This document describes the use of the NTP Project's sntp program,
that can be used to query a Network Time Protocol (NTP) server and
display the time offset of the system clock relative to the server
clock. Run as root, it can correct the system clock to this offset as
well. It can be run as an interactive command or from a cron job.
This document applies to version 4.2.7p103 of sntp.
The program implements the SNTP protocol as defined by RFC 5905, the NTPv4 IETF specification.
By default, sntp writes the local data and time (i.e., not UTC) to the
standard output in the format:
1996 Oct 15 20:17:25.123 +4.567 +/- 0.089 secs
where the +4.567 +/- 0.089 secs indicates the time offset and error bound of the system clock relative to the server clock.
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 or in 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 secs
where the
+4.567 +/- 0.089 secs
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),
and the (local) time of
1996-10-15 20:17:25.123
can be converted to UTC time by adding 8 hours and 0 minutes, and
is believed to be correct to within
+/- 0.089
seconds.
This section was generated by AutoGen, the aginfo template and the option descriptions for the sntp program. It documents the sntp usage text and option meanings.
This software is released under a specialized copyright license.
This is the automatically generated usage text for sntp:
sntp is unavailable - no --help
This is the “set (slew) the time with adjtime()” option.
This option has some usage constraints. It:
This is the “enable authentication with the key auth-keynumber” option. This option enables 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.
This is the “use broadcasts to the address specified for synchronisation” option. If specified SNTP will listen to the specified broadcast address for NTP broadcasts. The default maximum wait time, 68 seconds, can be modified with -t.
This is the “log to specified logfile” option.
This option has some usage constraints. It:
This option causes the client to write log messages to the specified logfile.
This is the “force ipv4 dns name resolution” option.
This option has some usage constraints. It:
Force DNS resolution of following host names on the command line to the IPv4 namespace.
This is the “force ipv6 dns name resolution” option.
This option has some usage constraints. It:
Force DNS resolution of following host names on the command line to the IPv6 namespace.
This is the “specify a keyfile. sntp will look in this file for the key specified with -a” option. This option specifies the keyfile. SNTP will search for the key specified with -a keyno in this file. Key files follow the following format:
keyid keytype key
Where keyid is a number identifying this key keytype is one of the follow: S Key in 64 Bit hexadecimal number as specified in in the DES specification. N Key in 64 Bit hexadecimal number as specified in the NTP standard. A Key in a 1-to-8 character ASCII string. M Key in a 1-to-8 character ASCII string using the MD5 authentication scheme.
For more information see ntp.keys(5).
This is the “kod history filename” option. Modifies the filename to be used to persist the history of KoD responses received from servers. The default is /var/db/ntp-kod.
This is the “normal verbose” option. 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.
This is the “set (step) the time with settimeofday()” option.
This option has some usage constraints. It:
This is the “logging with syslog” option.
This option has some usage constraints. It:
When this option is set all logging will be done using syslog.
This is the “specify the number of seconds to wait for broadcasts” option. When waiting for a broadcast packet SNTP will wait the number of seconds specified before giving up. Default 68 seconds.
The simplest use of this program is as an unprivileged command to check the current time, offset, and error in the local clock. For example:
sntp ntpserver.somewhere
With suitable privilege, it can be run as a command or in a
crom job to reset the local clock from a reliable server, like
the ntpdate and rdate commands.
For example:
sntp -a ntpserver.somewhere