First, at present, booting from USB is impossible with VirtualBox! But there is a really easy workaround to use VMDK, which is just a container file describing physical devices (or files) to use in virtual machines like VirtualBox or VMware.
Because the USB is just another physical device attached to the machine this article will help to attach the USB drive to a virtual machine – Add a raw disk to a virtualbox virtual machine. Then boot from the newly attached disk.
Here is the quick tip for the USB drive:
Attach the USB drive and find its device path. Under Windows, it would be something like “\\.\PhysicalDrive3” (open “Disk Management” if not sure) and under Linux it would be /dev/sdc, for example. This is the third disk device (including USB disk devices) connected to the machine.
Make the VMDK from the USB physical device.
Under Windows:
Attach it the virtual machine: Settings -> Storage -> Storage Devices.
First, a click on “Adds hard disk” would show a menu to add a new hard disk and then a click on “Add” (“Add Disk Image”) shows a file browse dialog to locate the VMDK file.
Storage Devices
Boot from this device by selecting it manually from the boot menu (F12 would boot in Boot menu) or set the VMKD disk to be on the Port 0 in the above step.
In CentOS 7 the initramfs consists of two concatenated gzipped cpio files. If you want to check what files and probably configuration files are included you can unpack it, but you should use
early_cpio – dracut set this file at the beginning of the CentOS 7 initramfs. It contains the CPU microcode.
You can check it with “file” command and if it shows: “ASCII cpio archive (SVR4 with no CRC)” there is a microcode prepended to the initramfs file.
And here without the dracut skipcpio tool with an example:
cpio the original initramfs and write down the number of blocks reported
use dd to skip the first blocks from the above step
Uncompress (and unpack) the file created by dd – this is the real initramfs file.
If you want to use software raid device in your Gentoo Linux system (init boot, not systemd) with boot partition resided in the raid for better redundancy but using metadata 1.2 version you won’t have autodetection feature on boot and there are some additional steps you may consider!
Linux kernel’s autodetection feature of the software raid is only for superblock (metadata) version 0.90!
If you create a software raid with superblock version 1, 1.1 or 1.2 you want to boot from it you must use:
Grub 2, lilo won’t load the kernel from such paritions.
include mdadm in initramfs
initramfs booted with aditional parameter “domdadm” (in fact, it is not a “native” kernel option, read below)
We have a CentOS 7 server with a simple two hard drives setup in RAID1 of total 4 devices for boot, root, swap and storage. The storage device (/dev/md5) was removed and recreated with RAID0 for better performance, because the server was promoted as only cache server. Then the server was restarted and it never went up.
On IPMI KVM it just started loading the kernel and hanged up after several seconds without any additional information:
The kernel loads the mdadm devices and do not continue and the device md5 is missing.
CentOS 7 kernel loading the mdadm RAID devices
To boot successfully you must remove the missing device
On the Grub 2 menu press “e” and you’ll get this screen. Here you can edit all lines if you need. You must remove the last rd.md.uuid in our case or the one you deleted. Remove it and press Ctrl+x to load the kernel. Grub 2 edit
There are two options you can do:
OPTION 1) Remove rd.md.uuid option of your old mdadm device
OPTION 2) Replace the ID in rd.md.uuid= with the new ID of the mdadm device.
Each of these two options could be used to solve the booting problem. Edit /etc/default/grub and replace or remove rd.md.uuid and generate the grub.conf.
You can find old mdadm ID in /etc/mdadm.conf (if you have not replace it there).
Here we edit our /boot/grub2/grub.cfg, replace the old uuid and generate grub.cfg (legacy BIOS):
[root@srv ~]# cat /etc/default/grub
GRUB_TIMEOUT=1
GRUB_DISTRIBUTOR="$(sed 's, release .*$,,g' /etc/system-release)"
GRUB_DEFAULT=saved
GRUB_DISABLE_SUBMENU=true
GRUB_TERMINAL="serial console"
GRUB_SERIAL_COMMAND="serial --speed=115200"
GRUB_CMDLINE_LINUX="rd.md.uuid=9c08f218:cd5c0f8f:d96bc0d1:57b77e99 rd.md.uuid=1f74a2e0:757bfb9f:9c860e50:325f37cb rd.md.uuid=29bf4aa8:b7dae21a:45f4c188:baea4c13 rd.md.uuid=901074eb:16ba7c5b:0af69934:e9444102 console=tty0 crashkernel=auto console=ttyS0,115200 net.ifnames=1"
[root@srv ~]# grub2-mkconfig -o /boot/grub2/grub.cfg
Generating grub configuration file ...
Found linux image: /boot/vmlinuz-3.10.0-957.5.1.el7.x86_64
Found initrd image: /boot/initramfs-3.10.0-957.5.1.el7.x86_64.img
Found linux image: /boot/vmlinuz-0-rescue-05cb8c7b39fe0f70e3ce97e5beab809d
Found initrd image: /boot/initramfs-0-rescue-05cb8c7b39fe0f70e3ce97e5beab809d.img
done
[root@srv ~]# reboot
Use this for UEFI BIOS boot:
First check if /boot and /boot/efi are mounted and if not you must mount them with:
mount /boot
mount /boot/efi
Generate the grub.cfg
grub2-mkconfig -o /boot/efi/EFI/centos/grub.cfg
Bonus
In fact when the original device was removed and added a new one we formatted it as usual. But it was not possible to mount it, you just execute mount
/dev/md5 /mnt/stor1
no error, but no mount could be found, the device was not mounted and when you execute
umount /mnt/stor1
The OS told the “/mnt/stor1” was not mounted. Several more tries were made unsuccessfully to mount the “/dev/md5”, then the restart was performed and the server never went up.
Suppose the systemd just did not allow to mount the device because of the boot parameters rd.md.uuid!
Our motherboard is Asus ROG Zenith Extreme motherboard using X399 chipset https://www.asus.com/th/Motherboards/ROG-ZENITH-EXTREME/ and you’ll see the BIOS options for it, but they do not differ much with the other motherboard boot options. Here also setup the network and start up an openssh server to manage our Gentoo Linux installation – (coming soon).
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