linux 时间同步

//查看可用ntp的rpm包
[root@mdb ~]# rpm -qa|grep ntp
fontpackages-filesystem-1.41-1.1.el6.noarch
ntp-4.2.6p5-3.el6.centos.x86_64
ntpdate-4.2.6p5-3.el6.centos.x86_64

//查看是否安装了ntp
[root@mdb ~]# yum list|grep ntp
fontpackages-filesystem.noarch             1.41-1.1.el6                 @anaconda-CentOS-201303020151.x86_64/6.4
ntp.x86_64                                 4.2.6p5-3.el6.centos         @updates
ntpdate.x86_64                             4.2.6p5-3.el6.centos         @updates

//查看ntpd服务状态
[root@mdb ~]# service ntpd status
ntpd dead but pid file exists

//重启ntpd服务
[root@mdb ~]# service ntpd restart
Shutting down ntpd:                                        [FAILED]
Starting ntpd:                                             [  OK  ]

//再次查看ntpd服务状态
[root@mdb ~]# service ntpd status
ntpd (pid  31909) is running...

//查看曾经同步过的时间服务器
[root@mdb ~]# ntpq -p
remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
202.118.1.130   202.118.1.46     2 u    4   64    3   74.113  6512611   2.349
news.neu.edu.cn 202.118.1.46     2 u    3   64    3   45.810  6512613   8.422
dns1.synet.edu. 202.118.1.46     2 u    2   64    3  137.909  6512615   1.870
dns2.synet.edu. .INIT.          16 u    -   64    0    0.000    0.000   0.000

//查看当前时间
[root@mdb ~]# date
Sun Oct 25 16:19:42 CST 2015

//同步时间
[root@mdb ~]# ntpdate 202.118.1.130
26 Oct 10:27:48 ntpdate[32157]: the NTP socket is in use, exiting

//查看同步后的时间
[root@mdb ~]# date
Mon Oct 26 10:27:52 CST 2015

//同步时间计划任务
[root@mdb ~]# crontab -e

# system time sync leocen@2015-10-29
0 */4 * * * /usr/sbin/ntpdate 202.118.1.130 >/dev/null 2>&1; /usr/sbin/hwclock -w >/dev/null 2>&1