platform: fix reversed bytes.Contains arguments in CheckMachine's systemd state check

platform/platform.go

@@ -341,6 +341,19 @@ func NewMachines(c Cluster, userdata *conf.UserData, n int) ([]Machine, error) {
 	return machs, nil
 }
 
+// systemRunningState classifies `systemctl is-system-running` output. keep
+// is true while still on the way to "running"; anything else, including
+// empty output, means stop retrying.
+func systemRunningState(raw []byte) (state string, keep bool) {
+	state = strings.TrimSpace(string(raw))
+	switch state {
+	case "initializing", "starting", "running", "stopping":
+		return state, true
+	default:
+		return state, false
+	}
+}
+
 // CheckMachine tests a machine for various error conditions such as ssh
 // being available and no systemd units failing at the time ssh is reachable.
 // It also ensures the remote system is running Flatcar Container Linux.
@@ -353,11 +366,12 @@ func CheckMachine(ctx context.Context, m Machine) error {
 			return err
 		}
 		out, stderr, err := m.SSH("systemctl is-system-running")
-		if !bytes.Contains([]byte("initializing starting running stopping"), out) {
+		state, keep := systemRunningState(out)
+		if !keep {
 			return nil // stop retrying if the system went haywire, e.g., "degraded"
 		}
 		jobs := ""
-		if bytes.Contains([]byte("starting"), out) {
+		if state == "starting" {
 			startingOut, startingStderr, startingErr := m.SSH("systemctl list-jobs")
 			jobs = fmt.Sprintf(", systemctl list-jobs returned stdout: %q, stderr: %q, err: %v", startingOut, startingStderr, startingErr)
 		}

platform/platform_test.go

@@ -0,0 +1,48 @@
+// Copyright 2026 The Flatcar Maintainers.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package platform
+
+import "testing"
+
+func TestSystemRunningState(t *testing.T) {
+	tests := []struct {
+		name      string
+		raw       string
+		wantState string
+		wantKeep  bool
+	}{
+		{"running", "running", "running", true},
+		{"running with trailing newline", "running\n", "running", true},
+		{"initializing", "initializing", "initializing", true},
+		{"starting", "starting", "starting", true},
+		{"stopping", "stopping", "stopping", true},
+		{"degraded", "degraded", "degraded", false},
+		{"maintenance", "maintenance", "maintenance", false},
+		{"offline", "offline", "offline", false},
+		// A blank/empty SSH response (e.g. a transient connection hiccup)
+		// must not be mistaken for an in-progress state.
+		{"empty output", "", "", false},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			gotState, gotKeep := systemRunningState([]byte(tt.raw))
+			if gotState != tt.wantState || gotKeep != tt.wantKeep {
+				t.Errorf("systemRunningState(%q) = (%q, %v), want (%q, %v)",
+					tt.raw, gotState, gotKeep, tt.wantState, tt.wantKeep)
+			}
+		})
+	}
+}