peer address [ key key ] [ version
version ] [ prefer ]
server address [ key key ] [ version
version ] [ prefer ] [ mode mode ]
broadcast address [ key key ] [ version
version ] [ ttl ttl ]
- These three commands specify the time server name or address
address to be used and the mode in which to operate. The
address can be either a DNS name or a IP address in dotted-quad
peer command specifies that the local server
is to operate in symmetric active mode with the remote server. In this
mode, the local server can be synchronized to the remote server and, in
addition, the remote server can be synchronized by the local server.
This is useful in a network of servers where, depending on various
failure scenarios, either the local or remote server may be the better
source of time.
server command specifies that the local server
is to operate in client mode with the specified remote server. In this
mode, the local server can be synchronized to the remote server, but the
remote server can never be synchronized to the local server.
broadcast command specifies that the local
server is to operate in broadcast mode, where the local server sends
periodic broadcast messages to a client population at the
broadcast/multicast address specified. Ordinarily, this
specification applies only to the local server operating as a sender;
for operation as a broadcast client, see the
below. In this mode, address is usually the broadcast address on
(one of) the local network(s) or a multicast address assigned to NTP.
The Numbers Czar has assigned the address 22.214.171.124 to NTP; this is
presently the only address that should be used. Note that the use of
multicast features requires a multicast kernel, which is not yet
ubiquitous in vendor products.
- All packets sent to the address are to include authentication fields
encrypted using the specified key identifier, which is an
unsigned 32 bit integer. The default is to not include an encryption
- Specifies the version number to be used for outgoing NTP packets.
Versions 1, 2, and 3 are the choices, with version 3 the default.
- Marks the server as preferred. All other things being equal, this
host will be chosen for synchronization among a set of correctly
operating hosts. See the Mitigation Rules and
prefer Keyword page for further information.
- This option is used only with broadcast mode. It specifies the time-
to-live ttl to use on multicast packets. Selection of the proper
value, which defaults to 127, is something of a black art and must be
coordinated with the network administrator(s).
broadcastclient [ address ]
- This command directs the local server to listen for broadcast
messages at the broadcast address address of the local network.
The default address is the subnet address with the host field bits set
to ones. Upon hearing a broadcast message for the first time, the local
server measures the nominal network delay using a brief client/server
exchange with the remote server, then enters the broadcastclient mode,
in which it listens for and synchronizes to succeeding broadcast
messages. Note that, in order to avoid accidental or malicious
disruption in this mode, both the local and remote servers should
operate using authentication and the same trusted key and key
multicastclient [ address ] [ ... ]
- This command directs the local server to listen for multicast
messages at the group address(es) of the global network. The
default address is that assigned by the Numbers Czar to NTP (126.96.36.199).
This command operates in the same way as the
broadcastclient command, but uses IP multicasting. Support
for this command requires a multicast kernel.
- This command specifies the name of the file used to record the
frequency offset of the local clock oscillator. If the file exists, it
is read at startup in order to set the initial frequency offset and then
updated once per hour with the current frequency offset computed by the
daemon. If the file does not exist or this command is not given, the
initial frequency offset is assumed zero. In this case, it may take some
hours for the frequency to stabilize and the residual timing errors to
ntp.drift file format consists of a single line
containing a single floating point number, which records the frequency
offset measured in parts-per-million (PPM). That the file is updated
once per hour by first writing the current drift value into a temporary
file and then renaming this file to replace the old version. This
xntpd must have write permission for the
directory the drift file is located in, and that file system links,
symbolic or otherwise, should probably be avoided.
enable auth | bclient | monitor | pll | pps | stats
disable auth | bclient | monitor | pll | pps | stats
- Provides a way to enable or disable various server options. Flags
not mentioned are unaffected. Note that all of these flags can be
controlled remotely using the
xntpdc utility program.
- Enables the server to synchronize with unconfigured peers only if
the peer has been correctly authenticated using a trusted key and key
identifier. The default for this flag is disable.
- Enables the server to listen for a message from a broadcast or
multicast server, as in the
multicastclient command with
default address. The default for this flag is disable.
- Enables the monitoring facility. See the
monlist command or further information.
- Enables the server to adjust its local clock, with default enable.
If not set, the local clock free-runs at its intrinsic time and
frequency offset. This flag is useful in case the local clock is
controlled by some other device or protocol and NTP is used only to
provide synchronization to other clients. In this case, the local clock
driver is used. See the Reference Clock
Drivers page for further information.
- Enables the pulse-per-second (PPS) signal when frequency and time is
disciplined by the precision time kernel modifications. The default is
enable when these modifications are available and disable otherwise. See
the A Kernel Model for Precision Timekeeping
page for further information.
- Enables the statistics facility. For further information, see the
Monitoring Options section later in this document. The default for this
flag is enable.(see the Monitoring Options
page for further information.
David L. Mills (email@example.com)