NTP configuration statements

Below is a list of the configuration statements you can use in the NTP configuration file and an explanation of each statement. The term ``local host'' in the explanations refers to the host that you are configuring with these statements.

peer host_address [ key key_ID ] [ version version_number] [ minpoll ]

Specifies that the host with IP address host_address is to be polled in symmetric active mode. The key option indicates that all packets sent to the host at host_address are to include authentication fields encrypted using the specified key ID. The default is not to include authentication.

The version option allows you to specify the version number to use for outgoing NTP packets. The allowed values for version_number are 1 and 2. If this option is omitted, version 3 is assumed. The minpoll option specifies that the polling interval should be kept at the minimum value allowed. This maximizes the frequency with which the host is polled and should, therefore, be used only for debugging purposes.

server host_address [ key key_ID ] [ version version_number] [ minpoll ]

Specifies that the host with IP address host_address is to be polled in client mode. See the peer statement for an explanation of the remaining arguments.

broadcast IP_address [ key key_ID ] [ minpoll ]

Specifies that ntpd broadcast NTP packets to the address IP_address. This should be the broadcast address of your local network. See the peer statement for an explanation of the remaining arguments.

precision integer

Indicates the precision of the local clock as 2 raised to the integer power. The value of integer should be negative to indicate a fraction. See ``Testing and tuning NTP'' for more information.

driftfile filename

Specifies the name of the file used to record the drift that ntpd has computed. Drift is also known as ``frequency error''.

monitor flag

Indicates whether or not to enable the ntpd monitoring function. The allowed values for flag are yes and no. A valid requestkey statement must be included in the configuration file for monitoring to function. The default value for flag is no.

broadcastclient flag

Indicates whether or not the local host should listen for, and attempt to synchronize with, NTP packets broadcast by time servers on the local network. The allowed values for flag are yes and no. The default is no.

broadcastdelay seconds

Specifies the roundtrip delay in seconds between the local host and the time server that is broadcasting NTP packets. Note that you specify a roundtrip delay, even though NTP cares only about one-way delay when it actually computes the correct time. The default value for seconds is 0.008.

authenticate flag

Indicates whether or not the local server operates in authenticate mode. The allowed values for flag are yes and no. The default is no.

trustedkey key_ID

Specifies which key IDs are trusted.

keys pathname

Specifies the pathname of the keys file. At installation, the value of pathname is /etc/ntp.keys. This file must exist for the trustedkey, requestkey, and controlkey configuration statements to be valid. See ``The NTP keys file'' for more information.

requestkey key_ID . . .

Specifies the key IDs used to authenticate runtime reconfiguration requests made by ntpdc and ntpres using mode 7 control messages. The keys file must exist and properly define all of the listed key IDs for this statement to be valid. To disable runtime configuration of ntpd, omit this statement from the configuration file.

controlkey key_ID . . .

Specifies the key ID used to authenticate runtime reconfiguration requests made by ntpq and by trap receivers using mode 6 control messages. The keys file must exist and properly define all of the listed key IDs for this statement to be valid. To cause mode 6 control messages to be ignored, omit this statement from the configuration file. Doing so has the effect of disabling ntpq and trap receivers on your local host.

restrict host_address mask address_mask flag . . .

Specifies various restrictions on how certain hosts and networks can interact with the local host. See ``NTP address and mask facility'' for more information.

trap host_address port port_number interface interface_address

Configures a trap receiver at address host address and port port number. The value of interface_address must be the IP address of the local host. The host at host_address must be listening for NTP mode 6 control messages or it will not respond to the trap signal sent by the local host. This means that the host at host_address must have the controlkey statement in its configuration file and both that host and the local host must share at least one of the keys listed in that controlkey configuration statement. See ``The NTP keys file'' for more information.

resolver pathname

Indicates the full pathname of the ntpres program, which resolves network names to IP addresses. When NTP is installed, the pathname of the ntpres program is /etc/ntpres. If for some reason you move ntpres to another directory, use the pathname corresponding to its new location. You must also include the requestkey statement in the configuration file for ntpres to operate.