OSF DCE Administration Guide--Core Components

Managing the DCE DST
In order to use the clock set command effectively, you must have temporary access to a
trusted time reference. Such references can include the time signals that many standards
organizations disseminate by radio or telephone. You can also use a clock that you have
recently verified as accurate. (See Appendix C for suppliers of UTC time.)
Because it is a manually entered command that is used to modify an absolute time, the
clock set command is not useful for small inaccuracy settings. The minimum reliable
inaccuracy that you can achieve with the command is approximately 1 second. Human
error and processing delays combine to make lower settings unreliable. For example,
you enter the command and new time and then begin monitoring the reference. When
you perceive that the reference has reached the desired time, you press <Return> to
initiate the command. Your perception of the reference mark and your pressing of
<Return> do not exactly coincide. Furthermore, once the command is initiated, DTS
takes time to interpret and execute the command.
The following example shows how to monotonically update the time on a server system;
that is, how to reset the clock and eventually propagate the adjustment throughout the
network:
dcecp> clock set 1994-10-07-09:30:15.00I01.00
If your systems require synchronization that is closer than 1 second to a standard such as
UTC, consider purchasing one of the time-providers listed in Appendix C. All of the
time-providers that are described in the listing compensate for transmission and
processing delays, and can provide time references that are accurate to the millisecond
level.
25.7.2 Updating the Time Nonmonotonically
Use the clock set command with the -abruptly option when you want to abruptly set the
time for a server system. The clock set command with the -abruptly option immediately
(nonmonotonically) changes the system clock setting to the specified time, rather than
gradually (monotonically) adjusting the time.
Note: Exercise caution when changing the system time abruptly. The abrupt
adjustment of the time is appropriate at system startup or when the system
clock is faulty and you identify and correct the problem. Changing the
system time to a setting that falls outside the time intervals of the system’s
known servers causes DTS to declare the system faulty at the next
synchronization.
Because the clock set command is usually used to correct gross clock errors, it is likely
that the time you specify for a given system will appear faulty to the system’s known
servers if the system and servers have the same epoch number. You can prevent the
systems whose times you are changing from being declared faulty. Use the clock set
command’s -epoch option along with the -abruptly option to set the new time to isolate
it from the other systems. You can then change the time and epoch for the other systems
until all the systems once again share the same epoch. This process is useful in the rare
case when the majority of servers in the network are faulty.
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