ntp原理与配置
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注意:NTP服务并不是在任何情况下都会进行同步的。当时钟服务器时间和本地时间相差大于1000s时,NTP服务就会认为是人为调整了时钟或出现了硬件故障,例如CMOS电池损坏等。此时,NTP服务就会退出,需要人工(ntpdate …)进行时钟同步。在NTP中,定义了时间按照服务器的等级传播,按照离外部UTC源远近将所有的服务器归入不同的Stratum(层)中,例如把通过GPS(Global Positioning System,全球定位系统)取得发送标准时间的服务器叫Stratum-1的NTP服务器,而Stratum-2则从Stratum-1获取时间,Stratum-3从Stratum-2获取时间,以此类推,但Stratum层的总数限制在15以内。所有这些服务器在逻辑上形成阶梯式的架构相互连接,而Stratum-1的时间服务器是整个系统的基础。
当用ntpdate -d 来查询时会发现导
致 no server suitable for synchronization found 的错误的信息有以下2个:错误1.Server dropped: Strata too high在ntp客户端运行ntpdate serverIP,出现no server suitable for synchronization found的错误。在ntp客户端用ntpdate -d serverIP查看,发现有“Server dropped: strata too high”的错误,并且显示“stratum 16”。而正常情况下stratum这个值得范围是“0~15”。
这是因为NTP server还没有和其自身或者它的server同步上。以下的定义是让NTP Server和其自身保持同步,如果在/ntp.conf中定义的server都不可用时,将使用local时间作为ntp服务提供给ntp客户端。
server 127.127.1.0
fudge 127.127.1.0 stratum 8
在ntp server上重新启动ntp服务后,ntp server自身或者与其server的同步的需要一个时间段,这个过程可能是5分钟,在这个时间之内在客户端运行ntpdate命令时会产生no server suitable for synchronization found的错误。
# For more information about this file, 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 with our time source, but do not
# permit the source to query or modify the service on this system.
#restrict default kod nomodify notrap nopeer noquery
#restrict -6 default kod 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 ::1
# Hosts on local network are less restricted.
#restrict 192.168.1.0 mask 255.255.255.0 nomodify notrap
# 允许内网其他机器同步时间
#restrict 192.168.1.0 mask 255.255.255.0 nomodify notrap
# 默认允许任何主机进行时间同步
#restrict default ignore
# Use public servers from the pool.ntp.org project.
# Please consider joining the pool (http://www.pool.ntp.org/join.html).
# 中国这边最活跃的时间服务器 : http://www.pool.ntp.org/zone/cn
server 10.18.64.191 #ATS时钟源
#server cn.pool.ntp.org perfer # 中国国家受时中心
#server 0.cn.pool.ntp.org # 1.cn.pool.ntp.org
#server 1.cn.pool.ntp.org
#server asia.pool.ntp.org
#server 0.asia.pool.ntp.org
#server 1.asia.pool.ntp.org
#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
#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
# allow update time by the upper server
# # 允许上层时间服务器主动修改本机时间
restrict 10.18.64.191 nomodify notrap noquery
#restrict cn.pool.ntp.org nomodify notrap noquery
#restrict 0.cn.pool.ntp.org nomodify notrap noquery
#restrict 1.cn.pool.ntp.org nomodify notrap noquery
#restrict asia.pool.ntp.org nomodify notrap noquery
#restrict 0.asia.pool.ntp.org nomodify notrap noquery
#restrict 1.asia.pool.ntp.org nomodify notrap noquery
# 外部时间服务器不可用时,以本地时间作为时间服务
server 127.127.1.0 # local clock
fudge 127.127.1.0 stratum 11
# 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 4 8 42
# Specify the key identifier to use with the ntpdc utility.
#requestkey 8
# Specify the key identifier to use with the ntpq utility.
#controlkey 8
# Enable writing of statistics records.
#statistics clockstats cryptostats loopstats peerstats
[[email protected] ~]# date
2016年 10月 31日 星期一 10:35:39 CST
[[email protected] ~]# systemctl stop ntpd
[[email protected] ~]# ntpdate 10.18.64.191
30 May 12:31:25 ntpdate[36306]: step time server 10.18.64.191 offset 81309314.623949 sec
[[email protected] 4.5_ntp_server]# ntpq -p
remote refid st t when poll reach delay offset jitter
==============================================================================
*10.18.64.191 LOCAL(0) 4 u 51 128 377 0.320 0.012 0.021
LOCAL(0) .LOCL. 11 l 1869 64 0 0.000 0.000 0.000
[[email protected] 4.5_ntp_server]# ntpstat
synchronised to NTP server (10.18.64.191) at stratum 5
time correct to within 26 ms
polling server every 128 s
[[email protected] 4.5_ntp_server]# date
2019年 05月 30日 星期四 13:41:12 CST
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