# [2] mount docker
diskutil umountDisk /dev/disk2
$(cd $base_dir ; hdiutil mount $filename)
# [3] install docker
$(sudo cp -R /Volumes/Docker/Docker.app /Applications/)
# [4] change ownership
chown $(whoami) /Volumes/Docker/Docker.app

chown: /Volumes/Docker/Docker.app: Read-only file system

$ id
uid=501(romain) gid=20(staff) groups=20(staff),0(wheel),12(everyone),61(localaccounts),79(_appserverusr),80(admin),81(_appserveradm),98(_lpadmin),33(_appstore),100(_lpoperator),204(_developer),395(com.apple.access_ftp),398(com.apple.access_screensharing),101(com.apple.access_ssh-disabled)

$ ls -l /

drwxr-xr-x@  5 root  admin   170 Dec  4 00:45 Volumes

$ ls -l /Volumes/

drwxr-xr-x@ 9 romain  staff  374 Nov  8 18:37 Docker

$ ls -l /Volumes/Docker/

lrwxr-xr-x  1 romain  staff   13 Nov  8 18:37 Applications -> /Applications
drwxr-xr-x  3 romain  staff  102 Nov  8 18:36 Docker.app