diff --git a/cmd/server/main.go b/cmd/server/main.go
index dee87ae..5fbe503 100644
--- a/cmd/server/main.go
+++ b/cmd/server/main.go
@@ -5,6 +5,7 @@ import (
 	"llamactl/pkg/config"
 	"llamactl/pkg/manager"
 	"llamactl/pkg/server"
+	"log"
 	"net/http"
 	"os"
 	"os/signal"
@@ -38,8 +39,7 @@ func main() {
 	configPath := os.Getenv("LLAMACTL_CONFIG_PATH")
 	cfg, err := config.LoadConfig(configPath)
 	if err != nil {
-		fmt.Printf("Error loading config: %v\n", err)
-		fmt.Println("Using default configuration.")
+		log.Printf("Error loading config: %v\nUsing default configuration.", err)
 	}
 
 	// Set version information
@@ -50,13 +50,11 @@ func main() {
 	// Create the data directory if it doesn't exist
 	if cfg.Instances.AutoCreateDirs {
 		if err := os.MkdirAll(cfg.Instances.InstancesDir, 0755); err != nil {
-			fmt.Printf("Error creating config directory %s: %v\n", cfg.Instances.InstancesDir, err)
-			fmt.Println("Persistence will not be available.")
+			log.Printf("Error creating config directory %s: %v\nPersistence will not be available.", cfg.Instances.InstancesDir, err)
 		}
 
 		if err := os.MkdirAll(cfg.Instances.LogsDir, 0755); err != nil {
-			fmt.Printf("Error creating log directory %s: %v\n", cfg.Instances.LogsDir, err)
-			fmt.Println("Instance logs will not be available.")
+			log.Printf("Error creating log directory %s: %v\nInstance logs will not be available.", cfg.Instances.LogsDir, err)
 		}
 	}
 
@@ -81,7 +79,7 @@ func main() {
 	go func() {
 		fmt.Printf("Llamactl server listening on %s:%d\n", cfg.Server.Host, cfg.Server.Port)
 		if err := server.ListenAndServe(); err != nil && err != http.ErrServerClosed {
-			fmt.Printf("Error starting server: %v\n", err)
+			log.Printf("Error starting server: %v\n", err)
 		}
 	}()
 
@@ -90,7 +88,7 @@ func main() {
 	fmt.Println("Shutting down server...")
 
 	if err := server.Close(); err != nil {
-		fmt.Printf("Error shutting down server: %v\n", err)
+		log.Printf("Error shutting down server: %v\n", err)
 	} else {
 		fmt.Println("Server shut down gracefully.")
 	}
diff --git a/pkg/config/config.go b/pkg/config/config.go
index 517a3c3..6df9e42 100644
--- a/pkg/config/config.go
+++ b/pkg/config/config.go
@@ -1,6 +1,7 @@
 package config
 
 import (
+	"fmt"
 	"log"
 	"os"
 	"path/filepath"
@@ -231,6 +232,11 @@ func LoadConfig(configPath string) (AppConfig, error) {
 		cfg.Instances.LogsDir = filepath.Join(cfg.Instances.DataDir, "logs")
 	}
 
+	// Validate port range
+	if cfg.Instances.PortRange[0] <= 0 || cfg.Instances.PortRange[1] <= 0 || cfg.Instances.PortRange[0] >= cfg.Instances.PortRange[1] {
+		return AppConfig{}, fmt.Errorf("invalid port range: %v", cfg.Instances.PortRange)
+	}
+
 	return cfg, nil
 }
 
diff --git a/pkg/instance/logger.go b/pkg/instance/logger.go
index f836411..681875b 100644
--- a/pkg/instance/logger.go
+++ b/pkg/instance/logger.go
@@ -7,13 +7,14 @@ import (
 	"os"
 	"strings"
 	"sync"
+	"sync/atomic"
 	"time"
 )
 
 type logger struct {
 	name        string
 	logDir      string
-	logFile     *os.File
+	logFile     atomic.Pointer[os.File]
 	logFilePath string
 	mu          sync.RWMutex
 }
@@ -47,11 +48,11 @@ func (i *logger) create() error {
 		return fmt.Errorf("failed to create stdout log file: %w", err)
 	}
 
-	i.logFile = logFile
+	i.logFile.Store(logFile)
 
 	// Write a startup marker to both files
 	timestamp := time.Now().Format("2006-01-02 15:04:05")
-	fmt.Fprintf(i.logFile, "\n=== Instance %s started at %s ===\n", i.name, timestamp)
+	fmt.Fprintf(logFile, "\n=== Instance %s started at %s ===\n", i.name, timestamp)
 
 	return nil
 }
@@ -102,11 +103,12 @@ func (i *logger) close() {
 	i.mu.Lock()
 	defer i.mu.Unlock()
 
-	if i.logFile != nil {
+	logFile := i.logFile.Swap(nil)
+	if logFile != nil {
 		timestamp := time.Now().Format("2006-01-02 15:04:05")
-		fmt.Fprintf(i.logFile, "=== Instance %s stopped at %s ===\n\n", i.name, timestamp)
-		i.logFile.Close()
-		i.logFile = nil
+		fmt.Fprintf(logFile, "=== Instance %s stopped at %s ===\n\n", i.name, timestamp)
+		logFile.Sync() // Ensure all buffered data is written to disk
+		logFile.Close()
 	}
 }
 
@@ -117,9 +119,9 @@ func (i *logger) readOutput(reader io.ReadCloser) {
 	scanner := bufio.NewScanner(reader)
 	for scanner.Scan() {
 		line := scanner.Text()
-		if i.logFile != nil {
-			fmt.Fprintln(i.logFile, line)
-			i.logFile.Sync() // Ensure data is written to disk
+		// Use atomic load to avoid lock contention on every line
+		if logFile := i.logFile.Load(); logFile != nil {
+			fmt.Fprintln(logFile, line)
 		}
 	}
 }
diff --git a/pkg/manager/lifecycle_test.go b/pkg/manager/lifecycle_test.go
index 520f445..822d798 100644
--- a/pkg/manager/lifecycle_test.go
+++ b/pkg/manager/lifecycle_test.go
@@ -10,7 +10,7 @@ import (
 )
 
 func TestInstanceTimeoutLogic(t *testing.T) {
-	testManager := createTestManager()
+	testManager := createTestManager(t)
 	defer testManager.Shutdown()
 
 	idleTimeout := 1 // 1 minute
@@ -42,7 +42,7 @@ func TestInstanceTimeoutLogic(t *testing.T) {
 }
 
 func TestInstanceWithoutTimeoutNeverExpires(t *testing.T) {
-	testManager := createTestManager()
+	testManager := createTestManager(t)
 	defer testManager.Shutdown()
 
 	noTimeoutInst := createInstanceWithTimeout(t, testManager, "no-timeout-test", "/path/to/model.gguf", nil)
@@ -64,7 +64,7 @@ func TestInstanceWithoutTimeoutNeverExpires(t *testing.T) {
 }
 
 func TestEvictLRUInstance_Success(t *testing.T) {
-	manager := createTestManager()
+	manager := createTestManager(t)
 	defer manager.Shutdown()
 
 	// Create 3 instances with idle timeout enabled (value doesn't matter for LRU logic)
@@ -121,7 +121,7 @@ func TestEvictLRUInstance_Success(t *testing.T) {
 }
 
 func TestEvictLRUInstance_NoRunningInstances(t *testing.T) {
-	manager := createTestManager()
+	manager := createTestManager(t)
 	defer manager.Shutdown()
 
 	err := manager.EvictLRUInstance()
@@ -134,7 +134,7 @@ func TestEvictLRUInstance_NoRunningInstances(t *testing.T) {
 }
 
 func TestEvictLRUInstance_OnlyEvictsTimeoutEnabledInstances(t *testing.T) {
-	manager := createTestManager()
+	manager := createTestManager(t)
 	defer manager.Shutdown()
 
 	// Create mix of instances: some with timeout enabled, some disabled
diff --git a/pkg/manager/manager.go b/pkg/manager/manager.go
index 3f3733a..679474d 100644
--- a/pkg/manager/manager.go
+++ b/pkg/manager/manager.go
@@ -54,16 +54,10 @@ func New(globalConfig *config.AppConfig) InstanceManager {
 
 	// Initialize port allocator
 	portRange := globalConfig.Instances.PortRange
-	ports, err := newPortAllocator(portRange[0], portRange[1])
-	if err != nil {
-		log.Fatalf("Failed to create port allocator: %v", err)
-	}
+	ports := newPortAllocator(portRange[0], portRange[1])
 
 	// Initialize persistence
-	persistence, err := newInstancePersister(globalConfig.Instances.InstancesDir)
-	if err != nil {
-		log.Fatalf("Failed to create instance persister: %v", err)
-	}
+	persistence := newInstancePersister(globalConfig.Instances.InstancesDir)
 
 	// Initialize remote manager
 	remote := newRemoteManager(globalConfig.Nodes, 30*time.Second)
@@ -116,7 +110,7 @@ func (im *instanceManager) Shutdown() {
 				defer wg.Done()
 				fmt.Printf("Stopping instance %s...\n", inst.Name)
 				if err := inst.Stop(); err != nil {
-					fmt.Printf("Error stopping instance %s: %v\n", inst.Name, err)
+					log.Printf("Error stopping instance %s: %v\n", inst.Name, err)
 				}
 			}(inst)
 		}
diff --git a/pkg/manager/manager_test.go b/pkg/manager/manager_test.go
index 22a5d7f..b03ea12 100644
--- a/pkg/manager/manager_test.go
+++ b/pkg/manager/manager_test.go
@@ -85,7 +85,7 @@ func TestDeleteInstance_RemovesPersistenceFile(t *testing.T) {
 }
 
 func TestConcurrentAccess(t *testing.T) {
-	mgr := createTestManager()
+	mgr := createTestManager(t)
 	defer mgr.Shutdown()
 
 	// Test concurrent operations
@@ -113,7 +113,7 @@ func TestConcurrentAccess(t *testing.T) {
 	}
 
 	// Concurrent list operations
-	for i := 0; i < 3; i++ {
+	for range 3 {
 		wg.Add(1)
 		go func() {
 			defer wg.Done()
@@ -134,16 +134,17 @@ func TestConcurrentAccess(t *testing.T) {
 
 // Helper functions for test configuration
 func createTestAppConfig(instancesDir string) *config.AppConfig {
-	// Use 'sleep' as a test command instead of 'llama-server'
-	// This allows tests to run in CI environments without requiring actual LLM binaries
-	// The sleep command will be invoked with model paths and other args, which it ignores
+	// Use 'sh -c "sleep 999999"' as a test command instead of 'llama-server'
+	// The shell ignores all additional arguments passed after the command
 	return &config.AppConfig{
 		Backends: config.BackendConfig{
 			LlamaCpp: config.BackendSettings{
-				Command: "sleep",
+				Command: "sh",
+				Args:    []string{"-c", "sleep 999999"},
 			},
 			MLX: config.BackendSettings{
-				Command: "sleep",
+				Command: "sh",
+				Args:    []string{"-c", "sleep 999999"},
 			},
 		},
 		Instances: config.InstancesConfig{
@@ -162,28 +163,8 @@ func createTestAppConfig(instancesDir string) *config.AppConfig {
 	}
 }
 
-func createTestManager() manager.InstanceManager {
-	appConfig := &config.AppConfig{
-		Backends: config.BackendConfig{
-			LlamaCpp: config.BackendSettings{
-				Command: "sleep",
-			},
-			MLX: config.BackendSettings{
-				Command: "sleep",
-			},
-		},
-		Instances: config.InstancesConfig{
-			PortRange:            [2]int{8000, 9000},
-			LogsDir:              "/tmp/test",
-			MaxInstances:         10,
-			MaxRunningInstances:  10,
-			DefaultAutoRestart:   true,
-			DefaultMaxRestarts:   3,
-			DefaultRestartDelay:  5,
-			TimeoutCheckInterval: 5,
-		},
-		LocalNode: "main",
-		Nodes:     map[string]config.NodeConfig{},
-	}
+func createTestManager(t *testing.T) manager.InstanceManager {
+	tempDir := t.TempDir()
+	appConfig := createTestAppConfig(tempDir)
 	return manager.New(appConfig)
 }
diff --git a/pkg/manager/operations.go b/pkg/manager/operations.go
index 6c815de..14b86a7 100644
--- a/pkg/manager/operations.go
+++ b/pkg/manager/operations.go
@@ -330,7 +330,8 @@ func (im *instanceManager) DeleteInstance(name string) error {
 	lock.Lock()
 	defer im.unlockAndCleanup(name)
 
-	if inst.IsRunning() {
+	status := inst.GetStatus()
+	if status == instance.Running || status == instance.Restarting {
 		return fmt.Errorf("instance with name %s is still running, stop it before deleting", name)
 	}
 
diff --git a/pkg/manager/operations_test.go b/pkg/manager/operations_test.go
index a0b82a4..870e907 100644
--- a/pkg/manager/operations_test.go
+++ b/pkg/manager/operations_test.go
@@ -10,7 +10,7 @@ import (
 )
 
 func TestCreateInstance_FailsWithDuplicateName(t *testing.T) {
-	mngr := createTestManager()
+	mngr := createTestManager(t)
 	options := &instance.Options{
 		BackendOptions: backends.Options{
 			BackendType: backends.BackendTypeLlamaCpp,
@@ -36,6 +36,7 @@ func TestCreateInstance_FailsWithDuplicateName(t *testing.T) {
 }
 
 func TestCreateInstance_FailsWhenMaxInstancesReached(t *testing.T) {
+	tempDir := t.TempDir()
 	appConfig := &config.AppConfig{
 		Backends: config.BackendConfig{
 			LlamaCpp: config.BackendSettings{
@@ -44,6 +45,7 @@ func TestCreateInstance_FailsWhenMaxInstancesReached(t *testing.T) {
 		},
 		Instances: config.InstancesConfig{
 			PortRange:            [2]int{8000, 9000},
+			InstancesDir:         tempDir,
 			MaxInstances:         1, // Very low limit for testing
 			TimeoutCheckInterval: 5,
 		},
@@ -77,7 +79,7 @@ func TestCreateInstance_FailsWhenMaxInstancesReached(t *testing.T) {
 }
 
 func TestCreateInstance_FailsWithPortConflict(t *testing.T) {
-	manager := createTestManager()
+	manager := createTestManager(t)
 
 	options1 := &instance.Options{
 		BackendOptions: backends.Options{
@@ -115,7 +117,7 @@ func TestCreateInstance_FailsWithPortConflict(t *testing.T) {
 }
 
 func TestInstanceOperations_FailWithNonExistentInstance(t *testing.T) {
-	manager := createTestManager()
+	manager := createTestManager(t)
 
 	options := &instance.Options{
 		BackendOptions: backends.Options{
@@ -143,7 +145,7 @@ func TestInstanceOperations_FailWithNonExistentInstance(t *testing.T) {
 }
 
 func TestDeleteInstance_RunningInstanceFails(t *testing.T) {
-	mgr := createTestManager()
+	mgr := createTestManager(t)
 	defer mgr.Shutdown()
 
 	options := &instance.Options{
@@ -155,15 +157,13 @@ func TestDeleteInstance_RunningInstanceFails(t *testing.T) {
 		},
 	}
 
-	_, err := mgr.CreateInstance("test-instance", options)
+	inst, err := mgr.CreateInstance("test-instance", options)
 	if err != nil {
 		t.Fatalf("CreateInstance failed: %v", err)
 	}
 
-	_, err = mgr.StartInstance("test-instance")
-	if err != nil {
-		t.Fatalf("StartInstance failed: %v", err)
-	}
+	// Simulate starting the instance
+	inst.SetStatus(instance.Running)
 
 	// Should fail to delete running instance
 	err = mgr.DeleteInstance("test-instance")
@@ -173,7 +173,7 @@ func TestDeleteInstance_RunningInstanceFails(t *testing.T) {
 }
 
 func TestUpdateInstance(t *testing.T) {
-	mgr := createTestManager()
+	mgr := createTestManager(t)
 	defer mgr.Shutdown()
 
 	options := &instance.Options{
@@ -186,14 +186,14 @@ func TestUpdateInstance(t *testing.T) {
 		},
 	}
 
-	_, err := mgr.CreateInstance("test-instance", options)
+	inst, err := mgr.CreateInstance("test-instance", options)
 	if err != nil {
 		t.Fatalf("CreateInstance failed: %v", err)
 	}
 
-	_, err = mgr.StartInstance("test-instance")
-	if err != nil {
-		t.Fatalf("StartInstance failed: %v", err)
+	// Start the instance (will use 'yes' command from test config)
+	if err := inst.Start(); err != nil {
+		t.Fatalf("Failed to start instance: %v", err)
 	}
 
 	// Update running instance with new model
@@ -212,9 +212,9 @@ func TestUpdateInstance(t *testing.T) {
 		t.Fatalf("UpdateInstance failed: %v", err)
 	}
 
-	// Should still be running after update
+	// Should be running after update (was running before, should be restarted)
 	if !updated.IsRunning() {
-		t.Error("Instance should be running after update")
+		t.Errorf("Instance should be running after update, got: %v", updated.GetStatus())
 	}
 
 	if updated.GetOptions().BackendOptions.LlamaServerOptions.Model != "/path/to/new-model.gguf" {
@@ -223,7 +223,7 @@ func TestUpdateInstance(t *testing.T) {
 }
 
 func TestUpdateInstance_ReleasesOldPort(t *testing.T) {
-	mgr := createTestManager()
+	mgr := createTestManager(t)
 	defer mgr.Shutdown()
 
 	options := &instance.Options{
diff --git a/pkg/manager/persistence.go b/pkg/manager/persistence.go
index 01fe11f..a106efe 100644
--- a/pkg/manager/persistence.go
+++ b/pkg/manager/persistence.go
@@ -15,35 +15,18 @@ import (
 type instancePersister struct {
 	mu           sync.Mutex
 	instancesDir string
-	enabled      bool
 }
 
 // newInstancePersister creates a new instance persister.
 // If instancesDir is empty, persistence is disabled.
-func newInstancePersister(instancesDir string) (*instancePersister, error) {
-	if instancesDir == "" {
-		return &instancePersister{
-			enabled: false,
-		}, nil
-	}
-
-	// Ensure the instances directory exists
-	if err := os.MkdirAll(instancesDir, 0755); err != nil {
-		return nil, fmt.Errorf("failed to create instances directory: %w", err)
-	}
-
+func newInstancePersister(instancesDir string) *instancePersister {
 	return &instancePersister{
 		instancesDir: instancesDir,
-		enabled:      true,
-	}, nil
+	}
 }
 
 // Save persists an instance to disk with atomic write
 func (p *instancePersister) save(inst *instance.Instance) error {
-	if !p.enabled {
-		return nil
-	}
-
 	if inst == nil {
 		return fmt.Errorf("cannot save nil instance")
 	}
@@ -103,10 +86,6 @@ func (p *instancePersister) save(inst *instance.Instance) error {
 
 // Delete removes an instance's persistence file from disk.
 func (p *instancePersister) delete(name string) error {
-	if !p.enabled {
-		return nil
-	}
-
 	validatedName, err := p.validateInstanceName(name)
 	if err != nil {
 		return err
@@ -131,10 +110,6 @@ func (p *instancePersister) delete(name string) error {
 // LoadAll loads all persisted instances from disk.
 // Returns a slice of instances and any errors encountered during loading.
 func (p *instancePersister) loadAll() ([]*instance.Instance, error) {
-	if !p.enabled {
-		return nil, nil
-	}
-
 	p.mu.Lock()
 	defer p.mu.Unlock()
 
diff --git a/pkg/manager/ports.go b/pkg/manager/ports.go
index 18a3787..dfea196 100644
--- a/pkg/manager/ports.go
+++ b/pkg/manager/ports.go
@@ -24,15 +24,7 @@ type portAllocator struct {
 }
 
 // newPortAllocator creates a new port allocator for the given port range.
-// Returns an error if the port range is invalid.
-func newPortAllocator(minPort, maxPort int) (*portAllocator, error) {
-	if minPort <= 0 || maxPort <= 0 {
-		return nil, fmt.Errorf("invalid port range: min=%d, max=%d (must be > 0)", minPort, maxPort)
-	}
-	if minPort > maxPort {
-		return nil, fmt.Errorf("invalid port range: min=%d > max=%d", minPort, maxPort)
-	}
-
+func newPortAllocator(minPort, maxPort int) *portAllocator {
 	rangeSize := maxPort - minPort + 1
 	bitmapSize := (rangeSize + 63) / 64 // Round up to nearest uint64
 
@@ -42,7 +34,7 @@ func newPortAllocator(minPort, maxPort int) (*portAllocator, error) {
 		minPort:   minPort,
 		maxPort:   maxPort,
 		rangeSize: rangeSize,
-	}, nil
+	}
 }
 
 // allocate finds and allocates the first available port for the given instance.
diff --git a/pkg/server/routes.go b/pkg/server/routes.go
index 6587601..618dbc0 100644
--- a/pkg/server/routes.go
+++ b/pkg/server/routes.go
@@ -1,7 +1,7 @@
 package server
 
 import (
-	"fmt"
+	"log"
 
 	"github.com/go-chi/chi/v5"
 	"github.com/go-chi/chi/v5/middleware"
@@ -159,7 +159,7 @@ func SetupRouter(handler *Handler) *chi.Mux {
 
 	// Serve WebUI files
 	if err := webui.SetupWebUI(r); err != nil {
-		fmt.Printf("Failed to set up WebUI: %v\n", err)
+		log.Printf("Failed to set up WebUI: %v\n", err)
 	}
 
 	return r