ntpdate_2
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ntpdate(1) - Linux man page NAME ntpdate - set the date and time via NTP Disclaimer: The functionality of this program is now available in the ntpd program. See the -q command line option in the ntpd - Network Time Protocol (NTP) daemon page. After a suitable period of mourning, the ntpdate program is to be retired from this distribution SYNOPSI S ntpdate [ -bBdoqsuv ] [ -a key ] [ -e authdelay ] [ -k keyfile ] [ -o version ] [ -p samples ] [ -t timeout ] [ -U user_name ] server [ ... ] DESCRI PTI ON ntpdate sets the local date and time by polling the Network Time Protocol (NTP) server(s) given as the server arguments to determine the correct time. It must be run as root on the local host. A number of samples are obtained from each of the servers specified and a subset of the NTP clock filter and selection algorithms are applied to select the best of these. Note that the accuracy and reliability of ntpdate depends on the number of servers, the number of polls each time it is run and the interval between runs. ntpdate can be run manually as necessary to set the host clock, or it can be run from the host startup script to set the clock at boot time. This is useful in some cases to set the clock initially before starting the NTP daemon ntpd . It is also possible to run ntpdate from a cron script. However, it is important to note that ntpdate with contrived cron scripts is no substitute for the NTP daemon, which uses sophisticated algorithms to maximize accuracy and reliability while minimizing resource use. Finally, since ntpdate does not discipline the host clock frequency as does ntpd , the accuracy using ntpdate is limited. Time adjustments are made by ntpdate in one of two ways. If ntpdate determines the clock is in error more than 0.5 second it will simply step the time by calling the system settimeofday() routine. If the error is less than 0.5 seconds, it will slew the time by calling the system adjtime() routine. The latter technique is less disruptive and more accurate when the error is small, and works quite well when ntpdate is run by cron every hour or two. ntpdate will decline to set the date if an NTP server daemon (e.g., ntpd ) is running on the same host. When running ntpdate on a regular basis from cron as an alternative to running a daemon, doing so once every hour or two will result in precise enough timekeeping to avoid stepping the clock. If NetInfo support is compiled into ntpdate , then the server argument is optional if ntpdate can find a time server in the NetInfo configuration for ntpd . COMMAND LI NE OPTI ONS -a key Enable the authentication function and specify the key identifier to be used for authentication as the argument key ntpdate . The keys and key identifiers must match in both the client and server key files. The default is to disable the authentication function. -B Force the time to always be slewed using the adjtime() system call, even if the measured offset is greater than + -128 ms. The default is to step the time using settimeofday() if the offset is greater than +-128 ms. Note that, if the offset is much greater than +-128 ms in this case, that it can take a long time (hours) to slew the clock to the correct value. During this time. the host should not be used to synchronize clients. -b Force the time to be stepped using the settimeofday() system call, rather than slewed (default) using the adjtime() system call. This option should be used when called from a startup file at boot time. -d Enable the debugging mode, in which ntpdate will go through all the steps, but not adjust the local Ads by Goooooogle NTPDate Time Servers Synchronize network time using NTPDate. Accurate. Secure. www.ntp-systems.com Master Clock, Time Sync Industrial Master Clocks System, Atomic Clocks, Time Sync www.alzatex.com GPS Time Synchronization Manufacturer of Wireless GPS Time Synchronization Systems www.visiplex.com Telnet/SSH Server RemotelyAnywhere has a flexible Telnet/SSH server & key admin tools RemotelyAnywhere.com Page 1 of 2 ntpdate(1) - Linux man page 1/11/2005 http://www.die.net/doc/linux/man/man1/ntpdate.1.html
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ntpdate( 1 ) - Linux m an page
NAME
ntpdate - set the date and t im e via NTP
Disclaim er: The funct ionalit y of this program is now available in the ntpd program . See the - q com mand line opt ion in the ntpd - Network Time Protocol (NTP) daemon page. After a suitable per iod of mourning, the ntpdate program is to be ret ired from this dist r ibut ion
SYNOPSI S
ntpdate [ - bBdoqsuv ] [ - a key ] [ -e authdelay ] [ -k keyfile ] [ -o version ] [ -p samples ] [ - t t imeout ] [ -U user_name ] server [ . . . ]
DESCRI PTI ON
ntpdate sets the local date and t ime by polling the Network Tim e Protocol (NTP) server(s) given as the server argum ents to determ ine the correct t ime. I t must be run as root on the local host . A number of samples are obtained from each of the servers specified and a subset of the NTP clock filter and select ion algorithms are applied to select the best of these. Note that the accuracy and reliability of ntpdate depends on the number of servers, the num ber of polls each t ime it is run and the interval between runs.
ntpdate can be run manually as necessary to set the host clock, or it can be run from the host startup scr ipt to set the clock at boot t ime. This is useful in some cases to set the clock init ially before start ing the NTP daemon ntpd . I t is also possible to run ntpdate from a cron script . However, it is important to note that ntpdate with cont r ived cron scripts is no subst itute for the NTP daemon, which uses sophist icated algorithms to maxim ize accuracy and reliability while m inim izing resource use. Finally, since ntpdate does not discipline the host clock frequency as does ntpd , the accuracy using ntpdate is lim ited.
Time adjustments are m ade by ntpdate in one of two ways. I f ntpdate determ ines the clock is in error more than 0.5 second it will sim ply step the t im e by calling the system set t im eofday( ) rout ine. I f the error is less than 0.5 seconds, it will slew the t ime by calling the system adj t im e( ) rout ine. The lat ter technique is less disrupt ive and more accurate when the error is sm all, and works quite well when ntpdate is run by cron every hour or two.
ntpdate will decline to set the date if an NTP server daem on (e.g., ntpd ) is running on the sam e host . When running ntpdate on a regular basis from cron as an alternat ive to running a daem on, doing so once every hour or two will result in precise enough t imekeeping to avoid stepping the clock.
I f Net I nfo support is com piled into ntpdate , then the server argum ent is opt ional if ntpdate can find a t ime server in the Net I nfo configurat ion for ntpd .
COMMAND LI NE OPTI ONS
- a key Enable the authent icat ion funct ion and specify the key ident if ier to be used for authent icat ion as the argum ent key ntpdate . The keys and key ident ifiers m ust match in both the client and server key files. The default is to disable the authent icat ion funct ion.
- B Force the t ime to always be slewed using the adj t im e( ) system call, even if the measured offset is greater than + -128 m s. The default is to step the t ime using set t im eofday( ) if the offset is greater than + -128 m s. Note that , if the offset is much greater than + -128 m s in this case, that it can take a long t im e (hours) to slew the clock to the correct value. During this t im e. the host should not be used to synchronize clients.
- b Force the t ime to be stepped using the set t imeofday( ) system call, rather than slewed (default ) using the adj t ime( ) system call. This opt ion should be used when called from a startup file at boot t ime.
- d Enable the debugging m ode, in which ntpdate will go through all the steps, but not adjust the local
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NTPDate Time Servers Synchronize network time using NTPDate. Accurate. Secure. www.ntp-systems.com
Master Clock, Time Sync Industrial Master Clocks System, Atomic Clocks, Time Sync www.alzatex.com
GPS Time Synchronization Manufacturer of Wireless GPS Time Synchronization Systems www.visiplex.com
Telnet/SSH Server RemotelyAnywhere has a flexible Telnet/SSH server & key admin tools RemotelyAnywhere.com
Page 1 of 2ntpdate(1) - Linux man page
1/11/2005http://www.die.net/doc/linux/man/man1/ntpdate.1.html
clock. I nformat ion useful for general debugging will also be pr inted. - e
authdelay Specify the processing delay to perform an authent icat ion funct ion as the value authdelay , in seconds and fract ion (see ntpd for details) . This number is usually small enough to be negligible for most purposes, though specifying a value may im prove t im ekeeping on very slow CPU's.
- k keyfile Specify the path for the authent icat ion key file as the st r ing keyfile . The default is / etc/ ntp.keys . This file should be in the format described in ntpd .
- o version Specify the NTP version for outgoint packets as the integer version , which can be 1 or 2. The default is 3. This allows ntpdate to be used with older NTP versions.
- p samples Specify the num ber of samples to be acquired from each server as the integer samples , with values from 1 to 8 inclusive. The default is 4. - q Query only - don't set the clock.
- s Divert logging output from the standard output (default ) to the system syslog facility. This is designed pr imarily for convenience of cron scripts.
- t t imeout Specify the m aximum t ime wait ing for a server response as the value t imeout , in seconds and fract ion. The value is is rounded to a m ult iple of 0.2 seconds. The default is 1 second, a value suitable for polling across a LAN.
- u Direct ntpdate to use an unprivileged port or outgoing packets. This is most useful when behind a firewall that blocks incom ing t raffic to pr ivileged ports, and you want to synchronise with hosts beyond the firewall. Note that the
- U user_name ntpdate process drops root pr ivileges and changes user ID to user_name and group I D to the prim ary group of server_user .
- d opt ion always uses unprivileged ports.
- v Be verbose. This opt ion will cause ntpdate 's version ident if icat ion st r ing to be logged.
FI LES
/ etc/ ntp/ keys - encrypt ion keys used by ntpdate .
BUGS
The slew adjustm ent is actually 50% larger than the m easured offset , since this ( it is argued) will tend to keep a badly dr ift ing clock more accurate. This is probably not a good idea and m ay cause a t roubling hunt for som e values of the kernel variables t ick and t ickadj .
AUTHOR
David L. Mills < m [email protected]>
Page 2 of 2ntpdate(1) - Linux man page
1/11/2005http://www.die.net/doc/linux/man/man1/ntpdate.1.html
