实验环境：CentOS release 6.7

rpm -qa | grep ntp

yum install ntpdate ntp -y

修改ntp配置

# vim /etc/ntp.conf
# 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

#新增:日志目录.
logfile /var/log/ntpd.log

# 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
#这一行的含义是授权172.16.128.0网段上的所有机器可以从这台机器上查询和同步时间.
restrict 172.16.128.0 mask 255.255.255.0 nomodify notrap

# 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

#新增:时间服务器列表.
server 0.cn.pool.ntp.org iburst
server 1.cn.pool.ntp.org iburst
server 2.cn.pool.ntp.org iburst
server 3.cn.pool.ntp.org iburst

#新增:当外部时间不可用时，使用本地时间.
server 172.16.128.171 iburst
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

#新增:允许上层时间服务器主动修改本机时间.
restrict 0.cn.pool.ntp.org nomodify notrap noquery
restrict 1.cn.pool.ntp.org nomodify notrap noquery
restrict 2.cn.pool.ntp.org nomodify notrap noquery

# 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.ntpdate -u 1.cn.pool.ntp.org
# Note: Monitoring will not be disabled with the limited restriction flag.
disable monitor

 

设置开机自启

# systemctl enable ntpd
# systemctl enable ntpdate
# systemctl is-enabled ntpd

在启动时可以先同步时间

ntpdate -u 1.cn.pool.ntp.org

启动
# systemctl start ntpdate
# systemctl start ntpd
加入防火墙
# firewall-cmd --permanent --add-service=ntp
# firewall-cmd --reload