ntp 状态及含义
ntp 又叫 Network Protocol Protocol，是一种通过网络来同步时间的协议。
当在linux里维护自己的NTP server时，通过ntpq命令可以查看当前ntp server的状态。
而linux ntp客户端可以通过ntptime来查看当前ntp的同步情况，通过ntpdate来手动同步时间。
ntpdate
强制同步时间
- 如果有
ntpd，需要先关闭，再同步
service ntp stop
ntpdate time.nist.gov
service ntp start
- 或者是加上
-u参数
ntpdate -u time.nist.gov
- 或者是手动同步
date -u --set='2016-09-20 08:14:17.427319'
ntpq
ntpq -pn
root@owning:~# ntpq -pn
remote refid st t when poll reach delay offset jitter
==============================================================================
+193.228.143.14 192.36.143.151 2 u 142 256 317 247.201 20.400 15.036
-202.112.10.37 10.3.8.150 5 u 177 256 373 49.110 5.891 1.191
+61.216.153.106 118.163.81.63 3 u 151 256 377 53.737 -4.461 1.382
*120.25.108.11 10.137.53.7 2 u 215 256 377 7.486 7.879 1.613
-91.189.89.198 17.253.34.125 2 u 215 256 377 402.811 -35.993 9.119
root@owning:~#
输出含义
- remote and refid: remote NTP server, and its NTP server
- st: stratum of server
# from https://serverfault.com/questions/277375/ntpdate-d-server-dropped-strata-too-high NTP increases the stratum for each level in the hierarchy - a NTP server pulling time from a "stratum 1" server would advertise itself as "stratum 2" to its clients. A stratum value of "16" is reserved for unsynchronized servers meaning that your internal NTP server at 192.168.92.82 thinks not to have a reliable timesource (i.e. not synchronizing to a higher-level stratum server). - t: type of server (local, unicast, multicast, or broadcast)
- poll: how frequently to query server (in seconds)
- when: how long since last poll (in seconds)
-
reach: octal bitmask of success or failure of last 8 queries (left-shifted); 377 = 11111111 = all recent queries were successful; 257 = 10101111 = 4 most recent were successful, 5 and 7 failed
最后八次查询（每次查询间隔为
poll）的结果。这个值非常的 tricky，用了八位的bit，先转换成八进制，再以字符串的方式显示出来。
00 000 000 -> 0 00 000 001 -> 1 00 000 011 -> 3 00 000 111 -> 7 00 001 111 -> 17 00 011 111 -> 37 00 111 111 -> 77 01 111 111 -> 177 11 111 111 -> 377 10 101 111 -> 257测试发现，当ntp server重启后，值变为
17（即最近四次的query，除去刚启动时的一次，说明启动后间隔poll的三次query都成功），这时remote会加上*。下面是示例。# 第三次，reach 是 7。 Wed Aug 15 11:56:02 CST 2018 remote refid st t when poll reach delay offset jitter ============================================================================== 202.108.6.95 10.6.63.22 2 u 65 64 7 24.777 -15.577 0.082 # 第四次，reach 是 17。 Wed Aug 15 11:56:03 CST 2018 remote refid st t when poll reach delay offset jitter ============================================================================== *202.108.6.95 10.6.63.22 2 u - 64 17 24.327 -15.328 0.209 - delay: network round trip time (in milliseconds)
- offset: difference between local clock and remote clock (in milliseconds)
- jitter: difference of successive time values from server (high jitter could be due to an unstable clock or, more likely, poor network performance)
参考
remote 前的符号是什么意思？
从 NTP源码 查看，是根据查询上游服务器的结果的返回值来决定展示什么符号。
char flash3[] = " x.-+#*o"; /* flash decode for peer status version 3 */
所以得查 RFC1305，才能知道每个符号的具体含义：
' ' 0, rejected
'x' 1, passed sanity checks (tests 1 through 8 in Section 3.4.3)
'.' 2, passed correctness checks (intersection algorithm in Section 4.2.1)
'-' 3, passed candidate checks (if limit check implemented)
'+' 4, passed outlyer checks (clustering algorithm in Section 4.2.2)
'#' 5, current synchronization source; max distance exceeded (if limit check
implemented)
'*' 6, current synchronization source; max distance okay
只有ntp server的remote(upstream)为完全同步时，其它ntp client才能从这个server同步时间。
'o' 7, reserved
参考
- from ntp source code
-
t: type of server
case MODE_CLIENT:
if (ISREFCLOCKADR(&srcadr))
type = 'l'; /* local refclock*/
else if (SOCK_UNSPEC(&srcadr))
type = 'p'; /* pool */
else if (IS_MCAST(&srcadr))
type = 'a'; /* manycastclient */
else
type = 'u'; /* unicast */
break;
ntptime
[root@node01 ~]# ntptime
ntp_gettime() returns code 5 (ERROR)
time de9e7743.14f3881c Thu, May 10 2018 15:46:11.081, (.081841975),
maximum error 16000000 us, estimated error 16000000 us, TAI offset 0
ntp_adjtime() returns code 5 (ERROR)
modes 0x0 (),
offset 0.000 us, frequency -8.823 ppm, interval 1 s,
maximum error 16000000 us, estimated error 16000000 us,
status 0x2041 (PLL,UNSYNC,NANO),
time constant 9, precision 0.001 us, tolerance 500 ppm,
[root@node01 ~]#
如果系统起了 ntpd 服务，手动同步主机时间（date -u --set XXX）后，ntptime 可能会如上错误。
其它
timedatectl
root@owning:~# timedatectl status
Local time: Thu 2018-05-17 11:59:14 CST
Universal time: Thu 2018-05-17 03:59:14 UTC
RTC time: Thu 2018-05-17 03:59:12
Timezone: Asia/Shanghai (CST, +0800)
NTP enabled: yes
NTP synchronized: yes
RTC in local TZ: no
DST active: n/a
root@owning:~#
问题及排查
问题：ntpdate 同步，报 no server suitable for synchronization found
ntp client 从 ntp server 同步，报错 no server suitable for synchronization found
[root@client ~]# ntpdate -dv -b 192.168.2.61
15 Aug 11:38:35 ntpdate[3123]: ntpdate 4.2.6p5@1.2349-o Fri Jan 26 02:18:05 UTC 2018 (1)
Looking for host 192.168.2.61 and service ntp
host found : bigtable-01
transmit(192.168.2.61)
receive(192.168.2.61)
transmit(192.168.2.61)
receive(192.168.2.61)
transmit(192.168.2.61)
receive(192.168.2.61)
transmit(192.168.2.61)
receive(192.168.2.61)
192.168.2.61: Server dropped: strata too high
server 192.168.2.61, port 123
stratum 16, precision -22, leap 11, trust 000
refid [192.168.2.61], delay 0.02580, dispersion 0.00003
transmitted 4, in filter 4
reference time: 00000000.00000000 Mon, Jan 1 1900 8:05:43.000
originate timestamp: df1e1ebb.39c5652e Wed, Aug 15 2018 11:38:35.225
transmit timestamp: df1e1ebb.424aafc4 Wed, Aug 15 2018 11:38:35.258
filter delay: 0.02583 0.02591 0.02580 0.02589
0.00000 0.00000 0.00000 0.00000
filter offset: -0.03335 -0.03343 -0.03338 -0.03343
0.000000 0.000000 0.000000 0.000000
delay 0.02580, dispersion 0.00003
offset -0.033386
15 Aug 11:38:35 ntpdate[3123]: no server suitable for synchronization found
[root@client ~]#
从这段输出，stratum 为 16，16 是系统预留值，表明 ntp server 还未完全同步。
192.168.2.61: Server dropped: strata too high
server 192.168.2.61, port 123
stratum 16, precision -22, leap 11, trust 000
在 ntp server 上执行 ntpq -pn，也能发现，ntp server 和 upstream 的时间比较接近，但还没有完全同步（remote 前面没有 * 的标记）。
# ntp server 上检查
[root@server ~]# ntpq -pn
remote refid st t when poll reach delay offset jitter
==============================================================================
202.108.6.95 10.6.63.22 2 u 56 64 7 24.749 -23.655 0.091
[root@server ~]#
ntp server 在启动后，需要等几个poll周期（1+3个周期，可以根据reach字段来判断。）之后，才会认为和 upstream 已同步。
[root@server ~]# ntpq -pn
remote refid st t when poll reach delay offset jitter
==============================================================================
*202.108.6.95 10.6.63.22 2 u 43 64 17 24.478 -23.552 0.092
[root@server ~]#
等 ntp server 同步后，ntp client 重试下，就能同步了。
[root@client ~]# ntpdate -dv -b 192.168.2.61
15 Aug 11:51:56 ntpdate[6619]: ntpdate 4.2.6p5@1.2349-o Fri Jan 26 02:18:05 UTC 2018 (1)
Looking for host 192.168.2.61 and service ntp
host found : bigtable-01
transmit(192.168.2.61)
receive(192.168.2.61)
transmit(192.168.2.61)
receive(192.168.2.61)
transmit(192.168.2.61)
receive(192.168.2.61)
transmit(192.168.2.61)
receive(192.168.2.61)
server 192.168.2.61, port 123
stratum 3, precision -22, leap 00, trust 000
refid [192.168.2.61], delay 0.02580, dispersion 0.00003
transmitted 4, in filter 4
reference time: df1e21ae.f96502d4 Wed, Aug 15 2018 11:51:10.974
originate timestamp: df1e21dc.2d33be99 Wed, Aug 15 2018 11:51:56.176
transmit timestamp: df1e21dc.28b5ea58 Wed, Aug 15 2018 11:51:56.159
filter delay: 0.02588 0.02592 0.02580 0.02589
0.00000 0.00000 0.00000 0.00000
filter offset: 0.017501 0.017394 0.017443 0.017392
0.000000 0.000000 0.000000 0.000000
delay 0.02580, dispersion 0.00003
offset 0.017443
15 Aug 11:51:56 ntpdate[6619]: step time server 192.168.2.61 offset 0.017443 sec
[root@client ~]#
