peer address [ key key ] [ version
version ] [ prefer ] [ minpoll minpoll [ maxpoll
maxpoll ]
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
notation. The 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.
The 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.
The 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
broadcastclient or multicastclient commands
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 224.0.1.1 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.
Options
key key
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
field.
version version
Specifies the version number to be used for outgoing NTP packets.
Versions 1, 2, and 3 are the choices, with version 3 the default.
prefer
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
the prefer Keyword page for further information.
ttl ttl
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).
minpoll minpoll
This option specifies the minimum polling interval for NTP messages,
in seconds to the power of two. The allowable range is 4 (16 s to 14
(16384 s) inclusive. The default is 6 (64 s) for all except reference
clocks.
maxpoll maxpoll
This option specifies the maximum polling interval for NTP messages,
in seconds to the power of two. The allowable range is 4 (16 s to 14
(16384 s) inclusive. The default is 10 (1024 s) for all except reference
clocks.
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
identifier.
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 (224.0.1.1).
This command operates in the same way as the
broadcastclient command, but uses IP multicasting. Support
for this command requires a multicast kernel.
driftfile driftfile
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
subside.
The 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
implies that 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.
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.
auth
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 enable.
bclient
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.
monitor
Enables the monitoring facility. See the xntpdc program
and the monlist command or further information. The default
for this flag is enable.
pll
Enables the server to adjust its local clock by means of NTP. If
disabled, 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. The default for this flag is enable.
pps
Enables the pulse-per-second (PPS) signal when frequency and time is
disciplined by the precision time kernel modifications. See the A Kernel Model for Precision Timekeeping page for
further information. The default for this flag is disable.
stats
Enables the statistics facility. See the
Monitoring Options
page for further information. The default for this flag is enable.
tick value
If no value for tick can be found from the kernel, use
this value. This is the "normalized" value; if your system
keeps tick in nanoseconds you must divide your
value by 1000. The expected range of the value is between 900
and 11,000 (don't use the comma in the config file).
tickadj value
If no value for tickadj can be found in the
kernel, use this value. The value must be "normalized"; if
your system keeps tickadj in nanoseconds you must
divide your value by 1000. The expected range of the value is
between 1 and 50.