Grub2 ubuntu add kernel parameters that survive updates
If your Ubuntu Kernel is updated your kernel parameters will be lost. In my case one of my IBM systems will not boot unless iommu=soft exists as a kernel boot parameter. To make this change survive after kernel updates do the following.
edit /etc/default/grub and add the entry to GRUB_CMDLINE_LINUX_DEFAULT:
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash iommu=soft"
You can also make changes to grub 2 during system start-up by pressing 'e' and then 'f10' to boot. I had to change hd(1,msdos1) to hd(1,5). To make this change permanent when the OS booted I ran: