Using NTP in Integrity VM environments is recommended to keep
time-of-day clocks in sync and correct. Use xntpd on HP-UX and ntpd on Linux to synchronize time
use NTP.
NTP Configuration on a VM Host
On each VM Host, NTP should be configured just as it would be
on any typical (non-virtual) system. In /etc/ntp.conf, specify a drift file and one or more high quality time servers:
driftfile /etc/ntp.drift
server <A-HIGH-QUALITY-TIME-SERVER> prefer # a preferred time source
server <ANOTHER-HIGH-QUALITY-TIME-SERVER> # a backup time source
server <YET-ANOTHER-HIGH-QUALITY-TIME-SERVER> |
The local clock should also be configured as a fall back if
necessary:
server 127.127.1.0 # use local clock as backup
fudge 127.127.1.0 stratum 10 # show poor quality |
If you have a group of VM Hosts that you would like to synchronize,
you can add "peer" references in the /etc/ntp.conf file for each of those associated VM Hosts, so they will do mutual
synchronization:
peer <AN-ASSOCIATED-VM-HOST>
peer <ANOTHER-ASSOCIATED-VM-HOST>
peer <YET-ANOTHER-ASSOCIATED-VM-HOST> |
After configuring the Host's /etc/ntp.conf file, assuming the NTP is already enabled, (that is, the XNTPD variable
in /etc/rc.config.d/netdaemons is set to 1, as
in export XNTPD-1), you can execute /sbin/init.d/xntpd start to restart xntpd on the HP-UX VM Host.
NTP Configuration on a VM Guest
Because NTP was not designed to run inside a virtual machine,
using NTP on VM guests requires special configuration to be stable.
Using a typical default NTP configuration on a VM guest might result
in NTP instability and failure to synchronize, or in apparent lost
time on the guest. To avoid these virtualization related NTP issues,
each VM guest should get its time directly from the VM Host. Also,
VM guests should not serve time to any other systems.
You can monitor NTP status by using the ntpq -p command and noting the offset and the disp values. Ideally both values will be well under
100. For information about how to check NTP stability, see the HP-UX Internet Services Administrators Guide.
You can improve time stability on VM guests by tuning NTP to
poll more frequently for time corrections. The default NTP values
for the minpoll and maxpoll intervals are 6 (64 seconds) and 10 (1024 seconds) respectively.
NTP adjusts the current polling interval depending on network quality
and delays. A VM guest uses a virtual lan that can cause NTP to set
the polling value incorrectly. To help mitigate this issue use the minpoll and maxpoll directives
in the ntp.conf file to change the polling intervals.
Start with minpoll at 4 (16 seconds)
and maxpoll at 6 (64 seconds) and then reduce maxpoll towards 4 if necessary to force shorter polling
intervals. HP recommends that a VM guest never be allowed to deliver
time (allow guests only to be a time consumers). Because a VM guest
never delivers time, you do not need to configure the local clock
(server 127.127.1.0) or an ntp.drift file. So,
the ntp.conf file on a VM guest should be as
simple as the single line:
server <VM-HOST-SERVER-NAME> minpoll 4 maxpoll 6 |
After configuring the guest's /etc/ntp.conf file, assuming NTP is already enabled (that is, the XNTPD variable
in /etc/rc.config.d/netdaemons is set to 1, as
in export XNTPD=1), you can run the following commands on an HP-UX
guest to sync its time with the VM Host and restart xntpd:
/sbin/init.d/xntpd stop
/usr/sbin/ntpdate -b <VM-HOST-SERVER-NAME>
/sbin/init.d/xntpd start |
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 | NOTE: For VM guests that are on a different subnet than the VM Host,
the VM Host may not be the best source of time if there is another
accurate time server available with less network latency. In the case
of different subnets, measure latency from the guest to various time
servers using the ping and traceroute commands to determine which potential time server has the least
network latency. Using the VM Host may be the best solution, but
this depends on your local network topology and the relative network
distance to alternate time servers. If using an alternate (non-VM-Host)
time server appears best, it may be helpful for the alternate time
server and the VM Host to use each other for peer mutual time synchronization. |
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