[root@server yum.repos.d]# yum install ntp
已加载插件：fastestmirror, priorities, refresh-packagekit, security
设置安装进程
Loading mirror speeds from cached hostfile
 * epel: ftp.iij.ad.jp
解决依赖关系
--> 执行事务检查
---> Package ntp.x86_64 0:4.2.6p5-10.el6.centos.2 will be 升级
---> Package ntp.x86_64 0:4.2.6p5-15.el6.centos will be an update
--> 处理依赖关系 ntpdate = 4.2.6p5-15.el6.centos，它被软件包 ntp-4.2.6p5-15.el6.centos.x86_64 需要
--> 执行事务检查
---> Package ntpdate.x86_64 0:4.2.6p5-10.el6.centos.2 will be 升级
---> Package ntpdate.x86_64 0:4.2.6p5-15.el6.centos will be an update
--> 完成依赖关系计算

依赖关系解决

====================================================================================================================================
 软件包                      架构                       版本                                      仓库                         大小
====================================================================================================================================
正在升级:
 ntp                         x86_64                     4.2.6p5-15.el6.centos                     updates                     600 k
为依赖而更新:
 ntpdate                     x86_64                     4.2.6p5-15.el6.centos                     updates                      79 k

事务概要
====================================================================================================================================
Upgrade       2 Package(s)

总下载量：679 k
确定吗？[y/N]：y
下载软件包：
(1/2): ntp-4.2.6p5-15.el6.centos.x86_64.rpm                                                                  | 600 kB     00:01
(2/2): ntpdate-4.2.6p5-15.el6.centos.x86_64.rpm                                                              |  79 kB     00:00
------------------------------------------------------------------------------------------------------------------------------------
总计                                                                                                249 kB/s | 679 kB     00:02
运行 rpm_check_debug
执行事务测试
事务测试成功
执行事务
  正在升级   : ntpdate-4.2.6p5-15.el6.centos.x86_64                                                                             1/4
  正在升级   : ntp-4.2.6p5-15.el6.centos.x86_64                                                                                 2/4
  清理       : ntp-4.2.6p5-10.el6.centos.2.x86_64                                                                               3/4
  清理       : ntpdate-4.2.6p5-10.el6.centos.2.x86_64                                                                           4/4
  Verifying  : ntpdate-4.2.6p5-15.el6.centos.x86_64                                                                             1/4
  Verifying  : ntp-4.2.6p5-15.el6.centos.x86_64                                                                                 2/4
  Verifying  : ntp-4.2.6p5-10.el6.centos.2.x86_64                                                                               3/4
  Verifying  : ntpdate-4.2.6p5-10.el6.centos.2.x86_64                                                                           4/4

更新完毕:
  ntp.x86_64 0:4.2.6p5-15.el6.centos

作为依赖被升级:
  ntpdate.x86_64 0:4.2.6p5-15.el6.centos

完毕！
[root@server yum.repos.d]#

[root@server ~]# ntpdate ntp.api.bz
10 Jan 18:53:58 ntpdate[11156]: adjust time server 114.118.7.161 offset 0.000293 sec
[root@server ~]# dig  ntp.api.bz

; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.62.rc1.el6 <<>> ntp.api.bz
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 36024
;; flags: qr rd ra; QUERY: 1, ANSWER: 4, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;ntp.api.bz.            IN    A

;; ANSWER SECTION:
ntp.api.bz.        63    IN    CNAME    time.phpts.com.
time.phpts.com.        63    IN    CNAME    ntp.ntsc.ac.cn.
ntp.ntsc.ac.cn.        644    IN    A    114.118.7.163
ntp.ntsc.ac.cn.        644    IN    A    114.118.7.161

;; Query time: 31 msec
;; SERVER: 114.114.114.114#53(114.114.114.114)
;; WHEN: Mon Jan 10 18:54:03 2022
;; MSG SIZE  rcvd: 116

[root@server ~]# crontab -l
*/5     *     *    *    *   /usr/sbin/ntpdate ntp.api.bz>>/dev/null 2>&1
[root@server ~]#