When starting the daemon, the `/var/lib/docker` directory
is scanned for existing directories, so that the previously
selected graphdriver will automatically be used.
In some situations, empty directories are present (those
directories can be created during feature detection of
graph-drivers), in which case the daemon refuses to start.
This patch improves detection, and skips empty directories,
so that leftover directories don't cause the daemon to
fail.
Before this change:
$ mkdir /var/lib/docker /var/lib/docker/aufs /var/lib/docker/overlay2
$ dockerd
...
Error starting daemon: error initializing graphdriver: /var/lib/docker contains several valid graphdrivers: overlay2, aufs; Please cleanup or explicitly choose storage driver (-s <DRIVER>)
With this patch applied:
$ mkdir /var/lib/docker /var/lib/docker/aufs /var/lib/docker/overlay2
$ dockerd
...
INFO[2017-11-16T17:26:43.207739140Z] Docker daemon commit=ab90bc296 graphdriver(s)=overlay2 version=dev
INFO[2017-11-16T17:26:43.208033095Z] Daemon has completed initialization
And on restart (prior graphdriver is still picked up):
$ dockerd
...
INFO[2017-11-16T17:27:52.260361465Z] [graphdriver] using prior storage driver: overlay2
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
