UTC in Microsoft Windows

To dual boot with Windows, it is recommended to configure Windows to use UTC, rather than Linux to use localtime. (Windows by default uses localtime)

It can be done by a simple registry fix: Open regedit and add a DWORD value with hexadecimal value 1 to the registry HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\TimeZoneInformation\RealTimeIsUniversal

You can do this from an Administrator Command Prompt running:

C:\>reg add "HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\TimeZoneInformation" /v RealTimeIsUniversal /d 1 /t REG_DWORD /f

pacman upgrade packages in ArchLinux

pacman upgrade packages in ArchLinux
sudo pacman -Syu
-S – Synchronizes packages
-y – Refreshes the package database
-u – Upgrades all installed packages

Remove a package (keep dependencies)
sudo pacman -R package_name

Remove a package and unneeded dependencies
sudo pacman -Rns package_name

Remove orphaned packages (unneeded dependencies)
sudo pacman -Rns $(pacman -Qdtq)

Remove a package and ignore dependencies
sudo pacman -Rdd package_name

Remove a package and its cache (free up disk space)
sudo pacman -R package_name && sudo pacman -Sc

For a more aggressive cleanup, remove all cached package files:
sudo pacman -R package_name && sudo pacman -Scc

To install packages from a previously saved list of packages, while not reinstalling previously installed packages that are already up-to-date, run:
pacman -S --needed - < pkglist.txt

EFI BOOT ENTRY

DELETE

To delete a menu entry using efibootmgr
first list the current boot entries with sudo efibootmgr
Identify the boot number of the entry you want to delete, then use the command:
sudo efibootmgr -b XXXX -B
replacing XXXX with the boot number of the entry you wish to remove.

ADD

To add a menu entry using efibootmgr, use the following command format:
sudo efibootmgr -c -d /dev/sdX -p NN -L "Label" -l "\EFI\path\to\boot\file.efi"
where /dev/sdX is your disk, NN is the partition number,
“Label” is the name you want for the boot entry,
and \EFI\path\to\boot\file.efi is the path to the EFI executable.

!!! Make sure the path to the boot file is correct and uses backslashes, as required by the EFI specification!!!

proxmox import vm from kvm

Create a new VM in the web interface (leave other settings as default)
copy VM disk to proxmox (ex. using terminal) and import it to newly created VM machine
qm importdisk machine_id_number /var/lib/vz/images/file.qcow local-zfs
qm rescan

Go to your new created VM in the proxmox web interface.
Go to the Hardware section of the newly created VM in the Proxmox web interface
Look for the Unused Disk and select it.
Then you have to add the disk by clicking on Edit on the top.

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

AC power notify

upower -i $(upower -e | grep '_AC') | grep "online"

Unboud (DNS) – listen on IPv4 only

Add to /etc/unbound/unbound.conf

server:
interface: 0.0.0.0

TMUX

split-window -h: Ctrl+b %

split-window -v: Ctrl+b ”

wrong Video codec on Opera Linux Mint

install chromium and

mv /usr/lib/x86_64-linux-gnu/opera/libffmpeg.so /usr/lib/x86_64-linux-gnu/opera/libffmpeg.so.orig
ln -s /usr/lib/chromium/libffmpeg.so /usr/lib/x86_64-linux-gnu/opera/

snapshots of UEFI libvirt-based (KVM) virtual machines

Shut down VM and then

Listing
qemu-img snapshot -l <file>.qcow2

Create
qemu-img snapshot -c <snap-name> <file>.qcow2

Revert to 
qemu-img snapshot -a <snap-name> <file>.qcow2

Delete
qemu-img snapshot -d <snap-name> <file>.qcow2