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:new: 2016-03-11

Multi USB Boot

Similar to booting different operating systems via network, you can also boot multiple systems from a USB flash drive.

This is even a bit easier since you have a boot medium (the flash drive) and don’t have to jump through hoops to get a system to boot from the network.

Initial Setup

While you can use the whole flash drive for everything, I found it more neat to have separate partitions for each tool. So I started out by creating a 16 GiB partition on my 32 GiB flash drive. This serves as the main partition to boot from. Make it a primary partition and format it with ext41.

Now, we need to install the bootloader to it. I chose grub, others use syslinux. Both are suitable, so it’s up to you. I followed these instructions. (Omitting the wget command because I wanted to have my own grub.cfg.)

First, mount the new partition so the neccessary files can be copied to it. My partition is /dev/sdc1, so I mount it with:

sudo mount /dev/sdc1 /mnt/usb

Now, to install grub, just do a:

grub-install --force --no-floppy --boot-directory=/mnt/usb/boot /dev/sdc

You should now find a /boot/grub directory in that partition with a file grub.cfg. That’s what we will be fiddling with.

If that file doesn’t exist, create one with these contents:

set timeout=10
set default=0

insmod ext2

Adding Systems

As stated above, I prefer to have separate partitions for each system I want to boot. Since you can only have 4 primary partitions on a drive, we need to embed our additional systems into an extended partition. So, I created an extended partition in the remaining 16 GiB of my 32 GiB flash drive. That’s where new tools will go.

But besides the files, we also need to instruct our newly installed grub where to look for files and how to boot them.

You can find many boot settings on this blog post already. However, these are for syslinux. I’ll post some options for grub here.

Also, the needed files and configuration lines to boot the systems are very similar to those of iPXE for network booting. So you can check this post and use them.

System Rescue CD

If you mount the ISO image and have a look at the contents, you’ll see that the SysRescCD is about 410 MiB in size (all kernels + sysrcd.dat and a few others). To be safe for future (probably slightly larger) versions, I went with a 450 MiB (470 MB2) partition inside the newly created extended partition and also formatted it as ext4. For me, the partition is called sdc7.

Copy the following directories and files from the SysRescCD to that new partition:

  • isolinux/ (the whole directory incl. all files and subdirectories)
  • sysrcd.dat
  • sysrcd.md5
  • version

Now to find out the boot parameters, we have to look at the boot configuration for the SysRescCD itself. This is contained in the isolinux/isolinux.cfg file.

Search for these lines:

LABEL rescue32_2
MENU LABEL 2. SystemRescueCd with all files cached to memory
LINUX rescue32
INITRD initram.igz
APPEND docache
TEXT HELP
Boot standard 32bit kernel and run system from memory.
It requires 512 MB of memory to work and takes some time during the
boot process, but the cdrom can be removed and system will be faster.
ENDTEXT

This contains all information we need to create our grub.cfg lines. The kernel to boot is rescue32 with parameter docache. And the initfs is initram.igz.

Also, I have the files in a directory isolinux on partition sdc7, or #7 on the flash drive. Translated to grub-speak, this is (hd0,msdos7) (hd0 means the drive we are booting from.)

So the lines we need to add to the grub.cfg are:

menuentry "SystemRescueCd 4.9.0 (32bit)" {
 linux (hd0,msdos7)/isolinux/rescue32 docache
 initrd (hd0,msdos7)/isolinux/initram.igz
}

In the same way, the 64bit version with German keyboard layout would look like this:

menuentry "SystemRescueCd 4.9.0 (64bit)" {
 linux (hd0,msdos7)/isolinux/rescue64 setkmap=de docache
 initrd (hd0,msdos7)/isolinux/initram.igz
}

You can read about more parameters for the kernel on the official SysRescCD documentation.

That’s it. You should now be able to boot SysRescCD from your flash drive.

  1. If you’re afraid about wear&tear with ext4, you could also use ext2 but should fsck the partitions every once in a while. 

  2. “MiB” is MebiByte where 1 MiB = 1024 KiB = 1024 Bytes. Whereas “MB” is MegaByte where 1 MB = 1000 kB = 1000 Bytes. And although most system tools show “MB”, some mean “MiB” and others actually mean “MB”. And some mix it up completely. 

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