到最后环节一直提示缺少文件错误

[icase]

creating build/temp.linux-x86_64-2.7/build/temp.linux-x86_64-2.7
x86_64-linux-gnu-gcc -pthread -DNDEBUG -g -fwrapv -O2 -Wall -Wstrict-prototypes -fno-strict-aliasing -Wdate-time -D_FORTIFY_SOURCE=2 -g -fstack-protector-strong -Wformat -Werror=format-security -fPIC -I/usr/include/python2.7 -c build/temp.linux-x86_64-2.7/_openssl.c -o build/temp.linux-x86_64-2.7/build/temp.linux-x86_64-2.7/_openssl.o
x86_64-linux-gnu-gcc: internal compiler error: Killed (program cc1)
Please submit a full bug report,
with preprocessed source if appropriate.
See file:///usr/share/doc/gcc-5/README.Bugs for instructions.
error: command 'x86_64-linux-gnu-gcc' failed with exit status 4

----------------------------------------

Command "/root/.local/share/letsencrypt/bin/python2.7 -u -c "import setuptools, tokenize;file='/tmp/pip-build-PsNnf0/cryptography/setup.py';exec(compile(getattr(tokenize, 'open', open)(file).read().replace('
', '
'), file, 'exec'))" install --record /tmp/pip-evrzHW-record/install-record.txt --single-version-externally-managed --compile --install-headers /root/.local/share/letsencrypt/include/site/python2.7/cryptography" failed with error code 1 in /tmp/pip-build-PsNnf0/cryptography
You are using pip version 8.0.3, however version 9.0.1 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.

Ubuntu 16.04，然后升级pip，但提示已经是9.0.1了