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ntpd(8) System Manager's Manual ntpd(8)

Name
ntpd - network time protocol (NTP) daemon

Syntax
/usr/etc/ntpd [ -a threshold ][ -c file ][ -d ][ -D level ][ -l ][ -n ][ -s ]

Description
The University of Maryland's daemon synchronizes the local clock with a set of distributed time servers. The daemon distributes accurate,
reliable time from the best time source available at your site to hosts on wide area networks (WAN) and local area networks (LAN). The
three recommended time sources in decreasing order of accuracy are: Internet NTP service, local radio clock, and wristwatch. Note that
the daemon does not require time servers to be on the same LAN as time clients, and does not create a heavy broadcast load on the network.
If the NTP servers are not on your Local Area Network (LAN), you must run the daemon before running the daemon. To run remove the number
signs (#) from in front of the following lines in your file:
#[ -f /etc/routed ] && {
# /etc/routed & echo 'routed' >/dev/console
#}
The daemon will be invoked when you reboot your system. To start without rebooting, type the following on the command line:
/etc/routed
For information on setting up the network time services, see the Guide to System and Network Setup.

The daemon automatically splits the nodes running the daemon into a dynamically reconfigurable hierarchy of nodes. The nodes at the top
level of the hierarchy (low stratum numbers) are connected to the most accurate sources available. This information is transferred to the
lower-level nodes (higher stratum numbers) which set their clocks based on the calculated offset from a remote server, and then distribute
this time to lower levels of the hierarchy.

The daemon provides a solution for distributing time to a large number of individual workstations. It can also be used in conjunction with
a master daemon to distribute NTP time to workstations running If is run with the and options on at least one system that is also running
then all other systems on the network running can receive time updates from a host running Although is easier to set up on clients, NTP is
recommended because it is more accurate and more secure.

Normally, the daemon is invoked at boot time from the file. When is started, it reads configuration information from the file, unless you
have specified another configuration file with the option. The configuration file either specifies the list of NTP servers with which this
host should synchronize, or identifies this host as a local reference clock. See the reference page for more information on the configura-
tion file.

The daemon uses the system call to gradually adjust the local clock for small clock offsets (< 0.128 seconds). If the local clock lags the
time on the server by more than 0.128 seconds, the system call is used to make a forward step adjustment of the local clock. Clocks are
never stepped backwards; they are adjusted gradually, which can take a very long time. Therefore, it is important to initialize the time
using the command before running the daemon.

Options
-a threshold
Sets the threshold (in seconds) which limits how far the daemon can change the local clock. By default, the threshold is 1000 sec-
onds. This is set to avoid propagating major mistakes throughout the network. If you specify the string instead of a number, the
daemon can change the local clock by any amount.

-c file
Specifies a configuration file for the daemon. By default, the configuration file is

-d Increments the debug level by one. The option can be specified more than once. Higher debug levels provide more diagnostic informa-
tion.

-D level
Sets the debug level to the specified value.

-l Causes the daemon to log a message each time the local clock is adjusted. Specify this option only if you want to gather statistical
information to analyze the local clock behavior. If the option is set, a message may be logged every two minutes. Messages are
logged to

-n Inhibits the program from being swapped out of memory. Using the option is recommended for both time servers and time clients.

-s Prevents the daemon from altering the time on the local host. The daemon participates as an NTP server with the flag set, but it does
not change the time of the local host.

Examples
Before starting the daemon, either manually or from the file, you must edit the file with the appropriate information. If your system is a
client you must specify the time servers for it to query. If it is a time server, you must specify the time servers with which it peers.
See the reference page for more information.

To start the daemon manually (on a time client), enter the following commands:
# /etc/rdate -s
# /usr/etc/ntp -s -f server1 server2 server3
# /usr/etc/ntpd -n
The command initializes your time to the average network time. The command further refines the initial time to the NTP time. The servers
specified on the command line are the same as those specified in the file.

To start the daemon from the file (on a time client), place the following entries in the file. Multiple servers are included in case one
of the servers crashes, or is brought down. The servers specified in the file are the same as those specified in the file. These entries
should be placed after the entry:

[-f /etc/syslog] && {
/etc/syslog & echo -n ' syslog' >/dev/console
}
[-f /etc/rdate] && {
/etc/rdate -s & echo -n ' rdate' >/dev/console
}
[-f /usr/etc/ntp] && {
/usr/etc/ntp -s -f server1 server2 server3
& echo -n ' ntp' >/dev/console
}
[-f /usr/etc/ntpd] && {
/usr/etc/ntpd -n & echo -n ' ntpd' >/dev/console

}

Diagnostics
The daemon logs errors, major state changes, and statistics reports using the daemon; the log entries appear in the file with the word on
each relevant line. Normal log entries show when gains or loses synchronization with a lower-stratum host. Also, once an hour issues a
entry that gives information about its state.

Once an hour, if is synchronized, it updates the file. This file shows the estimated clock drift for each of the past 5 hours, with the
most recent hour listed first. (The 6th number in this file is the number of hours has been running). To convert the drift values to
parts per million (ppm), divide them by 4096 and multiply by 1000000. For example, +0.0107001161 means that estimates that the clock is
drifting by about 2.61 ppm, or is losing about 0.226 seconds per day. [(2.61/1000000) * 24 * 60 * 60 = 0.226]. Negative drift values mean
that the clock is gaining time. If is working, your computer's clock should be accurate to within a few seconds per day.

Another diagnostic tool is the command. You can use this to look at any host running The following command line returns the state of the
remote host's server:
% /usr/etc/ntpdc hostname

The value that is returned for the should contain values not greater than 100 milliseconds. See the reference page for more information.

If the daemon sets the time as frequently as every 10 minutes (indicated by messages in the file), then you should kill the daemon, remove
the file, run the command to initialize the time, and restart the daemon.

If your system clock is ahead of the server time by more than 1 second, you should kill the daemon, remove the file, run the command to
initialize the time, and restart the daemon.

If your clock is more than 1000 seconds off from the server time, and you did not specify the option, will not change your system time.
Rather, will repeatedly log messages to the file, indicating that the time is too far off to reset.

See Also
ntp(1), adjtime(2), settimeofday(2), ntp.conf(5), ntpdc(8), timed(8)
RFC 1129--Internet Time Synchronization: the Network Time Protocol
Guide to System and Network Setup
Introduction to Networking and Distributed System Services

ntpd(8)

ultrix man page for ntpd