diff --git a/common/step_provision.go b/common/step_provision.go
index 893f13431..d069a5c0c 100644
--- a/common/step_provision.go
+++ b/common/step_provision.go
@@ -4,6 +4,7 @@ import (
 	"github.com/mitchellh/multistep"
 	"github.com/mitchellh/packer/packer"
 	"log"
+	"time"
 )
 
 // StepProvision runs the provisioners.
@@ -22,13 +23,31 @@ func (*StepProvision) Run(state map[string]interface{}) multistep.StepAction {
 	hook := state["hook"].(packer.Hook)
 	ui := state["ui"].(packer.Ui)
 
+	// Run the provisioner in a goroutine so we can continually check
+	// for cancellations...
 	log.Println("Running the provision hook")
-	if err := hook.Run(packer.HookProvision, ui, comm, nil); err != nil {
-		state["error"] = err
-		return multistep.ActionHalt
-	}
+	errCh := make(chan error, 1)
+	go func() {
+		errCh <- hook.Run(packer.HookProvision, ui, comm, nil)
+	}()
+
+	for {
+		select {
+		case err := <-errCh:
+			if err != nil {
+				state["error"] = err
+				return multistep.ActionHalt
+			}
 
-	return multistep.ActionContinue
+			return multistep.ActionContinue
+		case <-time.After(1 * time.Second):
+			if _, ok := state[multistep.StateCancelled]; ok {
+				log.Println("Cancelling provisioning due to interrupt...")
+				hook.Cancel()
+				return multistep.ActionHalt
+			}
+		}
+	}
 }
 
 func (*StepProvision) Cleanup(map[string]interface{}) {}
diff --git a/packer/build.go b/packer/build.go
index b8e0fa165..e324fdea7 100644
--- a/packer/build.go
+++ b/packer/build.go
@@ -207,10 +207,12 @@ func (b *coreBuild) Run(originalUi Ui, cache Cache) ([]Artifact, error) {
 			hooks[HookProvision] = make([]Hook, 0, 1)
 		}
 
-		hooks[HookProvision] = append(hooks[HookProvision], &ProvisionHook{provisioners})
+		hooks[HookProvision] = append(hooks[HookProvision], &ProvisionHook{
+			Provisioners: provisioners,
+		})
 	}
 
-	hook := &DispatchHook{hooks}
+	hook := &DispatchHook{Mapping: hooks}
 	artifacts := make([]Artifact, 0, 1)
 
 	// The builder just has a normal Ui, but targetted
diff --git a/packer/build_test.go b/packer/build_test.go
index c5eedbc81..cbac0f208 100644
--- a/packer/build_test.go
+++ b/packer/build_test.go
@@ -13,10 +13,10 @@ func testBuild() *coreBuild {
 		builderConfig: 42,
 		builderType:   "foo",
 		hooks: map[string][]Hook{
-			"foo": []Hook{&TestHook{}},
+			"foo": []Hook{&MockHook{}},
 		},
 		provisioners: []coreBuildProvisioner{
-			coreBuildProvisioner{&TestProvisioner{}, []interface{}{42}},
+			coreBuildProvisioner{&MockProvisioner{}, []interface{}{42}},
 		},
 		postProcessors: [][]coreBuildPostProcessor{
 			[]coreBuildPostProcessor{
@@ -59,9 +59,9 @@ func TestBuild_Prepare(t *testing.T) {
 	assert.Equal(builder.prepareConfig, []interface{}{42, packerConfig}, "prepare config should be 42")
 
 	coreProv := build.provisioners[0]
-	prov := coreProv.provisioner.(*TestProvisioner)
-	assert.True(prov.prepCalled, "prepare should be called")
-	assert.Equal(prov.prepConfigs, []interface{}{42, packerConfig}, "prepare should be called with proper config")
+	prov := coreProv.provisioner.(*MockProvisioner)
+	assert.True(prov.PrepCalled, "prepare should be called")
+	assert.Equal(prov.PrepConfigs, []interface{}{42, packerConfig}, "prepare should be called with proper config")
 
 	corePP := build.postProcessors[0][0]
 	pp := corePP.processor.(*TestPostProcessor)
@@ -104,9 +104,9 @@ func TestBuild_Prepare_Debug(t *testing.T) {
 	assert.Equal(builder.prepareConfig, []interface{}{42, packerConfig}, "prepare config should be 42")
 
 	coreProv := build.provisioners[0]
-	prov := coreProv.provisioner.(*TestProvisioner)
-	assert.True(prov.prepCalled, "prepare should be called")
-	assert.Equal(prov.prepConfigs, []interface{}{42, packerConfig}, "prepare should be called with proper config")
+	prov := coreProv.provisioner.(*MockProvisioner)
+	assert.True(prov.PrepCalled, "prepare should be called")
+	assert.Equal(prov.PrepConfigs, []interface{}{42, packerConfig}, "prepare should be called with proper config")
 }
 
 func TestBuildPrepare_variables_default(t *testing.T) {
@@ -187,14 +187,14 @@ func TestBuild_Run(t *testing.T) {
 	dispatchHook := builder.runHook
 	dispatchHook.Run("foo", nil, nil, 42)
 
-	hook := build.hooks["foo"][0].(*TestHook)
-	assert.True(hook.runCalled, "run should be called")
-	assert.Equal(hook.runData, 42, "should have correct data")
+	hook := build.hooks["foo"][0].(*MockHook)
+	assert.True(hook.RunCalled, "run should be called")
+	assert.Equal(hook.RunData, 42, "should have correct data")
 
 	// Verify provisioners run
 	dispatchHook.Run(HookProvision, nil, nil, 42)
-	prov := build.provisioners[0].provisioner.(*TestProvisioner)
-	assert.True(prov.provCalled, "provision should be called")
+	prov := build.provisioners[0].provisioner.(*MockProvisioner)
+	assert.True(prov.ProvCalled, "provision should be called")
 
 	// Verify post-processor was run
 	pp := build.postProcessors[0][0].processor.(*TestPostProcessor)
diff --git a/packer/environment_test.go b/packer/environment_test.go
index e301e8c7a..6cda3f7d2 100644
--- a/packer/environment_test.go
+++ b/packer/environment_test.go
@@ -20,7 +20,7 @@ func init() {
 func testComponentFinder() *ComponentFinder {
 	builderFactory := func(n string) (Builder, error) { return testBuilder(), nil }
 	ppFactory := func(n string) (PostProcessor, error) { return new(TestPostProcessor), nil }
-	provFactory := func(n string) (Provisioner, error) { return new(TestProvisioner), nil }
+	provFactory := func(n string) (Provisioner, error) { return new(MockProvisioner), nil }
 	return &ComponentFinder{
 		Builder:       builderFactory,
 		PostProcessor: ppFactory,
@@ -227,7 +227,7 @@ func TestEnvironment_DefaultCli_Version(t *testing.T) {
 func TestEnvironment_Hook(t *testing.T) {
 	assert := asserts.NewTestingAsserts(t, true)
 
-	hook := &TestHook{}
+	hook := &MockHook{}
 	hooks := make(map[string]Hook)
 	hooks["foo"] = hook
 
@@ -309,7 +309,7 @@ func TestEnvironment_PostProcessor_Error(t *testing.T) {
 func TestEnvironmentProvisioner(t *testing.T) {
 	assert := asserts.NewTestingAsserts(t, true)
 
-	p := &TestProvisioner{}
+	p := &MockProvisioner{}
 	ps := make(map[string]Provisioner)
 	ps["foo"] = p
 
diff --git a/packer/hook.go b/packer/hook.go
index 4a79222f4..e5e7ad8a9 100644
--- a/packer/hook.go
+++ b/packer/hook.go
@@ -1,5 +1,9 @@
 package packer
 
+import (
+	"sync"
+)
+
 // This is the hook that should be fired for provisioners to run.
 const HookProvision = "packer_provision"
 
@@ -11,19 +15,40 @@ const HookProvision = "packer_provision"
 // you must reference the documentation for the specific hook you're interested
 // in. In addition to that, the Hook is given access to a UI so that it can
 // output things to the user.
+//
+// Cancel is called when the hook needs to be cancelled. This will usually
+// be called when Run is still in progress so the mechanism that handles this
+// must be race-free. Cancel should attempt to cancel the hook in the
+// quickest, safest way possible.
 type Hook interface {
 	Run(string, Ui, Communicator, interface{}) error
+	Cancel()
 }
 
 // A Hook implementation that dispatches based on an internal mapping.
 type DispatchHook struct {
 	Mapping map[string][]Hook
+
+	l           sync.Mutex
+	cancelled   bool
+	runningHook Hook
 }
 
 // Runs the hook with the given name by dispatching it to the proper
 // hooks if a mapping exists. If a mapping doesn't exist, then nothing
 // happens.
 func (h *DispatchHook) Run(name string, ui Ui, comm Communicator, data interface{}) error {
+	h.l.Lock()
+	h.cancelled = false
+	h.l.Unlock()
+
+	// Make sure when we exit that we reset the running hook.
+	defer func() {
+		h.l.Lock()
+		defer h.l.Unlock()
+		h.runningHook = nil
+	}()
+
 	hooks, ok := h.Mapping[name]
 	if !ok {
 		// No hooks for that name. No problem.
@@ -31,6 +56,15 @@ func (h *DispatchHook) Run(name string, ui Ui, comm Communicator, data interface
 	}
 
 	for _, hook := range hooks {
+		h.l.Lock()
+		if h.cancelled {
+			h.l.Unlock()
+			return nil
+		}
+
+		h.runningHook = hook
+		h.l.Unlock()
+
 		if err := hook.Run(name, ui, comm, data); err != nil {
 			return err
 		}
@@ -38,3 +72,16 @@ func (h *DispatchHook) Run(name string, ui Ui, comm Communicator, data interface
 
 	return nil
 }
+
+// Cancels all the hooks that are currently in-flight, if any. This will
+// block until the hooks are all cancelled.
+func (h *DispatchHook) Cancel() {
+	h.l.Lock()
+	defer h.l.Unlock()
+
+	if h.runningHook != nil {
+		h.runningHook.Cancel()
+	}
+
+	h.cancelled = true
+}
diff --git a/packer/hook_mock.go b/packer/hook_mock.go
new file mode 100644
index 000000000..7177329e3
--- /dev/null
+++ b/packer/hook_mock.go
@@ -0,0 +1,31 @@
+package packer
+
+// MockHook is an implementation of Hook that can be used for tests.
+type MockHook struct {
+	RunFunc func() error
+
+	RunCalled    bool
+	RunComm      Communicator
+	RunData      interface{}
+	RunName      string
+	RunUi        Ui
+	CancelCalled bool
+}
+
+func (t *MockHook) Run(name string, ui Ui, comm Communicator, data interface{}) error {
+	t.RunCalled = true
+	t.RunComm = comm
+	t.RunData = data
+	t.RunName = name
+	t.RunUi = ui
+
+	if t.RunFunc == nil {
+		return nil
+	}
+
+	return t.RunFunc()
+}
+
+func (t *MockHook) Cancel() {
+	t.CancelCalled = true
+}
diff --git a/packer/hook_test.go b/packer/hook_test.go
index e43dfd1fd..bf88e65df 100644
--- a/packer/hook_test.go
+++ b/packer/hook_test.go
@@ -2,52 +2,89 @@ package packer
 
 import (
 	"cgl.tideland.biz/asserts"
+	"sync"
 	"testing"
+	"time"
 )
 
-type TestHook struct {
-	runCalled bool
-	runComm   Communicator
-	runData   interface{}
-	runName   string
-	runUi     Ui
+// A helper Hook implementation for testing cancels.
+type CancelHook struct {
+	sync.Mutex
+	cancelCh chan struct{}
+	doneCh   chan struct{}
+
+	Cancelled bool
 }
 
-func (t *TestHook) Run(name string, ui Ui, comm Communicator, data interface{}) error {
-	t.runCalled = true
-	t.runComm = comm
-	t.runData = data
-	t.runName = name
-	t.runUi = ui
+func (h *CancelHook) Run(string, Ui, Communicator, interface{}) error {
+	h.Lock()
+	h.cancelCh = make(chan struct{})
+	h.doneCh = make(chan struct{})
+	h.Unlock()
+
+	defer close(h.doneCh)
+
+	select {
+	case <-h.cancelCh:
+		h.Cancelled = true
+	case <-time.After(1 * time.Second):
+	}
+
 	return nil
 }
 
+func (h *CancelHook) Cancel() {
+	h.Lock()
+	close(h.cancelCh)
+	h.Unlock()
+
+	<-h.doneCh
+}
+
 func TestDispatchHook_Implements(t *testing.T) {
 	assert := asserts.NewTestingAsserts(t, true)
 
 	var r Hook
-	c := &DispatchHook{nil}
+	c := &DispatchHook{}
 
 	assert.Implementor(c, &r, "should be a Hook")
 }
 
 func TestDispatchHook_Run_NoHooks(t *testing.T) {
 	// Just make sure nothing blows up
-	dh := &DispatchHook{make(map[string][]Hook)}
+	dh := &DispatchHook{}
 	dh.Run("foo", nil, nil, nil)
 }
 
 func TestDispatchHook_Run(t *testing.T) {
 	assert := asserts.NewTestingAsserts(t, true)
 
-	hook := &TestHook{}
+	hook := &MockHook{}
 
 	mapping := make(map[string][]Hook)
 	mapping["foo"] = []Hook{hook}
-	dh := &DispatchHook{mapping}
+	dh := &DispatchHook{Mapping: mapping}
 	dh.Run("foo", nil, nil, 42)
 
-	assert.True(hook.runCalled, "run should be called")
-	assert.Equal(hook.runName, "foo", "should be proper event")
-	assert.Equal(hook.runData, 42, "should be correct data")
+	assert.True(hook.RunCalled, "run should be called")
+	assert.Equal(hook.RunName, "foo", "should be proper event")
+	assert.Equal(hook.RunData, 42, "should be correct data")
+}
+
+func TestDispatchHook_cancel(t *testing.T) {
+	hook := new(CancelHook)
+
+	dh := &DispatchHook{
+		Mapping: map[string][]Hook{
+			"foo": []Hook{hook},
+		},
+	}
+
+	go dh.Run("foo", nil, nil, 42)
+	time.Sleep(100 * time.Millisecond)
+	dh.Cancel()
+
+	if !hook.Cancelled {
+		t.Fatal("hook should've cancelled")
+	}
 }
diff --git a/packer/plugin/hook.go b/packer/plugin/hook.go
index 90b0779d9..5d4dbf06a 100644
--- a/packer/plugin/hook.go
+++ b/packer/plugin/hook.go
@@ -19,8 +19,17 @@ func (c *cmdHook) Run(name string, ui packer.Ui, comm packer.Communicator, data
 	return c.hook.Run(name, ui, comm, data)
 }
 
+func (c *cmdHook) Cancel() {
+	defer func() {
+		r := recover()
+		c.checkExit(r, nil)
+	}()
+
+	c.hook.Cancel()
+}
+
 func (c *cmdHook) checkExit(p interface{}, cb func()) {
-	if c.client.Exited() {
+	if c.client.Exited() && cb != nil {
 		cb()
 	} else if p != nil && !Killed {
 		log.Panic(p)
diff --git a/packer/plugin/hook_test.go b/packer/plugin/hook_test.go
index e6880e616..6f897da19 100644
--- a/packer/plugin/hook_test.go
+++ b/packer/plugin/hook_test.go
@@ -1,17 +1,10 @@
 package plugin
 
 import (
-	"github.com/mitchellh/packer/packer"
 	"os/exec"
 	"testing"
 )
 
-type helperHook byte
-
-func (helperHook) Run(string, packer.Ui, packer.Communicator, interface{}) error {
-	return nil
-}
-
 func TestHook_NoExist(t *testing.T) {
 	c := NewClient(&ClientConfig{Cmd: exec.Command("i-should-not-exist")})
 	defer c.Kill()
diff --git a/packer/plugin/plugin_test.go b/packer/plugin/plugin_test.go
index 0610887ec..17018f82d 100644
--- a/packer/plugin/plugin_test.go
+++ b/packer/plugin/plugin_test.go
@@ -2,6 +2,7 @@ package plugin
 
 import (
 	"fmt"
+	"github.com/mitchellh/packer/packer"
 	"log"
 	"os"
 	"os/exec"
@@ -54,7 +55,7 @@ func TestHelperProcess(*testing.T) {
 	case "command":
 		ServeCommand(new(helperCommand))
 	case "hook":
-		ServeHook(new(helperHook))
+		ServeHook(new(packer.MockHook))
 	case "invalid-rpc-address":
 		fmt.Println("lolinvalid")
 	case "mock":
@@ -63,7 +64,7 @@ func TestHelperProcess(*testing.T) {
 	case "post-processor":
 		ServePostProcessor(new(helperPostProcessor))
 	case "provisioner":
-		ServeProvisioner(new(helperProvisioner))
+		ServeProvisioner(new(packer.MockProvisioner))
 	case "start-timeout":
 		time.Sleep(1 * time.Minute)
 		os.Exit(1)
diff --git a/packer/plugin/provisioner.go b/packer/plugin/provisioner.go
index 7445c4165..0feb9d727 100644
--- a/packer/plugin/provisioner.go
+++ b/packer/plugin/provisioner.go
@@ -28,6 +28,15 @@ func (c *cmdProvisioner) Provision(ui packer.Ui, comm packer.Communicator) error
 	return c.p.Provision(ui, comm)
 }
 
+func (c *cmdProvisioner) Cancel() {
+	defer func() {
+		r := recover()
+		c.checkExit(r, nil)
+	}()
+
+	c.p.Cancel()
+}
+
 func (c *cmdProvisioner) checkExit(p interface{}, cb func()) {
 	if c.client.Exited() && cb != nil {
 		cb()
diff --git a/packer/plugin/provisioner_test.go b/packer/plugin/provisioner_test.go
index 4a665411c..f0d7eb773 100644
--- a/packer/plugin/provisioner_test.go
+++ b/packer/plugin/provisioner_test.go
@@ -1,21 +1,10 @@
 package plugin
 
 import (
-	"github.com/mitchellh/packer/packer"
 	"os/exec"
 	"testing"
 )
 
-type helperProvisioner byte
-
-func (helperProvisioner) Prepare(...interface{}) error {
-	return nil
-}
-
-func (helperProvisioner) Provision(packer.Ui, packer.Communicator) error {
-	return nil
-}
-
 func TestProvisioner_NoExist(t *testing.T) {
 	c := NewClient(&ClientConfig{Cmd: exec.Command("i-should-not-exist")})
 	defer c.Kill()
diff --git a/packer/provisioner.go b/packer/provisioner.go
index 99a0a2ac2..3592fb919 100644
--- a/packer/provisioner.go
+++ b/packer/provisioner.go
@@ -1,5 +1,9 @@
 package packer
 
+import (
+	"sync"
+)
+
 // A provisioner is responsible for installing and configuring software
 // on a machine prior to building the actual image.
 type Provisioner interface {
@@ -13,6 +17,11 @@ type Provisioner interface {
 	// is guaranteed to be connected to some machine so that provisioning
 	// can be done.
 	Provision(Ui, Communicator) error
+
+	// Cancel is called to cancel the provisioning. This is usually called
+	// while Provision is still being called. The Provisioner should act
+	// to stop its execution as quickly as possible in a race-free way.
+	Cancel()
 }
 
 // A Hook implementation that runs the given provisioners.
@@ -20,11 +29,25 @@ type ProvisionHook struct {
 	// The provisioners to run as part of the hook. These should already
 	// be prepared (by calling Prepare) at some earlier stage.
 	Provisioners []Provisioner
+
+	lock               sync.Mutex
+	runningProvisioner Provisioner
 }
 
 // Runs the provisioners in order.
 func (h *ProvisionHook) Run(name string, ui Ui, comm Communicator, data interface{}) error {
+	defer func() {
+		h.lock.Lock()
+		defer h.lock.Unlock()
+
+		h.runningProvisioner = nil
+	}()
+
 	for _, p := range h.Provisioners {
+		h.lock.Lock()
+		h.runningProvisioner = p
+		h.lock.Unlock()
+
 		if err := p.Provision(ui, comm); err != nil {
 			return err
 		}
@@ -32,3 +55,13 @@ func (h *ProvisionHook) Run(name string, ui Ui, comm Communicator, data interfac
 
 	return nil
 }
+
+// Cancels the privisioners that are still running.
+func (h *ProvisionHook) Cancel() {
+	h.lock.Lock()
+	defer h.lock.Unlock()
+
+	if h.runningProvisioner != nil {
+		h.runningProvisioner.Cancel()
+	}
+}
diff --git a/packer/provisioner_mock.go b/packer/provisioner_mock.go
new file mode 100644
index 000000000..b61f642af
--- /dev/null
+++ b/packer/provisioner_mock.go
@@ -0,0 +1,34 @@
+package packer
+
+// MockProvisioner is an implementation of Provisioner that can be
+// used for tests.
+type MockProvisioner struct {
+	ProvFunc func() error
+
+	PrepCalled   bool
+	PrepConfigs  []interface{}
+	ProvCalled   bool
+	ProvUi       Ui
+	CancelCalled bool
+}
+
+func (t *MockProvisioner) Prepare(configs ...interface{}) error {
+	t.PrepCalled = true
+	t.PrepConfigs = configs
+	return nil
+}
+
+func (t *MockProvisioner) Provision(ui Ui, comm Communicator) error {
+	t.ProvCalled = true
+	t.ProvUi = ui
+
+	if t.ProvFunc == nil {
+		return nil
+	}
+
+	return t.ProvFunc()
+}
+
+func (t *MockProvisioner) Cancel() {
+	t.CancelCalled = true
+}
diff --git a/packer/provisioner_test.go b/packer/provisioner_test.go
index 1db8b55bc..a3d97d511 100644
--- a/packer/provisioner_test.go
+++ b/packer/provisioner_test.go
@@ -1,23 +1,10 @@
 package packer
 
-import "testing"
-
-type TestProvisioner struct {
-	prepCalled  bool
-	prepConfigs []interface{}
-	provCalled  bool
-}
-
-func (t *TestProvisioner) Prepare(configs ...interface{}) error {
-	t.prepCalled = true
-	t.prepConfigs = configs
-	return nil
-}
-
-func (t *TestProvisioner) Provision(Ui, Communicator) error {
-	t.provCalled = true
-	return nil
-}
+import (
+	"sync"
+	"testing"
+	"time"
+)
 
 func TestProvisionHook_Impl(t *testing.T) {
 	var raw interface{}
@@ -28,23 +15,68 @@ func TestProvisionHook_Impl(t *testing.T) {
 }
 
 func TestProvisionHook(t *testing.T) {
-	pA := &TestProvisioner{}
-	pB := &TestProvisioner{}
+	pA := &MockProvisioner{}
+	pB := &MockProvisioner{}
 
 	ui := testUi()
 	var comm Communicator = nil
 	var data interface{} = nil
 
-	hook := &ProvisionHook{[]Provisioner{pA, pB}}
+	hook := &ProvisionHook{
+		Provisioners: []Provisioner{pA, pB},
+	}
+
 	hook.Run("foo", ui, comm, data)
 
-	if !pA.provCalled {
+	if !pA.ProvCalled {
 		t.Error("provision should be called on pA")
 	}
 
-	if !pB.provCalled {
+	if !pB.ProvCalled {
 		t.Error("provision should be called on pB")
 	}
 }
 
+func TestProvisionHook_cancel(t *testing.T) {
+	var lock sync.Mutex
+	order := make([]string, 0, 2)
+
+	p := &MockProvisioner{
+		ProvFunc: func() error {
+			time.Sleep(50 * time.Millisecond)
+
+			lock.Lock()
+			defer lock.Unlock()
+			order = append(order, "prov")
+
+			return nil
+		},
+	}
+
+	hook := &ProvisionHook{
+		Provisioners: []Provisioner{p},
+	}
+
+	finished := make(chan struct{})
+	go func() {
+		hook.Run("foo", nil, nil, nil)
+		close(finished)
+	}()
+
+	// Cancel it while it is running
+	time.Sleep(10 * time.Millisecond)
+	hook.Cancel()
+	lock.Lock()
+	order = append(order, "cancel")
+	lock.Unlock()
+
+	// Wait
+	<-finished
+
+	// Verify order
+	if order[0] != "cancel" || order[1] != "prov" {
+		t.Fatalf("bad: %#v", order)
+	}
+}
+
 // TODO(mitchellh): Test that they're run in the proper order
diff --git a/packer/rpc/builder_test.go b/packer/rpc/builder_test.go
index 8dff67b30..5235de9b5 100644
--- a/packer/rpc/builder_test.go
+++ b/packer/rpc/builder_test.go
@@ -72,7 +72,7 @@ func TestBuilderRPC(t *testing.T) {
 
 	// Test Run
 	cache := new(testCache)
-	hook := &testHook{}
+	hook := &packer.MockHook{}
 	ui := &testUi{}
 	artifact, err := bClient.Run(ui, hook, cache)
 	assert.Nil(err, "should have no error")
@@ -83,7 +83,7 @@ func TestBuilderRPC(t *testing.T) {
 		assert.True(cache.lockCalled, "lock should be called")
 
 		b.runHook.Run("foo", nil, nil, nil)
-		assert.True(hook.runCalled, "run should be called")
+		assert.True(hook.RunCalled, "run should be called")
 
 		b.runUi.Say("format")
 		assert.True(ui.sayCalled, "say should be called")
diff --git a/packer/rpc/hook.go b/packer/rpc/hook.go
index 27840f080..687d991a7 100644
--- a/packer/rpc/hook.go
+++ b/packer/rpc/hook.go
@@ -2,6 +2,7 @@ package rpc
 
 import (
 	"github.com/mitchellh/packer/packer"
+	"log"
 	"net/rpc"
 )
 
@@ -37,6 +38,13 @@ func (h *hook) Run(name string, ui packer.Ui, comm packer.Communicator, data int
 	return h.client.Call("Hook.Run", args, new(interface{}))
 }
 
+func (h *hook) Cancel() {
+	err := h.client.Call("Hook.Cancel", new(interface{}), new(interface{}))
+	if err != nil {
+		log.Printf("Hook.Cancel error: %s", err)
+	}
+}
+
 func (h *HookServer) Run(args *HookRunArgs, reply *interface{}) error {
 	client, err := rpc.Dial("tcp", args.RPCAddress)
 	if err != nil {
@@ -50,3 +58,8 @@ func (h *HookServer) Run(args *HookRunArgs, reply *interface{}) error {
 	*reply = nil
 	return nil
 }
+
+func (h *HookServer) Cancel(args *interface{}, reply *interface{}) error {
+	h.hook.Cancel()
+	return nil
+}
diff --git a/packer/rpc/hook_test.go b/packer/rpc/hook_test.go
index fcc2aea7a..1d226056a 100644
--- a/packer/rpc/hook_test.go
+++ b/packer/rpc/hook_test.go
@@ -4,24 +4,17 @@ import (
 	"cgl.tideland.biz/asserts"
 	"github.com/mitchellh/packer/packer"
 	"net/rpc"
+	"reflect"
+	"sync"
 	"testing"
+	"time"
 )
 
-type testHook struct {
-	runCalled bool
-	runUi     packer.Ui
-}
-
-func (h *testHook) Run(name string, ui packer.Ui, comm packer.Communicator, data interface{}) error {
-	h.runCalled = true
-	return nil
-}
-
 func TestHookRPC(t *testing.T) {
 	assert := asserts.NewTestingAsserts(t, true)
 
 	// Create the UI to test
-	h := new(testHook)
+	h := new(packer.MockHook)
 
 	// Serve
 	server := rpc.NewServer()
@@ -37,7 +30,11 @@ func TestHookRPC(t *testing.T) {
 	// Test Run
 	ui := &testUi{}
 	hClient.Run("foo", ui, nil, 42)
-	assert.True(h.runCalled, "run should be called")
+	assert.True(h.RunCalled, "run should be called")
+
+	// Test Cancel
+	hClient.Cancel()
+	assert.True(h.CancelCalled, "cancel should be called")
 }
 
 func TestHook_Implements(t *testing.T) {
@@ -48,3 +45,56 @@ func TestHook_Implements(t *testing.T) {
 
 	assert.Implementor(h, &r, "should be a Hook")
 }
+
+func TestHook_cancelWhileRun(t *testing.T) {
+	var finishLock sync.Mutex
+	finishOrder := make([]string, 0, 2)
+
+	h := &packer.MockHook{
+		RunFunc: func() error {
+			time.Sleep(100 * time.Millisecond)
+
+			finishLock.Lock()
+			finishOrder = append(finishOrder, "run")
+			finishLock.Unlock()
+			return nil
+		},
+	}
+
+	// Serve
+	server := rpc.NewServer()
+	RegisterHook(server, h)
+	address := serveSingleConn(server)
+
+	// Create the client over RPC and run some methods to verify it works
+	client, err := rpc.Dial("tcp", address)
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	hClient := Hook(client)
+
+	// Start the run
+	finished := make(chan struct{})
+	go func() {
+		hClient.Run("foo", nil, nil, nil)
+		close(finished)
+	}()
+
+	// Cancel it pretty quickly.
+	time.Sleep(10 * time.Millisecond)
+	hClient.Cancel()
+
+	finishLock.Lock()
+	finishOrder = append(finishOrder, "cancel")
+	finishLock.Unlock()
+
+	// Verify things are good
+	<-finished
+
+	// Check the results
+	expected := []string{"cancel", "run"}
+	if !reflect.DeepEqual(finishOrder, expected) {
+		t.Fatalf("bad: %#v", finishOrder)
+	}
+}
diff --git a/packer/rpc/provisioner.go b/packer/rpc/provisioner.go
index dbe366e56..7d3ed1617 100644
--- a/packer/rpc/provisioner.go
+++ b/packer/rpc/provisioner.go
@@ -2,6 +2,7 @@ package rpc
 
 import (
 	"github.com/mitchellh/packer/packer"
+	"log"
 	"net/rpc"
 )
 
@@ -47,6 +48,13 @@ func (p *provisioner) Provision(ui packer.Ui, comm packer.Communicator) error {
 	return p.client.Call("Provisioner.Provision", args, new(interface{}))
 }
 
+func (p *provisioner) Cancel() {
+	err := p.client.Call("Provisioner.Cancel", new(interface{}), new(interface{}))
+	if err != nil {
+		log.Printf("Provisioner.Cancel err: %s", err)
+	}
+}
+
 func (p *ProvisionerServer) Prepare(args *ProvisionerPrepareArgs, reply *error) error {
 	*reply = p.p.Prepare(args.Configs...)
 	if *reply != nil {
@@ -71,3 +79,8 @@ func (p *ProvisionerServer) Provision(args *ProvisionerProvisionArgs, reply *int
 
 	return nil
 }
+
+func (p *ProvisionerServer) Cancel(args *interface{}, reply *interface{}) error {
+	p.p.Cancel()
+	return nil
+}
diff --git a/packer/rpc/provisioner_test.go b/packer/rpc/provisioner_test.go
index 106ae62eb..e251d814f 100644
--- a/packer/rpc/provisioner_test.go
+++ b/packer/rpc/provisioner_test.go
@@ -7,32 +7,11 @@ import (
 	"testing"
 )
 
-type testProvisioner struct {
-	prepareCalled  bool
-	prepareConfigs []interface{}
-	provCalled     bool
-	provComm       packer.Communicator
-	provUi         packer.Ui
-}
-
-func (p *testProvisioner) Prepare(configs ...interface{}) error {
-	p.prepareCalled = true
-	p.prepareConfigs = configs
-	return nil
-}
-
-func (p *testProvisioner) Provision(ui packer.Ui, comm packer.Communicator) error {
-	p.provCalled = true
-	p.provComm = comm
-	p.provUi = ui
-	return nil
-}
-
 func TestProvisionerRPC(t *testing.T) {
 	assert := asserts.NewTestingAsserts(t, true)
 
 	// Create the interface to test
-	p := new(testProvisioner)
+	p := new(packer.MockProvisioner)
 
 	// Start the server
 	server := rpc.NewServer()
@@ -47,17 +26,23 @@ func TestProvisionerRPC(t *testing.T) {
 	config := 42
 	pClient := Provisioner(client)
 	pClient.Prepare(config)
-	assert.True(p.prepareCalled, "prepare should be called")
-	assert.Equal(p.prepareConfigs, []interface{}{42}, "prepare should be called with right arg")
+	assert.True(p.PrepCalled, "prepare should be called")
+	assert.Equal(p.PrepConfigs, []interface{}{42}, "prepare should be called with right arg")
 
 	// Test Provision
 	ui := &testUi{}
-	comm := new(packer.MockCommunicator)
+	comm := &packer.MockCommunicator{}
 	pClient.Provision(ui, comm)
-	assert.True(p.provCalled, "provision should be called")
+	assert.True(p.ProvCalled, "provision should be called")
 
-	p.provUi.Say("foo")
+	p.ProvUi.Say("foo")
 	assert.True(ui.sayCalled, "say should be called")
+
+	// Test Cancel
+	pClient.Cancel()
+	if !p.CancelCalled {
+		t.Fatal("cancel should be called")
+	}
 }
 
 func TestProvisioner_Implements(t *testing.T) {
diff --git a/packer/template_test.go b/packer/template_test.go
index 398e48975..2e3fbc672 100644
--- a/packer/template_test.go
+++ b/packer/template_test.go
@@ -589,7 +589,7 @@ func TestTemplate_Build(t *testing.T) {
 		"test-builder": builder,
 	}
 
-	provisioner := &TestProvisioner{}
+	provisioner := &MockProvisioner{}
 	provisionerMap := map[string]Provisioner{
 		"test-prov": provisioner,
 	}
@@ -677,7 +677,7 @@ func TestTemplate_Build_ProvisionerOverride(t *testing.T) {
 		"test-builder": builder,
 	}
 
-	provisioner := &TestProvisioner{}
+	provisioner := &MockProvisioner{}
 	provisionerMap := map[string]Provisioner{
 		"test-prov": provisioner,
 	}
diff --git a/provisioner/chef-solo/provisioner.go b/provisioner/chef-solo/provisioner.go
index 2d255375d..fe96ad467 100644
--- a/provisioner/chef-solo/provisioner.go
+++ b/provisioner/chef-solo/provisioner.go
@@ -183,6 +183,12 @@ func (p *Provisioner) Provision(ui packer.Ui, comm packer.Communicator) error {
 	return nil
 }
 
+func (p *Provisioner) Cancel() {
+	// Just hard quit. It isn't a big deal if what we're doing keeps
+	// running on the other side.
+	os.Exit(0)
+}
+
 func (p *Provisioner) uploadDirectory(ui packer.Ui, comm packer.Communicator, dst string, src string) error {
 	if err := p.createDir(ui, comm, dst); err != nil {
 		return err
diff --git a/provisioner/file/provisioner.go b/provisioner/file/provisioner.go
index c49047f65..096b10437 100644
--- a/provisioner/file/provisioner.go
+++ b/provisioner/file/provisioner.go
@@ -84,3 +84,9 @@ func (p *Provisioner) Provision(ui packer.Ui, comm packer.Communicator) error {
 	}
 	return err
 }
+
+func (p *Provisioner) Cancel() {
+	// Just hard quit. It isn't a big deal if what we're doing keeps
+	// running on the other side.
+	os.Exit(0)
+}
diff --git a/provisioner/salt-masterless/provisioner.go b/provisioner/salt-masterless/provisioner.go
index 24d29097c..8e0f11f1f 100644
--- a/provisioner/salt-masterless/provisioner.go
+++ b/provisioner/salt-masterless/provisioner.go
@@ -200,6 +200,12 @@ func (p *Provisioner) Provision(ui packer.Ui, comm packer.Communicator) error {
 	return nil
 }
 
+func (p *Provisioner) Cancel() {
+	// Just hard quit. It isn't a big deal if what we're doing keeps
+	// running on the other side.
+	os.Exit(0)
+}
+
 func UploadLocalDirectory(localDir string, remoteDir string, comm packer.Communicator, ui packer.Ui) (err error) {
 	visitPath := func(localPath string, f os.FileInfo, err error) (err2 error) {
 		localRelPath := strings.Replace(localPath, localDir, "", 1)
diff --git a/provisioner/shell/provisioner.go b/provisioner/shell/provisioner.go
index 29799cba9..e8a5f61a5 100644
--- a/provisioner/shell/provisioner.go
+++ b/provisioner/shell/provisioner.go
@@ -281,6 +281,12 @@ func (p *Provisioner) Provision(ui packer.Ui, comm packer.Communicator) error {
 	return nil
 }
 
+func (p *Provisioner) Cancel() {
+	// Just hard quit. It isn't a big deal if what we're doing keeps
+	// running on the other side.
+	os.Exit(0)
+}
+
 // retryable will retry the given function over and over until a
 // non-error is returned.
 func (p *Provisioner) retryable(f func() error) error {