Unix and C Programming

1. Unix and CProgramming Dr. Cong Xing Dept. of Math & CMPS

2. Access to Unix/Linux • Our Unix/Linux – (www.nicholls.edu) • telnet in MS Windows • Unsecured • Not supported any more (by most Unix systems) • Putty – freeware, (telnet, ssh) • http://www.putty.nl/download.html • Login id and password • Id: ex: xing (lower case) • Password: set it up (first time login) • Change your password • Type passwdat prompt • Exit Unix • Type: logout

3. Introduction to Unix • Some useful terms: • Bit: a binary digit, either 0 or 1 • Byte: a grouping of 8 bits • Kilo (K): thousand (10^3) • Mega (M): million (10^6) • Giga (G): billion (10^9) • Hertz: used to measure clock speed. 1 hz = 1 pulse per second. 3 Ghz = 3 billion pulse per second.

5. Ex: What is the max memory space (in terms of bytes) can a 32-bit CPU address? 232 = 22 210 210 210 = 4GB memory 32-bit long register

6. Flops: short for floating point operations per second. Also used to measure the speed of computers. • The origin of Unix • Unix: The best OS people have written so far • Dennis Ritchie and Ken Thompson from AT&T • Multics – a failed OS, 1969 • GE, MIT, and AT&T (joint project)

7. Space Travel – a game • Space Travel rewritten on PDP-7 • Unix was born in 1971 • Naming: Unics (a pun on Multics)  Unix • Turning Award (1983) • http://awards.acm.org/homepage.cfm?srt=all&awd=140

9. Unix and C • Unix written initially in assembly language (PDP series) (non-portable) • In 1973, Unix was rewritten in C • C was made for writing Unix

10. Major Components of Unix • Kernel: master control program. It manages resources and handles multitasking. • File System: organization of data. • Shell: interface between users and kernel. It interprets user commands and passes them to kernel. • Utilities: software tools built in Unix.

11. utilities shell user File sys kernel

12. Versions of Unix • System V Unix: developed at AT&T. AT&T Unix is the original Unix. Most Unix systems on market are based on this. (e.g. IBM AIX and Sun Solaris) • BSD Unix: modified at Berkeley and as popular as AT&T Unix. (MacOS X is based on BSD Unix)

13. Unix-like systems: systems that work much like Unix, but do not use any part of AT&T Unix. (e.g. Linux and Minix) • X Window System • A GUI for Unix, developed at MIT • X terminals: a hybrid I/O device, has CPU and memory and can run X but not a complete computer in itself. (early days, when I was at grad school) • X terminal emulator: software simulation of X terminals

14. Example: Mac OS X

15. X terminal in Mac OS X

16. Books? • Any introductory Unix book can help • Or, any online tutorial • Understanding Unix by Stan Kelly-Bootle • Unix for Dummies by J.R. Levine and M.L. Young

17. Your Unix Account • The system administrator creates your account (and delete your account). • System administrator is the “super user” who can access any user’s account • Your account info: • Account name (id) • Password • Home directory

18. Group id: you may be assigned to a group of users. • Login shell • Terminals • Called tty (abbr. for teletype) in Unix • Putty (use telnet or ssh)

19. Getting Started • Use putty ssn or telent to login to eclipse

20. Successful login shows:

21. Use Window’s (old version) telnet to login to eclipse • Start Run telnet • Type o • Type host-name • type your id and password at prompt

22. Shell prompt • $ -- Bourne shell, Korn shell, or bash shell • % -- C shell or TC shell • Will use $ throughout the slides • Script session • $script (to start a session) • $exit (to end a session) • Password change • $ passwd • Follow instructions

23. Trying out some simple commands • $ date Fri Jan 20 11:26:24 CST 2006 • $ w (check who is on the system) 11:30am up 116 day(s), 20:30, 3 users, load average: 1.92, 1.70, 1.67 User tty login@ idle JCPU PCPU what xing pts/6 9:11am 27 -bash xing pts/7 11:08am w root pts/4 10Oct05 2days bash

24. $ whoami • $ who • Email (built-in w/ Unix) • $ Mail <address> -- to send an email • $ Mail -- to read emails • Type x (or ^d or ^D) to quit reading emails • Elm: a menu-driven e-mailer (not built-in, needs to be installed) • Unix manual • $ man <any command> -- manual page for the command

25. Logging out • $ logout or • $ exit or • $ ^D • One of the above has to work • Spelling • Unix or UNIX? The latter is traditional, the former acceptable

26. Unix File System • File • Traditionally: a collection of related data • Unix extends the traditional meaning of file • To Unix, everything is a file (e.g., printer, disk drive,….) • File types • Ordinary files: common computer files • Special files: device file, represent physical devices.

27. Directory files: ordinary files and special files are organized into directory files or directories. • Ordinary files divided into two groups • Text files: (also called ASCII files) contains text and created/modified by text editors. • Binary files: containing non-textual data. Read and processed by programs.

28. Home and Working directories • Home directory: the directory when you log in the system. • Each user has a unique home directory • E.g.: /home/xing • To go to home directory (from anywhere): $ cd • Working directory: the current directory in which you are working. • Check what is your working directory: $ pwd

29. Unix File Tree • Files in Unix are organized in the form of a tree, typically as: Root (/) bin var dev etc home tmp usr Users’ home directories

30. Bin: short for “binary”. Contains shell software and common Unix commands • Dev: short for “devices”. Holds device files. • Etc: miscellaneous admin files (such as user list and passwords) • Home: holds users’ home directories • Tmp: temporary files are kept here. • Usr: user-related files, on-line manual are kept here. home directories (for some version of Unix),

31. Var: holds files whose contents varies frequently. Ex: users’ mail boxes are typically in /var/mail directory • File Names • 1 – 255 character long, combination of: • A – Z • a – z • 0 – 9 • period (.), underscore (_), dash (-)

32. avoid using any special symbols and Unix commands in file names. • Absolute pathnames • full pathnames that identify the location of a file in relation to root • ex: (tree on next slide) /home/al/cmps/hw1 /home/smith

33. root / home smith al cmps math hw2 hw1

34. ~ (tilde) represents the absolute pathname of your home directory • ~<username> represents the absolute pathname of the home directory of that user • Relative pathnames • relative to working directory • . -- the current working directory • .. -- parent of current working directory

35. ex: given the previous tree, assume you are at /home/smith, then $cd ../al/cmps/ changes to cmps directory • Listing files • $ ls -- list all files in working directory • $ ls ../al/cmps -- lists all files in /home/al/cmps (assume pwd is /home/smith)

36. Hidden Files and Directories • a file or directory is hidden if it cannot be listed by ls. • $ ls -a -- to list all files and directories • Moving Files • $ mv oldfilepathname newfilepathname • ex: $ mv hw1 ../math/ ( suppose at /home/al/cmps)

37. Copying Files • $ cp filepathname1 filepathname2 • ex: : $ cp hw1 ../math/ $ cp ./hw1 ../math/ ( suppose at /home/al/cmps) • Creating Files by Redirecting • redirect the “standard output” • ex: $ ls > file1 -- result is saved in file1

38. note: redirection into an existing file overwrite the file • “double redirection” >> fixes the problem: • $ ls >> file1 -- result is appended to file1 • Links (hard, and symbolic) • One file may have more than one name • Each file has a unique i-node – an internal data structure representing the location (disk sector) of the file, the mode of the file,

39. creation date & time, and other info. • A (hard) link is a name that refers to a file’s i- node. • A link is created using the ln command • Ex: $ lnexistingfnnewfn • A symbolic link is a name that refers to another (file) name. • Ex: $ ln –s exitingfnnewfn

40. name4 name1 name2 name3

41. Long Listing • More info about files can be shown by $ ls –l drwxr-xr-x 2 xing staff 512 Jan 23 11:40 t -rw-r--r-- 1 xing staff 8 Apr 26 2004 test drwxr-xr-x 2 xing staff 512 Aug 24 00:06 test1

42. drwxr-xr-x 2 xing staff 512 Jan 23 11:40 test File type links owner group name Size (byte) Date & time Access control

43. File access control: • First 3 symbols control what owner can do • Next 3 symbols control what group can do • Last 3 symbols control what public can do • for first position: d means directory - means file • r (read) – examine (but not change) the contents of a file • w (write) – change the contents of a file • x (execute) – run the file (program)

44. ex: rwxrwx--- owner and group users have read, write, and execute privileges, public has no privileges r--r--r-- everyone has read privilege only • changing file modes (1) • u – user (owner) • g – group • o – others (public) • a – all (owner, group, public)

45. = -- assign a permission (remove others) • + -- add a permission • - -- remove a permission • ex: • $ chmod u+x filename add execution to user • $ chmod g-rw filename remove read, write permission from group • $ chmod a=r filename add read to everyone and remove anything else • $ chmod u=rw,go=r filename give user read and write, everyone else read

46. changing file modes (2) • for each position, 1 indicates yes (permitted), 0 indicate no (not permitted) • ex: r--r--r-- is denoted by 100100100 • break down into 3 parts and regards each part a binary number, and convert it to decimal • then r--r--r-- can be denoted as 444 (1002=410)

47. more ex: rwxrwxrwx = 777 rwxr--r-- = 744 rw-rw---- = 660 --------- = 000

48. Conversion between binary and decimal numbers