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Lecture 2

Lecture 2. UNIX. Basics of Operating Systems. A Fast, Stupid Machine. Computers: Hardware Have limited capabilities Can only do basic mathematics and logical comparisons Must be instructed with programs what to do. User vs. Computer. Computer only knows zeros and ones

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Lecture 2

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  1. Lecture 2 UNIX

  2. Basics of Operating Systems  1999 Addison Wesley Longman

  3. A Fast, Stupid Machine • Computers: • Hardware • Have limited capabilities • Can only do basic mathematics and logical comparisons • Must be instructed with programs what to do  1999 Addison Wesley Longman

  4. User vs. Computer • Computer only knows zeros and ones • User want to edit text for example • How they interract?  1999 Addison Wesley Longman

  5. Chapter Outline • Software contains instructionsthat tell a computer whatto do • Operating System (OS) • Application • User interface  1999 Addison Wesley Longman

  6. What the Operating System Does • The operating system controls: • Communication with peripherals • Coordination of concurrent processing • Memory management • Monitoring of resources and security • Management of programs and data • Coordinating network communications  1999 Addison Wesley Longman

  7. The User Interface: The Human-Machine Connection • The user interface is what the user sees on the screen and interacts with • Two major user interface types: • Character-based interface • Graphical user interface  1999 Addison Wesley Longman

  8. A Character-Based User Interface: MS-DOS • This is a disk operating system in which the user interacts with characters • letters • numbers • symbols  1999 Addison Wesley Longman

  9. UNIX • Slides of Dave Hollinger, Department of Computer Science, Rensselaer Polytechnic Institute • http://www.cs.rpi.edu/~hollingd/introunix  1999 Addison Wesley Longman

  10. Unix History and Motivation • The first version of Unix came from AT&T in the early 1970s (Unix is old!). • Why to study UNIX? • to understand Internet better • Linux becomes widely used in industry • to understand command line interface in general (present also in Windows OSes) • to comment on hacker movies to your friends   1999 Addison Wesley Longman

  11. Flavors of Unix • There are many versions of Unix that are used by lots of people: • SysV (from AT&T) • BSD (from Berkeley) • Solaris (Sun) • IRIX (SGI) • AIX (IBM) • LINUX (free software)  1999 Addison Wesley Longman

  12. Unix Help • There is online help available on any Unix system. • The help system is call the "Unix man pages" • set of help files and a command to view them. • the book has some of the same information, but you might need to check the man pages for your specific system for details.  1999 Addison Wesley Longman

  13. Single vs. Multitasking • Some old operating systems could only do one thing at a time (DOS). • Most modern systems can support multiple applications (tasks) and some can support multiple users (at the same time). • Supporting multiple tasks/users means the OS must manage memory, CPU time, network interfaces, ...  1999 Addison Wesley Longman

  14. Single vs. Multiuser • In Windows only one user can be on the computer • In UNIX, many users can log in from the console (that is keyboard and monitor attached to computer) or log in remotely (using telnet or ssh)  1999 Addison Wesley Longman

  15. Unix Accounts • To access a Unix system you need to have an account. • Unix account includes: • username • password • home directory • Supervisor ”root” account  1999 Addison Wesley Longman

  16. Home Directory • A home directory is a place in the file system where the account files are stored. • A directory is like a Windows folder (more on this later). • Many unix commands and applications make use of the account home directory (as a place to look for customization files).  1999 Addison Wesley Longman

  17. Shell • A Shell is a unix program that provides an interactive session - a text-based user interface. • When you log in to a Unix system the program you initially interact with is your shell. • There are a number of popular shells that are available.  1999 Addison Wesley Longman

  18. Some Simple Commands • Here are some simple commands to get you started: • ls lists file names (like DOS dir command). • who lists users currently logged in. • date shows the current time and date. • pwd print working directory  1999 Addison Wesley Longman

  19. Files and File Names • A file is a basic unit of storage (usually storage on a disk). • Every file has a name. • Unix file names can contain any characters (although some make it difficult to access the file). • Unix file names can be long  1999 Addison Wesley Longman

  20. File Contents • Each file can hold some raw data. • Unix does not impose any structure on files • files can hold any sequence of bytes. • Many programs interpret the contents of a file as having some special structure • text file, sequence of integers, database records, etc.  1999 Addison Wesley Longman

  21. / bin etc users tmp usr hollid2 scully bin etc netprog unix X ls who The Filesystem  1999 Addison Wesley Longman

  22. Pathnames • The pathname of a file includes the file name and the name of the directory that holds the file, and the name of the directory that holds the directory that holds the file, and the name of the … up to the root • The pathname of every file in a Unix filesystem is unique.  1999 Addison Wesley Longman

  23. Pathnames (cont.) • To create a pathname you start at the root (so you start with "/"), then follow the path down the hierarchy (including each directory name) and you end with the filename. • In between every directory name you put a "/".  1999 Addison Wesley Longman

  24. bin etc users tmp usr hollid2 scully bin etc Pathname Examples / netprog unix X ls who Syllabus /usr/bin/ls /users/hollid2/unix/Syllabus  1999 Addison Wesley Longman

  25. Absolute Pathnames • The pathnames described in the previous slides start at the root. • These pathnames are called "absolute pathnames". • We can also talk about the pathname of a file relative to a directory.  1999 Addison Wesley Longman

  26. Relative Pathnames • If we are in the directory /users/hollid2, the relative pathname of the file Syllabus is: unix/Syllabus • Most unix commands deal with pathnames! • We will usually use relative pathnames when specifying files.  1999 Addison Wesley Longman

  27. bin etc users tmp usr Disk vs. Filesystem • The entire hierarchy can actually include many disk drives. • some directories can be on other computers / hollid2 scully  1999 Addison Wesley Longman

  28. The current directory and parent directory • There is a special relative pathname for the current directory: . • There is a special relative pathname for the parent directory: ..  1999 Addison Wesley Longman

  29. The ls command • The ls command displays the names of some files. • If you give it the name of a directory as a command line parameter it will list all the files in the named directory.  1999 Addison Wesley Longman

  30. Some things to try ls list files in current directory ls / list files in the root directory ls . list files in the current directory ls .. list files in the parent directory ls /usr list files in the directory /usr  1999 Addison Wesley Longman

  31. ls command line options • To use a command line option precede the option letter with a minus: ls -a or ls -l • You can use 2 or more options at the same time like this: ls -al  1999 Addison Wesley Longman

  32. General ls command line • The general form for the ls command is: ls [options] [names] • The options must come first! • You can mix any options with any names. • An example: ls -al /usr/bin  1999 Addison Wesley Longman

  33. Moving Around in the Filesystem • There cd command can change the current working directory: • cdchange directory • The general form is: cd [directoryname]  1999 Addison Wesley Longman

  34. cd • With no parameter, the cd command changes the current directory to your home directory. • You can also give cd a relative or absolute pathname: cd /usr cd ..  1999 Addison Wesley Longman

  35. Some more commands and command line options • ls -R will list everything in a directory and in all the subdirectories recursively (the entire hierarchy). • you might want to know that Ctrl-C will cancel a command (stop the command)! • pwd: print working directory • df: shows what disk holds a directory.  1999 Addison Wesley Longman

  36. Copying Files • The cp command copies files: cp [options] source dest • The source is the name of the file you want to copy. • dest is the name of the new file. • source and dest can be relative or absolute.  1999 Addison Wesley Longman

  37. Deleting (removing) Files • The rm command deletes files: rm [options] names... • rm stands for "remove". • You can remove many files at once: rm foo /tmp/blah /users/clinton/intern  1999 Addison Wesley Longman

  38. File Owners • Each file is owned by a user. • You can find out the username of the file's owner with the "-l" option to ls, • Each file is also owned by a Unix group. • ls -l also shows the group that owns the file.  1999 Addison Wesley Longman

  39. File Permissions • Each file has a set of permissions that control who can mess with the file. • There are three kinds of permissions: • read abbreviated r • write abbreviated w • execute abbreviated x • There are separate permissions for • the file owner, group owner and everyone else.  1999 Addison Wesley Longman

  40. ls -l > ls -l foo -rw-rw---- 1 hollingd grads 13 Jan 10 23:05 foo size permissions name owner group time  1999 Addison Wesley Longman

  41. ls -l and permissions -rwxrwxrwx OwnerGroup Others Type of file: - means plain file d means directory  1999 Addison Wesley Longman

  42. Changing Permissions • The chmod command changes the permissions associated with a file or directory. • There are a number of forms of chmod, this is the simplest: chmod mode file  1999 Addison Wesley Longman

  43. chmod mode file • Mode has the following form*: [ugoa][+-=][rwx] u=user g=group o=other a=all + add permission - remove permission = set permission *The form is really more complicated, but this simple version will do enough for now.  1999 Addison Wesley Longman

  44. chmod examples > ls -al foo rwxrwx--x 1 hollingd grads … > chmod g-wx foo > ls -al foo -rwxrw---- 1 hollingd grads >chmod u-r . >ls -al foo ls: .: Permission denied  1999 Addison Wesley Longman

  45. Other filesystem and file commands • mkdir make directory • rmdir remove directory • lessprint out to terminal.  1999 Addison Wesley Longman

  46. Startup files DOS: autoexec.bat & config.sys bash: ~/.bash_profile ~/.bashrc ~/.bash_logout csh: ~/.cshrc ~/.login ~/.logout  1999 Addison Wesley Longman

  47. Wildcards • “a*b” matches all files in the current directory that start with a and end with b. • “a?b” matches all 3-letter files in the current directory that start with a and end with b. • Things to try: ls * ls –al * ls a* ls ?b  1999 Addison Wesley Longman

  48. Programs and Standard I/O Program Standard Input (STDIN) Standard Output (STDOUT) Standard Error (STDERR)  1999 Addison Wesley Longman

  49. Input Redirection • The shell can attach things other than your keyboard to standard input. • A file (the contents of the file are fed to a program as if you typed it). • A pipe (the output of another program is fed as input as if you typed it).  1999 Addison Wesley Longman

  50. Output Redirection • The shell can attach things other than your screen to standard output (or stderr). • A file (the output of a program is stored in file). • A pipe (the output of a program is fed as input to another program).  1999 Addison Wesley Longman

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