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NTPD(8)                   BSD System Manager's Manual                  NTPD(8)

NAME
     ntpd -- Network Time Protocol (NTP) daemon

SYNOPSIS
     ntpd [-aAbdm] [-c conffile] [-f driftfile] [-g] [-i chrootdir]
          [-k keyfile] [-l logfile] [-p pidfile] [-r broadcastdelay]
          [-s statsdir] [-t key] [-u user[:group]] [-v variable] [-V variable]
          [-x]

DESCRIPTION
     ntpd is an operating system daemon which sets and maintains the system
     time-of-day in synchronism with Internet standard time servers.  ntpd is
     a complete implementation of the Network Time Protocol (NTP) version 4,
     but also retains compatibility with version 3, as defined by RFC-1305,
     and version 1 and 2, as defined by RFC-1059 and RFC-1119, respectively.
     ntpd does most computations in 64-bit floating point arithmetic and does
     relatively clumsy 64-bit fixed point operations only when necessary to
     preserve the ultimate precision, about 232 picoseconds. While the ulti-
     mate precision is not achievable with ordinary workstations and networks
     of today, it may be required with future nanosecond CPU clocks and giga-
     bit LANs.

     The daemon can operate in any of several modes, including symmetric
     active/passive, client/server broadcast/multicast and manycast. A broad-
     cast/multicast or manycast client can discover remote servers, compute
     server-client propagation delay correction factors and configure itself
     automatically. This makes it possible to deploy a fleet of workstations
     without specifying configuration details specific to the local environ-
     ment.

     Ordinarily, ntpd reads the ntp.conf configuration file at startup time in
     order to determine the synchronization sources and operating modes. It is
     also possible to specify a working, although limited, configuration
     entirely on the command line, obviating the need for a configuration
     file. This may be particularly appropriate when the local host is to be
     configured as a broadcast/multicast client or manycast client, with all
     peers being determined by listening to broadcasts at run time.

     If NetInfo support is built into ntpd, then ntpd will attempt to read its
     configuration from the NetInfo if the default ntp.conf file cannot be
     read and no file is specified by the -c option.

     Various internal ntpd variables can be displayed and configuration
     options altered while the daemon is running using the ntpq(8) and
     ntpdc(8) utility programs.

     When ntpd starts it looks at the value of umask , and if it's zero ntpd
     will set the umask to 022

COMMAND LINE OPTIONS
     -a      Enable authentication mode (default).

     -A      Disable authentication mode.

     -b      Synchronize using NTP broadcast messages.

     -c conffile
             Specify the name and path of the configuration file.

     -d      Specify debugging mode. This flag may occur multiple times, with
             each occurrence indicating greater detail of display.

     -D level
             Specify debugging level directly.

     -f driftfile
             Specify the name and path of the drift file.

     -g      Normally, the daemon exits if the offset exceeds a 1000-s sanity
             limit. This option overrides this limit and allows the time to be
             set to any value without restriction; however, this can happen
             only once. After that, the daemon will exit if the limit is
             exceeded.

     -i chrootdir
             Specify the path to a directory in which ntpd will run chrooted.

     -k keyfile
             Specify the name and path of the file containing the NTP authen-
             tication keys.

     -l logfile
             Specify the name and path of the log file. The default is the
             system log facility.

     -m      Synchronize using NTP multicast messages on the IP multicast
             group address 224.0.1.1 (requires multicast kernel).

     -p pidfile
             Specify the name and path to record the daemon's process ID.

     -P      Override the priority limit set by the operating system. Not rec-
             ommended for sissies.

     -r broadcastdelay
             Specify the default propagation delay from the broadcast/multi-
             cast server and this computer. This is necessary only if the
             delay cannot be computed automatically by the protocol.

     -s statsdir
             Specify the directory path for files created by the statistics
             facility.

     -t key  Add a key number to the trusted key list.

     -u user[:group]
             Specify user (and optionally group) as which ntpd will run.

     -v variable

     -V variable
             Add a system variable listed by default.

     -x      Ordinarily, if the time is to be adjusted more than 128 ms, it is
             stepped, not gradually slewed. This option forces the time to be
             slewed in all cases. Note: Since the slew rate is limited to 0.5
             ms/s, each second of adjustment requires an amortization interval
             of 2000 s. Thus, an adjustment of many seconds can take hours or
             days to amortize.

THE CONFIGURATION FILE
     The ntpd configuration file is read at initial startup in order to spec-
     ify the synchronization sources, modes and other related information.
     Usually, it is installed in the /etc directory, but could be installed
     elsewhere (see the -c conffile command line option). The file format is
     similar to other Unix configuration files - comments begin with a # char-
     acter and extend to the end of the line; blank lines are ignored. Config-
     uration commands consist of an initial keyword followed by a list of
     arguments, some of which may be optional, separated by whitespace. Com-
     mands may not be continued over multiple lines. Arguments may be host
     names, host addresses written in numeric, dotted-quad form, integers,
     floating point numbers (when specifying times in seconds) and text
     strings.  Optional arguments are delimited by [ ] in the following
     descriptions, while alternatives are separated by |.  The notation [...]
     means an optional, indefinite repetition of the last item before the
     [...]

     See the following pages for configuration and control options. While
     there is a rich set of options available, the only required option is one
     or more server, peer, broadcast or manycastclient commands described in
     the Configuration Options page. The Notes on Configuring NTP and Setting
     up a NTP Subnet page in /usr/share/doc/html/ntp/notes.htm contains an
     extended discussion of these options.  For Configuration Options, refer
     to /usr/share/doc/html/ntp/confopt.htm.

     For Authentication Options, refer to /usr/share/doc/html/ntp/authopt.htm.

     For Monitoring Options, refer to /usr/share/doc/html/ntp/monopt.htm.

     For Access Control Options, refer to /usr/share/doc/html/ntp/accopt.htm.

     For Reference Clock Options, refer to
     /usr/share/doc/html/ntp/clockopt.htm.

     For Miscellaneous Options, refer to /usr/share/doc/html/ntp/miscopt.htm.

FILES
     /etc/ntp.conf   the default name of the configuration file
     /etc/ntp.drift  the default name of the drift file
     /etc/ntp.keys   the default name of the key file

AUTHORS
     David L. Mills <millsATudel.edu>

BUGS
     ntpd has gotten rather fat. While not huge, it has gotten larger than
     might be desirable for an elevated-priority daemon running on a worksta-
     tion, particularly since many of the fancy features which consume the
     space were designed more with a busy primary server, rather than a high
     stratum workstation, in mind.

BSD                            February 21, 2002                           BSD