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ntp(1)
NAME
ntp - query a clock running a Network Time Protocol daemon, either ntpd or
xntpd
SYNOPSIS
/usr/bin/ntp [-v] [-s] [-f] host1 | IPaddress1 ...
OPTIONS
-v Specifies verbose output. The output shows the full contents of the
received NTP packets, plus the calculated offset and delay.
-s 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.
-f 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.
DESCRIPTION
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.
RESTRICTIONS
Using the -s and -f options require that you be logged on as superuser.
ERRORS
The following error messages can be returned by NTP:
*Timeout*
hostname is not responding
May indicate that the NTP daemon is not running on the remote host.
No such host: hostname
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.
EXAMPLES
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.
1. 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
2. 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:
Packet from: [internet address]
The address of the remote host from which this NTP packet was
received.
Leap n
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.
version n
The NTP protocol version.
mode type
The NTP mode can be Server, Client, Symmetric Passive, Symmetric
Active, or Broadcast. See RFC 1129 for more information on NTP
modes.
Poll x
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.
Precision x
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.
Stratum n (source)
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.
Synch Distance is nn.nn nn.nn
The values reported are used internally by the NTP daemon.
Synch Dispersion is nn.nn nn.nn
The values reported are used internally by the NTP daemon.
The next five timestamps are given as NTP fixed-point 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.
Reference Timestamp is hex-timestamp ctime_string
This specifies the last time the remote host clock was adjusted.
(remote time)
Originate Timestamp is hex-timestamp ctime_string
This specifies when the NTP request was transmitted by the local
host to the remote host. (local time)
Receive Timestamp is hex-timestamp ctime_string
This specifies when the NTP request was received at the remote
host. (remote time)
Transmit Timestamp is hex-timestamp ctime_string
This specifies when the NTP response was transmitted by the remote
host. (remote time)
Input Timestamp is hex-timestamp ctime_string
This specifies when the NTP response was received by the local
host. (local time)
hostname: delay:time offset: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).
SEE ALSO
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
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