VM using KVM, time is not synchronized. After a 2 minute suspend, it keeps a permanent 2 min gap. Setting up another VM with different network config shows that network config prevents ntp from working. Fixing this network issue is out of topic.
However, the new VM that does not have the network issue does not synchronize either after a resume. Same test: suspend 2 minutes. Check the date difference with a machine that is properly synced. The 2 min delay is permanent.
This seems to be a common issue and there is controversy about how to keep a VM synchronized, and about using NTP and kvm-clock at the same time. I found many references to that but no answer.
I have a Debian VM with
ntpd running but not correcting time. For instance, after a suspend/resume, I get a permanent 2 minute offset.
/etc/ntp.conf is default or close to default, nothing fancy:
# /etc/ntp.conf, configuration for ntpd; see ntp.conf(5) for help driftfile /var/lib/ntp/ntp.drift # Enable this if you want statistics to be logged. #statsdir /var/log/ntpstats/ statistics loopstats peerstats clockstats filegen loopstats file loopstats type day enable filegen peerstats file peerstats type day enable filegen clockstats file clockstats type day enable # You do need to talk to an NTP server or two (or three). #server ntp.your-provider.example # pool.ntp.org maps to about 1000 low-stratum NTP servers. Your server will # pick a different set every time it starts up. Please consider joining the # pool: <http://www.pool.ntp.org/join.html> server 0.debian.pool.ntp.org iburst server 1.debian.pool.ntp.org iburst server 2.debian.pool.ntp.org iburst server 3.debian.pool.ntp.org iburst # Access control configuration; see /usr/share/doc/ntp-doc/html/accopt.html for # details. The web page <http://support.ntp.org/bin/view/Support/AccessRestrictions> # might also be helpful. # # Note that "restrict" applies to both servers and clients, so a configuration # that might be intended to block requests from certain clients could also end # up blocking replies from your own upstream servers. # By default, exchange time with everybody, but don't allow configuration. restrict -4 default kod notrap nomodify nopeer noquery restrict -6 default kod notrap nomodify nopeer noquery # Local users may interrogate the ntp server more closely. restrict 127.0.0.1 restrict ::1 # Clients from this (example!) subnet have unlimited access, but only if # cryptographically authenticated. #restrict 192.168.123.0 mask 255.255.255.0 notrust # If you want to provide time to your local subnet, change the next line. # (Again, the address is an example only.) #broadcast 192.168.123.255 # If you want to listen to time broadcasts on your local subnet, de-comment the # next lines. Please do this only if you trust everybody on the network! #disable auth #broadcastclient
ntpq seems to report a problem:
# cat ntpq -pn remote refid st t when poll reach delay offset jitter ============================================================================== 126.96.36.199 .INIT. 16 u - 1024 0 0.000 0.000 0.000 188.8.131.52 .INIT. 16 u - 1024 0 0.000 0.000 0.000 184.108.40.206 .INIT. 16 u - 1024 0 0.000 0.000 0.000 220.127.116.11 .INIT. 16 u - 1024 0 0.000 0.000 0.000
However, I'm not a netcat wizard, but AFAIU outgoing traffic on UDP port 123 goes through:
# nc -vvzu 18.104.22.168 123 mail.lafkor.de [22.214.171.124] 123 (ntp) open sent 0, rcvd 0
Is this test enough to rule out the firewall issue?
The host (also a Debian machine) has the same NTP configuration and synchronization is working. The network config for both machines is different, which is why I'm thinking it might be a network issue.
Any other useful test I could run?
I don't think the
tinker panic 0 parameter is relevant here as it is meant to force updates on huge gaps, not 2 minute gaps. And anyway, AFAIU, it would affect the behavior in case of time offset, but it would not solve
ntpq -pn returning only zeros.
FWIW, other test outputs inspired from this question:
# ntpq ntpq> pe remote refid st t when poll reach delay offset jitter ============================================================================== mail.lafkor.de .INIT. 16 u - 1024 0 0.000 0.000 0.000 atoll.tropicdre .INIT. 16 u - 1024 0 0.000 0.000 0.000 oods.roflcopter .INIT. 16 u - 1024 0 0.000 0.000 0.000 ntp-3.arkena.ne .INIT. 16 u - 1024 0 0.000 0.000 0.000 ntpq> as ind assid status conf reach auth condition last_event cnt =========================================================== 1 21025 8011 yes no none reject mobilize 1 2 21026 8011 yes no none reject mobilize 1 3 21027 8011 yes no none reject mobilize 1 4 21028 8011 yes no none reject mobilize 1 ntpq> rv associd=0 status=c012 leap_alarm, sync_unspec, 1 event, freq_set, version="ntpd email@example.com Fri Apr 10 19:04:04 UTC 2015 (1)", processor="x86_64", system="Linux/3.16.0-4-amd64", leap=11, stratum=16, precision=-23, rootdelay=0.000, rootdisp=6683.055, refid=INIT, reftime=00000000.00000000 Mon, Jan 1 1900 0:09:21.000, clock=d9b51587.b7a1085f Tue, Sep 29 2015 15:49:59.717, peer=0, tc=3, mintc=3, offset=0.000, frequency=-0.125, sys_jitter=0.000, clk_jitter=0.000, clk_wander=0.000 ntpq> rv 21025 associd=21025 status=8011 conf, sel_reject, 1 event, mobilize, srcadr=mail.lafkor.de, srcport=123, dstadr=126.96.36.199, dstport=123, leap=11, stratum=16, precision=-23, rootdelay=0.000, rootdisp=0.000, refid=INIT, reftime=00000000.00000000 Mon, Jan 1 1900 0:09:21.000, rec=00000000.00000000 Mon, Jan 1 1900 0:09:21.000, reach=000, unreach=1137, hmode=3, pmode=0, hpoll=10, ppoll=10, headway=0, flash=1600 peer_stratum, peer_dist, peer_unreach, keyid=0, offset=0.000, delay=0.000, dispersion=15937.500, jitter=0.000, xleave=0.167, filtdelay= 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00, filtoffset= 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00, filtdisp= 16000.0 16000.0 16000.0 16000.0 16000.0 16000.0 16000.0 16000.0
tcpdump / ntpdate tests
On a machine where NTP sync works correctly, I launch
tcpdump udp port ntp and when I restart
ntpd, I see this kind of output:
# tcpdump udp port ntp tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on eth0, link-type EN10MB (Ethernet), capture size 262144 bytes 17:31:33.719166 IP 10.0.2.15.ntp > spica.beduzar.fr.ntp: NTPv4, Client, length 48 17:31:33.736804 IP spica.beduzar.fr.ntp > 10.0.2.15.ntp: NTPv4, Server, length 48 17:31:35.973551 IP 10.0.2.15.ntp > ntp.tuxfamily.net.ntp: NTPv4, Client, length 48 17:31:35.992671 IP ntp.tuxfamily.net.ntp > 10.0.2.15.ntp: NTPv4, Server, length 48 [...]
On the machine I have the issue with, I don't see any output at all when restarting
ntpd (no request, no reply). Shouldn't I at least see the requests?
On the good machine:
# ntpdate 0.debian.pool.ntp.org 29 Sep 17:24:49 ntpdate: adjust time server 188.8.131.52 offset -0.005196 sec
On the bad machine:
# ntpdate 0.debian.pool.ntp.org 29 Sep 17:43:18 ntpdate: no server suitable for synchronization found
Test with another VM
We setup another VM with the same NTP configuration but another network configuration.
This results of
ntpdate are correct and
ntpq -pn returns good results. So apparently, the network configuration is indeed an issue on the faulty VM.
However, the new VM does not synchronize either. If I suspend it so that it has about 100s lag, it does not synchronize (I mean after a few minutes, the gap is still the same number of seconds). However, when restarting ntpd, it synchronize instantly.
I appear to have two issues:
Network config on the first VM
ntp does not synchronize on both (unless restarted)