问题描述：这里需要下载kitti的3D检测数据，从一个raw.githubusercontent.com的网站上进行wget下载txt文件，但是返回无法访问的错误。Connecting to raw.githubusercontent.com (raw.githubusercontent.com)|0.0.0.0|:443… failed: Connection refused.
解决方法：
1）通过ip查询网站（https://site.ip138.com/raw.Githubusercontent.com/），查找raw.githubusercontent.com的IP地址
2）在linux的 /etc/hosts 路径上，添加上诉查询到的IP，sudo vi /etc/hosts
此时，发现raw.githubusercontent.com可以正常ping通，重新执行命令：
wget -c https://raw.githubusercontent.com/traveller59/second.pytorch/master/second/data/ImageSets/test.txt --no-check-certificate --content-disposition -O ./data/kitti/ImageSets/test.txt
可以正常执行，问题解决。
执行过程：
```python (base) lab@user-AS-5014A-TT:~/LLC/PointCloud$ wget -c https://raw.githubusercontent.com/traveller59/second.pytorch/master/second/data/ImageSets/test.txt --2022-10-12 10:21:16-- https://raw.githubusercontent.com/traveller59/second.pytorch/master/second/data/ImageSets/test.txt Resolving raw.githubusercontent.com (raw.githubusercontent.com)... 185.199.111.133, 185.199.108.133, 185.199.110.133 Connecting to raw.githubusercontent.com (raw.githubusercontent.com)|185.199.111.133|:443... connected. HTTP request sent, awaiting response... 200 OK Length: 52625 (51K) [text/plain] Saving to: ‘test.txt’ test.txt 100%[===============================================>] 51.39K --.-KB/s in 0.08s 2022-10-12 10:21:16 (672 KB/s) - ‘test.txt’ saved [52625/52625] (base) lab@user-AS-5014A-TT:~/LLC/PointCloud/mmdetection3d$ wget -c https://raw.githubusercontent.com/traveller59/second.pytorch/master/second/data/ImageSets/trainval.txt --no-check-certificate --content-disposition -O ./data/kitti/ImageSets/trainval.txt --2022-10-12 10:27:05-- https://raw.githubusercontent.com/traveller59/second.pytorch/master/second/data/ImageSets/trainval.txt Resolving raw.githubusercontent.com (raw.githubusercontent.com)... 185.199.108.133, 185.199.110.133 Connecting to raw.githubusercontent.com (raw.githubusercontent.com)|185.199.108.133|:443... connected. HTTP request sent, awaiting response... 200 OK Length: 52366 (51K) [text/plain] --2022-10-12 10:27:05-- https://raw.githubusercontent.com/traveller59/second.pytorch/master/second/data/ImageSets/trainval.txt Reusing existing connection to raw.githubusercontent.com:443. HTTP request sent, awaiting response... 200 OK Length: 52366 (51K) [text/plain] Saving to: ‘./data/kitti/ImageSets/trainval.txt’ ./data/kitti/ImageSets/trainv 100%[===============================================>] 51.14K --.-KB/s in 0.08s 2022-10-12 10:27:06 (643 KB/s) - ‘./data/kitti/ImageSets/trainval.txt’ saved [52366/52366] (base) lab@user-AS-5014A-TT:~/LLC/PointCloud/mmdetection3d$ wget -c https://raw.githubusercontent.com/traveller59/second.pytorch/master/second/data/ImageSets/val.txt --no-check-certificate --content-disposition -O ./data/kitti/ImageSets/val.txt --2022-10-12 10:26:58-- https://raw.githubusercontent.com/traveller59/second.pytorch/master/second/data/ImageSets/val.txt Resolving raw.githubusercontent.com (raw.githubusercontent.com)... 185.199.108.133, 185.199.110.133 Connecting to raw.githubusercontent.com (raw.githubusercontent.com)|185.199.108.133|:443... connected. HTTP request sent, awaiting response... 200 OK Length: 26382 (26K) [text/plain] --2022-10-12 10:26:58-- https://raw.githubusercontent.com/traveller59/second.pytorch/master/second/data/ImageSets/val.txt Reusing existing connection to raw.githubusercontent.com:443. HTTP request sent, awaiting response... 200 OK Length: 26382 (26K) [text/plain] Saving to: ‘./data/kitti/ImageSets/val.txt’ ./data/kitti/ImageSets/val.tx 100%[===============================================>] 25.76K --.-KB/s in 0.02s 2022-10-12 10:26:58 (1.04 MB/s) - ‘./data/kitti/ImageSets/val.txt’ saved [26382/26382] (base) lab@user-AS-5014A-TT:~/LLC/PointCloud/mmdetection3d$ wget -c https://raw.githubusercontent.com/traveller59/second.pytorch/master/second/data/ImageSets/trainval.txt --no-check-certificate --content-disposition -O ./data/kitti/ImageSets/trainval.txt --2022-10-12 10:27:05-- https://raw.githubusercontent.com/traveller59/second.pytorch/master/second/data/ImageSets/trainval.txt Resolving raw.githubusercontent.com (raw.githubusercontent.com)... 185.199.108.133, 185.199.110.133 Connecting to raw.githubusercontent.com (raw.githubusercontent.com)|185.199.108.133|:443... connected. HTTP request sent, awaiting response... 200 OK Length: 52366 (51K) [text/plain] --2022-10-12 10:27:05-- https://raw.githubusercontent.com/traveller59/second.pytorch/master/second/data/ImageSets/trainval.txt Reusing existing connection to raw.githubusercontent.com:443. HTTP request sent, awaiting response... 200 OK Length: 52366 (51K) [text/plain] Saving to: ‘./data/kitti/ImageSets/trainval.txt’ ./data/kitti/ImageSets/trainv 100%[===============================================>] 51.14K --.-KB/s in 0.08s 2022-10-12 10:27:06 (643 KB/s) - ‘./data/kitti/ImageSets/trainval.txt’ saved [52366/52366]
感觉这个方法对于xxx.com 无法访问同样可以使用。
参考资料：
Ubuntu下连接raw.githubusercontent.com失败
