In the configuration files you’ll see reference to two files, the `initrd` file and the `vmlinuz` file.
`initrd`, is the temporary root file system that is loaded into memory to make preparations before the real root file system can be mounted.
`vmlinuz` is the statically linked executable file that contains the Linux kernel.
You will see lines that begin with the command: “insmod”, which is a contraction of “install module”. These will be linked into the linux kernel, thereby extending the functionality of it.
There is an other command: `rmmod`, which removes a module. The command `modprobe` is a superset of `insmod` and `rmmod`, it can load or unload a module.
You will see a line like:
set root=’hd0,gpt2’
| parameter | meaning |
|---|---|
| hd | is hard drive |
| hd0 | means the first hard drive (counting from 0) |
| gpt | GUID Partition Table |
| the ‘2’ from: ‘gpt2’ | means the 3rd partition |
aside: a GPT is a newer replacement for MBR (Master Boot Record), and you should consider using it instead of MBR.
The main configuration files for GRUB are: `/etc/default/grub` and `/etc/grub.d/*`.
To regenerate grub.cfg after updating configuration or boot script files do:
% sudo grub-mkconfig -o /boot/grub/grub.cfg
Normally I set the timeout for GRUB to be 1 second, because I like to keep my reboot time to a minimum. But when we need to have time to choose other OS’s to load we may want to change that.
| File | Setting | Meaning |
|---|---|---|
| /etc/default/grub | GRUB_TIMEOUT | time in seconds |
Now lets say we’d like to be able to boot from an ISO image, such as a GParted iso image so we can, in future, more easily rearrange our partitions.
NOTE: this info comes from: http://gparted.sourceforge.net/livehd.php
Any file that is put into the folder:
etc/grub.d
and has an execute permission set will run. To achieve this we could append the following to the file: `/etc/grub.d/40_custom`
“` menuentry “Gparted live” { set isofile=”/boot/isos/gparted-live-0.5.2-9.iso” loopback loop $isofile linux (loop)/live/vmlinuz boot=live config union=aufs noswap noprompt vga=788 ip=frommedia toram=filesystem.squashfs findiso=$isofile initrd (loop)/live/initrd.img } “`
Remember to put your iso image in the `/boot/isos` folder as per above.
I installed syslinux with: “pacman -S syslinux” then I copied the memdisk from `/usr/lib/syslinux/memdisk` to `/boot/memdisk`.
Then i put the freedos iso here: `/boot/isos/freedos-1.1.iso`
I appended the file: `/etc/grub.d/40_custom`, with:
menuentry “FreeDOS” { linux16 /boot/memdisk iso initrd16 /boot/isos/freedos-1.1.iso }
ref: https://wiki.ubuntu.com/DellBIOS
menuentry “BIOS Updater” { linux16 /boot/memdisk raw initrd16 /boot/dosdisk8192.img }
menuentry “Boot Hardware Detection Tool from floppy” { linux16 /memdisk initrd16 /hdt.img }
menuentry “Boot Hardware Detection Tool from iso” { linux16 /memdisk iso initrd16 /hdt.iso }
menuentry “Boot DOS from floppy image (with ‘raw’ parameter)” { linux16 /memdisk raw initrd16 /dosboot.img }
One thing we could do is have 2 arch linuxes running, and select which we want to load from GRUB. To achieve this we could append the following to the file: `/etc/grub.d/40_custom`
“` menuentry “GParted live” { set root=(hd0,4) linux /live-hd/vmlinuz boot=live config union=aufs noswap noprompt vga=788 ip=frommedia live-media-path=/live-hd bootfrom=/dev/hda4 toram=filesystem.squashfs initrd /live-hd/initrd.img } “`