1sntp(8)                          User Commands                         sntp(8)
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NAME

6       sntp - standard Simple Network Time Protocol client program
7

SYNOPSIS

9       sntp  [-flags]  [-flag [value]] [--option-name[[=| ]value]] [ hostname-
10       or-IP ...]
11
12

DESCRIPTION

14       sntp can be used as an SNTP client to query a NTP or  SNTP  server  and
15       either  display the time or set the local system's time (given suitable
16       privilege).  It can be run as an interactive command  or  from  a  cron
17       job.  NTP (the Network Time Protocol) and SNTP (the Simple Network Time
18       Protocol) are defined and described by RFC 5905.
19
20       The default is to write the estimated correct local date and time (i.e.
21       not  UTC)  to  the  standard  output  in  a  format  like:  '1996-10-15
22       20:17:25.123 (+0800) +4.567 +/- 0.089 [host] IP sN' where the '(+0800)'
23       means  that  to  get to UTC from the reported local time one must add 8
24       hours and 0 minutes, the '+4.567' indicates the local  clock  is  4.567
25       seconds  behind the correct time (so 4.567 seconds must be added to the
26       local clock to get it to be correct).  Note that the number of decimals
27       printed  for  this value will change based on the reported precision of
28       the server.  '+/- 0.089' is the reported synchronization  distance  (in
29       seconds), which represents the maximum error due to all causes.  If the
30       server does not report valid data needed to calculate the  synchroniza‐
31       tion  distance,  this will be reported as '+/- ?'.  If the host is dif‐
32       ferent from the IP, both will be displayed.  Otherwise, only the IP  is
33       displayed.   Finally,  the stratum of the host is reported and the leap
34       indicator is decoded and displayed.
35

OPTIONS

37       -4, --ipv4
38              Force IPv4 DNS name resolution.  This option must not appear  in
39              combination with any of the following options: ipv6.
40
41              Force  DNS resolution of the following host names on the command
42              line to the IPv4 namespace.
43
44       -6, --ipv6
45              Force IPv6 DNS name resolution.  This option must not appear  in
46              combination with any of the following options: ipv4.
47
48              Force  DNS resolution of the following host names on the command
49              line to the IPv6 namespace.
50
51       -a auth-keynumber, --authentication=auth-keynumber
52              Enable authentication with the key auth-keynumber.  This  option
53              takes an integer number as its argument.
54
55              Enable  authentication  using the key specified in this option's
56              argument.  The argument of this option is the  keyid,  a  number
57              specified in the keyfile as this key's identifier.  See the key‐
58              file option (-k) for more details.
59
60       -b broadcast-address, --broadcast=broadcast-address
61              Listen to the address specified for broadcast time  sync.   This
62              option may appear an unlimited number of times.
63
64              If  specified  sntp will listen to the specified address for NTP
65              broadcasts.  The default maximum wait  time  can  (and  probably
66              should) be modified with -t.
67
68       -c host-name, --concurrent=host-name
69              Concurrently  query all IPs returned for host-name.  This option
70              may appear an unlimited number of times.
71
72              Requests from an NTP "client" to a "server" should never be sent
73              more  rapidly  than  one  every  2 seconds.  By default, any IPs
74              returned as part of a DNS lookup are assumed to be for a  single
75              instance  of ntpd, and therefore sntp will send queries to these
76              IPs one after another, with  a  2-second  gap  in  between  each
77              query.
78
79              The  -c  or --concurrent flag says that any IPs returned for the
80              DNS lookup of the supplied host-name are on different  machines,
81              so we can send concurrent queries.
82
83       -d, --debug-level
84              Increase  debug  verbosity  level.   This  option  may appear an
85              unlimited number of times.
86
87
88       -D number, --set-debug-level=number
89              Set the debug verbosity level.  This option may appear an unlim‐
90              ited  number  of  times.  This option takes an integer number as
91              its argument.
92
93
94       -g milliseconds, --gap=milliseconds
95              The gap (in milliseconds) between time  requests.   This  option
96              takes  an integer number as its argument.  The default millisec‐
97              onds for this option is:
98                   50
99
100              Since we're only going to use the first valid  response  we  get
101              and  there  is benefit to specifying a good number of servers to
102              query, separate the queries we send out by the specified  number
103              of milliseconds.
104
105       -K file-name, --kod=file-name
106              KoD history filename.  The default file-name for this option is:
107                   /var/lib/sntp/kod
108
109              Specifies  the filename to be used for the persistent history of
110              KoD responses received from  servers.   If  the  file  does  not
111              exist,  a  warning message will be displayed.  The file will not
112              be created.
113
114       -k file-name, --keyfile=file-name
115              Look in this file for the key specified with  -a.   The  default
116              file-name for this option is:
117                   /etc/ntp.keys
118
119              This option specifies the keyfile.  sntp will search for the key
120              specified with -a keyno in this file.  See ntp.keys(5) for  more
121              information.
122
123       -l file-name, --logfile=file-name
124              Log to specified logfile.
125
126              This option causes the client to write log messages to the spec‐
127              ified logfile.
128
129       -M number, --steplimit=number
130              Adjustments less than  steplimit  msec  will  be  slewed.   This
131              option  takes  an  integer number as its argument.  The value of
132              number is constrained to being:
133                  greater than or equal to 0
134
135              If the time adjustment is less than steplimit milliseconds, slew
136              the amount using adjtime(2).  Otherwise, step the correction
137              using settimeofday(2).  The default value is 0, which means all
138              adjustments will be stepped.  This is a feature, as different
139              situations demand different values.
140
141       -o number, --ntpversion=number
142              Send int as our NTP protocol version.  This option takes an
143              integer number as its argument.  The value of number is con‐
144              strained to being:
145                  in the range  0 through 7
146              The default number for this option is:
147                   4
148
149              When sending requests to a remote server, tell them we are run‐
150              ning NTP protocol version ntpversion .
151
152       -r, --usereservedport
153              Use the NTP Reserved Port (port 123).
154
155              Use port 123, which is reserved for NTP, for our network commu‐
156              nications.
157
158       -S, --step
159              OK to 'step' the time with settimeofday(2).
160
161
162       -s, --slew
163              OK to 'slew' the time with adjtime(2).
164
165
166       -t seconds, --timeout=seconds
167              The number of seconds to wait for responses.  This option takes
168              an integer number as its argument.  The default seconds for this
169              option is:
170                   5
171
172              When waiting for a reply, sntp will wait the number of seconds
173              specified before giving up.  The default should be more than
174              enough for a unicast response.  If sntp is only waiting for a
175              broadcast response a longer timeout is likely needed.
176
177       --wait, - Fl -no-wait
178              Wait for pending replies (if not setting the time).  The no-wait
179              form will disable the option.  This option is enabled by
180              default.
181
182              If we are not setting the time, wait for all pending responses.
183
184       -?, --help
185              Display usage information and exit.
186
187       -!, --more-help
188              Pass the extended usage information through a pager.
189
190       -> [cfgfile], --save-opts [=cfgfile]
191              Save the option state to cfgfile.  The default is the last con‐
192              figuration file listed in the OPTION PRESETS section, below.
193              The command will exit after updating the config file.
194
195       -< cfgfile, --load-opts=cfgfile, --no-load-opts
196              Load options from cfgfile.  The no-load-opts form will disable
197              the loading of earlier config/rc/ini files.  --no-load-opts is
198              handled early, out of order.
199
200       --version [{v|c|n}]
201              Output version of program and exit.  The default mode is `v', a
202              simple version.  The `c' mode will print copyright information
203              and `n' will print the full copyright notice.
204

OPTION PRESETS

206       Any option that is not marked as not presettable may be preset by load‐
207       ing values from configuration ("RC" or ".INI") file(s) and values from
208       environment variables named:
209         SNTP_<option-name> or SNTP
210       The  environmental  presets  take precedence (are processed later than)
211       the configuration files.  The homerc files are "$HOME",  and  ".".   If
212       any  of  these  are  directories,  then the file .ntprc is searched for
213       within those directories.
214

USAGE

216       sntp ntpserver.somewhere
217              is the simplest use of this program and can be run as an unpriv‐
218              ileged  command to check the current time and error in the local
219              clock.
220
221       sntp -Ss -M 128 ntpserver.somewhere
222              With suitable privilege, run as a command or from a cron(8) job,
223              sntp  -Ss  -M 128 ntpserver.somewhere will request the time from
224              the server, and if that server reports that it  is  synchronized
225              then  if the offset adjustment is less than 128 milliseconds the
226              correction will be slewed, and if the correction  is  more  than
227              128 milliseconds the correction  will be stepped.
228
229       sntp -S ntpserver.somewhere
230              With suitable privilege, run as a command or from a cron(8) job,
231              sntp -S ntpserver.somewhere will set (step) the local clock from
232              a  synchronized  specified  server,  like  the (deprecated) ntp‐
233              date(8), or rdate(8) commands.
234

ENVIRONMENT

236       See OPTION PRESETS for configuration environment variables.
237

FILES

239       See OPTION PRESETS for configuration files.
240

EXIT STATUS

242       One of the following exit values will be returned:
243
244       0  (EXIT_SUCCESS)
245              Successful program execution.
246
247       1  (EXIT_FAILURE)
248              The operation failed or the command syntax was not valid.
249
250       66  (EX_NOINPUT)
251              A specified configuration file could not be loaded.
252
253       70  (EX_SOFTWARE)
254              libopts had an internal operational error.  Please report it  to
255              autogen-users@lists.sourceforge.net.  Thank you.
256

AUTHORS

258       Johannes Maximilian Kuehn
259       Harlan Stenn
260       Dave Hart
261
263       Copyright  (C)  1992-2020  The  University of Delaware and Network Time
264       Foundation all rights reserved.  This program  is  released  under  the
265       terms of the NTP license, <http://ntp.org/license>.
266

BUGS

268       Please send bug reports to: http://bugs.ntp.org, bugs@ntp.org
269

NOTES

271       This manual page was AutoGen-erated from the sntp option definitions.
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2754.2.8p15                          23 Jun 2020                          sntp(8)
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