tickadj(8) [centos man page]
tickadj(8) System Manager's Manual tickadj(8) NAME
tickadj - set time-related kernel variables SYNOPSIS
tickadj [ tick ] tickadj [ -Aqs ] [ -a tickadj ] [ -t tick ] DESCRIPTION
The tickadj program reads, and optionally modifies, several timekeeping-related variables in older kernels that do not have support for precision ttimekeeping, including HP-UX, SunOS, Ultrix, SGI and probably others. Those machines provide means to patch the kernel /dev/kmem. Newer machines with kernel time support, including Solaris, Tru64, FreeBSD and Linux, should NOT use the program, even if it appears to work, as it will destabilize the kernel time support. Use the ntptime program instead. The particular variables that can be changed with tickadj include tick, which is the number of microseconds added to the system time for a clock interrupt, tickadj, which sets the slew rate and resolution used by the adjtime system call, and dosynctodr, which indicates to the kernels on some machines whether they should internally adjust the system clock to keep it in line with time-of-day clock or not. On Linux, only the tick variable is supported and the only allowed argument is the tick value. By default, with no arguments, tickadj reads the variables of interest in the kernel and displays them. At the same time, it determines an "optimal" value for the value of the tickadj variable if the intent is to run the ntpd Network Time Protocol (NTP) daemon, and prints this as well. Since the operation of tickadj when reading the kernel mimics the operation of similar parts of the ntpd program fairly closely, this can be useful when debugging problems with ntpd. Note that tickadj should be run with some caution when being used for the first time on different types of machines. The operations which tickadj tries to perform are not guaranteed to work on all Unix machines and may in rare cases cause the kernel to crash. COMMAND LINE OPTIONS
-a tickadj Set the kernel variable tickadj to the value tickadjspecified. -A Set the kernel variable tickadj to an internally computed "optimal" value. -t tick Set the kernel variable tick to the value tick specified. -s Set the kernel variable dosynctodr to zero, which disables the hardware time-of-year clock, a prerequisite for running the ntpd daemon under SunOS 4.x. -q Normally, tickadj is quite verbose about what it is doing. The -q flag tells it to shut up about everything except errors. FILES
/vmunix /unix /dev/kmem BUGS
Fiddling with kernel variables at run time as a part of ordinary operations is a hideous practice which is only necessary to make up for deficiencies in the implementation of adjtime in many kernels and/or brokenness of the system clock in some vendors' kernels. It would be much better if the kernels were fixed and the tickadj program went away. SEE ALSO
ntpd(8) The official HTML documentation. This file was automatically generated from HTML source. tickadj(8)
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NTPDATE(8) BSD System Manager's Manual NTPDATE(8) NAME
ntpdate -- set the date and time via NTP SYNOPSIS
ntpdate [-bBdoqsuv] [-a key] [-e authdelay] [-k keyfile] [-o version] [-p samples] [-t timeout] server ... DESCRIPTION
Note: The functionality of this program is now available in the ntpd(8) program. See the -q command line option in the ntpd(8) page. After a suitable period of mourning, the ntpdate utility is to be retired from this distribution. The ntpdate utility sets the local date and time by polling the Network Time Protocol (NTP) server(s) given as the server arguments to deter- mine 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. The following options are available: -a key Enable the authentication function and specify the key identifier to be used for authentication as the argument key. 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(2) system call, even if the measured offset is greater than +-128 ms. The default is to step the time using settimeofday(2) if the offset is greater than +-128 ms. Note that, if the offset is much greater than +-128 ms in this case, 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(2) system call, rather than slewed (default) using the adjtime(2) 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 clock. Information useful for general debugging will also be printed. -e authdelay Specify the processing delay to perform an authentication function as the value authdelay, in seconds and fraction (see ntpd(8) for details). This number is usually small enough to be negligible for most purposes, though specifying a value may improve timekeeping on very slow CPU's. -k keyfile Specify the path for the authentication key file as the string keyfile. The default is /etc/ntp.keys. This file should be in the format described in ntpd(8). -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 number 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(3) facility. This is designed primarily for conve- nience of cron(8) scripts. -t timeout Specify the maximum time waiting for a server response as the value timeout, in seconds and fraction. The value is rounded to a mul- tiple 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 for outgoing packets. This is most useful when behind a firewall that blocks incoming traffic to privileged ports, and you want to synchronise with hosts beyond the firewall. Note that the -d option always uses unpriv- ileged ports. -v Be verbose. This option will cause ntpdate's version identification string to be logged. The ntpdate utility 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(8). It is also possible to run ntpdate from a cron(8) script. However, it is important to note that ntpdate with contrived cron(8) 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(8), 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(2) routine. If the error is less than 0.5 seconds, it will slew the time by calling the system adjtime(2) 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(8) every hour or two. The ntpdate utility will decline to set the date if an NTP server daemon (e.g., ntpd(8)) is running on the same host. When running ntpdate on a regular basis from cron(8) as an alternative to running a daemon, doing so once every hour or two will result in precise enough time- keeping to avoid stepping the clock. ntpd(8). FILES
/etc/ntp.keys contains the encryption keys used by ntpdate. SEE ALSO
ntpd(8) BUGS
The slew adjustment is actually 50% larger than the measured offset, since this (it is argued) will tend to keep a badly drifting clock more accurate. This is probably not a good idea and may cause a troubling hunt for some values of the kernel variables kern.clockrate.tick and kern.clockrate.tickadj. BSD
January 6, 2000 BSD