Ubuntu18.04，默认自带python2和python3，如果只想安装python3环境下的virtualenv，可以采用下面的方法
1. pip3 install virtualenv
2. pip3 install virtualenvwrapper
3.mkdir $HOME/.virtualenvs
4.vim ~/.bashrc
在文本的最后添加：
export WORKON_HOME=$HOME/.virtualenvs
export PROJECT_HOME=$HOME/ENV
source ~/.local/bin/virtualenvwrapper.sh
但是以上操作完成后，每次打开终端，都会出现如下界面
Command '' not found, but can be installed with:
sudo apt install libpam-mount
sudo apt install openssh-server
sudo apt install openvswitch-common
sudo apt install openvswitch-switch
sudo apt install php-common
sudo apt install bpfcc-tools
sudo apt install burp
sudo apt install cryptmount
sudo apt install dolphin-emu
sudo apt install mailutils-mh
sudo apt install mmh
sudo apt install nmh
virtualenvwrapper.sh: There was a problem running the initialization hooks.
If Python could not import the module virtualenvwrapper.hook_loader,
check that virtualenvwrapper has been installed for
VIRTUALENVWRAPPER_PYTHON= and that PATH is
set properly.
并且此时用workvirtualenv 命令无法创建虚拟空间，这主要是因为，我们配置的是python3下的虚拟环境，但是系统还是默认调用python2的配置文件，但是python2我们并没有配置，所以我们要修改配置文件
5. cd .local/bin
vim virtualenvwrapper.sh
在文件中将VIRTUALENVWRAPPER_PYTHON="$(command \which python)"改为 VIRTUALENVWRAPPER_PYTHON="$(command \which python3)"
完成以上5步，虚拟环境便可以正常使用了