CP1300 Introduction to UNIX

UNIX History

• Developed in 1969 by Ken Thompson and Dennis Ritchie at AT&T Bell Labs
• A shared multi-user environment, compact and highly portable
• Closely related to (and in some ways based upon) the earlier Multics operating system
• Designed for groups of users
• General purpose programming
• Used within Bell Labs until the late 1970's, when some universities also began using it as a research environment
• Many variations have been produced over the years, among them
  • Berkeley Unix (BSD)
  • Ultrix and OSF/1 (the DEC versions of Unix)
  • Xenix (the Microsoft version of Unix)
  • SunOS and Solaris (the Sun versions of Unix)
  • Linux (a PC version of Unix)

UNIX Users

• Users have a
  • User name
  • User groups
  • Password
• Logging in
• The JCU menu (never again)
• Shell
  • Prompts
  • Commands (pine :-)
• Setting your password
  passwd sets your password
• Logging out

UNIX File Systems

• The tree structure
  • Directory files
    • The root directory
    • The current directory
      pwd returns the path name of the current directory
    • Your home directory
  • Normal files
    • ASCII files
    • Binary files
    • Executable binary files
  • Every file has an owner and a group

• Listings
  
  • ls lists the non-hidden files in the current directory
  • ls -a causes all files to be listed
  • ls -F causes files to have a type indicator appended
    • Nothing for normal files
    • / for directories
    • * for executable binaries
  • ls -l causes all details to be listed

• Special directory names
  • The root directory /
  • Your home directory ~
    ~ "magically" expands to the path name of your home directory
  • The current directory .
    In this context . is followed by /
  • The parent directory ..
  • Moving around the tree
    cd directory changes the current directory to directory

• File names
  • Individual file names
    • Can contain any character
    • Alphabetics are case sensitive
    • Avoid using other than alphanumeric and the specials _ . + -
  • Absolute names start with / or ~
  • Relative names are relative to the current directory
  • Hidden files start with . not followed by /
  • File name expansion
    • ? stands for any character in a file name
    • * stands for any number of characters in a file name

UNIX File Manipulation

• Viewing files
  • cat filename will display filename on the screen
  • more filename will display filename on the screen one page at a time
  • less filename will display filename on the screen one page at a time, and allows movement up and down in the file

• Creating and changing files
  • pico filename will (create and) edit filename
  • vi, vim, and emacs are better than pico, but harder to learn
    • vilearn is a tutorial for vi
    • vitutor is a tutorial for vim
  • rm filename removes the normal file filename

• Creating and deleting directories
  • mkdir directory will make the directory file directory
  • rmdir directory removes the empty directory directory

• Copying files
  • cp filename newname copies the normal file filename to newname
  • cp -r directory newname copies the directory directory and its contents to newname

• Moving files
  • mv filename directory moves filename (normal or directory) into directory
  • mv filename newname moves filename to newname
  • Moving a file is the way to rename it.

• Controlling access
  • Every file has user, group, other access control
    ls -l lists this information in the format TRWXRWXRWX
  • Normal files have read, write, execute permission flags
  • Directory files have read, write, axcess permission flags
  • chmod WOP filenames changes the permission flags for the filenames
    • W can be any combination of u, g, o, a (a means ugo)
    • O can be + to add permission, - to remove permission
    • P can be any combination of r, w, x

Compiling C++

• A text editor (pico, vim, etc) is used to create source code
• There are two compilers cxx and g++
• cxx filename.cpp -o outputname will compile filename.cpp to produce outputname
• outputname will execute the program

Self assessments

• History of UNIX
• File Systems
• File Manipulation

Tutorial Questions

• Introduction to UNIX

Exam style questions

1. Briefly describe how timesharing was proposed.
2. What was one of the first timesharing computers?
3. Briefly describe the birth of the Unix operating system.
4. Briefly describe how information is organised in the unix file system.
5. What are the basic file system actions.
6. What is the current directory?
7. What is the main account directory?
8. Explain what pathnames are.
9. What are the possible characters that can be used in a pathname?
10. True/false:
    • Every file/directory has a unique relative pathname?
    • Every file/directory has a unique absolute pathname?
    • Pathnames are case-sensitive?
11. Explain what the meaning of the pathname "/usr/local/bin/perl"
12. What sequence of unix commands will:
    • display a basic contents list of the current directory
    • display a list showing access permissions
    • display a list showing directories differently from files
13. If the current directory contains a sub-directory named: "sub1" what sequence of commands will:
    • change the current directory to be sub1
    • change the current directory to be the parent of sub1
    • list the contents of sub1 (while in the parent directory)
    • display the absolute pathname for the current directory
    • change the current directory to be the main account directory
14. What Unix command to performs each of the following independent actions:
    • display the file "verySmallFile.txt"
    • display the file "tooLargeFile.txt"
    • rename the file "theAnswer.cc" to "42.cc"
    • move the file "theAnswer.cc" to the sub-directory "42"
    • move the file "theAnswer.cc" to the sub-directory "42", renaming it to "42.cc"
    • create a new sub-directory "subdir1"
    • delete the empty directory "emptyDir"
15. From the current directory, what sequence of commands perform the following tasks (don't change directories):
    • create a sub-sub-directory "subdir2" inside "subdir1" (neither directory exists)
    • delete the directory "dir" which contains the file "data.txt"
    • if the current directory contains the file "theAnswer.txt", create two new sub-directories "42" and "backups". Move "theAnswer.txt" inside "42". Copy "theAnswer.txt" inside "backups" and rename it to "theAnswer.bak"
16. What are the meanings of the letters "a, u, g, o" in the command chmod ?
17. In the current directory, there is a file "shared.txt" and a directory "private" which contains the file "data.txt". What sequence of chmod commands will:
    • make "shared.txt" readable and writable by any user
    • make "private" readable by any user, but writable only by the account owner
    • make all files and directories under the current directory group readable
18. Is it dangerous to have the main account directory writable by any user? What can happen?