ntp - query a clock running a Network Time Protocol daemon,
either ntpd or xntpd
/usr/bin/ntp [-v] [-s] [-f] host1 | IPaddress1 ...
Specifies verbose output. The output shows the full contents
of the received NTP packets, plus the calculated
offset and delay. Sets local clock to remote time. This
only happens if the offset between the local and remote
time is less than 1000 seconds. The local clock is not
reset if the remote host is unsynchronized.
If you specify more than one host name on the command
line, ntp queries each host in order, waiting
for each host to answer or timeout before querying
the next host. The local clock is set to the time
of the first remote host that responds. Forces
setting local clock regardless of offset. The -f
option must be used with -s option. The local
clock is not reset if the remote host is unsynchronized.
The ntp command may be retired in a future release; use
the ntpdate(8) command instead.
The ntp command is used to determine the offset between
the local clock and a remote clock. It can also be used
to set the local host's time to a remote host's time. The
ntp command sends an NTP packet to the NTP daemon running
on each of the remote hosts specified on the command line.
The remote hosts must be running either the ntpd daemon or
xntpd daemon. When the NTP daemon on the remote host
receives the NTP packet, it fills in the fields (as specified
in RFC 1129), and sends the packet back. The ntp
command then formats and prints the results on the standard
output.
Note
You can specify hosts by either host name or Internet
address. The hosts that you specify must either exist in
the /etc/hosts file, or in the master hosts database, if
the database is being served to your system by BIND or
Network Information Service (NIS).
The default output shows the roundtrip delay of the NTP
packet in seconds, the estimated offset between the local
time and remote time in seconds, and the date in ctime
format. See the ctime(3) reference page for more information.
The -s and -f options can be used to reset the time of the
local clock.
Using the -s and -f options require that you be logged on
as superuser.
The following error messages can be returned by NTP: May
indicate that the NTP daemon is not running on the remote
host. The NTP command cannot resolve the specified host
name in the /etc/hosts file. Check that the host exists
in the /etc/hosts file, or that it exists in the master
hosts database, if the database is being served to your
system by BIND or NIS.
In the following examples, some output text lines may be
broken. The line end are marked with the backslash symbol
(\) and the following line is indented. Such text may
appear as a single line on your terminal. The following
is the default output to an ntp query about a remote host
with an internet address of 555.5.55.5: # /usr/bin/ntp
555.5.55.5 555.5.55.5: delay:1.845207 offset:-0.358460 \
Mon Aug 20 08:05:44 1991 The following is the verbose
output to an ntp query about the same remote host: #
/usr/bin/ntp -v 555.5.55.5
Packet from: [555.5.55.5] Leap 0, version 1, mode Server,
poll 6, precision \
-10 stratum 1 (WWVB) Synch Distance is 0000.1999
0.099991 Synch Dispersion is 0000.0000 0.000000 Reference
Timestamp is a7bea6c3.88b40000 \
Tue Aug 20 14:06:43 1991 Originate Timestamp is
a7bea6d7.d7e6e652 \
Tue Aug 20 14:07:03 1991 Receive Timestamp is
a7bea6d7.cf1a0000 \
Tue Aug 20 14:07:03 1991 Transmit Timestamp is
a7bea6d8.0ccc0000 \
Tue Aug 20 14:07:04 1991 Input Timestamp is
a7bea6d8.1a77e5ea \
Tue Aug 20 14:07:04 1991 555.5.55.5: delay:0.019028 offset:-0.043890
\
Tue Aug 20 14:07:04 1991
The fields are interpreted as follows: The address
of the remote host from which this NTP packet was
received. The leap second indicator. Non-zero if
there is to be a leap second inserted in the NTP
timescale. The bits are set before 23:59 on the
day of insertion and reset after 00:00 on the following
day. The NTP protocol version. The NTP
mode can be Server, Client, Symmetric Passive, Symmetric
Active, or Broadcast. See RFC 1129 for more
information on NTP modes. The desired poll rate of
the peer in seconds as a power of 2. For example,
if poll is equal to 6, that means that the poll
rate is one message exchanged every 2**6 seconds.
The precision of the remote host's clock in seconds
as a power of 2. For example, if precision is equal
to -10, that means that the precision is 2**-10.
The NTP daemon sets this automatically. The stratum
of the clock in the NTP hierarchy, along with
the source of the clock. The source is either the
name of a reference standard (such as WWVB or
GOES), or the Internet address of the clock that
this clock references. The values reported are
used internally by the NTP daemon. The values
reported are used internally by the NTP daemon.
The next five timestamps are given as NTP fixedpoint
values, in both hexadecimal and ctime. The
timestamps are set either by this NTP process, or
by the remote host you are querying. These timestamps
are used by the local host to calculate delay
and offset for this query. This specifies the last
time the remote host clock was adjusted. (remote
time) This specifies when the NTP request was
transmitted by the local host to the remote host.
(local time) This specifies when the NTP request
was received at the remote host. (remote time)
This specifies when the NTP response was transmitted
by the remote host. (remote time) This specifies
when the NTP response was received by the
local host. (local time) This field summarizes the
results of the query, giving the host name or
internet address of the responding clock specified
in the command line, the round-trip delay in seconds,
and the offset between the two clocks in seconds
(assuming symmetric round-trip times).
ctime(3), ntp.conf(4), ntpdate(8), xntpd(8), xntpdc(8),
ntpq(8)
Internet time synchronization: The Network Time Protocol
(RFC 1129)
Network Administration: Services
ntp(1)
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