NTP简介
NTP（Network Time Protocol，网络时间协议）是用来使网络中的各个计算机时间同步的一种协议。它的用途是把计算机的时钟同步到世界协调时UTC，其精度在局域网内可达0.1ms，在互联网上绝大多数的地方其精度可以达到1-50ms。NTP服务器就是利用NTP协议提供时间同步服务的。
系统版本
1 [root@test ~]# cat /etc/redhat-release 2 CentOS release 6.9 (Final)
1.2 NTP服务器安装
[root@test ~]# rpm -qa ntpntp-4.2.6p5-10.el6.centos.2.x86_64
如果没有安装就yum install ntp -y进行安装
配置NTP服务
备份配置文件
[root@test ~]# cp /etc/ntp.conf{,.bak}[root@test ~]# ll /etc/ntp.conf*-rw-r--r--. 1 root root 1778 Jan 11 2017 /etc/ntp.conf-rw-r--r-- 1 root root 1778 Oct 23 23:10 /etc/ntp.conf.bak
精简化配置文件
[root@test ~]# egrep -v "^$|#" /etc/ntp.conf.bak >/etc/ntp.conf
修改配置文件
# 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). 3 4 driftfile /var/lib/ntp/drift 5 6
# Permit time synchronization with our time source, but do not 7
# permit the source to query or modify the service on this system. 8 restrict default kod nomodify notrap nopeer noquery 9 restrict -6 default kod nomodify notrap nopeer noquery10 11
# Permit all access over the loopback interface. This could12
# be tightened as well, but to do so would effect some of13
# the administrative functions.14 restrict 127.0.0.1 15 restrict -6 ::116 17
# Hosts on local network are less restricted.18 #restrict 192.168.1.0 mask 255.255.255.0 nomodify notrap19
# 允许内网其他机器同步时间20 restrict 172.16.1.0 mask 255.255.255.0 nomodify notrap21 22
# Use public servers from the pool.ntp.org project.23
# Please consider joining the pool (http://www.pool.ntp.org/join.html).24
#server 0.centos.pool.ntp.org iburst25
#server 1.centos.pool.ntp.org iburst26
#server 2.centos.pool.ntp.org iburst27
#server 3.centos.pool.ntp.org iburst28 29
# 定义使用的上游 ntp服务器，将原来的注释30 server time1.aliyun.com31 server ntp1.aliyun.com32 33
#broadcast 192.168.1.255 autokey
# broadcast server34 #broadcastclient
# broadcast client35 #broadcast 224.0.1.1 autokey
# multicast server36 #multicastclient 224.0.1.1
# multicast client37 #manycastserver 239.255.254.254
# manycast server38 #manycastclient 239.255.254.254 autokey
# manycast client39 40
# 允许上层时间服务器主动修改本机时间41 restrict time1.aliyun.com nomodify notrap noquery42 restrict ntp1.aliyun.com nomodify notrap noquery43 44 # 外部时间服务器不可用时，以本地时间作为时间服务45 server 127.127.1.0 46 fudge 127.127.1.0 stratum 1047 48
# Enable public key cryptography.49 #crypto50 51 includefile /etc/ntp/crypto/pw52 53
# Key file containing the keys and key identifiers used when operating54
# with symmetric key cryptography. 55 keys /etc/ntp/keys56 57
# Specify the key identifiers which are trusted.58
#trustedkey 4 8 4259 60 # Specify the key identifier to use with the ntpdc utility.61
#requestkey 862 63
# Specify the key identifier to use with the ntpq utility.64 #controlkey 865 66
# Enable writing of statistics records.67 #statistics clockstats cryptostats loopstats peerstats
启动NTP服务器
注意：如果有同步时间的定时任务要将其注销，否则会冲突
[root@test ~]# /etc/init.d/ntpd startStarting ntpd: [ OK ]
显示节点列表
[root@test ~]# ntpq -p remote refid st t when poll reach delay offset jitter============================================================================== time5.aliyun.co 10.137.38.86 2 u 28 64 3 5.092 6241215 185.623 132.163.96.4 .INIT. 16 u - 64 0 0.000 0.000 0.000
客户机时间同步
客户机要等几分钟再与新启动的ntp服务器进行时间同步，否则会提示
no server suitable for synchronization found错误
[root@client ~]# ntpdate 10.0.0.25024 Oct 16:46:58 ntpdate[26694]: adjust time server 10.0.0.250 offset 0.320652 sec