NTPD(8) NetBSD 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 ac- tive/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 en- tirely on the command line, obviating the need for a configuration file. This may be particularly appropriate when the local host is to be config- ured 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 op- tions 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 ex- ceeded. -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 de- lay 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 speci- fy the synchronization sources, modes and other related information. Usu- ally, it is installed in the /etc directory, but could be installed else- where (see the -c conffile command line option). The file format is simi- lar to other Unix configuration files - comments begin with a # character and extend to the end of the line; blank lines are ignored. Configuration commands consist of an initial keyword followed by a list of arguments, some of which may be optional, separated by whitespace. Commands may not be continued over multiple lines. Arguments may be host names, host ad- dresses 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 alter- natives are separated by . The notation [...] means an optional, indefi- nite 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 ex- tended 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 <mills@udel.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. NetBSD 1.6.2 February 21, 2002 3
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