Linux

Nix

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Updated: 30 January 2026

Notes

Taken from here

  • Search for the packages which provide a program https://search.nixos.org/packages
  • A package name is not the same as a program name. Many packages provide multiple programs, or no programs at all if they are libraries. Even for packages that provide exactly one program, the package and program name are not necessarily the same.
  • Free up some disk space occupied by the different versions of programs downloaded nix-collect-garbage.

Flakes

  • Flakes are experimental but recommended.
  • A flake reference is a string representation of where the flake is located.
  • A Nix flake is a directory with a flake.nix and flake.lock at the root.
  • Flakes take Nix expressions as input.
  • Flakes can use the outputs of other flakes as inputs.
  • Flake outputs are defined by a function.
  • Flakes can have multiple simultaneous outputs.
  • The output of a flake is a Nix expression.

A flake output can be used to:

  • Build Nix packages.
  • Run programs.
  • Create development environments.
  • Launch NixOS systems.

See here for more details.

Home manager

https://github.com/nix-community/home-manager

Nix Shell

Run a program without entering a nix shell

nix-shell -p cowsay --run "cowsay Nix"

Enter a nix shell making 2 new packages available

nix-shell --packages cowsay lolcat

Enter a nix shell including Java Development Kit version 17

nix-shell -p jdk17

Enter a nix shell which includes PHP 8.4

nix --extra-experimental-features "nix-command flakes" shell nixpkgs#php84

Enter a nix shell which includes PHP 5.6

nix --extra-experimental-features "nix-command flakes" shell nixpkgs#php56

Snap

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Updated: 18 April 2025

Remove snap, without saving a snapshot of its data

snap remove --purge lxd

Show detailed information about snaps

snap info lxd

Search for a snap package

snap find lxd

List installed snaps

snap list

List installed snaps

ls -l /var/lib/snapd/snaps

Show symbolic links to snap applications

ls -l /snap/bin

Delete snapd cache

sudo rm -rf /var/lib/snapd/cache/*

APT

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Updated: 06 April 2025

Advanced Packaging Tool.

From man apt-get

update is used to resynchronize the package index files from their sources. The indexes of available packages are fetched from the location(s) specified in /etc/apt/sources.list. For example, when using a Debian archive, this command retrieves and scans the Packages.gz files, so that information about new and updated packages is available. An update should always be performed before an upgrade or dist-upgrade. Please be aware that the overall progress meter will be incorrect as the size of the package files cannot be known in advance.

sudo apt-get update

From man apt-get

upgrade is used to install the newest versions of all packages currently installed on the system from the sources enumerated in /etc/apt/sources.list. Packages currently installed with new versions available are retrieved and upgraded; under no circumstances are currently installed packages removed, or packages not already installed retrieved and installed. New versions of currently installed packages that cannot be upgraded without changing the install status of another package will be left at their current version. An update must be performed first so that apt-get knows that new versions of packages are available.

sudo apt-get upgrade

Install a single package:

sudo apt install unattended-upgrades

List installed packages

apt list --installed

Upgrade a single package

apt-get install --only-upgrade <packagename>

Remove a package

sudo apt --purge remove package-name
sudo apt --purge autoremove

Show currently installed and candidate versions of a package

apt-cache policy doxygen

LXD LXC

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Updated: 12 December 2025

See https://canonical.com/lxd
Support https://discuss.linuxcontainers.org/

List instances

lxc ls

List instances in longer json format

lxc list --format=json | jq

Start instance win11 and immediately attach to the console

lxc start win11 --console=vga

Prevent a container from automatically starting whenever the LXD host starts

lxc config set the_container boot.autostart false

Stop the instance called win11, with force

lxc stop --force win11

Delete container win11

lxc delete win11

Enter a container as user sammy

lxc exec the_container -- su sammy

lxc launch

Start a container

lxc launch ubuntu:24.04

Start a virtual machine

lxc launch ubuntu:24.04 --vm

Start a NixOS virtual machine (credit)

lxc launch images:nixos/25.05 --vm nix

Snapshots

Create a snapshot of a container

lxc snapshot container_name snapshot_name

Show a list of available snapshots

lxc info container_name

Select and restore a snapshot

lxc restore container_name snapshot_name

Delete a snapshot

lxc delete win11d/the_first_shot

Devices

Remove a device e.g. iso CD

lxc config device remove container_name device_name

List devices associated with an instance

lxc config device list container_name

Networking

Hit host IP address from inside a LXC container, assuming container uses lxdbr0 attached to same network as host

# Get IP of host.
curl ifconfig.me

# From container curl for http service running on host port 80.
# IPv6 version address in this case.
curl -6 http://[2401:d800:3f1:ba7b:f02c:a795:f128:864]

Linux users

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Updated: 26 January 2026

Remove user sammy from the docker group

deluser sammy docker

Change a user password

sudo passwd the_user_name

List all users on a Linux system

cat /etc/passwd

Linux

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Updated: 31 August 2025

Distribution

Print distribution specific information

lsb_release -d

dpkg

Package manager for Debian

Get architecture (e.g. AMD or ARM) of machine this command is run on i.e. the architecture of packages installed by dpkg.

dpkg --print-architecture

Ubuntu shortcuts

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Updated: 07 September 2024

Super + Shift + PageUp Move active window to a workspace left of the current workspace
Super + Shift + PageDown Move active window to a workspace right of the current workspace
Ctrl + Alt + T Open new terminal

Ubuntu select and paste with Mouse Keys

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Updated: 04 February 2021

On Linux I like to make use of the select and paste feature i.e. selecting text copies it and the middle mouse button pastes it. When a laptop touchpad has no buttons a middle mouse click can be simulated with a three-finger tap, but this is awkward.

Here is my workaround (for keyboards with a numeric keypad only):

  1. From the Accessibility menu turn on Mouse Keys.
  2. Ensure the Number Lock is off.
  3. Select text.
  4. Paste text by pressing 5 on the numeric keypad.

Furthermore, in a terminal and some other applications SHIFT + INSERT will paste text which has been previously selected.

I am using Ubuntu 20.04.1 and GNOME 3.36.8