今天用Ubuntu 发现有几个命令不能用，提示如下:
root@ubuntu:/# tree /home/
The program 'tree' is currently not installed. You can install it by typing:
apt install tree
然后找了找实际就是因为没有安装tree这个东西，执行安装
sudo apt-get install tree
然后再执行命令如下:
root@ubuntu:/home# tree /home/
/home/
└── lhw
├── Desktop
├── Documents
├── Downloads
│ └── sogoupinyin.deb
├── Music
├── Pictures
├── Public
├── Templates
└── Videos
9 directories, 1 file