Introduction to Unix

1. Introduction to Unix Bent Thomsen Institut for Datalogi Aalborg Universitet

2. Unix Philosophy • Designed by programmers for programmers • Toolbox approach • Flexibility and freedom • Networked – designed for server use • Multi-user / Multitasking • Conciseness • Everything is a file or a process • File system has places • Processes have life Bent Thomsen - FIT 1-2

3. Programs Kernel System Calls Hardware Unix Structure Bent Thomsen - FIT 1-2

4. Interacting with Unix • Sometimes through a GUI interface Bent Thomsen - FIT 1-2

5. OpenLook on Sun Bent Thomsen - FIT 1-2

6. Common Desktop Environment Bent Thomsen - FIT 1-2

7. MacOS X Bent Thomsen - FIT 1-2

8. Interacting with Unix • But most likely through a shell • Xterm, telnet, Secure Shell • A shell is the command line interpreter (like the DOS or command prompt in Windows) • A shell is just another program • There are several shells (sh, csh, tcsh, bash …) • A program or command • Interacts with the kernel • May be any of: • Built-in shell command • Interpreted script • Compiled object code file Bent Thomsen - FIT 1-2

9. Telnet Bent Thomsen - FIT 1-2

10. SSH Secure Shell Bent Thomsen - FIT 1-2

11. Getting started - login • The login is the user’s unique name • Password is changeable • Only known to user, not to system staff • Except initial issued password • Unix is case sensitive • Login and password prompt • System messages – you have new mail • The command prompt % $ [machine]> Bent Thomsen - FIT 1-2

12. Example of login Bent Thomsen - FIT 1-2

13. Password - Do • Make sure nobody is looking over your shoulder when you type your password • Change your password often • Choose a password you can remember • Use eight characters or more, some numeric, some not letters, i.e. # ! ( ] … Bent Thomsen - FIT 1-2

14. Password – Don’t • Use a word (or words) in any language • Use a proper name • Use information in your wallet • Use information commonly known about you • Use control characters • Write your password anywhere • EVER give your password to anybody Bent Thomsen - FIT 1-2

15. Passwords Your password is your account security: • Change your initial password immediately • Use the passwdcommand to change your password % passwd -where '%' is the prompt Changing password for bt Old password: -type in your oldpassword New password: -type in your new password Retype new password: -and again, to make sure % Bent Thomsen - FIT 1-2

16. The command prompt • Commands are the way to do things in Unix • Commands are typed at the prompt • Commands, as everything else, are case sensitive in Unix • A command consists of a name, options (or flags) and sometimes arguments [prompt]> <command> <flags> <args> Bent Thomsen - FIT 1-2

17. Two Basic Commands • The most useful commands you’ll ever learn: • man (short for “manual”) • help • They help you find information about other commands • man <cmd> retrieves detailed information about <cmd> • help lists useful commands Bent Thomsen - FIT 1-2

18. Who am I? • Commands that tell you who you are: • whoamidisplays your username • iddisplays your username and groups • Commands that tell you who others are: • finger [<name>]displays info for <name> • id [<username>]displays info for <username> • Commands that change who you are: • su <username>“switch user” to <username> • login login as a different user Bent Thomsen - FIT 1-2

19. Files and Directories • In Unix, files are grouped together in other files called directories, which are analogous to folders in Windows • Directory paths are separated by a forward slash / • Example /home/bt/FIT/docs • The hierarchical structure of directories (the directory tree) begins at a special directory called the root, or / • Absolute paths start at / • Example /home/bt/FIT/docs • Relative paths start in the current directory • Example FIT/docs (if you’re currently in /home/bt) • Your home directory is where your personal files are located, and where you start when you log in. • Example /home/bt Bent Thomsen - FIT 1-2

20. The File System Bent Thomsen - FIT 1-2

21. Directories (cont’d) • Handy directories to know ~ Your home directory .. The parent directory . The current directory • Other important directories /bin /tmp Bent Thomsen - FIT 1-2

22. Simple commands • ls • LiSts the contents of specified files or directories (or the current directory if no files are specified) • Syntax: ls [<file> … ] • Example: ls backups • pwd • Print Working Directory Bent Thomsen - FIT 1-2

23. More commands • cd • Change Directory (or your home directory if unspecified) • Syntax: cd <directory> • Examples: • cd backups/unix-tutorial • cd ../class-notes • mkdir • MaKe DIRectory • Syntax: mkdir <directories> • Example: mkdir backups class-notes Bent Thomsen - FIT 1-2

24. More commands • rm • ReMove • Syntax: rm [<options>] <files> • Example: rm class-notes.txt • Example: rm –ir backups • rmdir • ReMove DIRectory, which must be empty • Syntax: rmdir <directories> • Example: rmdir backups class-notes Bent Thomsen - FIT 1-2

25. Files (cont’d) • cp • CoPies a file, preserving the original • Syntax: cp <sources> <destination> • Example: cp tutorial.txt tutorial.txt.bak • mv • MoVes or renames a file, destroying the original • Syntax: mv <sources> <destination> • Examples: • mv tutorial.txt tutorial.txt.bak • mv tutorial.txt tutorial-slides.ppt backups/ Note: Both of these commands will over-write existing files without warning you! Bent Thomsen - FIT 1-2

26. File Permissions • Every file has three access levels: • user (the user owner of the file) • group (the group owner of the file) • other (everyone else) • At each level, there are three access types: • read (looking at the contents) • write (altering the contents) • execute (executing the contents) Bent Thomsen - FIT 1-2

27. What You Can Do With Permissions Bent Thomsen - FIT 1-2

28. Changing Permissions • The “change mode” command: chmod <level><op><permissions>[,…] <filename> <level> string of: u, g, o, a (user, group, other, all) <op> one of +, -, = (gets, loses, equals) <permissions> string of: r, w, x, s, t, u, g, o (read, write, execute, set-id, text, same as user, same as group, same as other), • Examples: chmod u+rwx,go-w foobar chmod g=u,+t temp/ chmod u=rwx,g=rwxs,o= shared/ Bent Thomsen - FIT 1-2

29. Process Management • What can you do with it? • Start programs in the background • Run more than one program per terminal • Kill bad and/or crashing programs • Suspend programs mid-execution • List all jobs running in a shell • Move foreground jobs to the background • More … Bent Thomsen - FIT 1-2

30. Three States of a Process • Foreground • Attached to keyboard • Outputs to the screen • Shell waits until the process ends • Background, running • Not attached to keyboard • Might output to the screen • Shell immediately gives you another prompt • Background, suspended • Paused mid-execution • Can be resumed in background or foreground Bent Thomsen - FIT 1-2

31. Background Processes • Listing jobs: • jobslists background “jobs” and job #’s • ps lists processes and their process id (“pid”) • %<job#>expands to the process id of the job • Stopping foreground jobs • Press ^Z(Ctrl-Z) in the terminal window • Starting a process in the background • Append a & character to the command line • Examples: ls –lR > ls-lR.out & • Resuming a stopped job • In the foreground: fg [<pid>] • In the background: bg [<pid>] Bent Thomsen - FIT 1-2

32. Killing Processes • The “kill” command: kill [-<signal>] <pid> Send <signal>to process <pid> • The “killall” command: killall [-<signal>] <command> Send <signal>to all processes that start with <command> • Useful signals (kill –lfor the complete list): TERM the default, “terminate”, kills things nicely KILL will kill anything, but not nicely HUP “hangup”, used to reload configurations STOP stops (suspends) a running process Bent Thomsen - FIT 1-2

33. Redirecting input and output • Simple!<program> < <FILE> <program> > <FILE> • Examplesort < my_grades.txtls > dirlist Note a file called dirlist will be created if it doesn’t exist Dirlist will be overwritten. >> appends Bent Thomsen - FIT 1-2

34. Piping • Piping is connecting programs together by using the output of one program as the input to the next. • Syntax:<program1> | <program2> | … | <programN> • A simple example (view a sorted file-listing a page at a time):ls | sort | less • By combining Unix utilities in a pipeline, you can build tools “on-the-fly” as you need them. Bent Thomsen - FIT 1-2

35. Shell Shortcuts • Tab completion • Type part of a file/directory name, hit <tab>, and the shell will finish as much of the name as it can • Works if you’re running tcsh or bash • Command history • Don’t re-type previous commands – use the up-arrow to access them • Wildcards • Special character(s) which can be expanded to match other file/directory names * Zero or more characters ? Zero or one character • Examples: • ls *.txt • rm may-?-notes.txt Bent Thomsen - FIT 1-2

36. Editing Text • Which text editor is “the best” is a holy war. Pick one and get comfortable with it. • Three text editors you should be aware of: • vi – A lighter editor, used in programming • emacs – A heavily-featured editor commonly used in programming • pico – Comes with pine (Dante’s email program) Bent Thomsen - FIT 1-2

37. Printing • Printing: • Use lpr to print • Check the print queue with lpq • lprm to remove print jobs • For the above commands, you’ll need to specify the printer with –P<printer name> Bent Thomsen - FIT 1-2

38. Exiting • Logout – leave the system • Exit – leave the shell • ^C interrupt • ^D can log user off – often disabled Bent Thomsen - FIT 1-2

39. Remember • In Unix, you’re expected to know what you’re doing. • Many commands will print a message only if something went wrong. • Most often there is no undo button • Make a backup copy if you are unsure • Some commands have interactive options • E.g. rm –i • Unix can be hard to learn, but it is loads of fun to use when you know what you are doing! Bent Thomsen - FIT 1-2