render images on headless ubuntu server

I am trying to render images via a Unity build on an Ubuntu ssh server without a graphical interface. In the player log file the render is always a null device. How do I get a renderer?

In windows 10 it works even in -batchmode it finds a renderer and save the "test_pic".

I am also trying to debug this issue with a Ubuntu virtual machine but in the log file it also says: " No supported renderers found, exiting". When I am using the -bachmode cammand line argument it saves an image but it is gray because there is no renderer.

Thank you for any help I am stuck on this problem for a while now...

If you need any further information please let me know.

I have the following script attached to the camera:

 public class test : MonoBehaviour
     {
         void Start()
         {
             StartCoroutine(CapturePNGasBytes());
         }
     
         private IEnumerator CapturePNGasBytes()
         {
             Camera currentCamera = GetComponent<Camera>();
             yield return new WaitForEndOfFrame();
     
             int width = new int();
             int height = new int();
             width = 256;
             height = 256;
             //create rendertexture, Texture2D and 
             RenderTexture rt = new RenderTexture(width, height, 24, RenderTextureFormat.ARGB32);
             Texture2D sceneTexture = new Texture2D(width, height, TextureFormat.RGB24, false);
             Rect rectangle = new Rect(0,0,width,height);
     
     
             currentCamera.targetTexture = rt;
             currentCamera.Render();
             RenderTexture.active = rt;
             sceneTexture.ReadPixels(rectangle,0,0);
             sceneTexture.Apply();
     
             //clean up
             currentCamera.targetTexture = null;
             RenderTexture.active = null;
     
             //save image
             byte[] bytesPNG = sceneTexture.EncodeToPNG();
             System.IO.File.WriteAllBytes("test_pic.PNG", bytesPNG);
         }    
 }

My PlayerLog file:

 Multi-casting "[IP] 129.206.117.192 [Port] 55137 [Flags] 3 [Guid] 3521465150 [EditorId] 3375015719 [Version] 1048832 [Id] LinuxPlayer(129.206.117.192) [Debug] 1 [PackageName] LinuxPlayer" to [225.0.0.222:54997]...
     Waiting for connection from host on [0.0.0.0:55137]...
     Remaining time:8s
     Remaining time:7s
     Remaining time:6s
     Remaining time:5s
     Remaining time:4s
     Remaining time:3s
     Remaining time:2s
     Remaining time:1s
     Remaining time:0s
     Timed out. Continuing without host connection.
     Started listening to [0.0.0.0:55137]
     Starting managed debugger on port 56150
     Using monoOptions --debugger-agent=transport=dt_socket,embedding=1,server=y,suspend=n,address=0.0.0.0:56150
     Preloaded 'ScreenSelector.so'
     PlayerConnection already initialized - listening to [0.0.0.0:55137]
     Initialize engine version: 2019.2.10f1 (923acd2d43aa)
     [XR] Discovering subsystems at path /net/hcihome/storage/rhaecker/scratch/documents/newupload/testpic_Data/UnitySubsystems
     Forcing GfxDevice: Null
     GfxDevice: creating device client; threaded=0
     NullGfxDevice:
         Version:  NULL 1.0 [1.0]
         Renderer: Null Device
         Vendor:   Unity Technologies
     Begin MonoManager ReloadAssembly
     - Completed reload, in  0.341 seconds
     UnloadTime: 1.052370 ms
     Setting up 16 worker threads for Enlighten.
       Thread -> id: 7f8366fb2700 -> priority: 1 
       Thread -> id: 7f83667b1700 -> priority: 1 
       Thread -> id: 7f8365fb0700 -> priority: 1 
       Thread -> id: 7f83657af700 -> priority: 1 
       Thread -> id: 7f8364fae700 -> priority: 1 
       Thread -> id: 7f8343fff700 -> priority: 1 
       Thread -> id: 7f83437fe700 -> priority: 1 
       Thread -> id: 7f8342ffd700 -> priority: 1 
       Thread -> id: 7f83427fc700 -> priority: 1 
       Thread -> id: 7f8341ffb700 -> priority: 1 
       Thread -> id: 7f83417fa700 -> priority: 1 
       Thread -> id: 7f8340ff9700 -> priority: 1 
       Thread -> id: 7f8323fff700 -> priority: 1 
       Thread -> id: 7f83237fe700 -> priority: 1 
       Thread -> id: 7f8322ffd700 -> priority: 1 
       Thread -> id: 7f83227fc700 -> priority: 1 
     ##utp:{"type":"MemoryLeaks","version":2,"phase":"Immediate","time":1572882315208,"processId":7294,"allocatedMemory":5259,"memoryLabels":[{"Default":1584},{"NewDelete":109},{"Thread":-192},{"Manager":256},{"Audio":192},{"Physics":32},{"Serialization":40},{"Terrain":88},{"String":1886},{"DynamicArray":64},{"PoolAlloc":-88},{"VR":1288}]}
     Comment