$ sudo apt-get update
$ sudo apt-get upgrade

$ dpkg -l |grep lxd   <- checking
$ sudo apt install lxd
$ dpkg -l |grep lxd   <- checking

$ sudo systemctl status lxd.service  <- checking
$ sudo systemctl start lxd.service
$ sudo systemctl enable lxd.service
$ sudo systemctl status lxd.service  <- checking

$ lxd --version
2.0.0
$ lxc --version
2.0.0

sudo apt-get install bridge-utils

sudo apt-get install zfsutils-linux

/etc/network/interfaces

source /etc/network/interfaces.d/*

auto lo
iface lo inet loopback

auto br0
iface br0 inet dhcp
        bridge_ports enp0s3

iface enp0s3 inet manual

source /etc/network/interfaces.d/*

auto lo
iface lo inet loopback

auto enp0s3
iface enp0s3 inet manual

auto br0
iface br0 inet dhcp
    bridge-ifaces enp0s3
    bridge-ports enp0s3
    ip link set enp0s3 up

source /etc/network/interfaces.d/*

auto lo
iface lo inet loopback

auto ens1f1
iface ens1f1 inet manual

auto br0
iface br0 inet static
  address 192.168.0.100
  network 192.168.0.0
  netmask 255.255.255.0
  gateway 192.168.0.1
  bridge_ports ens1f1

# sysctl net.ipv4.ip_forward  < - checking the parameter
net.ipv4.ip_forward = 0
# vi /etc/sysctl.conf
...
net.ipv4.ip_forward=1
...
# sysctl -p
# sysctl net.ipv4.ip_forward  < - checking the parameter
net.ipv4.ip_forward = 1

$ sudo vi /etc/sysctl.conf
....
net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1
....
$ sudo sysctl -p

$ sudo iptalbes -F
$ sudo iptables-save

# ip a  <- check

# lxd init
Name of the storage backend to use (dir or zfs) [default=zfs]: 
Create a new ZFS pool (yes/no) [default=yes]? 
Name of the new ZFS pool [default=lxd]: 
Would you like to use an existing block device (yes/no) [default=no]? 
Size in GB of the new loop device (1GB minimum) [default=15]: 30
Would you like LXD to be available over the network (yes/no)? no
Do you want to configure the LXD bridge (yes/no)? yes

Would you like to setup a network bridge for LXD containers now? yes
Do you want to use an existing bridge? yes  
Bridge interface name:  br0

Do you want to setup an IPv4 subnet?
No

Do you want to setup an IPv6 subnet?
No

LXD has been successfully configured. 

$ sudo lxd init
Name of the storage backend to use (dir or zfs) [default=dir]: dir
Would you like LXD to be available over the network (yes/no) [default=no]?no
Do you want to configure the LXD bridge (yes/no) [default=yes]?yes

Would you like to setup a network bridge for LXD containers now? yes
Do you want to use an existing bridge? yes  
Bridge interface name:  br0

Do you want to setup an IPv4 subnet?
No

Do you want to setup an IPv6 subnet?
No

LXD has been successfully configured. 

# dpkg-reconfigure -p medium lxd