demo.txt

root@k8s:~# cat pod.yaml
apiVersion: v1
kind: Pod
metadata:
  name: admin
spec:
  containers:
    - name: shell
      image: ubuntu:22.04
      command: ["sleep", "infinity"]
      securityContext:
        privileged: true
  hostNetwork: true
  hostPID: true
  hostIPC: true

root@k8s:~# cat test.sh
#!/bin/bash
while true; do
        echo "alive"
        sleep 1
done

root@k8s:~# k exec -it admin -- bash
root@k8s:/# nsenter -t 1 -m -p -n -i -u systemd-run --unit test -- /root/test.sh
Running as unit: test.service
root@k8s:/# exit
exit

root@k8s:~# systemctl status test
● test.service - /root/test.sh
     Loaded: loaded (/run/systemd/transient/test.service; transient)
  Transient: yes
     Active: active (running) since Tue 2024-03-26 06:32:20 UTC; 9s ago
   Main PID: 45729 (test.sh)
      Tasks: 2 (limit: 19043)
     Memory: 532.0K
        CPU: 14ms
     CGroup: /system.slice/test.service
             ├─45729 /bin/bash /root/test.sh
             └─45818 sleep 1

Mar 26 06:32:20 k8s test.sh[45729]: alive
Mar 26 06:32:21 k8s test.sh[45729]: alive
Mar 26 06:32:22 k8s test.sh[45729]: alive
Mar 26 06:32:23 k8s test.sh[45729]: alive
Mar 26 06:32:24 k8s test.sh[45729]: alive
Mar 26 06:32:25 k8s test.sh[45729]: alive
Mar 26 06:32:26 k8s test.sh[45729]: alive
Mar 26 06:32:27 k8s test.sh[45729]: alive
Mar 26 06:32:28 k8s test.sh[45729]: alive
Mar 26 06:32:29 k8s test.sh[45729]: alive

root@k8s:~# ps -ef | grep test.sh
root       45729       1  0 06:32 ?        00:00:00 /bin/bash /root/test.sh
root       47075    1758  0 06:34 pts/0    00:00:00 grep --color=auto test.sh

  
  
root@k8s:~# k delete -f pod.yaml
pod "admin" deleted

root@k8s:~# systemctl status test
● test.service - /root/test.sh
     Loaded: loaded (/run/systemd/transient/test.service; transient)
  Transient: yes
     Active: active (running) since Tue 2024-03-26 06:32:20 UTC; 4min 3s ago
   Main PID: 45729 (test.sh)
      Tasks: 2 (limit: 19043)
     Memory: 580.0K
        CPU: 308ms
     CGroup: /system.slice/test.service
             ├─45729 /bin/bash /root/test.sh
             └─48153 sleep 1

Mar 26 06:36:14 k8s test.sh[45729]: alive
Mar 26 06:36:15 k8s test.sh[45729]: alive
Mar 26 06:36:16 k8s test.sh[45729]: alive
Mar 26 06:36:17 k8s test.sh[45729]: alive
Mar 26 06:36:18 k8s test.sh[45729]: alive
Mar 26 06:36:19 k8s test.sh[45729]: alive
Mar 26 06:36:20 k8s test.sh[45729]: alive
Mar 26 06:36:21 k8s test.sh[45729]: alive
Mar 26 06:36:22 k8s test.sh[45729]: alive
Mar 26 06:36:23 k8s test.sh[45729]: alive