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156 lines
5.2 KiB
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156 lines
5.2 KiB
Markdown
---
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title: Multi USB Boot
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layout: default
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created: 2016-03-11 19:36:55 +0100
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updated: 2016-03-11 19:36:55 +0100
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toc: false
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tags:
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- know-how
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- software
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- usb
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- flash-drive
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- booting
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---
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Similar to [booting different operating systems via network]({% post_url 2016-03-05-ipxe-network-boot %}),
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you can also boot multiple systems from a USB flash drive.
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{: width="400px"}
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This is even a bit easier since you have a boot medium (the flash drive) and
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don't have to jump through hoops to get a system to boot from the network.
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Initial Setup
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=============
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While you *can* use the whole flash drive for everything, I found it more neat
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to have separate partitions for each tool. So I started out by creating a 16 GiB
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partition on my 32 GiB flash drive. This serves as the main partition to boot
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from. Make it a primary partition and format it with ext4[^1].
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Now, we need to install the bootloader to it. I chose `grub`, others use
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`syslinux`. Both are suitable, so it's up to you. I followed [these](https://www.pendrivelinux.com/boot-multiple-iso-from-usb-via-grub2-using-linux/)
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instructions. (Omitting the `wget` command because I wanted to have my own
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`grub.cfg`.)
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First, mount the new partition so the neccessary files can be copied to it. My
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partition is `/dev/sdc1`, so I mount it with:
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sudo mount /dev/sdc1 /mnt/usb
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Now, to install `grub`, just do a:
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grub-install --force --no-floppy --boot-directory=/mnt/usb/boot /dev/sdc
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You should now find a `/boot/grub` directory in that partition with a file
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`grub.cfg`. That's what we will be fiddling with.
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If that file doesn't exist, create one with these contents:
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```
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set timeout=10
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set default=0
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insmod ext2
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```
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Adding Systems
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==============
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As stated above, I prefer to have separate partitions for each system I want to
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boot. Since you can only have 4 primary partitions on a drive, we need to embed
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our additional systems into an extended partition. So, I created an extended
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partition in the remaining 16 GiB of my 32 GiB flash drive. That's where new
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tools will go.
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But besides the files, we also need to instruct our newly installed `grub` where
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to look for files and how to boot them.
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You can find many boot settings on [this blog post](http://pongup.blogspot.de/2010/10/multipleboot-usb.html)
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already. However, these are for `syslinux`. I'll post some options for `grub`
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here.
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Also, the needed files and configuration lines to boot the systems are very
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similar to those of iPXE for network booting. So you can check [this post]({% post_url 2016-03-05-ipxe-scripts-for-tools %})
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and use them.
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System Rescue CD
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----------------
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If you mount the ISO image and have a look at the contents, you'll see that the
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SysRescCD is about 410 MiB in size (all kernels + `sysrcd.dat` and a few
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others). To be safe for future (probably slightly larger) versions, I went with
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a 450 MiB (470 MB[^2]) partition inside the newly created extended partition and
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also formatted it as ext4. For me, the partition is called `sdc7`.
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{: width="800px"}
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Copy the following directories and files from the SysRescCD to that new
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partition:
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* `isolinux/` (the whole directory incl. all files and subdirectories)
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* `sysrcd.dat`
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* `sysrcd.md5`
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* `version`
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Now to find out the boot parameters, we have to look at the boot configuration
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for the SysRescCD itself. This is contained in the `isolinux/isolinux.cfg` file.
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Search for these lines:
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```
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LABEL rescue32_2
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MENU LABEL 2. SystemRescueCd with all files cached to memory
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LINUX rescue32
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INITRD initram.igz
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APPEND docache
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TEXT HELP
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Boot standard 32bit kernel and run system from memory.
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It requires 512 MB of memory to work and takes some time during the
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boot process, but the cdrom can be removed and system will be faster.
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ENDTEXT
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```
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This contains all information we need to create our `grub.cfg` lines. The kernel
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to boot is `rescue32` with parameter `docache`. And the initfs is `initram.igz`.
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Also, I have the files in a directory `isolinux` on partition `sdc7`, or #7 on
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the flash drive. Translated to grub-speak, this is `(hd0,msdos7)` (`hd0` means
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the drive we are booting from.)
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So the lines we need to add to the `grub.cfg` are:
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```
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menuentry "SystemRescueCd 4.9.0 (32bit)" {
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linux (hd0,msdos7)/isolinux/rescue32 docache
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initrd (hd0,msdos7)/isolinux/initram.igz
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}
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```
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In the same way, the 64bit version with German keyboard layout would look like
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this:
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```
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menuentry "SystemRescueCd 4.9.0 (64bit)" {
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linux (hd0,msdos7)/isolinux/rescue64 setkmap=de docache
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initrd (hd0,msdos7)/isolinux/initram.igz
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}
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```
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You can read about more parameters for the kernel on the [official SysRescCD
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documentation](https://www.system-rescue-cd.org/Sysresccd-manual-en_Booting_the_CD-ROM).
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That's it. You should now be able to boot SysRescCD from your flash drive.
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[^1]: If you're afraid about wear&tear with ext4, you could also use ext2 but
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should `fsck` the partitions every once in a while.
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[^2]: "MiB" is MebiByte where 1 MiB = 1024 KiB = 1024 Bytes. Whereas "MB" is
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MegaByte where 1 MB = 1000 kB = 1000 Bytes. And although most system tools
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show "MB", some mean "MiB" and others actually mean "MB". And some mix it
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up completely.
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