You can use Canvas to draw a View by the following code: 
    public Bitmap createViewBitmap(View v)
    {
        Bitmap bitmap = Bitmap.CreateBitmap(v.Width, v.Height,
                Bitmap.Config.Argb8888);
        Canvas canvas = new Canvas(bitmap);
        v.Draw(canvas);
        return bitmap;
    }
Linear layout is a kind of View. So you can create a Linear layout BitMap : 
 View v = FindViewById<LinearLayout>(Resource.Id.myLinearLayout);
 Bitmap myBitMap = createViewBitmap(v);
And then save it in the DCIM folder: 
 public static void saveImage(Bitmap bmp)
 {
      try
      {
          using (var os = new System.IO.FileStream(Android.OS.Environment.ExternalStorageDirectory + "/DCIM/Camera/MikeBitMap2.jpg", System.IO.FileMode.CreateNew))
           {
               bmp.Compress(Bitmap.CompressFormat.Jpeg, 95, os);
           }
       }
       catch (Exception e)
       {
       }
   }

You can refer to my github for the more code information.