Friday, 6 November 2015

knowing the unknowns

Known knowns, known unknowns & unknown unknowns.

When I first heard this from a video I was watching from Brendan on Dtrace I asked what does that even mean? 

I found other quotes that expand on this thought i.e.

"There are known knowns. These are things we know that we know. There are known unknowns. That is to say, there are things that we know we don't know. But there are also unknown unknowns. There are things we don't know we don't know."
- Donald Rumsfeld

which led me down more thoughts and questions...
such as how can I be more aware of things I don't even have awareness about?
Do I know someone with much more experience & understanding than me?

so why post this?

It is important to be more aware of this (it seems kind of obvious in some regard) but you need others to point things out to you or ask questions to make you think a little differently and question what you are doing and why you are doing something. This immediately gives you another angle towards things, allowing you to learn in another way

For example I learnt last year something I didn't realize was possible, on Windows, Linux, BSDs, OSX etc when you reboot you must wait until after BIOS and POST then load the system etc. This can take some time however is it possible to bypass these to boot much faster into the OS? Can this also be done after you do something such as upgrade the host kernel? 

This can be done in Solaris by default reboot command (which is same as reboot -f) as per the man page - "Fast reboot, bypassing firmware and boot  loader.  The  new  kernel will  be loaded into memory by the running kernel, and control will be transferred to the newly loaded kernel. If  disk or kernel arguments are specified, they must be specified before other boot arguments"

This allows reboot within seconds and in my case I have in a desktop an nvidia graphics card which the device driver implementation does not support quiesce. Nevertheless this can also be forced to do so anyway provided only the nvidia graphics are the issue. I did using the following:

echo "force_fastreboot/W 1" | mdb -kw
echo "set force_fast reboot = 1" #x26;#x26;#x3e;#x26;#x26;#x3e; /etc/system

then done.

I have since found out it is possible to do a similar thing on Linux using kexec however it does not look stable so I'm uneasy about using it but could test it out.

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