System Administration Commands ntpd(1M)
NAME
ntpd - Network Time Protocol daemon Version 4
SYNOPSIS
/usr/lib/inet/ntpd [-46aAbdDgLmnNqvx] [-c conffile]
[-f driftfile] [-k keyfile] [-l logfile] [-p pidfile]
[-P priority] [-r broadcastdelay] [-s statsdir]
[-t trustedkey] [-U interface_update_time]
DESCRIPTION
The ntpd program is an operating system daemon that syn-
chronises the system clock with remote NTP time servers or local reference clocks. It 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 versions 1 and 2, as defined by RFC 1059 and RFC 1119, respectively. How NTP OperatesThe ntpd program operates by exchanging messages with one or
more configured servers at designated intervals ranging fromabout one minute to about 17 minutes. When started, the pro-
gram requires several exchanges while the algorithms accumu-
late and groom the data before setting the clock. The ini-
tial delay to set the clock can be reduced using options as described in the server options page at file:///usr/share/doc/ntp/confopt.html. When the machine is booted, the hardware time of day (TOD) chip is used to initialize the operating system time. After the machine has synchronized to a NTP server, the operating system corrects the chip from time to time. During the course of operation if for some reason the system time ismore than 1000s offset from the server time, ntpd assumes
something must be terribly wrong and exits with a panic mes-
sage to the system log. If it was started via SMF, the ntp service is placed into maintainance mode and must be clearedmanually. The -g option overrides this check at startup and
allows ntpd to set the clock to the server time regardless
of the chip time, but only once.Under ordinary conditions, ntpd slews the clock so that the
time is effectively continuous and never runs backwards. If due to extreme network congestion an error spike exceeds the step threshold (128ms by default), the spike is discarded. However, if the error persists for more than the stepout threshold (900s by default) the system clock is stepped to the correct value. In practice the need for a step is extremely rare and almost always the result of a hardwarefailure. With the -x option the step threshold is increased
to 600s. Other options are available using the tinker SunOS 5.10 Last change: 1System Administration Commands ntpd(1M)
command as described in the miscellaneous options page at file:///usr/share/doc/ntp/miscopt.html. The issues should be carefully considered before using these options. The maximum slew rate possible is limited to 500parts-per-million (PPM) by the Unix kernel. As a result, the
clock can take 2000s for each second the clock is outside the acceptable range. During this interval the clock willnot be consistent with any other network clock and the sys-
tem cannot be used for distributed applications that require correctly synchronized network time. Frequency Discipline The frequency file, usually called ntp.drift, contains the latest estimate of clock frequency. If this file does notexist when ntpd is started, it enters a special mode
designed to measure the particular frequency directly. The measurement takes 15 minutes, after which the frequency isset and ntpd resumes normal mode where the time and fre-
quency are continuously adjusted. The frequency file is updated at intervals of an hour or more depending on the measured clock stability. Operating ModesThe ntpd daemon can operate in any of several modes, includ-
ing symmetric active/passive, client/serverbroadcast/multicast and manycast, as described in the Asso-
ciation Management page at file:///usr/share/doc/ntp/assoc.html. It normally operates continuously while monitoring for small changes in frequency and trimming the clock for the ultimate precision. However,it can operate in a one-time mode where the time is set from
an external server and frequency is set from a previously recorded frequency file. A broadcast/multicast or manycastclient 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 environment.By default, ntpd runs in continuous mode where each of pos-
sibly several external servers is polled at intervals deter-
mined by an intricate phase/frequency-lock feedback loop.
The feedback loop measures the incidental roundtrip delay jitter and oscillator frequency wander and determines the best poll interval using a heuristic algorithm. Ordinarily, and in most operating environments, the state machine will start with 64s intervals and eventually increase in steps to 1024s. A small amount of random variation is introduced in order to avoid bunching at the servers. In addition, should a server become unreachable for some time, the poll interval is increased in steps to 1024s in order to reduce network SunOS 5.10 Last change: 2System Administration Commands ntpd(1M)
overhead. In general it is best not to force ntpd to use
specific poll intervals, allowing it to choose the best intervals based its current needs and the quality of the available servers and the clock.In some cases it may not be practical for ntpd to run con-
tinuously. In the past a common workaround has been to runthe ntpdate program from a cron job at designated times.
However, ntpdate does not have the crafted signal process-
ing, error checking and mitigation algorithms of ntpd. The
ntpd daemon with -q option is intended to replace ntpdate
when used in this manner. Setting this option will causentpd to exit just after setting the clock for the first
time. The procedure for initially setting the clock is the same as in continuous mode; most applications will probablywant to specify the iburst keyword with the server confi-
guration command. With this keyword a volley of messages are exchanged to groom the data and the clock is set in about10s. If nothing is heard after a couple of minutes, the dae-
mon times out and exits. Eventually the ntpdate program may
be retired. Kernel Clock DisciplineThe kernel supports a method specific to ntpd to discipline
the clock frequency. First, ntpd is run in continuous mode
with selected servers in order to measure and record the intrinsic clock frequency offset in the frequency file. It may take some hours for the frequency and offset to settledown. Then ntpd is run in normal mode as required. At each
startup, the frequency is read from the file and initializes the kernel frequency, thus avoiding the settling period. When the kernel discipline is in use, the system's clock is adjusted at each system tick and thus the system clock is always as accurate as possible. When the kernel discipline is not used the clock is adjusted once each second. It isimportant to delete the ntp.drift file before starting ntpd
if the intrinsic frequency might have changed, such as by a motherboard swap. Poll Interval ControlThe ntpd program includes an intricate clock discipline to
reduce the network load while maintaining a quality of syn-
chronization consistent with the observed jitter and wander. There are a number of ways to tailor the operation in order to enhance accuracy by reducing the interval or to reduce network overhead by increasing it. However, the user is advised to carefully consider the consequences of changing the poll adjustment range from the default. It is not the case that shorter poll intervals will necessarily lead to more accuracy. Most device drivers will not operate properlyif the poll interval is less than 64 s and that the broad-
cast server and manycast client associations will also use SunOS 5.10 Last change: 3System Administration Commands ntpd(1M)
the default, unless overridden. In general, it is best tolet ntpd determine the best polling interval.
In some cases involving dial up or toll services, it may be useful to increase the minimum interval to a few tens of minutes and maximum interval to a day or so. Under normal operation conditions, once the clock discipline loop has stabilized the interval will be increased in steps from the minimum to the maximum. However, this assumes the intrinsic clock frequency error is small enough for the discipline loop correct it. The capture range of the loop is 500 PPM at an interval of 64s decreasing by a factor of two for each doubling of interval. At a minimum of 1,024 s, for example, the capture range is only 31 PPM.The Huff-n'-Puff Filter
In scenarios where a considerable amount of data are to bedownloaded or uploaded over bandwidth limited links, time-
keeping quality can be seriously degraded due to the dif-
ferent delays in the two directions. In many cases the apparent time errors are so large as to exceed the step threshold and a step correction can occur during and after the data transfer is in progress.The huff-n'-puff filter is designed to correct the apparent
time offset in these cases. It depends on knowledge of the propagation delay when no other traffic is present. The filter maintains a shift register that remembers the minimum delay over the most recent interval measured usually in hours. Under conditions of severe delay, the filter corrects the apparent offset using the sign of the offset and the difference between the apparent delay and minimum delay. The name of the filter reflects the negative (huff) and positive (puff) correction, which depends on the sign of the offset. The filter is activated by the tinker command and huffpuff keyword, as described in the Miscellaneous Options page at file:///usr/share/doc/ntp/miscopt.html. Leap Second Processing As provided by international agreement, an extra second is sometimes inserted in Coordinated Universal Time (UTC) at the end of a selected month, usually June or December. TheNational Institutes of Standards and Technology (NIST) pro-
vides an historic leapseconds file at time.nist.gov forretrieval via FTP. This file, usually called ntp-
leapseconds.list, is copied into the /etc/inet directory and the leapfile configuration command then specifies the pathto this file. At startup, ntpd reads it and initializes
three leapsecond values: the NTP seconds at the next leap event, the offset of UTC relative to International Atomic Time (TAI) after the leap and the NTP seconds when the SunOS 5.10 Last change: 4System Administration Commands ntpd(1M)
leapseconds file expires and should be retrieved again. If a host does not have the leapsecond values, they can be obtained over the net using the Autokey security protocol. Ordinarily, the leapseconds file is installed on the primary servers and the values flow from them via secondary servers to the clients. When multiple servers are involved, the values with the latest expiration time are used. If the latest leap is in the past, nothing further is done other than to install the TAI offset. If the leap is in the future less than 28 days, the leap warning bits are set. If in the future less than 23 hours, the kernel is armed to insert one second at the end of the current day. Additional details are in the The NTP Timescale and Leap Seconds white paper at http://www.eecis.udel.edu/~mills/leap.html. If none of the above provisions are available, dsependent servers and clients tally the leap warning bits of survivingservers and reference clocks. When a majority of the sur-
vivors show warning, a leap is programmed at the end of the current month. During the month and day of insertion, they operate as above. In this way the leap is is propagated at all dependent servers and clients. OPTIONS-4, --ipv4
Force DNS resolution of following host names on the command line to the IPv4 namespace. Cannot be used withthe --ipv6 option.
-6, --ipv6
Force DNS resolution of following host names on the command line to the IPv6 namespace. Cannot be used withthe --ipv6 option.
-a, --authreq
Require cryptographic authentication for broadcastclient, multicast client and symmetric passive associa-
tions. This is the default. This option must not appear with authnoreq option.-A, --authnoreq
Do not require cryptographic authentication for broad-
cast client, multicast client and symmetric passive associations. This is almost never a good idea. This option must not appear with the authreq option.-b, --bcastsync
Enable the client to sync to broadcast servers. SunOS 5.10 Last change: 5System Administration Commands ntpd(1M)
-c string, --configfile=string
The name and path of the configuration file, /etc/inet/ntp.conf by default.-d, --debug-level
Increase output debug message level. This option may appear an unlimited number of times.-D string, --set-debug-level=string
Set the output debugging level. Can be supplied multi-
ple times, but each overrides the previous value(s).-f string, --driftfile=string
The name and path of the frequency file, /var/ntp/ntp.drift by default.-g, --panicgate
Allow the first adjustment to exceed the panic limit.Normally, ntpd exits with a message to the system log
if the offset exceeds the panic threshold, which is 1000s by default. This option allows the time to be set to any value without restriction; however, this can happen only once. If the threshold is exceeded afterthat, ntpd will exit with a message to the system log.
This option can be used with the -q and -x options.
See the tinker configuration file directive for other options.-k string, --keyfile=string
Specify the name and path of the symmetric key file. /etc/inet/ntp.keys is the default.-l string, --logfile=string
Specify the name and path of the log file. The default is the system log file.-L, --novirtualips
Do not listen to virtual IPs. The default is to listen.-m, --mdns
Register as a NTP server with mDNS system. Implies that you are willing to serve time to others.-n, --nofork
Do not fork.-N, --nice
To the extent permitted by the operating system, runntpd at the highest priority.
SunOS 5.10 Last change: 6System Administration Commands ntpd(1M)
-p string, --pidfile=string
Specify the name and path of the file used to recordntpd's process ID.
-P number, --priority=number
To the extent permitted by the operating system, runntpd at the specified sched_setscheduler(SCHED_FIFO)
priority.-q, --quit
Set the time and quit. ntpd will exit just after the
first time the clock is set. This behavior mimics thatof the ntpdate program, which is to be retired. The -g
and -x options can be used with this option. Note: The
kernel time discipline is disabled with this option.-r string, --propagationdelay=string
Specify the default propagation delay from the broadcast/multicast server to this client. This isnecessary only if the delay cannot be computed automat-
ically by the protocol.-s string, --statsdir=string
Specify the directory path for files created by the statistics facility. This is the same operation as the statsdir statsdir command.-t number, --trustedkey=number
Add a key number to the trusted key list. This option can occur more than once. This is the same operation as the trustedkey key command.-U number, --updateinterval=number
interval in seconds between scans for new or dropped interfaces. This option takes an integer number as its argument. Give the time in seconds between two scans for new or dropped interfaces. For systems with routing socket support the scans will be performed shortly after the interface change has been detected by the system. Use 0 to disable scanning. 60 seconds is the minimum time between scans.--var=nvar
make ARG an ntp variable (RW). This option may appear an unlimited number of times.--dvar=ndvar
make ARG an ntp variable (RW|DEF). This option may appear an unlimited number of times. SunOS 5.10 Last change: 7System Administration Commands ntpd(1M)
-x, --slew
Slew up to 600 seconds. Normally, the time is slewed if the offset is less than the step threshold, which is 128 ms by default, and stepped if above the threshold. This option sets the threshold to 600 s, which is well within the accuracy window to set the clock manually. Note: Since the slew rate of typical Unix kernels is limited to 0.5 ms/s, each second of adjustment requires an amortization interval of 2000 s. Thus, an adjustment as much as 600 s will take almost 14 days to complete. This optioncan be used with the -g and -q options. See the tinker
configuration file directive for other options. Note: The kernel time discipline is disabled with this option.-?, --help
Display usage information and exit.-!, --more-help
Extended usage information passed thru pager.--version
Output version of program and exit. OPTION PRESETS All of the above options except the last three may be preset by loading values from environment variables named:NTPD_
The environmental presets take precedence (are processedor NTPD later than) the configuration files. The option-name should
be in all capital letters. For example, to set the --quit
option, you would set the NTPD_QUIT environment variable.
AUTOMATIC SERVICE MANAGEMENT (SMF)NTP on Solaris is managed via the service management facil-
ity described in smf(5). There are several options controlled by services properties which can be set by the system administrator. The available options can be listed by executing the following command:svccfg -s svc:/network/ntp:default listprop config
Each of these properties can be set using this command:svccfg -s svc:/network/ntp:default setprop propname = value
The available options and there meaning are as follows:config/always_allow_large_step
A boolean which when false, prevents ntpd from allowing
step larger than 17 minutes except once when the system boots. The default is true, which allows such a largestep once each time ntpd starts.
SunOS 5.10 Last change: 8System Administration Commands ntpd(1M)
config/debuglevel An integer specifying the level of debugging requested. A zero means no debugging. The default is zero. config/logfile A string specifying the location of the file used for log output. The defualt is /var/ntp/ntp.logconfig/no_auth_required
A boolean which when true, specifies that anonymous servers such as broadcast, multicast and active peerscan be accepted without any pre-configured keys. This
is very insecure and should only be used if the nework is secure and all the systems on it are trusted. The defualt is false.config/slew_always
A boolean which when true, instructs ntpd to slew the
clock as much as possible, instead of stepping the clock. It does not prevent all stepping, but increases the threshold above which stepping is used. It also disables the use of the kernel NTP=fP facility, which is incompatible with long slew times. The default is false.config/wait_for_sync
A boolean which when true, causes the NTP service todelay coming completely on-line until after the first
time the system clock is synchronized. This can pote-
tially delay the system start up by a significant amount. The default is false. config/mdnsregister A boolean which when true, will cause the daemon to register with the network mDNS system. The default is false.config/verbose_logging
A boolean which when true, cause the daemon to issue logging messages. The default is false. NOTES The system clock must be set to within 68 years of theactual time before ntpd is started.
The ntpd service is managed by the service management facil-
ity, smf(5), under the service identifier: svc:/network/ntp:default Administrative actions on this service, such as enabling, disabling, or requesting restart, can be performed using SunOS 5.10 Last change: 9System Administration Commands ntpd(1M)
svcadm(1M). The service's status can be queried using the svcs(1) command.In contexts where a host name is expected, a -4 qualifier
preceding the host name forces DNS resolution to the IPv4namespace, while a -6 qualifier forces DNS resolution to the
IPv6 namespace.Various internal ntpd variables can be displayed and confi-
guration options altered while the ntpd is running using the
ntpq and ntpdc utility programs.
When ntpd starts it looks at the value of umask, and if zero
ntpd will set the umask to 022.
Source for ntpd is available on http://src.opensolaris.org.
The documentation available at /usr/share/doc/ntp is pro-
vided as is from the NTP distribution and may contain infor-
mation that is not applicable to the software as provided in this partIcular distribution.ATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|_____________________________|_____________________________|
| Availability | service/network/ntp ||_____________________________|______________________________|_
| Interface Stability | Uncommitted ||_____________________________|_____________________________|
SEE ALSO
svcs(1), sntp(1M), ntp-keygen(1M), ntpdate(1m), ntpq(1M),
ntptrace(1M), ntptime(1M), svcadm(1M), ntpdc(1M), rename(2),
attributes(5), smf(5) SunOS 5.10 Last change: 10