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, 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.

FILES

     /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).

SEE ALSO

     date(1), adjfreq(2), adjtime(2), ntpd.conf(5), 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

     The ntpd program first appeared in OpenBSD 3.6.