场景：
- 一般部署大数据相关应用服务，各个节点之间需要时间同步；
- 内网情况下，很可能各节点之前时间可能不一致，或者过一段时间后 又不一致了
ntp 时钟服务器：
- 可用于内网各个节点之前得时间同步，安全方便。
- 大致有个 ntp-server 各个 节点有个 ntp-client 间隔一段时间就去同步 服务端得时间。
流程图：
安装配置：
centos7-rpm包分享下载
在有网环境自我导出：
yum install --downloadonly --downloaddir=/opt compat-openssl ntp ntpdate
# 各个节点安装
rpm -ivh compat-openssl10-1.0.2o-3.el8.x86_64.rpm
rpm -ivh ntp-4.2.6p5-29.el7.centos.2.x86_64.rpm
rpm -ivh ntpdate-4.2.6p5-29.el7.centos.2.x86_64.rpm
配置文件修改-
server端：
- vi /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
# 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.
# 同步ip断, 设置同步ip断 1
restrict 192.168.0.0 mask 255.255.255.0 nomodify notrap
# 同步ip断, 设置同步ip断 2
restrict 177.180.110.0 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
# 联网时配置
server 0.cn.pool.ntp.org
server 1.cn.pool.ntp.org
server 2.cn.pool.ntp.org
server 3.cn.pool.ntp.org
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
restrict 3.cn.pool.ntp.org nomodify notrap noquery
# 外部时间服务器不可用时，以本地时间作为时间服务
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
# 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.
# 运行修改硬件时间
SYNC_HWCLOCK=yes
disable monitor
ntp 客户端配置：
- vi /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
# 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 1.centos.pool.ntp.org iburst
#server 2.centos.pool.ntp.org iburst
#server 3.centos.pool.ntp.org iburst
# 从配置的时钟服务器中同步时间，服务端ip
server 177.180.20.10
# 允许修改本地时间
restrict 177.180.20.10 nomodify notrap noquery
# 如果时间服务器不可用，用本地的时间服务
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
# 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.
SYNC_HWCLOCK=yes
disable monitor
启动配置：
- 先启动
服务端得 ntp-server ，再启动各节点 ntp-client；systemctl status ntpdsystemctl start ntpdsystemctl enable ntpdntpdate ${ntp-server-ip}- 各节点可先，手动同步一次
查看命令：
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ntpstat//ntp 客户端,查看时间同步状态