Add warning about systemd socket activation to changelog

Docker 1.12 ships with an updated unit file on RPM based distros. Users that have local modifications to the unit file, or have a drop-in file installed may not automatically get the updated unit file, or get an error when starting docker. This adds a warning to the changelog, and instructions on how to resolve the issue. Signed-off-by: Sebastiaan van Stijn <[email protected]>
tiborvass · Aug 10, 2016 · 66b6566 · 66b6566
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diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -7,6 +7,36 @@ be found.
 
 ## 1.12.0 (2016-07-14)
 
+
+**IMPORTANT**:
+
+Docker 1.12.0 ships with an updated systemd unit file for rpm based installs
+(which includes RHEL, Fedora, CentOS, and Oracle Linux 7). When upgrading from
+an older version of docker, the upgrade process may not automatically install
+the updated version of the unit file, or fail to start the docker service if;
+
+- the systemd unit file (`/usr/lib/systemd/system/docker.service`) contains local changes, or
+- a systemd drop-in file is present, and contains `-H fd://` in the `ExecStart` directive
+
+Starting the docker service will produce an error:
+
+    Failed to start docker.service: Unit docker.socket failed to load: No such file or directory.
+
+or
+
+    no sockets found via socket activation: make sure the service was started by systemd.
+
+To resolve this:
+
+- Backup the current version of the unit file, and replace the file with the
+  version that ships with docker 1.12 (https://raw.githubusercontent.com/docker/docker/v1.12.0/contrib/init/systemd/docker.service.rpm)
+- Remove the `Requires=docker.socket` directive from the `/usr/lib/systemd/system/docker.service` file if present
+- Remove `-H fd://` from the `ExecStart` directive (both in the main unit file, and in any drop-in files present).
+
+After making those changes, run `sudo systemctl daemon-reload`, and `sudo
+systemctl restart docker` to reload changes and (re)start the docker daemon.
+
+
 ### Builder
 
 + New `HEALTHCHECK` Dockerfile instruction to support user-defined healthchecks [#23218](https://github.com/docker/docker/pull/23218)