* In -dev mode, `ioutil.TempDir` is used for the alloc and state
directories.
* `TempDir` uses `$TMPDIR`, which os OS X contains a per user
directory which is under `/var/folder`.
* `/var` is actually a symlink to `/private/var`
* Docker For Mac validates the directories that are passed to bind and on
OS X. That whitelist contains `/private`, but not `/var`. It does not
expand the path, and so any paths in `$TMPDIR` fail the whitelist check.
And thusly, by expanding the alloc/state directories the value passed
for binding does contain `/private` and Docker For Mac is happy.
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