Technical data

Configuring and Managing NTP
12.8 NTP Utilities
Use the following syntax when entering commands:
NTPTRACE [option...]
The following example shows output from an NTPTRACE. In this example, the
chain of servers from the local host to the stratum 1 server FRED, which is
synchronizing to a GPS reference clock.
$ NTPTRACE
LOCALHOST: stratum 3, offset -0.000000, synch distance1.50948
parrot.birds.com: stratum 2, offset -0.126774, synch distance 0.00909
fred.birds.com: stratum 1, offset -0.129567, synch distance 0.00168,
refid ’GPS’
All times are in seconds. The output fields on each line are as follows:
• Host name
• Host’s stratum
• Time offset between the host and the local host (not always zero for
LOCALHOST).
• Synchronization distance
• Reference clock ID (only for stratum-1 servers)
Table 12–4 describes the NTPTRACE command options.
Table 12–4 NTPTRACE Options
Option Description
-d Enables debugging output.
-n Displays IP addresses instead of host names. This may be necessary if
a name server is down.
-r retries Sets the number of retransmission attempts for each host. The default
is 5.
-t timeout Sets the retransmission timeout (in seconds). The default is 2.
-v Displays additional information about the NTP servers.
12.8.3 Making Run-Time Requests with NTPDC
Section 12.3 discussed how to use the configuration file to configure NTP on your
system. In addition to using a configuration file, you can make run-time changes
to NTP with query commands by running the NTPDC utility. NTPDC displays
time values in seconds.
Run-time requests are always authenticated requests. Authentication provides
verification that the requester has permission to make such changes but also
gives an extra degree of protection against transmission errors.
The reconfiguration facility works well with a server on the local host and
between time-synchronized hosts on the same LAN. The facility works poorly
for more distant hosts. Authenticated requests include a timestamp. The server
compares the timestamp to its receive timestamp. If they differ by more than a
small amount, the request is rejected. This is done for two reasons:
• It makes it more difficult for an intruder to overhear traffic on your LAN.
Configuring and Managing NTP 12–17