Set linux time to millisecond precision
date, linux, system, time-precision
Solution
The `settimeofday(2)` method given in other answers has a serious problem: it does exactly what you say you want. :)
The problem with directly changing a system's time, instantaneously, is that it can confuse programs that get the time of day before and after the change if the adjustment was negative. That is, they can perceive time to go backwards.
The fix for this is `adjtime(3)` which is simple and portable, or `adjtimex(2)` which is complicated, powerful and Linux-specific. Both of these calls use sophisticated algorithms to slowly adjust the system time over some period, forward only, until the desired change is achieved.
By the way, are you sure you aren't reinventing the wheel here? I recommend that you read Julien Ridoux and Darryl Veitch's ACM Queue paper Principles of Robust Timing over the Internet. You're working on embedded systems, so I would expect the ringing in Figure 5 to give you cold shivers. Can you say "damped oscillator?" `adjtime()` and `adjtimex()` use this troubled algorithm, so in some sense I am arguing against my own advice above, but the Mills algorithm is still better than the step adjustment non-algorithm. If you choose to implement RADclock instead, so much the better.
Problem
I have an embedded Linux device that interfaces with another "master" device over a serial comm protocol. Periodically the master passes its date down to the slave device, because later the slave will return information to the master that needs to be accurately timestamped. However, the Linux 'date' command only sets the system date to within a second accuracy. This isn't enough for our uses. Does anybody know how to set a Linux machine's time more precisely than 1 second?