System Administration Introduction to Unix Session 2 – Fri 02 Nov 2007

1. System AdministrationIntroduction to UnixSession 2 – Fri 02 Nov 2007 • Reference: • chapter 1, The Unix Programming Environment, Kernighan & Pike, ISBN 0-13-937681-X Albert Lingelbach, Jr.alingelb@yahoo.com

2. History of Unix • Begun in 1969 at Bell Labs • Timesharing / MultiuserOne computer, many terminals • Programming • Typesetting • Group Communication

3. Architecture • Kernel • Windowing System • Gnome • Shell • Programs

4. The shell environment • tty (teletype) / terminal • text only • 24 lines, 80 columns • default shell: Bourne shell • to open a tty: right-click on desktop, choose “Open Terminal” • echo • print text to the tty • try: echo Hello • what shell is running ?echo $0

5. Simple commands • bash • compatible with sh, added features: • command history with up arrow • editable command line • backspace (vs. delete)‏ • date • system date and time • who • what users are on the system

6. Flow Control characters • ctrl-C • stop a running command • try: troff • ctrl-S / ctrl-Q • pause/unpause output • try: countdown 1000 • end input • ctrl-D

7. Command Arguments / Parameters • mis-typed command • gold: not found • command arguments / parameters • try: who am i • try: gold coins

8. User Communication • news • get local system news (written by the system administrator)‏ • try: news • write • write messages to another user on the system; like IM but local • try: • pair off • using who, find userid of your partner • write userid(and your partner does same)exchange messages

9. Manual Pages • You have seen the following commands: • date • who • news • write • sh • bash • How to find more about them ? • command -?often returns a short command synopsis • mancommandreturns the complete manual page reference for the command

10. Files • As in any computer system, data is stored in files • Most Unix files are (ASCII) text • Many Unix commands manipulate text files

11. File Naming • case sensitive • spaces are problematic • dot and underscore are useful separators

12. File Commands – 1 • current (“working”) directory • pwd • print the working directory • ls • list the files in the working directory • cdpath • change the working directory

13. File Paths 1 • filenames without a path default to the current directory • example: myfile.txt • / is the root or top of the file system tree • a file path contains directories separated by “/”(not “\” as in DOS/windows)‏ • example: /home/export/staff/alingelb/file.txt

14. File Paths 2 • relative paths (not starting with “/”) start at the current directory • current directory (.)‏ • parent directory (..)‏ • relative to any preceding directory • examples: • ./file.txt(the same as file.txt)‏ • ../../student/kate/file.txt • in general, any command that takes a file as an argument, will accept a path + file (path/file)‏

15. File Commands - 2 • touchfilename • create an empty file • example: touchmyfile.txt • rmfilename • delete a file (forever – be careful!)‏ • example: rmmyfile.txt • cporiginal_file new_file • copy a file • example: cpmyfile.txt copy_of_myfile.txt

16. File Commands - 3 • mvoriginal_file new_filename • mvoriginal_file new_location • new_location must already exist • file keeps same name • mv original_file new_location/new_filename • move a file • examples: mv myfile.txt newname.txtmv myfile.txt ..mv myfile.txt /usr/bin/students.txt

17. File Commands - 4 • catfile • catfile1 file2 ... • display the contents of the file(s) on the screen • morefile • display the contents of the file on the screen, on screenful at a time (press space for the next screen, return to advance one line)‏ • geditfile • edit the file in the gnome graphical editor

18. Directory Commands • mkdirdirname • mkdirpath/dirname • create the directory • rmdirdirname • remove the directory (it must be empty)‏

19. Shell filename wildcards 1 • it can be useful to match filenames by pattern: • * matches any set of characters (or no characters)‏ • ? matches one character • examples: • *file*matches any filename containing “file” • *.txtmatches any filename that ends in “.txt” • this*matches any filename that starts with “this”

20. Shell filename 2 wildcards • More examples:

21. Shell filename wildcards 3 • More examples: • cat chapter*.txtwill output to the screen all files that start in chapter and end in .txt • ls *.txtwill list all files that end in .txt • mv *.txt /export/home/alingelbwill move all files ending in .txt to the directory /export/home/alingelb

22. More useful (text) file commands 1 • greppattern filesearch for the pattern in the file, and output the line(s) containing the pattern • sortfilesort the lines of the file in alphabetical order • headfiledisplay the first 10 lines of the file

23. More useful (text) file commands 2 • tailfiledisplay the last 10 lines of the file • wcfilecount the number of lines, words, and characters in the file • difffile1file2display the differences between the two files

24. File permissions 1 • Every file has read, write, and execute permissions (RWX)‏ • These are set by the owner, for the owner, the group, and everyone else; so there are 9 permissions total (plus a few special ones to be discussed later).

25. File permissions 2 • ls -lwill display file permissions, along with the group and owner • example:$ ls -ltotal 3-rwxr-xr-x 2 alingelb staff 512 Nov 2 10:38 Desktopdrwxr-xr-x 3 alingelb staff 512 Oct 16 11:15 Documents-rw------- 1 alingelb staff 40 Nov 2 12:13 foonly.txt

26. File permissions 3 • chmod### fileis used to change file permissions • the first # is owner permissions • the second # is group permissions • the third # is everyone else permissions • the # is composed of(add the numbers): • 4 for read • 2 for write • 1 for execute

27. File permissions 4 • chmod example: • chmod 744 file • sets owner to read/write/execute • sets group to read • sets everyone else to read

28. Shell theory • The shell is a command interpreter • It interfaces between the user and programs and the kernel • It has its own syntax • In addition to providing access to programs and to the kernel, the shell has some powerful features of its own, including • wildcards • I/O redirection • scripting

29. I/O management 1 • Every process has 3 channels of information: • “standard” input • “standard” output • error output • These can be controlled by the shell: • command > file • sends the standard output of the command to a file • command < file • sends the contents of a file to the standard input of the command • command >> file • appends the standard output of the command to the end of a file

30. std I/O management • Examples • ls > listing.txt • echo “this is a test” > test.txt • echo “the test continues” >> test.txt • echo “6 + 6” > math.txt • bc < math.txt

31. more I/O management • More I/O redirection • There is a special empty file/dev/null • it discards all output • command 2> /dev/null • discards all error output • example:touch testfilechmod 000 testfilecat testfile 2> /dev/null • command1 | command2 • send the output of command1 as the input of command 2 • example: ls | wc

32. I/O management: pipe • Advanced example of pipe • wanted: list of users on system. build it incrementally using pipe. • whogives list of users, but there are duplicates (because user appears once for each session);also, who gives too much information • using cut to remove extraneous information:who | cut -d\ -f1gives list of users, still with duplicates • who | cut -d\ -f1 | sortsorts list, putting duplicates together • who | cut -d\ -f1 | sort | uniqremoves duplicates; this is the desired list

33. Review • Concepts • Unix history, multiuser/timesharing, kernel, shell, man pages, file permissions • Flow control • ctrl-C, ctrl-S, ctrl-Q, ctrl-D • Commands: • echo, bash, date, who, pwd, ls, cd, touch, rm, cp, mv, cat, more, gedit, mkdir, rmdir, grep, sort, head, tail, wc, diff, chmod, bc • File paths & wildcards • *, ? • I/O management • >, >>, <, |, 2>