CentOS7-ntp時間同步服務器
NTP時鐘同步方式說明
NTP在linux下有兩種時鐘同步方式，分別為直接同步和平滑同步：
直接同步
使用ntpdate命令進行同步，直接進行時間變更。如果服務器上存在一個12點運行的任務，當前服務器時間是13點，但標準時間時11點，使用此命令可能會造成任務重復執行。因此使用ntpdate同步可能會引發風險，因此該命令也多用於配置時鐘同步服務時第一次同步時間時使用。
平滑同步
使用ntpd進行時鐘同步，可以保證一個時間不經歷兩次，它每次同步時間的偏移量不會太陡，是慢慢來的，這正因為這樣，ntpd平滑同步可能耗費的時間比較長。
標準時鐘同步服務
http://www.pool.ntp.org/zone/cn網站包含全球的標準時間同步服務，也包括對中國時間的同步，對應的
server1.cn.pool.ntp.org
server3.asia.pool.ntp.org
server2.asia.pool.ntp.org
2. 環境情況
準備兩臺電腦，分別為：
IP 用途
10.0.0.202 ntpd服務器，用於與外部公共ntpd同步標準時間
10.0.0.203 ntpd客戶端，用於與ntpd同步時間
3. 檢查服務是否安裝
使用rpm檢查ntp包是否安裝
[[email protected]]# rpm -q ntp
ntp-4.2.6p5-19.el7.centos.3.x86_64
如果已經安裝則略過此步，否則使用yum進行安裝，並設置系統開機自動啟動並啟動服務
[[email protected]]# yum -y install ntp
[[email protected]]# systemctl enable ntpd
[[email protected]]# systemctl start ntpd
4. 設置ntp服務器: 10.0.0.202
配置前先使用命令：ntpdate -u cn.pool.ntp.org，同步服務器
修改/etc/ntp.conf文件，紅色字體是修改的內容
# For more information about thisfile, 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 withour time source, but do not
# permit the source to query ormodify the service on this system.
restrict default nomodify notrapnopeer noquery
# Permit all access over the loopbackinterface. This could
# be tightened as well, but to do sowould effect some of
# the administrative functions.
restrict 127.0.0.1
restrict ::1
# Hosts on local network are lessrestricted.
#restrict 192.168.1.0 mask255.255.255.0 nomodify notrap
restrict 10.0.0.0 mask255.255.255.0 nomodify notrap
# Use public servers from thepool.ntp.org project.
# Please consider joining the pool(http://www.pool.ntp.org/join.html).
#server0.centos.pool.ntp.org iburst
#server1.centos.pool.ntp.org iburst ###註意此處四行要註釋掉
#server2.centos.pool.ntp.org iburst
#server3.centos.pool.ntp.org iburst
server 2.cn.pool.ntp.org
server 1.asia.pool.ntp.org
server 2.asia.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 239.255.254.254autokey # manycast client
restrict 2.cn.pool.ntp.orgnomodify notrap noquery
restrict 1.asia.pool.ntp.orgnomodify notrap noquery
restrict 2.asia.pool.ntp.orgnomodify notrap noquery
server 127.0.0.1 # localclock
fudge 127.0.0.1 stratum 10
# Enable public key cryptography.
#crypto
includefile /etc/ntp/crypto/pw
# Key file containing the keys andkey identifiers used when operating
# with symmetric key cryptography.
keys /etc/ntp/keys
# Specify the key identifiers whichare trusted.
#trustedkey 4 8 42
# Specify the key identifier to usewith the ntpdc utility.
#requestkey 8
# Specify the key identifier to usewith the ntpq utility.
#controlkey 8
# Enable writing of statistics records.
#statistics clockstats cryptostatsloopstats peerstats
# Disable the monitoring facility toprevent amplification attacks using ntpdc
# monlist command when defaultrestrict does not include the noquery flag. See
# CVE-2013-5211 for more details.
# Note: Monitoring will not bedisabled with the limited restriction flag.
disable monitor
[[email protected] ~]#
修改完成後重啟ntpd服務systemctlrestart ntpd
使用ntpq -p 查看網絡中的NTP服務器，同時顯示客戶端和每個服務器的關系
使用ntpstat 命令查看時間同步狀態，這個一般需要5-10分鐘後才能成功連接和同步。所以，服務器啟動後需要稍等下：
剛啟動的時候，一般是：
# ntpstat
unsynchronised
time server re-starting
polling server every 64 s
連接並同步後:
# ntpstat
synchronised to NTP server(202.112.10.36) at stratum 3
time correct to within 275 ms
polling server every 256 s
5. 設置ntp客戶端: 10.0.0.203
安裝ntp服務並設置為自動啟動，和前面的設置方式相同。然後編輯/etc/ntp.conf文件，紅色字體為變化的內容。
# For more information about thisfile, 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 withour time source, but do not
# permit the source to query ormodify the service on this system.
restrict default nomodify notrapnopeer noquery
# Permit all access over the loopbackinterface. This could
# be tightened as well, but to do sowould effect some of
# the administrative functions.
restrict 127.0.0.1
restrict ::1
# Hosts on local network are lessrestricted.
#restrict 192.168.1.0 mask255.255.255.0 nomodify notrap
# Use public servers from thepool.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
server 10.0.0.202
restrict 10.0.0.202 nomodify notrap noquery
server 127.0.0.1
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 239.255.254.254autokey # manycast client
# Enable public key cryptography.
#crypto
includefile /etc/ntp/crypto/pw
# Key file containing the keys andkey identifiers used when operating
# with symmetric key cryptography.
keys /etc/ntp/keys
# Specify the key identifiers whichare trusted.
#trustedkey 4 8 42
# Specify the key identifier to usewith the ntpdc utility.
#requestkey 8
# Specify the key identifier to usewith the ntpq utility.
#controlkey 8
# Enable writing of statisticsrecords.
#statistics clockstats cryptostatsloopstats peerstats
# Disable the monitoring facility toprevent amplification attacks using ntpdc
# monlist command when defaultrestrict does not include the noquery flag. See
# CVE-2013-5211 for more details.
# Note: Monitoring will not bedisabled with the limited restriction flag.
disable monitor
[[email protected] ~]#
重啟ntpd服務
systemctl restart ntpd
啟動後，查看同步情況，這個步驟一般根據服務器配置，同步時間不同，我的虛擬機同步為約兩分鐘
ntpq -p
[[email protected] opt]# ntpstat
synchronised to NTP server(10.0.0.202) at stratum 4
time correct to within 1243 ms
polling server every 64 s
本文出自 “藍葉子Sheep” 博客，請務必保留此出處http://dellinger.blog.51cto.com/12445009/1947889
CentOS7-ntp時間同步服務器