ntpd —
Network
Time Protocol daemon
| ntpd |
[-dnSsv]
[-f file]
[-p file] |
The
ntpd daemon synchronizes the local clock to one
or more remote NTP servers or local timedelta sensors.
ntpd can also act as an NTP server itself,
redistributing the local time. It implements the Simple Network Time Protocol
version 4, as described in RFC 5905, and the Network Time Protocol version 3,
as described in RFC 1305. Time can also be fetched from TLS HTTPS servers to
reduce the impact of unauthenticated NTP man-in-the-middle attacks, but
support is currently
not enabled on Debian due to
missing LibreSSL's libtls implementation at this time.
The options are as follows:
- -d
- Do not daemonize. If this option is specified,
ntpd will run in the foreground and log to
stderr.
-
-f
file
- Use file as the
configuration file, instead of the default
/etc/openntpd/ntpd.conf.
- -n
- Configtest mode. Only check the configuration file for
validity.
-
-p
file
- Write pid to file
- -S
- Do not set the time immediately at startup. This is the
default.
- -s
- Try to set the time immediately at startup, as opposed to
slowly adjusting the clock. ntpd will stay in
the foreground for up to 15 seconds waiting for one of the configured NTP
servers to reply.
- -v
- This option allows ntpd to
send DEBUG priority messages to syslog.
ntpd uses the
adjtime(2) system call to correct the local
system time without causing time jumps. Adjustments of 32ms and greater are
logged using
syslog(3). The threshold value is
chosen to avoid having local clock drift thrash the log files. Should
ntpd be started with the
-d or
-v option, all
calls to
adjtime(2) will be logged.
After the local clock is synchronized,
ntpd adjusts
the clock frequency using the
adjfreq(2) system
call to compensate for systematic drift.
When
ntpd starts up, it reads settings from its
configuration file, typically
ntpd.conf(5), and
its initial clock drift from
/var/lib/openntpd/ntpd.drift. Clock drift is
periodically written to the drift file thereafter.
- /etc/openntpd/ntpd.conf
- Default configuration file.
- /var/lib/openntpd/ntpd.drift
- Drift file.
- /var/lib/openntpd/run/ntpd.sock
- Socket file for communication with
ntpctl(8).
date(1),
adjfreq(2),
adjtime(2),
ntpd.conf(5),
ntpctl(8),
David L. Mills,
Network Time Protocol (Version 3): Specification,
Implementation and Analysis, RFC 1305,
March 1992.
David L. Mills,
Jim Martin, Jack Burbank,
and William Kasch, Network Time
Protocol Version 4: Protocol and Algorithms Specification,
RFC 5905, June 2010.
The
ntpd program first appeared in
OpenBSD 3.6.