使用NTP進行CentOS7時間同步

1. NTP時鐘同步方式說明

   
   

NTP在linux下有兩種時鐘同步方式，分別爲直接同步和平滑同步：

直接同步

使用ntpdate命令進行同步，直接進行時間變動。若是服務器上存在一個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，使用此命令可能會形成任務重複執行。所以使用ntpdate同步可能會引起風險，所以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，能夠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，這正由於這樣，ntpd平滑同步可能耗費的時間比較長。

 

標準時鍾同步服務

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URL爲cn.pool.ntp.org，在其中也描述了ntp配置文件中的建議寫法：

server1.cn.pool.ntp.org

server3.asia.pool.ntp.org

server2.asia.pool.ntp.org

2. 環境狀況

準備兩臺電腦，分別爲：

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

[root@localhostkevin]# rpm -q ntp

ntp-4.2.6p5-19.el7.centos.3.x86_64

若是已經安裝則略過此步，不然使用yum進行安裝，並設置系統開機自動啓動並啓動服務

[root@localhostkevin]# yum -y install ntp

[root@localhostkevin]# systemctl enable ntpd

[root@localhostkevin]# 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 le***estricted.

#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     ###注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

[root@lb01 ~]#

修改完成後重啓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一個服務器的關係

使用ntpstat 命令查看時間同步狀態，這個通常須要5-10分鐘後才能成功鏈接和同步。因此，服務器啓動後須要稍等下：

剛啓動的時候，通常是：

# ntpstat

unsynchronised

 time server re-starting

  polling server every 64 s

鏈接並同步後:

# 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服務並設置爲自動啓動，和前面的設置方式相同。而後編輯/etc/ntp.conf文件，紅色字體爲變化的內容。

# 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 le***estricted.

#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

[root@docker02 ~]#

重啓ntpd服務

systemctl restart ntpd

啓動後，查看同步狀況，這個步驟通常根據服務器配置，同步時間不一樣，個人虛擬機同步爲約兩分鐘

 ntpq -p

 [root@lb01 opt]# ntpstat

synchronised to NTP server(10.0.0.202) at stratum 4

  time correct to within 1243 ms

  polling server every 64 s