pwd ls detailed cd directories mkdir parents touch file copy file move file remove file

cat file head lines tail lines grep pattern cut fields sort lines uniq counts wc counts

stdout redirect append redirect stderr redirect pipe commands tee output here document command substitution xargs

chmod symbolic chmod numeric chown chgrp umask execute permission setuid concept sticky bit

ps process list pgrep kill signal jobs background process foreground job nice priority top batch view

tar create tar extract gzip gunzip find by name find by size locate concept du disk usage

ip address ss sockets curl request wget download ping host dig DNS ssh command scp copy

systemctl status journalctl unit df filesystem free memory environment variables export PATH cron entry shell script strict mode