//系統
# cat /etc/redhat-release
CentOS release 6.8 (Final)
# uname -r
2.6.32-642.el6.x86_64
//SELinux設定
# setenforce 0
# sed -i 's/SELINUX=enforcing/SELINUX=disable/g' /etc/selinux/config
//iptables設定（打開123端口）（可參考 http://man.linuxde.net/iptables）
# iptables -I INPUT 5 -m state --state NEW -m udp -p udp --dport 123 -j ACCEPT
# iptables-save > /home/iptables.save
# iptables-restore </home/iptables.save
# iptables -L -n
//server端操作
# yum -y install ntpdate ntp
//配置開機啟動
# echo "/etc/init.d/ntpd start" >> /etc/rc.local
//配置檔案
# cat /etc/ntp.conf
============分割線============
# 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 kod nomodify notrap nopeer noquery
restrict -6 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
restrict -6 ::1
# Hosts on local network are less restricted.
# 允許内網其他機器同步時間
restrict 172.16.12.0 mask 255.255.240.0 nomodify notrap
#restrict default ignore
# Use public servers from the pool.ntp.org project.
# Please consider joining the pool (http://www.pool.ntp.org/join.html).
# 中國國家受時中心
server 210.72.145.44 perfer
server 202.112.10.36
server 59.124.196.83
# 允許上層時間伺服器主動修改本機時間
restrict 210.72.145.44 nomodify notrap noquery
testrict 202.112.10.36 nomodify notrap noquery
restrict 59.124.196.83 nomodify notrap noquery
#外部時間伺服器不可用時，以本地時間作為時間服務
server 127.127.1.0
fudge 127.127.1.0 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
============分割線============
//啟動服務
# /etc/init.d/ntpd start
//檢視端口和監聽
# netstat -tlunp |grep ntp
udp 0 0 172.16.12.214:123 0.0.0.0:* 9749/ntpd
udp 0 0 172.16.12.211:123 0.0.0.0:* 9749/ntpd
udp 0 0 119.44.21.221:123 0.0.0.0:* 9749/ntpd
udp 0 0 127.0.0.1:123 0.0.0.0:* 9749/ntpd
udp 0 0 0.0.0.0:123 0.0.0.0:* 9749/ntpd
udp 0 0 fe80::b283:feff:fede:81c:123 :::* 9749/ntpd
udp 0 0 fe80::b283:feff:fede:81c:123 :::* 9749/ntpd
udp 0 0 ::1:123 :::* 9749/ntpd
udp 0 0 :::123 :::* 9749/ntpd
//檢視用戶端和伺服器關系
# ntpq -p
remote refid st t when poll reach delay offset jitter
==============================================================================
210.72.145.44 .INIT. 16 u - 256 0 0.000 0.000 0.000
*gus.buptnet.edu 10.3.8.150 5 u 2 64 375 62.214 -16.650 4.626
59-124-196-83.H .INIT. 16 u - 256 0 0.000 0.000 0.000
LOCAL(0) .LOCL. 10 l 212 64 370 0.000 0.000 0.000
//ntpstat 指令檢視時間同步狀态，這個一般需要5-10分鐘後才能成功連接配接和同步
# ntpstat
synchronised to NTP server (202.112.10.36) at stratum 6
time correct to within 167 ms
polling server every 128 s
//client端
# yum install ntp
//配置檔案
# cat /etc/ntp.conf
============分割線============
# 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 kod nomodify notrap nopeer noquery
#restrict -6 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
restrict -6 ::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 1.centos.pool.ntp.org iburst
#server 2.centos.pool.ntp.org iburst
#server 3.centos.pool.ntp.org iburst
# 配置時間伺服器為本地的時間伺服器
server 172.16.12.211
restrict 172.16.12.211 nomodify notrap noquery
server 127.127.1.0
fudge 127.127.1.0 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
============分割線============
//client同步server時間
# ntpdate 172.16.12.211 && clock -w
26 Mar 14:37:10 ntpdate[23443]: adjust time server 172.16.12.211 offset 0.010673 sec
參考連結：https://www.linuxidc.com/Linux/2014-11/109412p2.htm