Interactive Commands

A number of interactive format commands are executed entirely within the ntpdc utility itself and do not result in NTP mode 7 requests being sent to a server. These are described following.

? command_keyword

help command_keyword

A ‘?’ will print a list of all the command keywords known to this incarnation of ntpdc. A ‘?’ followed by a command keyword will print function and usage information about the command. This command is probably a better source of information about ntpq(8) than this manual page.

delay milliseconds

Specify a time interval to be added to timestamps included in requests which require authentication. This is used to enable (unreliable) server reconfiguration over long delay network paths or between machines whose clocks are unsynchronized. Actually the server does not now require timestamps in authenticated requests, so this command may be obsolete.

host hostname

Set the host to which future queries will be sent. Hostname may be either a host name or a numeric address.

hostnames [yes | no]

If yes is specified, host names are printed in information displays. If no is specified, numeric addresses are printed instead. The default is yes, unless modified using the command line -n switch.

keyid keyid

This command allows the specification of a key number to be used to authenticate configuration requests. This must correspond to a key number the server has been configured to use for this purpose.

quit

Exit ntpdc.

passwd

This command prompts you to type in a password (which will not be echoed) which will be used to authenticate configuration requests. The password must correspond to the key configured for use by the NTP server for this purpose if such requests are to be successful.

timeout milliseconds

Specify a timeout period for responses to server queries. The default is about 8000 milliseconds. Note that since ntpdc retries each query once after a timeout, the total waiting time for a timeout will be twice the timeout value set.

Control Message Commands

listpeers

Obtains and prints a brief list of the peers for which the server is maintaining state. These should include all configured peer associations as well as those peers whose stratum is such that they are considered by the server to be possible future synchronization candidates.

peers

Obtains a list of peers for which the server is maintaining state, along with a summary of that state. Summary information includes the address of the remote peer, the local interface address (0.0.0.0 if a local address has yet to be determined), the stratum of the remote peer (a stratum of 16 indicates the remote peer is unsynchronized), the polling interval, in seconds, the reachability register, in octal, and the current estimated delay, offset and dispersion of the peer, all in seconds.

The character in the left margin indicates the mode this peer entry is operating in. A ‘+’ denotes symmetric active, a ‘-’ indicates symmetric passive, a ‘=’ means the remote server is being polled in client mode, a ‘^’ indicates that the server is broadcasting to this address, a ‘~’ denotes that the remote peer is sending broadcasts and a ‘~’ denotes that the remote peer is sending broadcasts and a ‘*’ marks the peer the server is currently synchronizing to.

The contents of the host field may be one of four forms. It may be a host name, an IP address, a reference clock implementation name with its parameter or REFCLK(implementation_number, parameter). On hostnames no only IP-addresses will be displayed.

dmpeers

A slightly different peer summary list. Identical to the output of the peers command, except for the character in the leftmost column. Characters only appear beside peers which were included in the final stage of the clock selection algorithm. A ‘.’ indicates that this peer was cast off in the falseticker detection, while a ‘+’ indicates that the peer made it through. A ‘*’ denotes the peer the server is currently synchronizing with.

showpeer peer_address [...]

Shows a detailed display of the current peer variables for one or more peers. Most of these values are described in the NTP Version 2 specification.

pstats peer_address [...]

Show per-peer statistic counters associated with the specified peer(s).

clockinfo clock_peer_address [...]

Obtain and print information concerning a peer clock. The values obtained provide information on the setting of fudge factors and other clock performance information.

kerninfo

Obtain and print kernel phase-lock loop operating parameters. This information is available only if the kernel has been specially modified for a precision timekeeping function.

loopinfo [oneline | multiline]

Print the values of selected loop filter variables. The loop filter is the part of NTP which deals with adjusting the local system clock. The ‘offset’ is the last offset given to the loop filter by the packet processing code. The ‘frequency’ is the frequency error of the local clock in parts-per-million (ppm). The ‘time_const’ controls the stiffness of the phase-lock loop and thus the speed at which it can adapt to oscillator drift. The ‘watchdog timer’ value is the number of seconds which have elapsed since the last sample offset was given to the loop filter. The oneline and multiline options specify the format in which this information is to be printed, with multiline as the default.

sysinfo

Print a variety of system state variables, i.e., state related to the local server. All except the last four lines are described in the NTP Version 3 specification, RFC-1305.

The ‘system flags’ show various system flags, some of which can be set and cleared by the enable and disable configuration commands, respectively. These are the auth, bclient, monitor, pll, pps and stats flags. See the ntpd(8) documentation for the meaning of these flags. There are two additional flags which are read only, the kernel_pll and kernel_pps. These flags indicate the synchronization status when the precision time kernel modifications are in use. The ‘kernel_pll’ indicates that the local clock is being disciplined by the kernel, while the ‘kernel_pps’ indicates the kernel discipline is provided by the PPS signal.

The ‘stability’ is the residual frequency error remaining after the system frequency correction is applied and is intended for maintenance and debugging. In most architectures, this value will initially decrease from as high as 500 ppm to a nominal value in the range .01 to 0.1 ppm. If it remains high for some time after starting the daemon, something may be wrong with the local clock, or the value of the kernel variable kern.clockrate.tick may be incorrect.

The ‘broadcastdelay’ shows the default broadcast delay, as set by the broadcastdelay configuration command.

The ‘authdelay’ shows the default authentication delay, as set by the authdelay configuration command.

sysstats

Print statistics counters maintained in the protocol module.

memstats

Print statistics counters related to memory allocation code.

iostats

Print statistics counters maintained in the input-output module.

timerstats

Print statistics counters maintained in the timer/event queue support code.

reslist

Obtain and print the server's restriction list. This list is (usually) printed in sorted order and may help to understand how the restrictions are applied.

monlist [version]

Obtain and print traffic counts collected and maintained by the monitor facility. The version number should not normally need to be specified.

clkbug clock_peer_address [...]

Obtain debugging information for a reference clock driver. This information is provided only by some clock drivers and is mostly undecodable without a copy of the driver source in hand.

Runtime Configuration Requests

Authenticated requests always include a timestamp in the packet data, which is included in the computation of the authentication code. This timestamp is compared by the server to its receive time stamp. If they differ by more than a small amount the request is rejected. This is done for two reasons. First, it makes simple replay attacks on the server, by someone who might be able to overhear traffic on your LAN, much more difficult. Second, it makes it more difficult to request configuration changes to your server from topologically remote hosts. While the reconfiguration facility will work well with a server on the local host, and may work adequately between time-synchronized hosts on the same LAN, it will work very poorly for more distant hosts. As such, if reasonable passwords are chosen, care is taken in the distribution and protection of keys and appropriate source address restrictions are applied, the run time reconfiguration facility should provide an adequate level of security.

The following commands all make authenticated requests.

addpeer peer_address [keyid] [version] [prefer]

Add a configured peer association at the given address and operating in symmetric active mode. Note that an existing association with the same peer may be deleted when this command is executed, or may simply be converted to conform to the new configuration, as appropriate. If the optional keyid is a nonzero integer, all outgoing packets to the remote server will have an authentication field attached encrypted with this key. If the value is 0 (or not given) no authentication will be done. The version can be 1, 2 or 3 and defaults to 3. The prefer keyword indicates a preferred peer (and thus will be used primarily for clock synchronisation if possible). The preferred peer also determines the validity of the PPS signal - if the preferred peer is suitable for synchronisation so is the PPS signal.

addserver peer_address [keyid] [version] [prefer]

Identical to the addpeer command, except that the operating mode is client.

broadcast peer_address [keyid] [version] [prefer]

Identical to the addpeer command, except that the operating mode is broadcast. In this case a valid key identifier and key are required. The peer_address parameter can be the broadcast address of the local network or a multicast group address assigned to NTP. If a multicast address, a multicast-capable kernel is required.

unconfig peer_address [...]

This command causes the configured bit to be removed from the specified peer(s). In many cases this will cause the peer association to be deleted. When appropriate, however, the association may persist in an unconfigured mode if the remote peer is willing to continue on in this fashion.

fudge peer_address [time1] [time2] [stratum] [refid]

This command provides a way to set certain data for a reference clock. See the source listing for further information.

enable [auth | bclient | calibrate | kernel | monitor | ntp | pps | stats]

disable [auth | bclient | calibrate | kernel | monitor | ntp | pps | stats]

These commands operate in the same way as the enable and disable configuration file commands of ntpd(8).

auth

Enables the server to synchronize with unconfigured peers only if the peer has been correctly authenticated using either public key or private key cryptography. 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.

calibrate

Enables the calibrate feature for reference clocks. The default for this flag is disable.

kernel

Enables the kernel time discipline, if available. The default for this flag is enable if support is available, otherwise disable.

monitor

Enables the monitoring facility. See the documentation here about the monlist command or further information. The default for this flag is enable.

ntp

Enables time and frequency discipline. In effect, this switch opens and closes the feedback loop, which is useful for testing. 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” (available as part of the HTML documentation provided in /usr/share/doc/ntp) page for further information. The default for this flag is disable.

stats

Enables the statistics facility. See the Monitoring Options section of ntp.conf(5) for further information. The default for this flag is disable.

restrict address mask flag [...]

This command operates in the same way as the restrict configuration file commands of ntpd(8).

unrestrict address mask flag [...]

Unrestrict the matching entry from the restrict list.

delrestrict address mask [ntpport]

Delete the matching entry from the restrict list.

readkeys

Causes the current set of authentication keys to be purged and a new set to be obtained by rereading the keys file (which must have been specified in the ntpd(8) configuration file). This allows encryption keys to be changed without restarting the server.

trustedkey keyid [...]

untrustedkey keyid [...]

These commands operate in the same way as the trustedkey and untrustedkey configuration file commands of ntpd(8).

authinfo

Returns information concerning the authentication module, including known keys and counts of encryptions and decryptions which have been done.

traps

Display the traps set in the server. See the source listing for further information.

addtrap address [port] [interface]

Set a trap for asynchronous messages. See the source listing for further information.

clrtrap address [port] [interface]

Clear a trap for asynchronous messages. See the source listing for further information.

reset

Clear the statistics counters in various modules of the server. See the source listing for further information.