1.教程
https://www.linuxidc.com/Linux/2019-03/157199.htm
2.密鑰錯誤，則：這個可以用
sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys F42ED6FBAB17C654
3.
sudo rosdep init
此時，卻遇到了一個問題
ERROR: cannot download default sources list from: https://raw.github.com/ros/rosdistro/master/rosdep/sources.list.d/20-default.list Website may be down.
解法1：該問題可能是The Great Wall的原因，反正在開啟VPN之后此問題得到了解決，有時通過手機熱點也能成功，可能是網絡問題。
解法2：修改/ros/rosdep/source.list.d/20-default.list文件（githubusercontent全改為github）（這種方法還沒試過）
解法3：在/etc目錄下新建/ros/rosdep/sources.list.d/20-default.list 寫入以下代碼：
# os-specific listings first yaml https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/osx-homebrew.yaml osx # generic yaml https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/base.yaml yaml https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/python.yaml yaml https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/ruby.yaml gbpdistro https://raw.githubusercontent.com/ros/rosdistro/master/releases/fuerte.yaml fuerte # newer distributions (Groovy, Hydro, ...) must not be listed anymore, they are being fetched from the rosdistro index.yaml instead
注：這里雖然手動新建了20-default.list，但執行sudo rosdep init依然會出現之前的錯誤，這里我們無視，繼續執行下一步。會在下一步出現問題：
4. rosdep update 出現以下問題：
reading in sources list data from /etc/ros/rosdep/sources.list.d ERROR: unable to process source [https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/osx-homebrew.yaml]: <urlopen error [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed (_ssl.c:590)> (https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/osx-homebrew.yaml) ERROR: unable to process source [https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/base.yaml]: <urlopen error [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed (_ssl.c:590)> (https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/base.yaml) ERROR: unable to process source [https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/python.yaml]: <urlopen error [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed (_ssl.c:590)> (https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/python.yaml) ERROR: unable to process source [https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/ruby.yaml]: <urlopen error [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed (_ssl.c:590)> (https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/ruby.yaml) ERROR: unable to process source [https://raw.githubusercontent.com/ros/rosdistro/master/releases/fuerte.yaml]: Failed to download target platform data for gbpdistro: <urlopen error [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed (_ssl.c:590)> Query rosdistro index https://raw.githubusercontent.com/ros/rosdistro/master/index-v4.yaml ERROR: error loading sources list: <urlopen error <urlopen error [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed (_ssl.c:590)> (https://raw.githubusercontent.com/ros/rosdistro/master/index-v4.yaml)>
解決：
在/usr/lib/python2.7/dist-packages/rosdep2/sources_list.py中頂部直接插入兩行代碼取消SSL驗證
import ssl
ssl._create_default_https_context = ssl._create_unverified_context
再次rosdep update 成功升級，至此終於完成rosdep初始化，問題解決，大功告成。
轉自
https://zhuanlan.zhihu.com/p/77483614
感謝大神。另外，最好把自己的安裝環境作成系統盤，避免一次又一次的配置環境。祝好！！！