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Linux containers often considered as something in the middle between a chroot and a full fledged virtual machine. The goal of LXC is to create an environment as close as possible to a standard Linux installation but without the need for a separate kernel.
LXD is a system container and virtual machine manager. It offers a unified user experience around full Linux systems running inside containers or virtual machines.

Before start, use lxd init to configure LXD settings such as network, storage, clustering and other. All of them can be changed later.

Get Info:

lxc profile show default
lxc info container_name
lxc config show ansible-test1 -e  #all configurations
lxc storage list

lxc ls #List instances
lxc list -c ns4mDSb

All available column options:
    4 - IPv4 address
    6 - IPv6 address
    a - Architecture
    b - Storage pool
    c - Creation date
    d - Description
    D - disk usage
    l - Last used date
    m - Memory usage
    M - Memory usage (%)
    n - Name
    N - Number of Processes
    p - PID of the instances init process
    P - Profiles
    s - State
    S - Number of snapshots
    t - Type (persistent or ephemeral)
    u - CPU usage (in seconds)
    L - Location of the instance (e.g. its cluster member)
    f - Base Image Fingerprint (short)
    F - Base Image Fingerprint (long)

Launch new container

lxc launch images:centos/7/amd64 container_name
lxc launch ubuntu:20.04 container_name
lxc launch -p profile_name ubuntu:20.04 container_name   #-p for applying a profile

Configuration

Apply specific settings to a container:

lxc config set container_name limits.memory 512MB
lxc config set container_name limits.cpu 2
lxc config device set container_name root size 10GB
lxc config device set container_name eth0 limits.ingress 1Mbit

Run commands within container

lxc exec container_name -- /bin/bash #Get a shell inside a container as a root
lxc exec container_name bash
lxc exec container_name -- su --login username
lxc console container_name  # terminal inside container, use ```ctrl+a-q``` for detach.

Profile

Profile helps create container preconfiguration. Can be apply in launch moment. Uses cloud-init initialization.

lxc profile create profilename
lxc profile edit profilename

# example
oleg@t600:~$ lxc profile show dev1 
config:
  limits.cpu: "1"
  limits.memory: 1024MB
  user.user-data: |
    #cloud-config
    package_upgrade: true
    timezone: America/Los_Angeles
    # User setup
    users:
     - name: oleg
       ssh-authorized-keys:
         - ssh-rsa AAAA......== oleg@t800
       sudo: ['ALL=(ALL) NOPASSWD:ALL']
       groups: sudo
       shell: /bin/bash
description: dev environment for tests
devices:
  eth0:
    nictype: bridged
    parent: br0
    type: nic
  root:
    path: /
    pool: zfs-pool
    type: disk
name: dev1
used_by:
- /1.0/instances/nodejs
...

Network

#Create bridge:
lxc network create testbr0 ipv6.address=none ipv4.address=none
lxc network create dev1br0 ipv6.address=none ipv4.address=172.20.5.10/24 ipv4.nat=true

#containers get IP from your LAN using a bridge. Profile:
devices:
  eth0:
    nictype: bridged
    parent: br0
    type: nic
https://blog.simos.info/how-to-make-your-lxd-containers-get-ip-addresses-from-your-lan-using-a-bridge/

#containers get IP from your LAN using macvlan
lxc profile device add dev1 eth0 nic nictype=macvlan parent=br0
https://blog.simos.info/how-to-make-your-lxd-container-get-ip-addresses-from-your-lan/

#Set static ip (stop container before):
lxc network attach lxdbr0 container_name eth0 eth0
lxc config device set container_name eth0 ipv4.address 192.168.10.5

Snapshots

lxc snapshot container_name snapshot_name # reate the snapshot
lxc restore container_name snapshot_name # restore the snapshot
lxc delete container_name/snapshot_name  # delete a snapshot

Files

lxc file pull container_name/path-in-container path-on-host  #from an instance to host
lxc file pull -r container_name/path-in-container path-on-host  # Pull a folder
lxc file push path-on-host container_name/path-in-container   #  from host to instance
lxc file push -r path-on-host container_name/path-in-container  # folder

Storage

lxc storage create NAME type source=/some/empty/directory
lxc storage create zfs-pool zfs source=/dev/mapper/vg_lxd-lv_lxd_zfs
lxc storage list  
lxc storage show zfs-pool
https://linuxcontainers.org/lxd/docs/master/storage

Export & import(or backups), publish

lxc export container_name /tmp/container_name_date.tar.gz
lxc import container_name_date.tar.gz 

#Publish - turns a container or snapshot into an image in the local LXD image store
lxc publish container_name/snapshot --alias new_local_image
lxc publish container_name --alias image_name

lxc image import container_name.tar.gz  --alias custom-imagename
lxc image export imagename [target folder] [flags]

#https://discuss.linuxcontainers.org/t/backup-the-container-and-install-it-on-another-server/463

Privileges

Set special privileges for container, this example is for NFS:

lxc config set container_name security.privileged true
lxc config set container_name raw.apparmor "mount fstype=nfs,"

Recommendations

Use this alias to prevent accidental deletion of an container.
lxc alias add delete "delete -i"

Gui

Source