安裝Jenkins在Kubernetes集群中需要以下步驟：

1. 創建一個Jenkins的命名空間：

kubectl create namespace jenkins

2. 創建一個PersistentVolumeClaim（持久化存儲）來存儲Jenkins數據：

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: jenkins-pvc
  namespace: jenkins
spec:
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 5Gi

3. 安裝Jenkins的相關配置文件，例如Deployment和Service：

apiVersion: apps/v1
kind: Deployment
metadata:
  name: jenkins
  namespace: jenkins
spec:
  replicas: 1
  selector:
    matchLabels:
      app: jenkins
  template:
    metadata:
      labels:
        app: jenkins
    spec:
      containers:
      - name: jenkins
        image: jenkins/jenkins
        ports:
        - containerPort: 8080
        volumeMounts:
        - name: jenkins-data
          mountPath: /var/jenkins_home
      volumes:
      - name: jenkins-data
        persistentVolumeClaim:
          claimName: jenkins-pvc

---
apiVersion: v1
kind: Service
metadata:
  name: jenkins
  namespace: jenkins
spec:
  selector:
    app: jenkins
  ports:
    - protocol: TCP
      port: 80
      targetPort: 8080
  type: NodePort

4. 應用這些配置文件：

kubectl apply -f jenkins-deployment.yaml
kubectl apply -f jenkins-service.yaml

5. 查找Jenkins的端口號，并使用瀏覽器訪問Jenkins的UI：

kubectl get svc jenkins -n jenkins

這樣就完成了在Kubernetes集群中安裝Jenkins的步驟。