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RHEL7学习之NTP配置
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一，安装NTP
[root@localhost ~]# yum install ntp
Loaded plugins: product-id, subscription-manager
This system is not registered to Red Hat Subscription Management. You can use subscription-manager to register.
cdrom | 4.1 kB ::
Resolving Dependencies
--> Running transaction check
---> Package ntp.x86_64 :4.2.6p5-.el7 will be installed
--> Processing Dependency: ntpdate = 4.2.6p5-.el7 for package: ntp-4.2.6p5-.el7.x86_64
--> Processing Dependency: libopts.so.()(64bit) for package: ntp-4.2.6p5-.el7.x86_64
--> Running transaction check
---> Package autogen-libopts.x86_64 :5.18-.el7 will be installed
---> Package ntpdate.x86_64 :4.2.6p5-.el7 will be installed
--> Finished Dependency Resolution Dependencies Resolved =============================================================================================
Package Arch Version Repository Size
=============================================================================================
Installing:
ntp x86_64 4.2.6p5-.el7 cdrom k
Installing for dependencies:
autogen-libopts x86_64 5.18-.el7 cdrom k
ntpdate x86_64 4.2.6p5-.el7 cdrom k Transaction Summary
=============================================================================================
Install Package (+ Dependent packages) Total download size: k
Installed size: 1.6 M
Is this ok [y/d/N]: y
Downloading packages:
---------------------------------------------------------------------------------------------
Total MB/s | kB ::
Running transaction check
Running transaction test
Transaction test succeeded
Running transaction
Installing : autogen-libopts-5.18-.el7.x86_64 /
Installing : ntpdate-4.2.6p5-.el7.x86_64 /
Installing : ntp-4.2.6p5-.el7.x86_64 /
Verifying : ntpdate-4.2.6p5-.el7.x86_64 /
Verifying : autogen-libopts-5.18-.el7.x86_64 /
Verifying : ntp-4.2.6p5-.el7.x86_64 / Installed:
ntp.x86_64 :4.2.6p5-.el7 Dependency Installed:
autogen-libopts.x86_64 :5.18-.el7 ntpdate.x86_64 :4.2.6p5-.el7 Complete!
二，编辑NTP配置文件"/etc/ntp.conf"
[root@localhost ~]# vim /etc/ntp.conf # For more information about this file, see the man pages
# ntp.conf(), ntp_acc(), ntp_auth(), ntp_clock(), ntp_misc(), ntp_mon(). 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 :: # Hosts on local network are less restricted.
restrict 192.168.1.0 mask 255.255.255.0 nomodify notrap //允许"192.168.1.0"使用NTP服务，nomodify notrap 不允许客户端配置服务器或者作为同步时间的节点。 # Use public servers from the pool.ntp.org project.
# Please consider joining the pool (http://www.pool.ntp.org/join.html).
#server .rhel.pool.ntp.org iburst
#server .rhel.pool.ntp.org iburst
#server .rhel.pool.ntp.org iburst
#server .rhel.pool.ntp.org iburst
server 0.asia.pool.ntp.org //NTP官方服务器池：http://www.pool.ntp.org/zone/asia
server 1.asia.pool.ntp.org
server 2.asia.pool.ntp.org
server 3.asia.pool.ntp.org
server 127.127.1.0
fudge 127.127.1.0 stratum 8 //当NTP服务不可用时，使用NTP服务器当前时间同步给客户机
#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 # Specify the key identifier to use with the ntpdc utility.
#requestkey # Specify the key identifier to use with the ntpq utility.
#controlkey # 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-- for more details.
# Note: Monitoring will not be disabled with the limited restriction flag.
disable monitor
logfile /var/log/ntp.log
三，验证NTP服务
1，验证NTP服务器从官方NTP服务器同步时间
[root@localhost ~]# ntpstat //查看这台服务器是否连接到NTP官方服务器
synchronised to NTP server (160.16.201.66) at stratum
time correct to within ms
polling server every s
更改下时间，改为“错误”的时间。然后等待NTP服务自动同步准确的时间。
[root@localhost ~]# date
Wed Jan :: CST
使用命令"watch ntpq -p"查看NTP详细信息
Every .0s: ntpq -p Sat Jan ::
remote refid st t when poll reach delay offset jitter
==============================================================================
y.ns.gin.ntt.ne 249.224.99.213 u 110.259
time1.maxonline .GPS. u 330.752
send.mx.cdnetwo 133.100.8.2 u 87.927
*LOCAL() .LOCL. l 0.000 0.000 0.000
大约10分钟，同步成功。下面是同步成功的时间。时间同步成功后，并不会同步给硬件时间。系统重启后还会读取硬件时间同步给系统时间，所以需要重启前"clock -w"或者写入crontab。
Every .0s: ntpq -p Fri Feb ::
remote refid st t when poll reach delay offset jitter
==============================================================================
LOCAL() .LOCL. l 0.000 0.000 0.000
+218.189.210.4 118.143.17.82 u 80.928 4.568 0.000
*x.ns.gin.ntt.ne 249.224.99.213 u 84.978 -9.332 0.000
+31.193.144.2.ar 131.107.13.100 u 311.808 -52.737 0.000
----. 218.100.41.254 u 464.010 114.567 0.000
2，验证Linux客户端从NTP服务器（192.168.10.10）同步时间
手动同步时间成功，说明NTP服务没问题。可以在Linux客户机上建立crontab任务或者配置NTP服务来同步时间。
[root@localhost ~]# ntpdate -u 192.168.1.10
Feb :: ntpdate[]: adjust time server 192.168.1.10 offset -0.000051 sec
[root@localhost ~]# date
Thu Feb :: CST
四，配置Linux客户机自动同步时间的两种方法
1，使用crontab从NTP服务器同步时间
[root@localhost ~]# crontab -e 30 3 * * * /usr/sbin/ntpdate -u 192.168.10.10; /usr/sbin/clock -w //每天3:30从NTP服务器同步时间，并把系统时间同步给硬件时间。
2，使用NTP服务同步时间
安装NTP服务
[root@localhost ~]# yum install ntp
Loaded plugins: product-id, subscription-manager
This system is not registered to Red Hat Subscription Management. You can use subscription-manager to register.
Resolving Dependencies
--> Running transaction check
---> Package ntp.x86_64 :4.2.6p5-.el7 will be installed
--> Finished Dependency Resolution Dependencies Resolved ===========================================================================================================================================================================
Package Arch Version Repository Size
===========================================================================================================================================================================
Installing:
ntp x86_64 4.2.6p5-.el7 cdrom k Transaction Summary
===========================================================================================================================================================================
Install Package Total download size: k
Installed size: 1.4 M
Is this ok [y/d/N]: y
Downloading packages:
Running transaction check
Running transaction test
Transaction test succeeded
Running transaction
Installing : ntp-4.2.6p5-.el7.x86_64 /
Verifying : ntp-4.2.6p5-.el7.x86_64 / Installed:
ntp.x86_64 :4.2.6p5-.el7
更改"/etc/ntp.conf"，注释掉原有NTP服务器地址，加入"server 192.168.10.10"
# Use public servers from the pool.ntp.org project.
# Please consider joining the pool (http://www.pool.ntp.org/join.html).
#server .rhel.pool.ntp.org iburst
#server .rhel.pool.ntp.org iburst
#server .rhel.pool.ntp.org iburst
#server .rhel.pool.ntp.org iburst
server 192.168.10.10
将当前时间修改成“错误时间”，通过NTP服务来验证是否能够同步时间。
[root@localhost ~]# date
Sat Feb :: CST
[root@localhost ~]# date -s 20130123
Wed Jan :: CST
[root@localhost ~]# watch ntpq -p
Every .0s: ntpq -p Wed Jan :: remote refid st t when poll reach delay offset jitter
==============================================================================
192.168.10.10 211.233.84.186 u 0.707
Every .0s: ntpq -p Sat Feb ::
remote refid st t when poll reach delay offset jitter
==============================================================================
*192.168.10.10 194.225.150.25 u 0.746 98.114 70.556
