Reducing the size of a QEMU virtual disk (thin disk)

On all mounting points
dd if=/dev/zero of=/nul;sync;sync;sync;rm -f /nul;sync

Stop VM

Convert disk

qemu-img convert -O qcow2 -c disk1.qcow disk1.new.qcow

Windows recovery

bootrec /scanos

bootrec /fixmbr

bootrec /fixboot

bootrec /rebuildbcd

Rsync copy

rsync -azP -e "ssh -p PORT_NUMBER" source destination

KVM Snapshot with only one disk

virsh snapshot-create-as --domain ${VM}
--name "backup-${VM}" \
--atomic \
--disk-only \
--no-metadata \
--diskspec vda,file=${SNAP}/backup-snapshot-${VM} \
--diskspec vdb,snapshot=no

Customized boot in Zbook

Add in bios
\EFI\debian\shimx64.efi

wipe all partitions on disk

wipefs --all /dev/sdX

wipefs can erase filesystem, raid or partition-table signatures (magic strings) from the specified device to make the signatures invisible for libblkid.

wipefs does not erase the filesystem itself nor any other data from the device. When used without any options, wipefs lists all visible filesystems and the offsets of their basic signatures.

wipefs calls the BLKRRPART ioctl when it has erased a partition-table signature to inform the kernel about the change.

Install / Reinstall Grub

For UEFI, assuming the system partition is sda2 and the EFI partition is sda1.

sudo mount /dev/sda2 /mnt
sudo mount /dev/sda1 /mnt/boot/efi
for i in /dev /dev/pts /proc /sys; do sudo mount -B $i /mnt$i; done
sudo cp /etc/resolv.conf /mnt/etc
modprobe efivars
sudo chroot /mnt
apt purge grub-common
# for secure boot enabled
apt install grub-efi-amd64-signed os-prober shim-signed
# for secure boot disabled
apt install grub-efi-amd64 os-prober
exit
sudo umount /mnt/boot/efi 
sudo umount -R /mnt

For BIOS, assuming the system partition is sda1:

sudo mount /dev/sda1 /mnt
for i in /dev /dev/pts /proc /sys; do sudo mount -B $i /mnt$i; done
sudo cp /etc/resolv.conf /mnt/etc
sudo chroot /mnt
apt purge grub-common
apt install grub-pc os-prober
exit
sudo umount -R /mnt

short brief from https://forums.linuxmint.com/viewtopic.php?t=320504

elilo.conf

chooser=simple
# interactive mode
prompt
# delay when not in interactive mode (0.1 sec)
delay=100
# timeout when in interactive mode (0.1 sec)
timeout=100
default=vmlinuz
#
image=vmlinuz
label=vmlinuz
read-only
append="root=/dev/sdc2 vga=normal ro"

image=vmlinuz-generic
label=vmlinuz-generic
initrd=initrd.gz
read-only
append="root=/dev/sdc2 vga=normal ro"

image=vmlinuz-huge-5.15.27
label=huge-5.15.27
read-only
append="root=/dev/sdc2 vga=normal ro"

image=vmlinuz-generic-5.15.27
label=generic-5.15.27
initrd=initrd-5.15.27.gz
read-only
append="root=/dev/sdc2 vga=normal ro"

Show modules in mkinitrd

mkdir /tmp/initrd
/tmp/initrd
cp /boot/initrd.gz .
gunzip initrd.gz
cpio -id < initrd

# mkinitrd.conf.sample
# See "man mkinitrd.conf" for details on the syntax of this file
#
#SOURCE_TREE="/boot/initrd-tree"
#CLEAR_TREE="0"
#OUTPUT_IMAGE="/boot/initrd.gz"
#KERNEL_VERSION="$(uname -r)"
#KEYMAP="us"
MODULE_LIST="ext4:hv_vmbus:scsi_transport_fc:hv_storvcs:jbd2:mbchache"
#LUKSDEV="/dev/sda2"
#LUKSTRIM="/dev/sda2" # verify support with 'hdparm -I $dev | grep TRIM'
#LUKSKEY="LABEL=TRAVELSTICK:/keys/alienbob.luks"
ROOTDEV="/dev/sda2"
ROOTFS="ext4"
#RESUMEDEV="/dev/sda2"
#RAID="0"
#LVM="0"
#UDEV="1"
#MODCONF="0"
#MICROCODE_ARCH="/boot/intel-ucode.cpio"
#WAIT="1"

mkinitrd -F -k 5.15.63
or
/usr/share/mkinitrd/mkinitrd_command_generator.sh -k 5.15.63
cp /boot/initrd.gz /boot/efi/EFI/Slackware/
cp /boot/vmlinuz-generic-5.15.63 /boot/efi/EFI/Slackware/vmlinuz

cp /boot/initrd.gz /boot/efi/EFI/Slackware/initrd-5.15.63.gz
cp /boot/vmlinuz-generic-5.15.63 /boot/efi/EFI/Slackware/vmlinuz-5.15.63

Convert a drive from MBR to GPT

mbr2gpt /validate /allowFullOS
mbr2gpt /convert /allowfullOS