Lab 8

(Chapter 8)

Learning Objectives

1. To learn concept of file access permissions/privileges in UNIX, i.e., types of users and types of file privileges
2. To learn how to determine access privileges for a file
3. To learn how to set or change access privileges for files that you own
4. To learn what kinds of access privileges are needed for various file operations such as copy and move
5. To learn how to set default access permissions for newly created files and directories
6. To learn how to set and reset special access privileges bits: Set-User-ID bit, Set-Group-ID bit, and Sticky bit.

Lab Work

In UNIX, there are three types of users of a file: user (the owner of the file), group (users in owner’s group), and others (everyone else). File permissions/privileges for each user type may be set to a combination of read, write, and execute. Execute permission for a directory means that it can be searched.

1. Log on to your UNIX system
2. Write down the following and show the session that you used to obtain the required information:
   1. Your user name (also known as login name)

2. Your user ID

3. Your group ID and group name

4. User names of users in your group

5. Number of groups that you are a member of

6. Write down the user names of the users on your system who are members of more than one group, including the names of their group

3. What are the permissions for your home directory set by your system administrator? What command did you use to answer the question? Show your session.

4. Suppose that you want to block everyone at the main door of your directory hierarchy (i.e., your home directory), as shown in Figure Lab7.1. Take the necessary steps to do this. Show the session that you used to accomplish the task and confirm that the task has actually been done.

5. Consider the following files (or directories): /, /etc/passwd, /usr/bin/df, ~, .profile (in your home directory). Show the long listings for these files and complete the following table. Show file size (in bytes) for non-directory files only.

6. For files and directories given in 5, show permissions as octal numbers.

7. Set permissions for the temp, professional, and personal directories in your home directory to read, write, and execute for yourself, and read and execute for everyone else. If the permissions are already set like this, keep them so. Create a directory hierarchy d1, d2, and d3 directories under the ~/temp directory. Now create a file, called f1, under the d1 directory by using touch command, which can be used to create empty files. Read the manual page for touch for further information. Show permissions for d1, d2, d3, and f1. Capture your session and draw the picture for the ~/temp directory hierarchy.
    
8. Change directory to your home directory. Set permissions for ~/temp to execute only and run the ls –ld temp command. Now execute the ls –l temp command. What happens? Does it make sense to you? What are the minimum permissions required for the ls –l temp directory executes successfully. Set permissions for the temp directory to the minimum required and re-execute the ls –l temp command. Show the output of this command.

9. Display the current value of your ‘umask’. Change directory to your home directory and create a file f2 and a directory d11 under the ~/temp/d1 directory. Use the touch command for creating f2. Change directory to ~/temp/d1. Use an editor to create a file hello.c under the temp directory that contains the following C program.

#include <stdio.h>

main(void)

{

     printf (“Hello, world!\n”);

}

Now run the gcc –o greeting hello.c command to generate the executable for the C program in the hello.c file and place it in the greeting file. Display long listing of d1 to display permissions for f2, hello.c, greeting, and d1.

Change the mask value to 077 and repeat the above task but use the ~/temp/d2 directory this time. Do the permissions for f2, hello.c, greeting, and d21 under the ~/temp/d2 directory make sense with the new umask value? Finally, fill in the following table and explain the relationship between the ‘umask’ value and permissions for new text files, executable files, and directories.

Note that in UNIX the default permissions for executable files and directories are 777, and for text files permissions are 666.

10. Create the ~/temp/d3/d31 directory with mkdir ~/temp/d3/d31. Display the long listing of the newly created directory. If you cannot do this because of improper permissions on a component of the pathname, set the minimum permissions required for this operations on the pathname and then display the long listing. Now copy ~/temp/d1/f1 and move ~/temp/d2/f2 to the ~/temp/d3/d31 directory and then remove ~/temp/d1/f1 with the following commands:

cp ~/temp/d1/f1 ~/temp/d3/d31

mv ~/temp/d2/f2 ~/temp/d3/d31

rm ~/temp/d1/f1

What are the minimum permissions needed for these files and directories in order for the copy, move, and remove operations to be successful? Set permissions on the above files and directories to these minimum values and complete the copy, move, and remove operations. Show the minimum permissions needed in the following table and capture your session below.

11. Log out.

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This page was last modified September 26, 2004
wmorales@pcc.edu