今天用pip安装软件包，死活安装不上，出现如下错误：
Retrying (Retry(total=4, connect=None, read=None, redirect=None, status=None)) after connection broken by 'NewConnectionError('<pip._vendor.urllib3.connection.VerifiedHTTPSConnection object at 0x10f5a7748>: Failed to establish a new connection: [Errno 8] nodename nor servname provided, or not known')': /packages/5c/e0/be401c003291b56efc55aeba6a80ab790d3d4cece2778288d65323009420/pip-19.1.1-py2.py3-none-any.whl
Retrying (Retry(total=3, connect=None, read=None, redirect=None, status=None)) after connection broken by 'NewConnectionError('<pip._vendor.urllib3.connection.VerifiedHTTPSConnection object at 0x10f5a7668>: Failed to establish a new connection: [Errno 8] nodename nor servname provided, or not known')': /packages/5c/e0/be401c003291b56efc55aeba6a80ab790d3d4cece2778288d65323009420/pip-19.1.1-py2.py3-none-any.whl
Retrying (Retry(total=2, connect=None, read=None, redirect=None, status=None)) after connection broken by 'NewConnectionError('<pip._vendor.urllib3.connection.VerifiedHTTPSConnection object at 0x10f5a76a0>: Failed to establish a new connection: [Errno 8] nodename nor servname provided, or not known')': /packages/5c/e0/be401c003291b56efc55aeba6a80ab790d3d4cece2778288d65323009420/pip-19.1.1-py2.py3-none-any.whl
Retrying (Retry(total=1, connect=None, read=None, redirect=None, status=None)) after connection broken by 'NewConnectionError('<pip._vendor.urllib3.connection.VerifiedHTTPSConnection object at 0x10f5a7860>: Failed to establish a new connection: [Errno 8] nodename nor servname provided, or not known')': /packages/5c/e0/be401c003291b56efc55aeba6a80ab790d3d4cece2778288d65323009420/pip-19.1.1-py2.py3-none-any.whl
Retrying (Retry(total=0, connect=None, read=None, redirect=None, status=None)) after connection broken by 'NewConnectionError('<pip._vendor.urllib3.connection.VerifiedHTTPSConnection object at 0x10f5a7978>: Failed to establish a new connection: [Errno 8] nodename nor servname provided, or not known')': /packages/5c/e0/be401c003291b56efc55aeba6a80ab790d3d4cece2778288d65323009420/pip-19.1.1-py2.py3-none-any.whl
Could not install packages due to an EnvironmentError: HTTPSConnectionPool(host='files.pythonhosted.org', port=443): Max retries exceeded with url: /packages/5c/e0/be401c003291b56efc55aeba6a80ab790d3d4cece2778288d65323009420/pip-19.1.1-py2.py3-none-any.whl (Caused by NewConnectionError('<pip._vendor.urllib3.connection.VerifiedHTTPSConnection object at 0x10f5a7b00>: Failed to establish a new connection: [Errno 8] nodename nor servname provided, or not known'))
还以为是特定软件包的问题，很快发现升级pip也有问题。
网上找了一圈，把代理、vpn等都关了，问题依旧。仔细看错误的最后一行，看到有files.pythonhosted.org这个域名，心想难道这个域名挂了？
ping这个域名，竟然提示解析错误。于是登陆到境外的服务器上ping，解析正常。想到应该是dns解析问题，接着把dns换成了1.1.1.1和8.8.8.8，再次安装，问题顺利解决。