How do you find out when a specific kernel version was last booted?

Solution 1:

Use the stat command:

   %x     time of last access, human-readable
   %X     time of last access, seconds since Epoch

So:

stat -c %X /some/file

Or with find:

find /some/path -printf "%A@ %p\n"

Since for find's -printf:

  %a     File's  last  access time in the format returned by the C
         `ctime' function.

  %Ak    File's last access time in the  format  specified  by  k,
         which  is  either `@' or a directive for the C `strftime'
         function.  The possible values for k  are  listed  below;
         some  of  them might not be available on all systems, due
         to differences in `strftime' between systems.

         @      seconds  since  Jan.  1,  1970,  00:00  GMT,  with
                fractional part.