Daemon "docker" not enabled after installation of "docker.io" on Ubuntu 18.04

[Francois Lafont]

Hi @all,

On a updated Ubuntu 18.04, if I installed docker via the package "docker.io" (from universe), the daemon "docker" is not enabled by default as you can seen in the following paste:

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~# lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 18.04.1 LTS
Release: 18.04
Codename: bionic

~# apt-get install -y docker.io
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following additional packages will be installed:
  libltdl7
Suggested packages:
  aufs-tools btrfs-progs debootstrap docker-doc rinse zfs-fuse | zfsutils
Recommended packages:
  cgroupfs-mount | cgroup-lite git pigz ubuntu-fan
The following NEW packages will be installed:
  docker.io libltdl7
0 upgraded, 2 newly installed, 0 to remove and 0 not upgraded.
Need to get 40.2 MB of archives.
After this operation, 198 MB of additional disk space will be used.
Get:1 http://fr.archive.ubuntu.com/ubuntu bionic/main amd64 libltdl7 amd64 2.4.6-2 [38.8 kB]
Get:2 http://fr.archive.ubuntu.com/ubuntu bionic-updates/universe amd64 docker.io amd64 18.06.1-0ubuntu1~18.04.1 [40.2 MB]
Fetched 40.2 MB in 1s (73.5 MB/s)
Preconfiguring packages ...
Selecting previously unselected package libltdl7:amd64.
(Reading database ... 100286 files and directories currently installed.)
Preparing to unpack .../libltdl7_2.4.6-2_amd64.deb ...
Unpacking libltdl7:amd64 (2.4.6-2) ...
Selecting previously unselected package docker.io.
Preparing to unpack .../docker.io_18.06.1-0ubuntu1~18.04.1_amd64.deb ...
Unpacking docker.io (18.06.1-0ubuntu1~18.04.1) ...
Processing triggers for ureadahead (0.100.0-20) ...
Processing triggers for libc-bin (2.27-3ubuntu1) ...
Processing triggers for systemd (237-3ubuntu10.9) ...
Setting up libltdl7:amd64 (2.4.6-2) ...
Processing triggers for man-db (2.8.3-2ubuntu0.1) ...
Setting up docker.io (18.06.1-0ubuntu1~18.04.1) ...
Adding group `docker' (GID 112) ...
Done.
Created symlink /etc/systemd/system/sockets.target.wants/docker.socket → /lib/systemd/system/docker.socket.
Processing triggers for libc-bin (2.27-3ubuntu1) ...
Processing triggers for systemd (237-3ubuntu10.9) ...
Processing triggers for ureadahead (0.100.0-20) ...

~# apt-cache policy docker.io
docker.io:
  Installed: 18.06.1-0ubuntu1~18.04.1
  Candidate: 18.06.1-0ubuntu1~18.04.1
  Version table:
 *** 18.06.1-0ubuntu1~18.04.1 500
        500 http://fr.archive.ubuntu.com/ubuntu bionic-updates/universe amd64 Packages
        100 /var/lib/dpkg/status
     17.12.1-0ubuntu1 500
        500 http://fr.archive.ubuntu.com/ubuntu bionic/universe amd64 Packages

~# systemctl is-enabled docker.service
disabled
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And of course, after a reboot, the daemon "docker" is not started automatically.

So in the postinst script of the package "docker.io" maybe a kind of "systemctl enable docker.service" is missing, no?

Regards.