以RHCE實(shí)驗(yàn)室為準(zhǔn),一個(gè)簡(jiǎn)單的NTP時(shí)間服務(wù)器標(biāo)準(zhǔn)配置如下:
服務(wù)器端:
首先修正下系統(tǒng)時(shí)間,并將系統(tǒng)時(shí)間寫(xiě)進(jìn)硬件時(shí)間里
date MMDDhhmmYYYY.ss;hwclock -w
vim /etc/ntp.conf
restrict default nomodify notrap noquery
restrict 127.0.0.1
restrict 192.168.1.0 mask 255.255.255.0 nomodify notrap
server 127.127.1.0
fudge 127.127.1.0 stratum 0

客戶機(jī)端:
vim /etc/ntp.conf
server 192.168.1.2
vim /etc/ntp/step-ticker
192.168.1.2
客戶端重啟ntpd服務(wù)即可看到效果 service ntpd restart

※在授課過(guò)程發(fā)現(xiàn)，虛擬的linux的時(shí)間比真實(shí)機(jī)越走越慢，具體原因分析如下:
Linux 2.6核心里把系統(tǒng)計(jì)時(shí)器的頻率加高到1000 Hz ，VMware沒(méi)辦法真的每隔1ms就報(bào)一次訊號(hào)給guestOS，所以guestOS里的Linux 2.6無(wú)法確實(shí)接到計(jì)時(shí)器的訊號(hào)。本來(lái)這也不應(yīng)該造成問(wèn)題，不過(guò)2.6核心處理這個(gè)"tick loss"的程式有問(wèn)題，以致于guestOS里的Linux 2.6系統(tǒng)時(shí)間走一秒會(huì)慢一秒；外面過(guò)了兩秒里面只過(guò)了一秒。具體解決方案也有:可以修改內(nèi)核及安裝vmware-tools軟件包，均麻煩。

下面是我家里的vmware5.5虛擬機(jī)(如果不能上外網(wǎng)的話，可以選擇內(nèi)部ntp時(shí)間服務(wù)器)
①直接用腳本解決不能對(duì)時(shí)的問(wèn)題，腳本如下: /root/ntptime.sh
#!/bin/bash
while :
do
/usr/sbin/ntpdate ntp.api.bz >/dev/null 2>&1
sleep 30
done
放入后臺(tái)執(zhí)行 nohup sh ntptime.sh &?

②當(dāng)然還是crontab出馬了，在這里注意下腳本與crontab的區(qū)別，腳本可以控制到秒，而crontab只能到分 vim /etc/crontab
*/1 * * * * root /usr/sbin/ntpdate ntp.api.bz >/dev/null 2>&1
效果很明顯，每隔一分鐘，系統(tǒng)自動(dòng)對(duì)時(shí)，呵呵。
[root@ltos mail]# tcpdump -v host 192.168.0.154 and 221.130.196.230
tcpdump: listening on eth0, link-type EN10MB (Ethernet), capture size 96 bytes
13:16:02.359384 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto: UDP (17), length: 76) yuhongchun027.com.ntp > 221.130.196.230.ntp: NTPv4, length 48
Client, Leap indicator: clock unsynchronized (192), Stratum 0, poll 4s, precision -6
Root Delay: 1.000000, Root dispersion: 1.000000, Reference-ID: (unspec)
?? Reference Timestamp: 0.000000000
?? Originator Timestamp: 0.000000000
?? Receive Timestamp:??? 0.000000000
?? Transmit Timestamp:?? 3464918162.358386999 (2009/10/19 13:16:02)
???? Originator - Receive Timestamp: 0.000000000
???? Originator - Transmit Timestamp: 3464918162.358386999 (2009/10/19 13:16:02)
13:16:02.511502 IP (tos 0x0, ttl 49, id 5224, offset 0, flags [none], proto: UDP (17), length: 76) 221.130.196.230.ntp > yuhongchun027.com.ntp: NTPv4, length 48
Server, Leap indicator: (0), Stratum 2, poll 4s, precision -18
Root Delay: 0.158142, Root dispersion: 0.027862, Reference-ID: clock.fmt.he.net
?? Reference Timestamp: 3464917189.288964740 (2009/10/19 12:59:49)
?? Originator Timestamp: 3464918162.358386999 (2009/10/19 13:16:02)
?? Receive Timestamp:??? 3464918182.209876791 (2009/10/19 13:16:22)
?? Transmit Timestamp:?? 3464918182.209906405 (2009/10/19 13:16:22)
???? Originator - Receive Timestamp: +19.851489782
???? Originator - Transmit Timestamp: +19.851519405
13:16:02.512579 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto: UDP (17), length: 76) yuhongchun027.com.ntp > 221.130.196.230.ntp: NTPv4, length 48
Client, Leap indicator: clock unsynchronized (192), Stratum 0, poll 4s, precision -6
Root Delay: 1.000000, Root dispersion: 1.000000, Reference-ID: (unspec)
?? Reference Timestamp: 0.000000000
?? Originator Timestamp: 0.000000000
?? Receive Timestamp:??? 0.000000000
?? Transmit Timestamp:?? 3464918162.512529999 (2009/10/19 13:16:02)
???? Originator - Receive Timestamp: 0.000000000
???? Originator - Transmit Timestamp: 3464918162.512529999 (2009/10/19 13:16:02)
13:16:02.688528 IP (tos 0x0, ttl 49, id 5242, offset 0, flags [none], proto: UDP (17), length: 76) 221.130.196.230.ntp > yuhongchun027.com.ntp: NTPv4, length 48
Server, Leap indicator: (0), Stratum 2, poll 4s, precision -18
Root Delay: 0.158142, Root dispersion: 0.027862, Reference-ID: clock.fmt.he.net

※另外值得注意的是，盡管時(shí)間是一件很麻煩的事(還有UTC與GMT、系統(tǒng)時(shí)間與硬件時(shí)間的區(qū)別)，但其實(shí)在生產(chǎn)環(huán)境中，這件事很簡(jiǎn)單--服務(wù)器投入運(yùn)行之前必須用crontab對(duì)時(shí)；如果時(shí)間不同步的話是件很麻煩的事，我維護(hù)的dovecot服務(wù)器經(jīng)常因?yàn)闀r(shí)間問(wèn)題出問(wèn)題，還有FreeBSD下的jail虛擬機(jī)。所以時(shí)間的同步是linux/unix一件非常重要的事情，希望大家注意。

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