SNTP(1) BSD General Commands Manual SNTP(1)NAMEsntp — standard Simple Network Time Protocol client program
SYNOPSISsntp [-flags] [-flag [value]] [--option-name[[=| ]value]] [ host‐
name-or-IP ...]
DESCRIPTIONsntp can be used as an 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 or from a cron job.
NTP (the Network Time Protocol) and SNTP (the Simple Network Time Proto‐
col) are defined and described by RFC 5905.
The default is to write the estimated correct local date and time (i.e.
not UTC) to the standard output in a format like: '1996-10-15
20:17:25.123 (+0800) +4.567 +/- 0.089 [host] IP sN' where the '(+0800)'
means that to get to UTC from the reported local time one must add 8
hours and 0 minutes, the '+4.567' indicates the local clock is 4.567 sec‐
onds behind the correct time (so 4.567 seconds must be added to the local
clock to get it to be correct). Note that the number of decimals printed
for this value will change based on the reported precision of the server.
'+/- 0.089' is the reported synchronization distance (in seconds), which
represents the maximum error due to all causes. If the server does not
report valid data needed to calculate the synchronization distance, this
will be reported as '+/- ?'. If the host is different from the IP, both
will be displayed. Otherwise, only the IP is displayed. Finally, the
stratum of the host is reported and the leap indicator is decoded and
displayed.
OPTIONS-4, --ipv4 Force IPv4 DNS name resolution. This option must not appear
in combination with any of the following options: ipv6.
Force DNS resolution of the following host names on the com‐
mand line to the IPv4 namespace.
-6, --ipv6 Force IPv6 DNS name resolution. This option must not appear
in combination with any of the following options: ipv4.
Force DNS resolution of the following host names on the com‐
mand line to the IPv6 namespace.
-a auth-keynumber, --authentication=auth-keynumber
Enable authentication with the key auth-keynumber. This
option takes an integer number as its argument.
Enable authentication using the key specified in this
option's argument. The argument of this option is the keyid,
a number specified in the keyfile as this key's identifier.
See the keyfile option (-k) for more details.
-b broadcast-address, --broadcast=broadcast-address
Listen to the address specified for broadcast time sync.
This option may appear an unlimited number of times.
If specified sntp will listen to the specified address for
NTP broadcasts. The default maximum wait time can (and prob‐
ably should) be modified with -t.
-c host-name, --concurrent=host-name
Concurrently query all IPs returned for host-name. This
option may appear an unlimited number of times.
Requests from an NTP "client" to a "server" should never be
sent more rapidly than one every 2 seconds. By default, any
IPs returned as part of a DNS lookup are assumed to be for a
single instance of ntpd, and therefore sntp will send queries
to these IPs one after another, with a 2-second gap in
between each query.
The -c or --concurrent flag says that any IPs returned for
the DNS lookup of the supplied host-name are on different
machines, so we can send concurrent queries.
-d, --debug-level
Increase debug verbosity level. This option may appear an
unlimited number of times.
-D number, --set-debug-level=number
Set the debug verbosity level. This option may appear an
unlimited number of times. This option takes an integer num‐
ber as its argument.
-g milliseconds, --gap=milliseconds
The gap (in milliseconds) between time requests. This option
takes an integer number as its argument. The default
milliseconds for this option is:
50
Since we're only going to use the first valid response we get
and there is benefit to specifying a good number of servers
to query, separate the queries we send out by the specified
number of milliseconds.
-K file-name, --kod=file-name
KoD history filename. The default file-name for this option
is:
/var/db/ntp-kod
Specifies the filename to be used for the persistent history
of KoD responses received from servers. If the file does not
exist, a warning message will be displayed. The file will
not be created.
-k file-name, --keyfile=file-name
Look in this file for the key specified with -a.
This option specifies the keyfile. sntp will search for the
key specified with -a keyno in this file. See ntp.keys(5)
for more information.
-l file-name, --logfile=file-name
Log to specified logfile.
This option causes the client to write log messages to the
specified logfile.
-M number, --steplimit=number
Adjustments less than steplimit msec will be slewed. This
option takes an integer number as its argument. The value of
number is constrained to being:
greater than or equal to 0
If the time adjustment is less than steplimit milliseconds,
slew the amount using adjtime(2). Otherwise, step the cor‐
rection using settimeofday(2). The default value is 0, which
means all adjustments will be stepped. This is a feature, as
different situations demand different values.
-o number, --ntpversion=number
Send int as our NTP protocol version. This option takes an
integer number as its argument. The value of number is con‐
strained to being:
in the range 0 through 7
The default number for this option is:
4
When sending requests to a remote server, tell them we are
running NTP protocol version ntpversion .
-r, --usereservedport
Use the NTP Reserved Port (port 123).
Use port 123, which is reserved for NTP, for our network com‐
munications.
-S, --step OK to 'step' the time with settimeofday(2).
-s, --slew OK to 'slew' the time with adjtime(2).
-t seconds, --timeout=seconds
The number of seconds to wait for responses. This option
takes an integer number as its argument. The default seconds
for this option is:
5
When waiting for a reply, sntp will wait the number of sec‐
onds specified before giving up. The default should be more
than enough for a unicast response. If sntp is only waiting
for a broadcast response a longer timeout is likely needed.
--wait, - Fl -no-wait
Wait for pending replies (if not setting the time). The
no-wait form will disable the option. This option is enabled
by default.
If we are not setting the time, wait for all pending
responses.
-?, --help Display usage information and exit.
-!, --more-help
Pass the extended usage information through a pager.
-> [cfgfile], --save-opts [=cfgfile]
Save the option state to cfgfile. The default is the last
configuration file listed in the OPTION PRESETS section,
below. The command will exit after updating the config file.
-< cfgfile, --load-opts=cfgfile, --no-load-opts
Load options from cfgfile. The no-load-opts form will dis‐
able the loading of earlier config/rc/ini files.
--no-load-opts is handled early, out of order.
--version [{v|c|n}]
Output version of program and exit. The default mode is `v',
a simple version. The `c' mode will print copyright informa‐
tion and `n' will print the full copyright notice.
OPTION PRESETS
Any option that is not marked as not presettable may be preset by loading
values from configuration ("RC" or ".INI") file(s) and values from envi‐
ronment variables named:
SNTP_<option-name> or SNTP
The environmental presets take precedence (are processed later than) the
configuration files. The homerc files are "$HOME", and ".". If any of
these are directories, then the file .ntprc is searched for within those
directories.
USAGEsntp ntpserver.somewhere
is the simplest use of this program and can be run as an unprivi‐
leged command to check the current time and error in the local
clock.
sntp-Ss -M 128 ntpserver.somewhere
With suitable privilege, run as a command or from a cron(8) job,
sntp-Ss -M 128 ntpserver.somewhere will request the time from
the server, and if that server reports that it is synchronized
then if the offset adjustment is less than 128 milliseconds the
correction will be slewed, and if the correction is more than 128
milliseconds the correction will be stepped.
sntp-S ntpserver.somewhere
With suitable privilege, run as a command or from a cron(8) job,
sntp-S ntpserver.somewhere will set (step) the local clock from
a synchronized specified server, like the (deprecated)
ntpdate(8), or rdate(8) commands.
ENVIRONMENT
See OPTION PRESETS for configuration environment variables.
FILES
See OPTION PRESETS for configuration files.
EXIT STATUS
One of the following exit values will be returned:
0 (EXIT_SUCCESS)
Successful program execution.
1 (EXIT_FAILURE)
The operation failed or the command syntax was not valid.
66 (EX_NOINPUT)
A specified configuration file could not be loaded.
70 (EX_SOFTWARE)
libopts had an internal operational error. Please report
it to autogen-users@lists.sourceforge.net. Thank you.
AUTHORS
Johannes Maximilian Kuehn
Harlan Stenn
Dave Hart
COPYRIGHT
Copyright (C) 1992-2017 The University of Delaware and Network Time Foun‐
dation all rights reserved. This program is released under the terms of
the NTP license, <http://ntp.org/license>.
BUGS
Please send bug reports to: http://bugs.ntp.org, bugs@ntp.org
NOTES
This manual page was AutoGen-erated from the sntp option definitions.
BSD March 21 2017 BSD
