Docker 1.12.4 发布了，Docker 1.12 版本附带了更新 rpm 的 systemd 单元文件（包括 RHEL、Fedora、CentOS 和 Oracle Linux 7 ），当从旧版本的 docker 升级，升级过程可能不会自动安装更新版本的单元文件，或因为某些原因无法启动 docker 服务。
更新内容：
Runtime
Fix issue where volume metadata was not removed
Asynchronously close streams to prevent holding container lock
Fix selinux labels for newly created container volumes
Remove hostname validation
Fix deadlocks caused by IO races
Return an empty stats if the container is restarting
Fix volume store locking
Ensure consistent status code in API
Fix incorrect opaque directory permission in overlay2
Detect plugin content and error out on docker pull
Swarm Mode
Update Swarmkit
orchestrator/global: Fix deadlock on updates
on leader switchover preserve the vxlan id for existing networks
Refuse swarm spec not named "default"
Networking
Update libnetwork
Fix panic in embedded DNS
Fix unmarhalling panic when passing --link-local-ip on global scope network
Fix panic when network plugin returns nil StaticRoutes
Fix panic in osl.(*networkNamespace).DeleteNeighbor
Fix panic in swarm networking concurrent map read/write
Allow encrypted networks when running docker inside a container
Do not block autoallocation of IPv6 pool
Set timeout for netlink calls
Increase networking local store timeout to one minute
Fix a panic in libnetwork.(*sandbox).execFunc
Honor icc=false for internal networks
Logging
Update syslog log driver
Contrib
Run "dnf upgrade" before installing in fedora
Add build-date back to RPM packages
Update selinux policy for distros based on RHEL7.3
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