• df -h report file system space usage

  -h,--human-readable
                print sizes in powers of 1024 (e.g., 1023M)
  

• free -h Display amount of free and used memory in the system

  -h,--human
                Show all output fields automatically scaled to shortest
                three digit unit and display the units of print out.
                Following units are used.
  
                  B = bytes
                  Ki = kibibyte
                  Mi = mebibyte
                  Gi = gibibyte
                  Ti = tebibyte
                  Pi = pebibyte
  
                If unit is missing, and you have exbibyte of RAM or swap,
                the number is in tebibytes and columns might not be
                aligned with header.
  

Vim

• delete all lines :%d
• delete whole line dd

In vi I use

:%d

where

• : tells vi to go in command mode
• % means all the lines
• d : delete

history 历史记录。 它显示了在终端中所执行过的所有命令的历史

Debian

• check version

  cat /etc/debian_version

sudo apt install htop