注意:NTP服務並不是在任何情況下都會進行同步的。當時鍾服務器時間和本地時間相差大於1000s時,NTP服務就會認爲是人爲調整了時鐘或出現了硬件故障,例如CMOS電池損壞等。此時,NTP服務就會退出,需要人工(ntpdate …)進行時鐘同步。
在NTP中,定義了時間按照服務器的等級傳播,按照離外部UTC源遠近將所有的服務器歸入不同的Stratum(層)中,例如把通過GPS(Global Positioning System,全球定位系統)取得發送標準時間的服務器叫Stratum-1的NTP服務器,而Stratum-2則從Stratum-1獲取時間,Stratum-3從Stratum-2獲取時間,以此類推,但Stratum層的總數限制在15以內。所有這些服務器在邏輯上形成階梯式的架構相互連接,而Stratum-1的時間服務器是整個系統的基礎。
當用ntpdate -d 來查詢時會發現導
致 no server suitable for synchronization found 的錯誤的信息有以下2個:錯誤1.Server dropped: Strata too high在ntp客戶端運行ntpdate serverIP,出現no server suitable for synchronization found的錯誤。在ntp客戶端用ntpdate -d serverIP查看,發現有“Server dropped: strata too high”的錯誤,並且顯示“stratum 16”。而正常情況下stratum這個值得範圍是“0~15”。
這是因爲NTP server還沒有和其自身或者它的server同步上。以下的定義是讓NTP Server和其自身保持同步,如果在/ntp.conf中定義的server都不可用時,將使用local時間作爲ntp服務提供給ntp客戶端。
server 127.127.1.0
fudge 127.127.1.0 stratum 8
在ntp server上重新啓動ntp服務後,ntp server自身或者與其server的同步的需要一個時間段,這個過程可能是5分鐘,在這個時間之內在客戶端運行ntpdate命令時會產生no server suitable for synchronization found的錯誤。
# 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
# 允許內網其他機器同步時間
#restrict 192.168.1.0 mask 255.255.255.0 nomodify notrap
# 默認允許任何主機進行時間同步
#restrict default ignore
# Use public servers from the pool.ntp.org project.
# Please consider joining the pool (http://www.pool.ntp.org/join.html).
# 中國這邊最活躍的時間服務器 : http://www.pool.ntp.org/zone/cn
server 10.18.64.191 #ATS時鐘源
#server cn.pool.ntp.org perfer # 中國國家受時中心
#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
# # 允許上層時間服務器主動修改本機時間
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
# 外部時間服務器不可用時,以本地時間作爲時間服務
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
[root@localhost ~]# date
2016年 10月 31日 星期一 10:35:39 CST
[root@localhost ~]# systemctl stop ntpd
[root@localhost ~]# ntpdate 10.18.64.191
30 May 12:31:25 ntpdate[36306]: step time server 10.18.64.191 offset 81309314.623949 sec
[root@localhost 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
[root@localhost 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
[root@localhost 4.5_ntp_server]# date
2019年 05月 30日 星期四 13:41:12 CST