Error response from daemon: client is newer than server (client API version: 1.21, server API version: 1.20)

ローカルのDockerMachine環境で

kohey% docker ps                                           
Error response from daemon: client is newer than server (client API version: 1.21, server API version: 1.20)

になった場合

• ローカルのdocker version

kohey% docker version                                       
Client:
 Version:      1.9.0
 API version:  1.21
 Go version:   go1.5.1
 Git commit:   76d6bc9
 Built:        Tue Nov  3 21:17:46 UTC 2015
 OS/Arch:      darwin/amd64

• docker-machine上のdocker version

kohey% docker-machine ssh dev                               
                        ##         .
                  ## ## ##        ==
               ## ## ## ## ##    ===
           /"""""""""""""""""\___/ ===
      ~~~ {~~ ~~~~ ~~~ ~~~~ ~~~ ~ /  ===- ~~~
           \______ o           __/
             \    \         __/
              \____\_______/
 _                 _   ____     _            _
| |__   ___   ___ | |_|___ \ __| | ___   ___| | _____ _ __
| '_ \ / _ \ / _ \| __| __) / _` |/ _ \ / __| |/ / _ \ '__|
| |_) | (_) | (_) | |_ / __/ (_| | (_) | (__|   <  __/ |
|_.__/ \___/ \___/ \__|_____\__,_|\___/ \___|_|\_\___|_|
Boot2Docker version 1.8.1, build master : 7f12e95 - Thu Aug 13 03:24:56 UTC 2015
Docker version 1.8.1, build d12ea79
docker@dev:~$ docker version
Client:
 Version:      1.8.1
 API version:  1.20
 Go version:   go1.4.2
 Git commit:   d12ea79
 Built:        Thu Aug 13 02:49:29 UTC 2015
 OS/Arch:      linux/amd64

Server:
 Version:      1.8.1
 API version:  1.20
 Go version:   go1.4.2
 Git commit:   d12ea79
 Built:        Thu Aug 13 02:49:29 UTC 2015
 OS/Arch:      linux/amd64

どうやら、ローカルのdockerのバージョンとdocker-machine上のdockerのバージョンが違うみたい。

以下で解決

$ docker-machine upgrade dev

これで両者ともにdockerのversionが1.9.0になった