== What the timestamps in Ubuntu kernel messages mean

Ubuntu kernels are configured so that they include cryptic time
information in kernel messages. An example looks like:

> _[8804849.737776] Kernel BUG at fs/nfs/file.c:321_

(In the general tradition of Linux kernel messages, this is just enough
to show you that there is useful stuff present without actually giving
you any clear idea of how to interpret it to get actual information.)

It turns out that the timestamp is seconds and microseconds since the
system booted. If the system is still running, the simple way to relate
it to wall clock time is to look at _/proc/uptime_ to get the current
number of seconds since the system booted and subtract the difference to
get the wall clock time. ('_date -d "now - NNN seconds"_' may be useful
here.)

(If the system is not still running you will have to work forward from
its boot time, which hopefully got recorded somewhere. I believe that
adjusting the system clock does not adjust the 'seconds since boot'
counters; beware of this if you had to make significant time adjustments
to your system.)

This configuration setting is controlled by the [[kernel config option
EasyKernelConfMods]] ((PRINTK_TIME)).  Well, sort of. The config option
sets the default value for this setting, which you can override in two
ways:

* at boot time, with '_printk.time=1_' (or 0, depending on preferences;
  'y', 'Y', 'n', and 'N' are also accepted)
* dynamically, by writing a suitable value to
  _/sys/module/printk/parameters/time_.

(I got this information from [[here
http://lkml.org/lkml/2007/5/30/335]].)