Show installation instructions if it looks like Docker isn't installed

fig/cli/command.py

@@ -11,7 +11,7 @@ import yaml
 from ..project import Project
 from .docopt_command import DocoptCommand
 from .formatter import Formatter
-from .utils import cached_property, docker_url, call_silently
+from .utils import cached_property, docker_url, call_silently, is_mac, is_ubuntu
 from .errors import UserError
 
 log = logging.getLogger(__name__)
@@ -23,7 +23,26 @@ class Command(DocoptCommand):
         try:
             super(Command, self).dispatch(*args, **kwargs)
         except ConnectionError:
-            if call_silently(['which', 'docker-osx']) == 0:
+            if call_silently(['which', 'docker']) != 0:
+                if is_mac():
+                    raise UserError("""
+Couldn't connect to Docker daemon. You might need to install docker-osx:
+
+https://github.com/noplay/docker-osx
+""")
+                elif is_ubuntu():
+                    raise UserError("""
+Couldn't connect to Docker daemon. You might need to install Docker:
+
+http://docs.docker.io/en/latest/installation/ubuntulinux/
+""")
+                else:
+                    raise UserError("""
+Couldn't connect to Docker daemon. You might need to install Docker:
+
+http://docs.docker.io/en/latest/installation/
+""")
+            elif call_silently(['which', 'docker-osx']) == 0:
                 raise UserError("Couldn't connect to Docker daemon - you might need to run `docker-osx shell`.")
             else:
                 raise UserError("""

fig/cli/utils.py

@@ -5,6 +5,7 @@ import datetime
 import os
 import socket
 import subprocess
+import platform
 from .errors import UserError
 
 
@@ -117,3 +118,11 @@ def call_silently(*args, **kwargs):
     """
     with open(os.devnull, 'w') as shutup:
         return subprocess.call(*args, stdout=shutup, stderr=shutup, **kwargs)
+
+
+def is_mac():
+    return platform.system() == 'Darwin'
+
+
+def is_ubuntu():
+    return platform.system() == 'Linux'