Install docker on ubuntu (virtualbox)

$ curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo apt-key add -
$ sudo apt install apt-transport-https ca-certificates curl software-properties-common
$ sudo add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/ubuntu bionic stable"
$ sudo apt update
$ apt-cache policy docker-ce
$ sudo apt install docker-ce
$ sudo systemctl status docker
● docker.service - Docker Application Container Engine
   Loaded: loaded (/lib/systemd/system/docker.service; enabled; vendor preset: enabled)
   Active: active (running) since Thu 2019-02-21 01:49:25 KST; 4min 3s ago
     Docs: https://docs.docker.com
 Main PID: 17674 (dockerd)
    Tasks: 9
   CGroup: /system.slice/docker.service
           └─17674 /usr/bin/dockerd -H fd://

 2월 21 01:49:24 shlee-VirtualBox dockerd[17674]: time="2019-02-21T01:49:24.282330531+09:00" level=w
 2월 21 01:49:24 shlee-VirtualBox dockerd[17674]: time="2019-02-21T01:49:24.282750349+09:00" level=w
 2월 21 01:49:24 shlee-VirtualBox dockerd[17674]: time="2019-02-21T01:49:24.283530253+09:00" level=w
 2월 21 01:49:24 shlee-VirtualBox dockerd[17674]: time="2019-02-21T01:49:24.289217028+09:00" level=i
 2월 21 01:49:24 shlee-VirtualBox dockerd[17674]: time="2019-02-21T01:49:24.561081241+09:00" level=i
 2월 21 01:49:25 shlee-VirtualBox dockerd[17674]: time="2019-02-21T01:49:25.162682683+09:00" level=i
 2월 21 01:49:25 shlee-VirtualBox dockerd[17674]: time="2019-02-21T01:49:25.657244633+09:00" level=i
 2월 21 01:49:25 shlee-VirtualBox dockerd[17674]: time="2019-02-21T01:49:25.665705060+09:00" level=i
 2월 21 01:49:25 shlee-VirtualBox systemd[1]: Started Docker Application Container Engine.
 2월 21 01:49:25 shlee-VirtualBox dockerd[17674]: time="2019-02-21T01:49:25.924950417+09:00" level=i