Ubuntu Manpage: ntpd — Network Time Protocol daemon

NAME

       ntpd — Network Time Protocol daemon

SYNOPSIS

       ntpd [-dnSsv] [-f file] [-p file]

DESCRIPTION

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.

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/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.

ntpd is usually started at boot time, and can be enabled by setting ntpd_flags in /etc/rc.conf.local.
See rc(8) and rc.conf(8) for more information on the boot process and enabling daemons.

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.

When ntpd (engine) receives a SIGINFO signal (or a SIGUSR1 signal on systems without SIGINFO), it writes
its peer and sensor status to syslog(3).

FILES

       /etc/ntpd.conf                   Default configuration file.
       /var/lib/openntpd/ntpd.drift     Drift file.
       /var/run/ntpd.sock               Socket file for communication with ntpctl(8).

STANDARDS

       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.

HISTORY