yum install ntp

Loaded plugins: fastestmirror

Loading mirror speeds from cached hostfile

* base: mirrors.zju.edu.cn

* extras: mirrors.ustc.edu.cn

* updates: mirrors.zju.edu.cn

Resolving Dependencies

…

Installed:

ntp.x86_64 0:4.2.6p5-12.el7

Complete!

安装完成后，在/etc/ntp.conf文件中可以看到ntpd默认的配置，具体内容如下：

```shell
[root@localhost ~]# 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

# 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
# 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
server 1.centos.pool.ntp.org
server 2.centos.pool.ntp.org
server 3.centos.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
# 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 restricted expression as the
# default restrict line will not usually contain the noquery flag.
disable monitor
# Additional options

# Additional options for ntpd include the following:

#-A       modify the NTPD access control list
#-d      enable debugging
#-e     set the maximum allowed skew in seconds
#-f      set the frequency adjustment
#-g      allow the time to jump more than one second
#-l       log all messages
#-n      turn off all NTP processing
#-p      set the precision of the service
#-q       adjust the time immediately when started
#-r      set the interval between polls
#-s      set the total number of seconds to wait
#-t      permit time changes
#-u      allow insecure NTP clients
#-v      enable verbosity

## 二、NTPD服务配置

接下来我们需要修改/etc/ntp.conf文件，添加NTP服务器的IP地址，一般可以在网上搜索到NTP服务器的IP地址。例如：

“`shell

server 0.pool.ntp.org

server 1.pool.ntp.org

server 2.pool.ntp.org

我们可以添加谷歌的NTP服务器到本文件中：

```shell
server time.google.com

在修改完/etc/ntp.conf文件后，我们要启动NTPD服务，可以使用下面的命令：

“`shell

systemctl start ntpd

之后可以使用`ntpq -p`命令查看当前server是否正常工作：
```shell
[root@localhost ~]# ntpq -p
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
 203.66.1.10     202.97.40.5     3 u   44   64  377   107.550  -17.340  16.129
*time.google.co .INIT.          16 u   35   64  377   572.467  -22.347   1.300

可以看到第一行显示*表示服务器已经连接上，开始进行时间同步。

## 三、总结

经过上面的实践，我们已经了解到如何在Linux平台安装和配置NTPD服务，NTPD服务的主要功能就是帮助系统进行时间同步，可以保证系统时间的正确性。