Let's Encrypt会自动安装在用户宿主目录~/.local/下，今天在续期证书时报错：

Creating virtual environment...
Installing Python packages...
Installation succeeded.
Traceback (most recent call last):
  File "/root/.local/share/letsencrypt/bin/letsencrypt", line 7, in <module>
    from certbot.main import main
  File "/root/.local/share/letsencrypt/lib/python2.7/site-packages/certbot/main.py", line 13, in <module>
    from acme import jose
  File "/root/.local/share/letsencrypt/lib/python2.7/site-packages/acme/jose/__init__.py", line 37, in <module>
    from acme.jose.interfaces import JSONDeSerializable
  File "/root/.local/share/letsencrypt/lib/python2.7/site-packages/acme/jose/interfaces.py", line 9, in <module>
    from acme.jose import util
  File "/root/.local/share/letsencrypt/lib/python2.7/site-packages/acme/jose/util.py", line 5, in <module>
    import OpenSSL
  File "/root/.local/share/letsencrypt/lib/python2.7/site-packages/OpenSSL/__init__.py", line 8, in <module>
    from OpenSSL import rand, crypto, SSL
  File "/root/.local/share/letsencrypt/lib/python2.7/site-packages/OpenSSL/rand.py", line 12, in <module>
    from OpenSSL._util import (
  File "/root/.local/share/letsencrypt/lib/python2.7/site-packages/OpenSSL/_util.py", line 6, in <module>
    from cryptography.hazmat.bindings.openssl.binding import Binding
  File "/root/.local/share/letsencrypt/lib/python2.7/site-packages/cryptography/hazmat/bindings/openssl/binding.py", line 14, in <module>
    from cryptography.hazmat.bindings._openssl import ffi, lib
ImportError: /root/.local/share/letsencrypt/lib/python2.7/site-packages/cryptography/hazmat/bindings/_openssl.so: undefined symbol: OPENSSL_sk_num

原因是pip编译安装相应模块时调用到系统的openssl库，而系统openssl不支持OPENSSL_sk_num

由于我之前已经编译过新版的openssl放在/usr/local/openssl下，将第一步自动安装上的openssl-devel包删除，然后pip重新安装cryptography、pyopenssl即可。注意：需先清除安装缓存目录，否则安装时不会重新编译。

yum remove openssl-devel
cd ~/.local/share/letsencrypt/bin/
pip uninstall cryptography pyopenssl -y
pip install --upgrade pip
rm -rf ~/.cache/
pip install cryptography pyopenssl
ldd ~/.local/share/letsencrypt/lib/python2.7/site-packages/cryptography/hazmat/bindings/_openssl.so

此时已经链接到编译的openssl库上，这样再执行命令便不会报错。