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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

iptables log to file

Create new chain:

iptables -N DROP-LOG
iptables -A DROP-LOG -m limit --limit 1/second -j LOG --log-prefix "[iptables-drop] "
iptables -A DROP-LOG -j DROP

Create /etc/rsyslog.d/10-iptables.conf and add lines:

:msg,contains,"[iptables-drop] " /var/log/iptables.log
# stop logging anything that matches the last rule.
# Doing this will stop logging kernel log messages to the file
# normally containing kern.* messages (eg, /var/log/kern.log)
& stop

KVM add device

Add hostdev for VF in <devices>. In <source>/<address> use physical address for VF

<hostdev mode='subsystem' type='pci' managed='yes'>
     <source>        
         <address domain='0x0000' bus='0x5e' slot='0x0e' function='0x0'/>
    </source>      
    <address type='pci' domain='0x0000' bus='0x07' slot='0x01' function='0x0'/>  
</hostdev>

KVM install VM with vnc server

Install from img file (with disk size 15G and bridge name inner)

virt-install \
--name=bull \
--vcpus=8 \
--memory=24576 \
--disk path=/var/lib/libvirt/images/bull.qcow2,size=15 \
--cdrom /var/lib/libvirt/iso/debian-11.6.0-amd64-netinst.iso \
--network bridge=inner,mac=52:54:00:40:4a:5e \
--boot hd,uefi \
--machine q35 \
--osinfo detect=on,require=off \
--graphics vnc,listen=<IP_HOST_TO_LISTEN_TO>,password=<SECRET>

Install from PXE

virt-install \
--name=rhpxe \
--vcpus=4 \
--memory=2048 \
--network bridge=br0,mac=52:54:00:0e:27:FF \
--pxe \
--disk none \
--boot uefi \
--osinfo detect=on,require=off \
--graphics vnc,listen=<IP_HOST_TO_LISTEN_TO>,password=<SECRET> 

Mikrotik port forward / redirect

/ip firewall nat add chain=dstnat dst-port=1234 action=dst-nat protocol=tcp to-address=192.168.1.1 to-port=1234

Delete old files

Find only executable
find

find /path/to/dir/ ( ( -type f -daystart -mtime +8 ) -o -type d -empty ) -delete

How to download all files (but not HTML) from a website using wget?

wget -A lst,meta,txt,txz,tgz,asc,md5 -m -p -E -k -K -np <URL>

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