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

abbreviation