diff --git a/usersession/agent/export_test.go b/usersession/agent/export_test.go
index 472e1ebe073..36b1d1243b5 100644
--- a/usersession/agent/export_test.go
+++ b/usersession/agent/export_test.go
@@ -19,7 +19,22 @@
 
 package agent
 
+import (
+	"time"
+)
+
 var (
 	SessionInfoCmd = sessionInfoCmd
 	ServicesCmd    = servicesCmd
 )
+
+func MockStopTimeouts(stop, kill time.Duration) (restore func()) {
+	oldStopTimeout := stopTimeout
+	stopTimeout = stop
+	oldKillWait := killWait
+	killWait = kill
+	return func() {
+		stopTimeout = oldStopTimeout
+		killWait = oldKillWait
+	}
+}
diff --git a/usersession/agent/rest_api.go b/usersession/agent/rest_api.go
index 02f17291221..e241e66dbbb 100644
--- a/usersession/agent/rest_api.go
+++ b/usersession/agent/rest_api.go
@@ -65,10 +65,13 @@ type serviceInstruction struct {
 	Services []string `json:"services"`
 }
 
-var killWait = 5 * time.Second
+var (
+	stopTimeout = time.Duration(timeout.DefaultTimeout)
+	killWait    = 5 * time.Second
+)
 
 func stopOneService(service string, sysd systemd.Systemd) error {
-	err := sysd.Stop(service, time.Duration(timeout.DefaultTimeout))
+	err := sysd.Stop(service, stopTimeout)
 	if err != nil && systemd.IsTimeout(err) {
 		// ignore errors for kill; nothing we'd do differently at this point
 		sysd.Kill(service, "TERM", "")
@@ -86,7 +89,7 @@ func serviceStart(inst *serviceInstruction, sysd systemd.Systemd) Response {
 		}
 	}
 
-	var startErrors map[string]string
+	startErrors := make(map[string]string)
 	var started []string
 	for _, service := range inst.Services {
 		if err := sysd.Start(service); err != nil {
@@ -114,7 +117,7 @@ func serviceStop(inst *serviceInstruction, sysd systemd.Systemd) Response {
 		}
 	}
 
-	var stopErrors map[string]string
+	stopErrors := make(map[string]string)
 	for _, service := range inst.Services {
 		if err := stopOneService(service, sysd); err != nil {
 			stopErrors[service] = err.Error()
diff --git a/usersession/agent/rest_api_test.go b/usersession/agent/rest_api_test.go
index 2692a0ddbf8..2acf221fd6d 100644
--- a/usersession/agent/rest_api_test.go
+++ b/usersession/agent/rest_api_test.go
@@ -57,6 +57,8 @@ func (s *restSuite) SetUpTest(c *C) {
 	s.AddCleanup(restore)
 	restore = systemd.MockStopDelays(time.Millisecond, 25*time.Second)
 	s.AddCleanup(restore)
+	restore = agent.MockStopTimeouts(20*time.Millisecond, time.Millisecond)
+	s.AddCleanup(restore)
 }
 
 func (s *restSuite) TearDownTest(c *C) {
@@ -141,7 +143,7 @@ func (s *restSuite) TestServicesStart(c *C) {
 	var rsp resp
 	c.Assert(json.Unmarshal(rec.Body.Bytes(), &rsp), IsNil)
 	c.Check(rsp.Type, Equals, agent.ResponseTypeSync)
-	c.Check(rsp.Result, IsNil)
+	c.Check(rsp.Result, DeepEquals, map[string]interface{}{})
 
 	c.Check(s.sysdLog, DeepEquals, [][]string{
 		{"--user", "start", "snap.foo.service"},
@@ -149,6 +151,66 @@ func (s *restSuite) TestServicesStart(c *C) {
 	})
 }
 
+func (s *restSuite) TestServicesStartNonSnap(c *C) {
+	_, err := agent.New()
+	c.Assert(err, IsNil)
+
+	req, err := http.NewRequest("POST", "/v1/services", bytes.NewBufferString(`{"action":"start","services":["snap.foo.service", "not-snap.bar.service"]}`))
+	req.Header.Set("Content-Type", "application/json")
+	c.Assert(err, IsNil)
+	rec := httptest.NewRecorder()
+	agent.ServicesCmd.POST(agent.ServicesCmd, req).ServeHTTP(rec, req)
+	c.Check(rec.Code, Equals, 500)
+	c.Check(rec.HeaderMap.Get("Content-Type"), Equals, "application/json")
+
+	var rsp resp
+	c.Assert(json.Unmarshal(rec.Body.Bytes(), &rsp), IsNil)
+	c.Check(rsp.Type, Equals, agent.ResponseTypeError)
+	c.Check(rsp.Result, DeepEquals, map[string]interface{}{
+		"message": "cannot start service not-snap.bar.service",
+	})
+
+	// No services were started on the error.
+	c.Check(s.sysdLog, HasLen, 0)
+}
+
+func (s *restSuite) TestServicesStartFailureStopsServices(c *C) {
+	var sysdLog [][]string
+	restore := systemd.MockSystemctl(func(cmd ...string) ([]byte, error) {
+		sysdLog = append(sysdLog, cmd)
+		if cmd[0] == "--user" && cmd[1] == "start" && cmd[2] == "snap.bar.service" {
+			return nil, fmt.Errorf("start failure")
+		}
+		return []byte("ActiveState=inactive\n"), nil
+	})
+	defer restore()
+
+	_, err := agent.New()
+	c.Assert(err, IsNil)
+
+	req, err := http.NewRequest("POST", "/v1/services", bytes.NewBufferString(`{"action":"start","services":["snap.foo.service", "snap.bar.service"]}`))
+	req.Header.Set("Content-Type", "application/json")
+	c.Assert(err, IsNil)
+	rec := httptest.NewRecorder()
+	agent.ServicesCmd.POST(agent.ServicesCmd, req).ServeHTTP(rec, req)
+	c.Check(rec.Code, Equals, 200)
+	c.Check(rec.HeaderMap.Get("Content-Type"), Equals, "application/json")
+
+	var rsp resp
+	c.Assert(json.Unmarshal(rec.Body.Bytes(), &rsp), IsNil)
+	c.Check(rsp.Type, Equals, agent.ResponseTypeSync)
+	c.Check(rsp.Result, DeepEquals, map[string]interface{}{
+		"snap.bar.service": "start failure",
+	})
+
+	c.Check(sysdLog, DeepEquals, [][]string{
+		{"--user", "start", "snap.foo.service"},
+		{"--user", "start", "snap.bar.service"},
+		{"--user", "stop", "snap.foo.service"},
+		{"--user", "show", "--property=ActiveState", "snap.foo.service"},
+	})
+}
+
 func (s *restSuite) TestServicesStop(c *C) {
 	_, err := agent.New()
 	c.Assert(err, IsNil)
@@ -164,7 +226,7 @@ func (s *restSuite) TestServicesStop(c *C) {
 	var rsp resp
 	c.Assert(json.Unmarshal(rec.Body.Bytes(), &rsp), IsNil)
 	c.Check(rsp.Type, Equals, agent.ResponseTypeSync)
-	c.Check(rsp.Result, IsNil)
+	c.Check(rsp.Result, DeepEquals, map[string]interface{}{})
 
 	c.Check(s.sysdLog, DeepEquals, [][]string{
 		{"--user", "stop", "snap.foo.service"},
@@ -173,3 +235,66 @@ func (s *restSuite) TestServicesStop(c *C) {
 		{"--user", "show", "--property=ActiveState", "snap.bar.service"},
 	})
 }
+
+func (s *restSuite) TestServicesStopNonSnap(c *C) {
+	_, err := agent.New()
+	c.Assert(err, IsNil)
+
+	req, err := http.NewRequest("POST", "/v1/services", bytes.NewBufferString(`{"action":"stop","services":["snap.foo.service", "not-snap.bar.service"]}`))
+	req.Header.Set("Content-Type", "application/json")
+	c.Assert(err, IsNil)
+	rec := httptest.NewRecorder()
+	agent.ServicesCmd.POST(agent.ServicesCmd, req).ServeHTTP(rec, req)
+	c.Check(rec.Code, Equals, 500)
+	c.Check(rec.HeaderMap.Get("Content-Type"), Equals, "application/json")
+
+	var rsp resp
+	c.Assert(json.Unmarshal(rec.Body.Bytes(), &rsp), IsNil)
+	c.Check(rsp.Type, Equals, agent.ResponseTypeError)
+	c.Check(rsp.Result, DeepEquals, map[string]interface{}{
+		"message": "cannot stop service not-snap.bar.service",
+	})
+
+	// No services were started on the error.
+	c.Check(s.sysdLog, HasLen, 0)
+}
+
+func (s *restSuite) TestServicesStopFallbackToKill(c *C) {
+	var sysdLog [][]string
+	restore := systemd.MockSystemctl(func(cmd ...string) ([]byte, error) {
+		// Ignore "show" spam
+		if cmd[1] != "show" {
+			sysdLog = append(sysdLog, cmd)
+		}
+		if cmd[len(cmd)-1] == "snap.bar.service" {
+			return []byte("ActiveState=active\n"), nil
+		}
+		return []byte("ActiveState=inactive\n"), nil
+	})
+	defer restore()
+
+	_, err := agent.New()
+	c.Assert(err, IsNil)
+
+	req, err := http.NewRequest("POST", "/v1/services", bytes.NewBufferString(`{"action":"stop","services":["snap.foo.service", "snap.bar.service"]}`))
+	req.Header.Set("Content-Type", "application/json")
+	c.Assert(err, IsNil)
+	rec := httptest.NewRecorder()
+	agent.ServicesCmd.POST(agent.ServicesCmd, req).ServeHTTP(rec, req)
+	c.Check(rec.Code, Equals, 200)
+	c.Check(rec.HeaderMap.Get("Content-Type"), Equals, "application/json")
+
+	var rsp resp
+	c.Assert(json.Unmarshal(rec.Body.Bytes(), &rsp), IsNil)
+	c.Check(rsp.Type, Equals, agent.ResponseTypeSync)
+	c.Check(rsp.Result, DeepEquals, map[string]interface{}{
+		"snap.bar.service": "snap.bar.service failed to stop: timeout",
+	})
+
+	c.Check(sysdLog, DeepEquals, [][]string{
+		{"--user", "stop", "snap.foo.service"},
+		{"--user", "stop", "snap.bar.service"},
+		{"--user", "kill", "snap.bar.service", "-s", "TERM", "--kill-who=all"},
+		{"--user", "kill", "snap.bar.service", "-s", "KILL", "--kill-who=all"},
+	})
+}