Docker on Ubuntu Won't Start

$ sudo systemctl status docker
● docker.service - Docker Application Container Engine
 Loaded: loaded (/lib/systemd/system/docker.service; enabled; vendor preset: enabled)
 Active: failed (Result: exit-code) since Mon 2019-07-01 07:48:16 JST; 7min ago
 Docs: https://docs.docker.com
 Process: 1521 ExecStart=/usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock -s overlay2 (code=exited, status=203/EXEC)
 Main PID: 1521 (code=exited, status=203/EXEC)
Jul 01 07:48:14 sagittarius systemd[1521]: docker.service: Failed at step EXEC spawning /usr/bin/dockerd: No such file or directory
Jul 01 07:48:14 sagittarius systemd[1]: docker.service: Main process exited, code=exited, status=203/EXEC
Jul 01 07:48:14 sagittarius systemd[1]: docker.service: Failed with result 'exit-code'.
Jul 01 07:48:14 sagittarius systemd[1]: Failed to start Docker Application Container Engine.
Jul 01 07:48:16 sagittarius systemd[1]: docker.service: Service hold-off time over, scheduling restart.
Jul 01 07:48:16 sagittarius systemd[1]: docker.service: Scheduled restart job, restart counter is at 3.
Jul 01 07:48:16 sagittarius systemd[1]: Stopped Docker Application Container Engine.
Jul 01 07:48:16 sagittarius systemd[1]: docker.service: Start request repeated too quickly.
Jul 01 07:48:16 sagittarius systemd[1]: docker.service: Failed with result 'exit-code'.
Jul 01 07:48:16 sagittarius systemd[1]: Failed to start Docker Application Container Engine.

$ grep ExecStart /lib/systemd/system/docker.service
ExecStart=/usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock

$ ls /usr/bin/docker*
/usr/bin/docker* /usr/bin/docker-init* /usr/bin/docker-proxy* /usr/bin/dockerd-ce*

/usr/bin/dockerd is missing

Replace /usr/bin/docker with /usr/bin/docker-ce

$ grep ExecStart /lib/systemd/system/docker.service
# ExecStart=/usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock
ExecStart=/usr/bin/dockerd-ce -H fd:// --containerd=/run/containerd/containerd.sock

$ sudo systemctl daemon-reload

$ sudo systemctl start docker

It started