ERROR: cannot verify tk.sdklib.com's certificate, issued by ‘/C=US/O=Let's Encrypt/CN=R3’:
Issued certificate has expired.

1.刚开始我输入的指令是这样的

wget https://pjreddie.com/media/files/yolov3-tiny.weights

2.发现报错 ERROR: cannot verify pjreddie.com's certificate, issued by /C=US/O=Let's Encrypt/CN=Let's Encrypt Authority X3': Unable to locally verify the issuer's authority. To connect to pjreddie.com insecurely, use--no-check-certificate'.
无法建立 SSL 连接。（这里报错是因为总是要先检查网站证书，而这样大多数时候会报错，这个时候加上--no-check-certificate就可以解决问题了）

3.解决方法

wget --no-check-certificate http://pjreddie.com/media/files/yolov3-tiny.weights

然后就成功了，成功下载