问题是我们的公司防火墙
原始问题：
尝试在Alpine（Docker）中安装py2-pip或py3-pip时，如果安装py-setuptools时出现“权限被拒绝”错误，则失败。
我以root用户身份运行。
/ # apk add -v py2-pip
(1/1) Installing py-setuptools (40.6.3-r0)
ERROR: py-setuptools-40.6.3-r0: Permission denied
1 error; 42 packages, 313 dirs, 8008 files, 194 MiB
可以直接复制：
docker run -ti alpine sh -c 'apk update && apk add py2-pip'
docker run -ti alpine sh -c 'apk update && apk add py2-pip'
fetch http://dl-cdn.alpinelinux.org/alpine/v3.9/main/x86_64/APKINDEX.tar.gz
fetch http://dl-cdn.alpinelinux.org/alpine/v3.9/community/x86_64/APKINDEX.tar.gz
v3.9.2-47-ge6bacb23e0 [http://dl-cdn.alpinelinux.org/alpine/v3.9/main]
v3.9.2-46-g5f44785996 [http://dl-cdn.alpinelinux.org/alpine/v3.9/community]
OK: 9758 distinct packages available
(1/12) Installing libbz2 (1.0.6-r6)
(2/12) Installing expat (2.2.6-r0)
(3/12) Installing libffi (3.2.1-r6)
(4/12) Installing gdbm (1.13-r1)
(5/12) Installing ncurses-terminfo-base (6.1_p20190105-r0)
(6/12) Installing ncurses-terminfo (6.1_p20190105-r0)
(7/12) Installing ncurses-libs (6.1_p20190105-r0)
(8/12) Installing readline (7.0.003-r1)
(9/12) Installing sqlite-libs (3.26.0-r3)
(10/12) Installing python2 (2.7.15-r3)
(11/12) Installing py-setuptools (40.6.3-r0)
ERROR: py-setuptools-40.6.3-r0: Permission denied
(12/12) Installing py2-pip (18.1-r0)
Executing busybox-1.29.3-r10.trigger
1 error; 62 MiB in 25 packages
似乎正在尝试返回返回403的网络资源：
sendto(7, "GET /alpine/v3.9/main/x86_64/py-"..., 67, MSG_NOSIGNAL, NULL, 0) = 67
sendto(7, "Host: dl-cdn.alpinelinux.org\r\n", 30, MSG_NOSIGNAL, NULL, 0) = 30
sendto(7, "User-Agent: libfetch/2.0\r\n", 26, MSG_NOSIGNAL, NULL, 0) = 26
sendto(7, "\r\n", 2, MSG_NOSIGNAL, NULL, 0) = 2
setsockopt(7, SOL_TCP, TCP_NODELAY, [1], 4) = 0
read(7, "HTTP/1.1 403 Forbidden\r\nDate: Th"..., 1024) = 1024
close(7) = 0
wr) = 6
writev(2, [{iov_base="", iov_len=0}, {iov_base="ERROR: ", iov_len=7}], 2ERROR: ) = 7
writev(2, [{iov_base="py-setuptools-40.6.3-r0: Permiss"..., iov_len=42}, {iov_base=NULL, iov_len=0}], 2py
-setuptools-40.6.3-r0: Permission denied) = 42