add basic systemd service monitoring (#1153)

Co-authored-by: Shelby Tucker <shelby.tucker@gmail.com>

agent/systemd.go

@@ -0,0 +1,229 @@
+//go:build linux
+
+package agent
+
+import (
+	"context"
+	"errors"
+	"log/slog"
+	"maps"
+	"math"
+	"strconv"
+	"strings"
+	"sync"
+	"time"
+
+	"github.com/coreos/go-systemd/v22/dbus"
+	"github.com/henrygd/beszel/internal/entities/systemd"
+)
+
+var (
+	errNoActiveTime = errors.New("no active time")
+)
+
+// systemdManager manages the collection of systemd service statistics.
+type systemdManager struct {
+	sync.Mutex
+	serviceStatsMap map[string]*systemd.Service
+	isRunning       bool
+	hasFreshStats   bool
+}
+
+// newSystemdManager creates a new systemdManager.
+func newSystemdManager() (*systemdManager, error) {
+	conn, err := dbus.NewSystemConnectionContext(context.Background())
+	if err != nil {
+		slog.Warn("Error connecting to systemd", "err", err, "ref", "https://beszel.dev/guide/systemd")
+		return nil, err
+	}
+
+	manager := &systemdManager{
+		serviceStatsMap: make(map[string]*systemd.Service),
+	}
+
+	manager.startWorker(conn)
+
+	return manager, nil
+}
+
+func (sm *systemdManager) startWorker(conn *dbus.Conn) {
+	if sm.isRunning {
+		return
+	}
+	sm.isRunning = true
+	// prime the service stats map with the current services
+	_ = sm.getServiceStats(conn, true)
+	// update the services every 10 minutes
+	go func() {
+		for {
+			time.Sleep(time.Minute * 10)
+			_ = sm.getServiceStats(nil, true)
+		}
+	}()
+}
+
+// getServiceStats collects statistics for all running systemd services.
+func (sm *systemdManager) getServiceStats(conn *dbus.Conn, refresh bool) []*systemd.Service {
+	// start := time.Now()
+	// defer func() {
+	// 	slog.Info("systemdManager.getServiceStats", "duration", time.Since(start))
+	// }()
+
+	var services []*systemd.Service
+	var err error
+
+	if !refresh {
+		// return nil
+		sm.Lock()
+		defer sm.Unlock()
+		for _, service := range sm.serviceStatsMap {
+			services = append(services, service)
+		}
+		sm.hasFreshStats = false
+		return services
+	}
+
+	if conn == nil || !conn.Connected() {
+		conn, err = dbus.NewSystemConnectionContext(context.Background())
+		if err != nil {
+			return nil
+		}
+		defer conn.Close()
+	}
+
+	units, err := conn.ListUnitsByPatternsContext(context.Background(), []string{"loaded"}, []string{"*.service"})
+	if err != nil {
+		slog.Error("Error listing systemd service units", "err", err)
+		return nil
+	}
+
+	for _, unit := range units {
+		service, err := sm.updateServiceStats(conn, unit)
+		if err != nil {
+			continue
+		}
+		services = append(services, service)
+	}
+	sm.hasFreshStats = true
+	return services
+}
+
+// updateServiceStats updates the statistics for a single systemd service.
+func (sm *systemdManager) updateServiceStats(conn *dbus.Conn, unit dbus.UnitStatus) (*systemd.Service, error) {
+	sm.Lock()
+	defer sm.Unlock()
+
+	ctx := context.Background()
+
+	// if service has never been active (no active since time), skip it
+	if activeEnterTsProp, err := conn.GetUnitTypePropertyContext(ctx, unit.Name, "Unit", "ActiveEnterTimestamp"); err == nil {
+		if ts, ok := activeEnterTsProp.Value.Value().(uint64); !ok || ts == 0 || ts == math.MaxUint64 {
+			return nil, errNoActiveTime
+		}
+	} else {
+		return nil, err
+	}
+
+	service, serviceExists := sm.serviceStatsMap[unit.Name]
+	if !serviceExists {
+		service = &systemd.Service{Name: unescapeServiceName(strings.TrimSuffix(unit.Name, ".service"))}
+		sm.serviceStatsMap[unit.Name] = service
+	}
+
+	memPeak := service.MemPeak
+	if memPeakProp, err := conn.GetUnitTypePropertyContext(ctx, unit.Name, "Service", "MemoryPeak"); err == nil {
+		// If memPeak is MaxUint64 the api is saying it's not available
+		if v, ok := memPeakProp.Value.Value().(uint64); ok && v != math.MaxUint64 {
+			memPeak = v
+		}
+	}
+
+	var memUsage uint64
+	if memProp, err := conn.GetUnitTypePropertyContext(ctx, unit.Name, "Service", "MemoryCurrent"); err == nil {
+		// If memUsage is MaxUint64 the api is saying it's not available
+		if v, ok := memProp.Value.Value().(uint64); ok && v != math.MaxUint64 {
+			memUsage = v
+		}
+	}
+
+	service.State = systemd.ParseServiceStatus(unit.ActiveState)
+	service.Sub = systemd.ParseServiceSubState(unit.SubState)
+
+	// some systems always return 0 for mem peak, so we should update the peak if the current usage is greater
+	if memUsage > memPeak {
+		memPeak = memUsage
+	}
+
+	var cpuUsage uint64
+	if cpuProp, err := conn.GetUnitTypePropertyContext(ctx, unit.Name, "Service", "CPUUsageNSec"); err == nil {
+		if v, ok := cpuProp.Value.Value().(uint64); ok {
+			cpuUsage = v
+		}
+	}
+
+	service.Mem = memUsage
+	if memPeak > service.MemPeak {
+		service.MemPeak = memPeak
+	}
+	service.UpdateCPUPercent(cpuUsage)
+
+	return service, nil
+}
+
+// getServiceDetails collects extended information for a specific systemd service.
+func (sm *systemdManager) getServiceDetails(serviceName string) (systemd.ServiceDetails, error) {
+	conn, err := dbus.NewSystemConnectionContext(context.Background())
+	if err != nil {
+		return nil, err
+	}
+	defer conn.Close()
+
+	unitName := serviceName
+	if !strings.HasSuffix(unitName, ".service") {
+		unitName += ".service"
+	}
+
+	ctx := context.Background()
+	props, err := conn.GetUnitPropertiesContext(ctx, unitName)
+	if err != nil {
+		return nil, err
+	}
+
+	// Start with all unit properties
+	details := make(systemd.ServiceDetails)
+	maps.Copy(details, props)
+
+	// // Add service-specific properties
+	servicePropNames := []string{
+		"MainPID", "ExecMainPID", "TasksCurrent", "TasksMax",
+		"MemoryCurrent", "MemoryPeak", "MemoryLimit", "CPUUsageNSec",
+		"NRestarts", "ExecMainStartTimestampRealtime", "Result",
+	}
+
+	for _, propName := range servicePropNames {
+		if variant, err := conn.GetUnitTypePropertyContext(ctx, unitName, "Service", propName); err == nil {
+			value := variant.Value.Value()
+			// Check if the value is MaxUint64, which indicates unlimited/infinite
+			if uint64Value, ok := value.(uint64); ok && uint64Value == math.MaxUint64 {
+				// Set to nil to indicate unlimited - frontend will handle this appropriately
+				details[propName] = nil
+			} else {
+				details[propName] = value
+			}
+		}
+	}
+
+	return details, nil
+}
+
+// unescapeServiceName unescapes systemd service names that contain C-style escape sequences like \x2d
+func unescapeServiceName(name string) string {
+	if !strings.Contains(name, "\\x") {
+		return name
+	}
+	unescaped, err := strconv.Unquote("\"" + name + "\"")
+	if err != nil {
+		return name
+	}
+	return unescaped
+}