【问题】bzip2 --version 2>&1 < /dev/null

https://unix.stackexchange.com/questions/230887/what-does-dev-null-mean

https://stackoverflow.com/questions/29142/getting-ssh-to-execute-a-command-in-the-background-on-target-machine

https://unix.stackexchange.com/questions/27955/the-usage-of-dev-null-in-the-command-line