MSNTP

NAME

SYNOPSIS

DESCRIPTION

msntp can be used as a NTP client to query a NTP or SNTP server and either display the time or set the local system's time (given suitable privilege). It can be run as an interactive command, in a cron job or as a daemon. It can be run as a daemon to provide a SNTP server for other clients. NTP is the Network Time Protocol (RFC 1305) and SNTP is the Simple Network Time Protocol (RFC 2030, which supersedes RFC 1769).

Options

msntp recognizes the following options:

-v

indicates that diagnostic messages for non-fatal errors and a limited amount of tracing should be written to standard error. Fatal ones always produce a diagnostic. This option should be set when there is a suspected problem with the server, network or the source.

-V

requests more and less comprehensible output, mainly for investigating problems with apparently inconsistent timestamps. This option should be set when the program fails with a message indicating that is the trouble.

-W

requests very verbose debugging output, and will interfere with the timing when writing to the terminal (because of line buffered output from C). Note that the times produced by this are the corrections needed, and not the error in the local clock. This option should be set only when debugging the source.

-B period

indicates that it should behave as a server, broadcasting time packets at intervals of period minutes. Acceptable values of period are from 1 to 1440 (a day), and the default (i.e. if -B is specified but period is omitted) is 60. Naturally, this will work only if the user has enough privilege.

-S

indicates that it should behave as a server, responding to time requests from clients. Naturally, this will work only if the user has enough privilege.

The default is that it should behave as a client, and the following options are then relevant:

-r

indicates that the system clock should be reset by settimeofday. Naturally, this will work only if the user has enough privilege.

-a

indicates that the system clock should be reset by adjtime. Naturally, this will work only if the user has enough privilege.

The default is to write the estimated correct local date and time (i.e. not UTC) to the standard output in a format like '1996 Oct 15 20:17:25.123 + 4.567 +/- 0.089 secs', where the '+ 4.567 +/- 0.089 secs' indicates the estimated error in the time on the local system. In daemon mode, it will add drift information in a format like ' + 1.3 +/- 0.1 ppm', and display this at roughly separation intervals (see under the -x option for details).

-e minerr

sets the maximum ignorable variation between the clocks to minerr. Acceptable values are from 0.001 to 1, and the default is 0.1 if a NTP host is is specified and 0.5 otherwise.

-E maxerr

sets the maximum clock change that will be made automatically to maxerr. Acceptable values are from 0.1 to 60, and the default is 5. If the program is being run interactively in ordinary client mode, and the system clock is to be changed, larger corrections will prompt the user for confirmation.

-c count

sets the maximum number of NTP packets required to count. Acceptable values are from 1 to 25 if a NTP host is specified and from 5 to 25 otherwise, and the default is 5. If the maximum isn't enough, the system needs a better consistency algorithm than this program uses.

-d delay

sets a rough limit on the total running time to delay seconds. Acceptable values are from 1 to 3600, and the default is 15 if a NTP host is specified and 300 otherwise.

-x separation

causes the program to run as a daemon (i.e. forever), and to estimate and correct for the clock drift. separation sets the minimum time between calls to the server in minutes if a NTP host is specified, and between broadcast packets if not. Acceptable values are from 1 to 1440 (a day), and the default (if -x is specified but separation is omitted) is 300.

-f savefile

may be used with the -x option to store a record of previous packets, which may speed up recalculating the drift after msntp has to be restarted (e.g. because of network or server outages). In order to restart the data, msntp must be restarted reasonably soon after it died (within a few times the value of separation), with the same value of the -c option and in the same mode (i.e. broadcast or client), though the NTP server need not be the same for client mode. Note that the file will be created with the default ownerships and permissions, using standard C facilities.

address is the DNS name or IP number of a host to use for the challenge and response protocol; if no name is given, the program waits for broadcasts. Polling a server is vastly more reliable than listening to broadcasts. Note that a single component numeric address is not allowed, to avoid ambiguities.

Constraints:

minerr must be less than maxerr which must be less than delay (or, if a NTP host is not specified delay/count), and count must be less than half of delay.

In daemon mode (i.e. when -x is specified), minerr must be less than maxerr which must be less than separation.

Note that none of the above values are closely linked to the limits described in the NTP protocol (RFC 1305).

USAGE

msntp ntpserver.somewhere

It can be run as a unprivileged background process to check on the clock drift as well as the current error; this will probably fail if the local clock is reset while it is running. For example:

msntp -x ntpserver.somewhere > output 2>1

With suitable privilege, it can be run as a command or in a cron job to reset the local clock from a reliable server, like the ntpdate and rdate commands. For example:

msntp -a ntpserver.somewhere

It can also be run as a daemon to keep the local clock in step. For example:

msntp -a -x ntpserver.somewhere > output 2>1

More information on how to use this utility is given in the README file in the distribution. In particular, this man page does not describe how to set it up as a server, which needs special care to avoid propagating misinformation.  

RETURN VALUE

BUGS

There are some errors, ambiguities and inconsistencies in the RFCs, and this code may not interwork with all other NTP implementations. Any unreasonable restrictions should be reported as bugs to whoever is responsible. It may be difficult to find out who that is.

The program will stop as soon as it feels that things have got out of control. In client daemon mode, it will usually fail during an extended period of network or server inaccessibility or excessively slow performance, or when the local clock is reset by another process. It will then need restarting manually. Experienced system administrators can write a shell script, a cron job or put it in inittab, to do this automatically.

The error cannot be estimated reliably with broadcast packets or for the drift in daemon mode (even with client-server packets), and the guess made by the program may be wrong (possibly even very wrong). If this is a problem, then setting the -c option to a larger value may help. Or it may not.

AUTHOR