How to configure kernel boot parameters with grub2
/etc/default/grub. Example:sudo gedit /etc/default/grub
GRUB_CMDLINE_LINUX_DEFAULT in the file /etc/default/grub to boot all the kernels with the new option. In this case, the kernel boot option isolcpus=2,3 has been used, on a 4 cores CPU, to boot the kernel (and the other OS processes) using CPU cores 0 and 1, while CPU cores 2 and 3 are isolated, i.e., not used.GRUB_CMDLINE_LINUX_DEFAULT="quiet splash isolcpus=2,3"
sudo update-grub
to make active the GRUB configuration at the next reboot.
If you want to boot the third kernel of the second sub-menu, you have to modify in file /etc/default/grub the variable GRUB_DEFAULT in the following way:
GRUB_DEFAULT=1>2
and to make effective modification you have to run the command:
sudo update-grub
If you want to choose directly an entry of the main menu, for instance the third entry, the variable GRUB_DEFAULT has to be modified in the following way:
GRUB_DEFAULT=2
There is also the option to specify directly the name of the kernel (this is the solution I prefer):
GRUB_DEFAULT="Advanced options for Ubuntu>Ubuntu, with Linux 3.2.0-18-generic-pae"
To know the names of the kernels you can type the command:
grep menuentry /boot/grub/grub.cfg
mount -o remount,rw /, if you want to enable write access to the filesystem