ubuntu18.04更新clang的版本

（可选）添加bionic相关的源

1. 备份/etc/apt/sources.list
2. 添加源到sources.list文件最后
sudo vim /etc/apt/sources.list
deb http://archive.ubuntu.com/ubuntu bionic main multiverse restricted universe
deb http://archive.ubuntu.com/ubuntu bionic-security main multiverse restricted universe
deb http://archive.ubuntu.com/ubuntu bionic-updates main multiverse restricted universe
3. 更新源
sudo apt update

安装相关版本的clang

sudo apt install clang-6.0
or
sudo apt install clang-9

添加配置选项

update-alternatives --install /usr/bin/clang++ clang++ /usr/bin/clang++-6.0 100
update-alternatives --install /usr/bin/clang++ clang++ /usr/bin/clang++-9 200

update-alternatives --install /usr/bin/clang clang /usr/bin/clang-6.0 100
update-alternatives --install /usr/bin/clang clang /usr/bin/clang-9 200

update-alternatives --config clang
update-alternatives --config clang++

install python 3.5 on ubuntu20.4

Step 1: Update and Refresh Repository Lists

Open a terminal window, and enter the following:

sudo apt update

Step 2: Install Supporting Software

The software-properties-common package gives you better control over your package manager by letting you add PPA (Personal Package Archive) repositories. Install the supporting software with the command:

sudo apt install software-properties-common

install additional software for python
Step 3: Add Deadsnakes PPA

Deadsnakes is a PPA with newer releases than the default Ubuntu repositories. Add the PPA by entering the following:

sudo add-apt-repository ppa:deadsnakes/ppa

The system will prompt you to press enter to continue. Do so, and allow it to finish. Refresh the package lists again:

sudo apt update

Step 4: Install Python 3

Now you can start the installation of Python 3.8 with the command:

sudo apt install python3.8


sudo update-alternatives --install /usr/bin/python python /usr/bin/python3.4 1
sudo update-alternatives --install /usr/bin/python python /usr/bin/python3.6 2

Then run :

sudo update-alternatives --config python