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. The
default file-name for this option is:
/etc/ntp.keys
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(1ntpdatemdoc),
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 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.