Detector Quick Start Guide

Get your first Tracee detector running in 30 minutes. This hands-on tutorial assumes basic Go knowledge but no prior Tracee experience.

What You'll Build

A detector that identifies when processes access sensitive system files like /etc/shadow or /etc/sudoers, with:

• Automatic threat metadata enrichment
• Full process ancestry (parent → grandparent → ...)
• Container context (if applicable)

Prerequisites

# Clone Tracee
git clone https://github.com/aquasecurity/tracee
cd tracee

# Verify build environment
make env

# Required: Linux kernel 4.18+, Go 1.24+, Clang 12+

Step 1: Create Your Detector File

Create detectors/sensitive_file_access.go:

package detectors

import (
    "context"

    "github.com/aquasecurity/tracee/api/v1beta1"
    "github.com/aquasecurity/tracee/api/v1beta1/detection"
)

// Auto-register the detector on startup
func init() {
    register(&SensitiveFileAccess{})
}

// SensitiveFileAccess detects access to sensitive system files
type SensitiveFileAccess struct {
    logger detection.Logger
}

// GetDefinition declares what this detector does and what it needs
func (d *SensitiveFileAccess) GetDefinition() detection.DetectorDefinition {
    return detection.DetectorDefinition{
        ID: "TRC-001",  // Unique identifier

        Requirements: detection.DetectorRequirements{
            Events: []detection.EventRequirement{
                {
                    Name: "security_file_open",
                    // Engine filters - only matching events reach OnEvent()
                    DataFilters: []string{
                        "pathname=/etc/shadow",
                        "pathname=/etc/sudoers",
                    },
                },
            },
        },

        // Define the output event this detector produces
        ProducedEvent: v1beta1.EventDefinition{
            Name:        "sensitive_file_access",
            Description: "Access to sensitive system files detected",
            Version: &v1beta1.Version{Major: 1, Minor: 0, Patch: 0},
            Fields: []*v1beta1.EventField{
                {Name: "file_path", Type: "const char*"},
                {Name: "executable", Type: "const char*"},
            },
        },

        // Threat information template (auto-copied to outputs)
        ThreatMetadata: &v1beta1.Threat{
            Name:        "Sensitive File Access",
            Description: "A process attempted to access a sensitive system file",
            Severity:    v1beta1.Severity_MEDIUM,
        },

        // Tell engine to auto-enrich our outputs
        AutoPopulate: detection.AutoPopulateFields{
            Threat:          true,  // Copy ThreatMetadata above
            DetectedFrom:    true,  // Link to triggering event
            ProcessAncestry: true,  // Add 5 levels of parent processes
        },
    }
}

// Init is called once at startup
func (d *SensitiveFileAccess) Init(params detection.DetectorParams) error {
    d.logger = params.Logger
    d.logger.Infow("SensitiveFileAccess detector initialized")
    return nil
}

// OnEvent processes each matching event
func (d *SensitiveFileAccess) OnEvent(
    ctx context.Context,
    event *v1beta1.Event,
) ([]detection.DetectorOutput, error) {
    // Type-safe data extraction
    pathname, found := v1beta1.GetData[string](event, "pathname")
    if !found {
        return nil, nil  // Skip if pathname missing
    }

    // Extract executable path (nil-safe protobuf getters)
    executablePath := event.GetWorkload().GetProcess().GetExecutable().GetPath()

    // Return output data - engine handles the rest (threat, ancestry, etc.)
    return []detection.DetectorOutput{{
        Data: []*v1beta1.EventValue{
            v1beta1.NewStringValue("file_path", pathname),
            v1beta1.NewStringValue("executable", executablePath),
        },
    }}, nil
}

Step 2: Build Tracee

# Build with your detector included
make tracee

# The detector is compiled in - no plugins or manual registration needed!

Step 3: Run Tracee

# Start Tracee with process tree and JSON output
sudo ./dist/tracee --stores process.source=both --output json | jq

Step 4: Trigger Your Detector

In a third terminal, access a sensitive file:

sudo cat /etc/shadow

Step 5: See the Detection

You should see output like:

{
  "id": 5001,
  "name": "sensitive_file_access",
  "version": "1.0.0",
  "timestamp": "2025-12-16T10:30:45.123Z",
  "threat": {
    "name": "Sensitive File Access",
    "description": "A process attempted to access a sensitive system file",
    "severity": "MEDIUM"
  },
  "data": {
    "file_path": "/etc/shadow",
    "executable": "/bin/cat"
  },
  "detected_from": {
    "event_id": 257,
    "event_name": "security_file_open"
  },
  "workload": {
    "process": {
      "entity_id": 12345,
      "pid": 67890,
      "executable": {"path": "/bin/cat"},
      "ancestors": [
        {"entity_id": 12344, "pid": 67889, "executable": {"path": "/bin/bash"}},
        {"entity_id": 12343, "pid": 67888, "thread": {"name": "sshd"}},
        {"entity_id": 1, "pid": 1, "thread": {"name": "systemd"}}
      ]
    }
  }
}

What Just Happened?

Let's break down the magic:

1. Auto-Registration

func init() {
    register(&SensitiveFileAccess{})
}

Your detector registered itself automatically. No manual list maintenance!

2. Engine Filtering

DataFilters: []string{
    "pathname=/etc/shadow",
    "pathname=/etc/sudoers",
},

Tracee's engine filtered millions of security_file_open events. Only those matching your paths reached OnEvent(). This happens in the engine - super efficient!

3. Type-Safe Extraction

pathname, found := v1beta1.GetData[string](event, "pathname")

Generic type parameter ensures compile-time type safety. No runtime casting errors!

4. Auto-Enrichment

AutoPopulate: detection.AutoPopulateFields{
    Threat:          true,
    DetectedFrom:    true,
    ProcessAncestry: true,
}

The engine automatically:

• ✅ Copied ThreatMetadata to output.Threat
• ✅ Set output.DetectedFrom pointing to the triggering event
• ✅ Queried the process tree and populated 5 ancestor levels
• ✅ Preserved timestamp, workload, and policies from input event

You just returned simple data fields - the engine did the heavy lifting!

Common Patterns

Multiple Outputs

A single input can produce multiple detections:

func (d *MyDetector) OnEvent(ctx context.Context, event *v1beta1.Event) ([]detection.DetectorOutput, error) {
    var outputs []detection.DetectorOutput

    // Check condition 1
    if isSuspicious {
        outputs = append(outputs, detection.DetectorOutput{
            Data: []*v1beta1.EventValue{
                v1beta1.NewStringValue("reason", "suspicious pattern"),
            },
        })
    }

    // Check condition 2
    if isMalicious {
        outputs = append(outputs, detection.DetectorOutput{
            Data: []*v1beta1.EventValue{
                v1beta1.NewStringValue("reason", "known malware signature"),
            },
        })
    }

    return outputs, nil
}

Custom Threat Severity

Override the default threat metadata per detection:

return []detection.DetectorOutput{{
    Data: []*v1beta1.EventValue{
        v1beta1.NewStringValue("file", pathname),
    },
    Threat: &v1beta1.Threat{
        Name:        "Critical System File Access",
        Severity:    v1beta1.Severity_CRITICAL,  // Override default MEDIUM
        Description: "Root accessed critical system file",
    },
}}, nil

Using DataStores

Access system state like process information:

func (d *MyDetector) OnEvent(ctx context.Context, event *v1beta1.Event) ([]detection.DetectorOutput, error) {
    entityId := event.GetWorkload().GetProcess().GetEntityId()

    // Query process store for process details
    proc, err := d.dataStores.Processes().GetProcess(entityId)
    if errors.Is(err, datastores.ErrNotFound) {
        // Process not in tree yet
        return nil, nil
    }
    if err != nil {
        return nil, err
    }

    // Use process info in detection logic
    if proc.GetInterpreter().GetPath() == "/bin/bash" {
        return []detection.DetectorOutput{{
            Data: []*v1beta1.EventValue{
                v1beta1.NewStringValue("shell", "bash"),
            },
        }}, nil
    }

    return nil, nil
}

Filtering by Container

Only detect events from containers:

Requirements: detection.DetectorRequirements{
    Events: []detection.EventRequirement{
        {
            Name: "security_file_open",
            ScopeFilters: []string{"container=started"},  // Containers only
        },
    },
}

Or only from host:

ScopeFilters: []string{"not-container"},  // Host only

Debugging Tips

Enable Debug Logging

# Run with debug logs
sudo ./dist/tracee --logging debug --stores process.source=both

Check Detector Registration

# List detector events
sudo ./dist/tracee list | grep detectors

Verify Event Filtering

Check that your event name is correct:

# List available events
sudo ./dist/tracee list | grep security_file_open

Test Without Filters

Temporarily remove DataFilters to see all events:

Requirements: detection.DetectorRequirements{
    Events: []detection.EventRequirement{
        {
            Name: "security_file_open",
            // DataFilters: []string{...},  // Commented out for testing
        },
    },
}

Add logging in OnEvent():

func (d *SensitiveFileAccess) OnEvent(ctx context.Context, event *v1beta1.Event) ([]detection.DetectorOutput, error) {
    d.logger.Debugw("Event received", "event", event.Name)
    // ... rest of logic
}

Next Steps

Congratulations! You've written your first Tracee detector. Now explore:

📚 Deep Dive into APIs

• API Reference: Complete detector API documentation
• DataStore API: Query process trees, containers, DNS, and more

🔄 Migration and Troubleshooting

• Migration Guide: Migrating from old signatures
• Troubleshooting: Common issues and solutions

🔍 Study Real Examples

• Browse detectors/ directory for production implementations
• See api/v1beta1/detection/detector.go for interface definitions

🧪 Write Tests

• Add unit tests in detectors/sensitive_file_access_test.go
• See Testing Guide for patterns

Troubleshooting

Detector Not Running

Problem: Your detector code changed but behavior didn't

Solution: Rebuild Tracee - detectors are compiled in, not dynamically loaded

make tracee

No Events Received

Problem: OnEvent() never called

Possible causes:

1. Wrong event name - check tracee list
2. Filters too restrictive - temporarily remove them
3. Event not enabled - Tracee enables events based on requirements automatically

Process Ancestry Empty

Problem: workload.process.ancestors is null

Solution: Enable process tree:

sudo ./dist/tracee --stores process.source=both

Build Errors

Problem: Compilation fails

Common fixes:

# Update dependencies
make go-tidy

# Clean build
make clean
make tracee

Quick Reference

Detector Skeleton

package detectors

import (
    "context"

    "github.com/aquasecurity/tracee/api/v1beta1"
    "github.com/aquasecurity/tracee/api/v1beta1/datastores"
    "github.com/aquasecurity/tracee/api/v1beta1/detection"
)

func init() {
    register(&MyDetector{})
}

type MyDetector struct {
    logger     detection.Logger
    dataStores datastores.Registry
}

func (d *MyDetector) GetDefinition() detection.DetectorDefinition {
    return detection.DetectorDefinition{
        ID: "TRC-XXX",
        Requirements: detection.DetectorRequirements{
            Events: []detection.EventRequirement{{Name: "event_name"}},
        },
        ProducedEvent: v1beta1.EventDefinition{
            Name:    "my_detection",
            Version: &v1beta1.Version{Major: 1},
        },
        AutoPopulate: detection.AutoPopulateFields{
            Threat:          true,
            DetectedFrom:    true,
            ProcessAncestry: true,
        },
    }
}

func (d *MyDetector) Init(params detection.DetectorParams) error {
    d.logger = params.Logger
    d.dataStores = params.DataStores
    return nil
}

func (d *MyDetector) OnEvent(ctx context.Context, event *v1beta1.Event) ([]detection.DetectorOutput, error) {
    // Your detection logic
    return []detection.DetectorOutput{{
        Data: []*v1beta1.EventValue{},
    }}, nil
}

Essential Commands

# Build
make tracee

# Run with process tree
sudo ./dist/tracee --stores process.source=both

# View detections in JSON
sudo ./dist/tracee --output json | jq

# List detector events
sudo ./dist/tracee list | grep detectors

# Debug mode
sudo ./dist/tracee --logging debug

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Ready for more? Continue to the API Reference for comprehensive documentation, including migration guides and troubleshooting.