1. ps------process status
2. tty-----teletype
3. ping----packet internet groper
4. nohup-----no hangup
5. su-------switch user
6. df--------disk free
7. cat--------concatenate
8. man-------manual
9. fsck---------file system check
10. chown-----change owner
11. fg-------foreground
12. bg-------background
13. chgrp-----change group
14. tar--------tape archive
15. apt-------advanced packet tool
16. etc--------etcetera
17. usr--------unix shared resources
18. var--------variable
19. grub-------grand unified bootloader
20. LILO------linux loader
21. awk-------aho weiberger and kernighan