Couldn't open file backup/yolov3-voc.backup on Ubuntu 18.04

[snowuyl]

I would like to train YOLOv3 for detecting person only on Ubuntu 18.04 without GPU. But the following error message occurred.

./darknet detector train cfg/voc.data cfg/yolov3-voc.cfg ./darknet53.conv.74 -gpus 0,1 | tee -a helmet1.txt
OpenCV version: 4.1.2
[yolo] params: iou loss: mse (2), iou_norm: 0.75, cls_norm: 1.00, scale_x_y: 1.00
Total BFLOPS 65.304
Loading weights from ./darknet53.conv.74...
seen 64
batch = 4, time_steps = 1, train = 1
Done! Loaded 75 layers from weights-file

./darknet detector train cfg/voc.data cfg/yolov3-voc.cfg backup/yolov3-voc.backup -gpus 0,1 | tee -a train7.log
OpenCV version: 4.1.2
[yolo] params: iou loss: mse (2), iou_norm: 0.75, cls_norm: 1.00, scale_x_y: 1.00
Total BFLOPS 65.304
Loading weights from backup/yolov3-voc.backup...0,1
yolov3-voc
batch = 4, time_steps = 1, train = 1
Couldn't open file: backup/yolov3-voc.backup
Can't_open_yolov3-voc.backup.zip