背景：
内网环境，需要通过代理才能上网。运行 sudo pip install xxx时报错
报错1：
The directory '/home/xxx/.cache/pip/http' or its parent directory is not owned by the current user and the cache has been disabled. Please check the permissions and owner of that directory. If executing pip with sudo, you may want sudo's -H flag.
The directory '/home/xxx/.cache/pip' or its parent directory is not owned by the current user and caching wheels has been disabled. check the permissions and owner of that directory. If executing pip with sudo, you may want sudo's -H flag.
解决：sudo -H pip install xxx
报错2：
Retrying (Retry(total=4, connect=None, read=None, redirect=None)) after connection broken by 'NewConnectionError('<pip._vendor.requests.packages.urllib3.connection.VerifiedHTTPSConnection object at 0x7fce305f1fd0>: Failed to establish a new connection: [Errno -3] Temporary failure in name resolution',)': /simple/pip/
Retrying (Retry(total=3, connect=None, read=None, redirect=None)) after connection broken by 'NewConnectionError('<pip._vendor.requests.packages.urllib3.connection.VerifiedHTTPSConnection object at 0x7fce30599198>: Failed to establish a new connection: [Errno -3] Temporary failure in name resolution',)': /simple/pip/
Retrying (Retry(total=2, connect=None, read=None, redirect=None)) after connection broken by 'NewConnectionError('<pip._vendor.requests.packages.urllib3.connection.VerifiedHTTPSConnection object at 0x7fce30599278>: Failed to establish a new connection: [Errno -3] Temporary failure in name resolution',)': /simple/pip/
Retrying (Retry(total=1, connect=None, read=None, redirect=None)) after connection broken by 'NewConnectionError('<pip._vendor.requests.packages.urllib3.connection.VerifiedHTTPSConnection object at 0x7fce30599358>: Failed to establish a new connection: [Errno -3] Temporary failure in name resolution',)': /simple/pip/
Retrying (Retry(total=0, connect=None, read=None, redirect=None)) after connection broken by 'NewConnectionError('<pip._vendor.requests.packages.urllib3.connection.VerifiedHTTPSConnection object at 0x7fce30599438>: Failed to establish a new connection: [Errno -3] Temporary failure in name resolution',)': /simple/pip/
解决：设置代理，sudo -H pip --proxy=http://xxx.xxx.xx.xxx:8080 install