Manual Pages for UNIX Darwin command on man sntp

SNTP(1) SNTP(1)

NAME

sntp - a SNTP utility (command and daemon)

SYNOPSIS

ssnnttpp [ -hh | --hheellpp | -?? ] [ -vv | -VV | -WW ] [ -qq [ -ff savefile ] | [ {

-rr | -aa } [ -PP prompt ] [ -ll lockfile ] ] [ -ee minerr ] [ -EE maxerr ] [

-cc count ] [ -dd delay | -xx [ separation ] ] [ -ff savefile ] ] [ -44 ] |

[ -66 ] [ address(es) ] ]

DESCRIPTION

sntp can be used as a SNTP 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

sntp recognizes the following options:

-hh displays the syntax error message. If there are no other argu-

ments, it then stops; otherwise it then does what was requested.

--hheellpp and -?? are synonyms.

-vv 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.

-VV requests more and less comprehensible output, mainly for inves-

tigating problems with apparently inconsistent timestamps. This

option should be set when the program fails with a message indi-

cating that is the trouble.

-WW 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.

-qq indicates that it should query a daemon save file being main-

tained by it. This needs no privilege and will change neither the save file nor the clock. The default is that it should behave as a client, and the following options are then relevant:

-rr indicates that the system clock should be reset by settimeofday.

Naturally, this will work only if the user has enough privilege.

-aa 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 ''11999966 OOcctt 1155

2200::1177::2255..112233 ++ 44..556677 ++//- 00..008899 sseeccss'', where the ''++ 44..556677 ++//- 00..008899

sseeccss'' indicates the estimated error in the time on the local system. In daemon mode, it will add drift information in a format like '' ++ 11..33

++//- 00..11 ppppmm'', and display this at roughly separation intervals (see

under the -xx option for details).

-ll lockfile

sets the name of the lock file to ensure that there is only one

copy of sntp running at once. The default is installation-

dependent, but will usually be /etc/sntp.pid.

-ee minerr

sets the maximum ignorable variation between the clocks to min-

err. 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.

-EE maxerr

sets the maximum value of various delays that are deemed accept-

able to maxerr. Acceptable values are from 1 to 60, and the default is 5. It should sometimes be increased if there are problems with the network, NTP server or system clock, but take care.

-PP prompt

sets the maximum clock change that will be made automatically to maxerr. Acceptable values are from 1 to 3600 or no, and the default is 30. 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. Spec-

ifying no will disable this and the correction will be made regardless.

-cc 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 maxi-

mum isn't enough, the system needs a better consistency algo-

rithm than this program uses.

-dd 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.

-xx 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 -xx is specified but separation is omitted) is 300.

-ff savefile

may be used with the -xx option to store a record of previous

packets, which speeds up recalculating the drift after sntp has

to be restarted (e.g. because of network or server outages). In

order to restart the data, sntp must be restarted reasonably

soon after it died (within a few times the value of separation),

with the same value of the -cc option, the same value of separa-

tion, in the same mode (i.e. broadcast or client), though the

NTP servers need not be the same for client mode, and with com-

patible values of other settings. Note that the file will be

created with the default ownerships and permissions, using stan-

dard C facilities. The default is installation-dependent, but

will usually be /etc/sntp.state.

-44 force IPv4 DNS resolution.

-66 force IPv6 DNS resolution.

aaddddrreessss((eess)) are the DNS names or IP numbers of hosts to use for the challenge and response protocol; if no names are 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. If more than one name is give,

they will be used in a round-robin fashion.

Constraints: mmiinneerrrr must be less than mmaaxxeerrrr which must be less than ddeellaayy (or, if a NTP host is not specified ddeellaayy/ccoouunntt), and ccoouunntt must be less than half of ddeellaayy. In update mode, mmaaxxeerrrr must be less than pprroommpptt..

In daemon mode (i.e. when -xx is specified), mmiinneerrrr must be less

than mmaaxxeerrrr which must be less than sseeppaarraattiioonn (note that this is in minutes, not seconds, but the numeric value is compared). Note that none of the above values are closely linked to the limits described in the NTP protocol (RFC 1305). UUSSAAGGEE The simplest use of this program is as an unprivileged command to check the current time and error in the local clock. For example: ssnnttpp nnttppsseerrvveerr..ssoommeewwhheerree 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:

ssnnttpp -xx nnttppsseerrvveerr..ssoommeewwhheerree >> oouuttppuutt 22>>11

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:

ssnnttpp -aa nnttppsseerrvveerr..ssoommeewwhheerree

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

ssnnttpp -aa -xx nnttppsseerrvveerr..ssoommeewwhheerree >> oouuttppuutt 22>>11

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 propa-

gating misinformation. RREETTUURRNN VVAALLUUEE

When used as a client in non-daemon mode, the program returns a zero

exit status for success, and a non-zero one otherwise. When used as a

daemon (either client or server), it does not return except after a serious error.

BUGS

The program implements the SNTP protocol, and does not provide all NTP facilities. In particular, it contains no checks against any form of

spoofing. If this is a serious concern, some network security mecha-

nism (like a firewall or even just tcpwrappers) should be installed. 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 administra-

tors 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 -cc option to a larger value may

help. Or it may not. AUTHOR

sntp was developed by N.M. Maclaren of the University of Cambridge Com-

puting Service. SNTP(1)