Provided by: ntp_4.2.8p4+dfsg-3ubuntu5.10_amd64 
NAME
sntp - standard Simple Network Time Protocol client program
SYNOPSIS
sntp [-flags] [-flag [value]] [--option-name[[=| ]value]] [ hostname-or-IP ...]
DESCRIPTION
sntp 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 Protocol) 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 seconds 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 command 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 command 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 probably 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 number 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 correction 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 constrained 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 communications.
-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 seconds 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 disable 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 information 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 environment 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.
USAGE
sntp ntpserver.somewhere
is the simplest use of this program and can be run as an unprivileged 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(1), 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) 1992-2015 The University of Delaware and Network Time Foundation 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.