How to test with low RAM and just one CPU core (using Grub)

[Jonathan Marsden]

On 06/01/2013 06:50 AM, Jose Lopez wrote:

> Hi Jonathan, I'm very interested in learning CLI from Grub, never done
> it before and I,m pretty new to (advance CLI) as I would look at it. is
> there a link or a tut that you can point me to.

I prefer to learn by doing, and by reading the docs that come with the
product.  I generally do not trust web tutorials very much!  So

  http://www.gnu.org/software/grub/manual/grub.html

and typing the commands

  info grub

and/or

  info grub-install

and reading the scripts under /etc/grub.d/ was enough.  There are also
tutorials out there, such as

  https://help.ubuntu.com/community/Grub2

but I have not used them.

HOWEVER, in this case, learning enough to do what we were discussing
(changing the kernel boot parameters to add something like

  mem=512MB nosmp

temporarily for test purposes) is pretty trivial.  Here it is, step by step:

1. Power on the machine.

2. If necessary, hold down the Shift key (this makes the Grub menu
display even if the Grub config is set to hide it).

3.  Once you see the Grub menu, press the space bar. (This stops the
countdown to booting a default menu entry).

4. If necessary, use the up and down arrow keys to select the entry you
want to boot (usually the one labelled "Ubuntu", which will be the
default, unless you did something creative with your configuration).

5. Type 'e' to edit that entry. (There is a hint on screen about this).

6. Find the line that starts with "linux".  Use the arrow keys to move
to the end of that line.

7.  Type in the parameters you want to add, in this case mem=512M nosmp

8. Press ctrl-x to boot the (temporarily) modified entry. (There is a
hint on screen about this).

For a list of all the kernel parameters and what they do, see

  https://www.kernel.org/doc/Documentation/kernel-parameters.txt

although that is a rather long and overwhelming document!

Jonathan