- apt tool
- fontconfig
- ssh login without password
 http://www.linuxproblem.org/art_9.html
 https://www.tecmint.com/ssh-passwordless-login-using-ssh-keygen-in-5-easy-steps/
- how to use scp
 https://twpower.github.io/138-send-file-using-scp-command
Linux/BSD 초급
- grep
- ln -s
- Ubuntu, Debian, OpenBSD directory hierarchy
 https://en.wikipedia.org/wiki/Unix_filesystem#Conventional_directory_layout
 https://en.wikipedia.org/wiki/Filesystem_Hierarchy_Standard