ntpdc(1) -- Linux man page
NAMEntpdc - special NTP query program
ntpdc is used to query the ntpd daemon about its current state and to request changes in that state. The program may be run either in interactive mode or controlled using command line arguments. Extensive state and statistics information is available through the ntpdc interface. In addition, nearly all the configuration options which can be specified at startup using ntpd's configuration file may also be specified at run time using ntpdc .
If one or more request options are included on the command line when ntpdc is executed, each of the requests will be sent to the NTP servers running on each of the hosts given as command line arguments, or on localhost by default. If no request options are given, ntpdc will attempt to read commands from the standard input and execute these on the NTP server running on the first host given on the command line, again defaulting to localhost when no other host is specified. ntpdc will prompt for commands if the standard input is a terminal device.
ntpdc uses NTP mode 7 packets to communicate with the NTP server, and hence can be used to query any compatable server on the network which permits it. Note that since NTP is a UDP protocol this communication will be somewhat unreliable, especially over large distances in terms of network topology. ntpdc makes no attempt to retransmit requests, and will time requests out if the remote host is not heard from within a suitable timeout time.
The operation of ntpdc are specific to the particular implementation of the ntpd daemon and can be expected to work only with this and maybe some previous versions of the daemon. Requests from a remote ntpdc program which affect the state of the local server must be authenticated, which requires both the remote program and local server share a common key and key identifier.
COMMAND LINE OPTIONSSpecifying a command line option other than -i or -n will cause the specified query (queries) to be sent to the indicated host(s) immediately. Otherwise, ntpdc will attempt to read interactive format commands from the standard input.
- Force ntpdc to operate in interactive mode. Prompts will be written to the standard output and commands read from the standard input.
- Obtain a list of peers which are known to the server(s). This switch is equivalent to -c listpeers .
- Output all host addresses in dotted-quad numeric format rather than converting to the canonical host names.
- Print a list of the peers known to the server as well as a summary of their state. This is equivalent to -c peers .
- Print a list of the peers known to the server as well as a summary of their state, but in a slightly different format than the -p switch. This is equivalent to -c dmpeers .
INTERACTIVE COMMANDSInteractive format commands consist of a keyword followed by zero to four arguments. Only enough characters of the full keyword to uniquely identify the command need be typed. The output of a command is normally sent to the standard output, but optionally the output of individual commands may be sent to a file by appending a < , followed by a file name, to the command line.
A number of interactive format commands are executed entirely within the ntpdc program itself and do not result in NTP mode 7 requests being sent to a server. These are described following.
- ? [
help [ command_keyword ] A ? by itself will print a list of all the command keywords known to this incarnation of ntpq . A ? followed by a command keyword will print funcation and usage information about the command. This command is probably a better source of information about ntpq than this manual page.
- 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.
- Exit ntpdc .
- 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.
CONTROL MESSAGE COMMANDSQuery commands result in NTP mode 7 packets containing requests for information being sent to the server. These are read-only commands in that they make no modification of the server configuration state.
- 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 synchonization candidates.
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
* marks the peer the server is currently synchonizing
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.
- 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.
- 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.
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
disable configuration commands, respectively. These are the
stats flags. See the
ntpd documentation for the meaning of these flags. There are two
additional flags which are read only, the
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 afterthe 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 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.
- Print statistics counters maintained in the protocol module.
- Print statistics counters related to memory allocation code.
- Print statistics counters maintained in the input-output module.
- Print statistics counters maintained in the timer/event queue support code.
- 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 [
RUNTIME CONFIGURATION REQUESTSAll requests which cause state changes in the server are authenticated by the server using a configured NTP key (the facility can also be disabled by the server by not configuring a key). The key number and the corresponding key must also be made known to xtnpdc. This can be done using the keyid and passwd commands, the latter of which will prompt at the terminal for a password to use as the encryption key. You will also be prompted automatically for both the key number and password the first time a command which would result in an authenticated request to the server is given. Authentication not only provides verification that the requester has permission to make such changes, but also gives an extra degree of protection again transmission errors.
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.
- enable [
disable [ flag ] [ ... ] These commands operate in the same way as the enable and disable configuration file commands of ntpd . Following is a description of the flags. Note that only the auth , bclient , monitor , pll , pps and stats flags can be set by ntpdc ; the pll_kernel and pps_kernel flags are read-only.
- 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.
- 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 ntpdc program and the monlist command or further information. The default for this flag is enable.
- 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.
- 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 Timekeepingpage for further information. The default for this flag is disable.
- Enables the statistics facility. See the Monitoring Options page for further information. The default for this flag is enable.
- When the precision time kernel modifications are installed, this indicates the kernel controls the clock discipline; otherwise, the daemon controls the clock discipline.
When the precision time kernel modifications are installed and
a pulse-per-second (PPS) signal is available, this indicates the
PPS signal controls the clock discipline; otherwise, the daemon or
kernel controls the clock discipline, as indicated by the
- 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 configuration file). This allows encryption keys to be changed without restarting the server.
- Returns information concerning the authentication module, including known keys and counts of encryptions and decryptions which have been done.
- Display the traps set in the server. See the source listing for further information.
- addtrap [
- clrtrap [
- Clear the statistics counters in various modules of the server. See the source listing for further information.
ntpdc is a crude hack. Much of the information it shows is deadly boring and could only be loved by its implementer. The program was designed so that new (and temporary) features were easy to hack in, at great expense to the program's ease of use. Despite this, the program is occasionally useful.
SEE ALSOPrimary source of documentation: /usr/share/doc/ntp-*/ntpdc.php
AUTHORDavid L. Mills <email@example.com>