IT 244: Introduction to Linux/Unix - Class 10 Exercise, Tuesday, March 3rd

IT 244: Introduction to Linux/Unix
Class 10 Exercise, Tuesday, March 3rd

When finished: Remember to check with instructor to make sure you are recorded as having worked on the class exercise -- even if you have not completed it!

Log in to users

Run the ssh client

Use the values in the table below to connect to users.

ssh configuration parameter	value
protocol	ssh
ssh version	2
ssh port	22
host	users.cs.umb.edu
user name	your Unix username
Authentication method	password

Enter your password
A dialog box will appear on the screen into which you must type the password for your Unix account.

Directory for this Exercise

(When you are ready for me to check this exercise, please scroll back up to where you entered these commands!)

Go to your ex directory
```
    cd  ~/it244/ex
```
Create an ex10 directory
```
    mkdir  ex10
```
Go to your ex10 directory
```
    cd  ex10
```

Start Up a Script Session

Execute the script command, using the --flush option

    script --flush

Setuid

Find the absolute path of the passwd program
```
    which passwd
```
Look at the permissions on this file
```
    ls -l /usr/bin/passwd
```
Notice that the execute column for user (owner) has an s in the execute column and that the owner is root.
Look at the permissions oof he file that contains the encrypted passwords
```
    ls -l /etc/shadow
```
Notice that no one can read this file -- only the owner, root, can read it.

But since the passwd command has setuid enabled, anyone who runs this command has the access permissions that root has.

Directory Permissions

Go to the dir_permissions directory in my course_files/it244_files directory
```
    cd ~ckelly/course_files/it244_files/dir_permissions
```
Make sure you are in the right directory
```
    pwd
```
Look at the permissions of the contents of this directory
```
    ls -l
```
Look at the contents of dir1 and their permissions
```
    ls -l dir1
```
You have read permission for this directory, so you can run ls on it.
Enter dir1
```
    cd dir1
```
You have execute permission so you can enter the directory.
Make sure you are in the right directory
```
    pwd
```
Create a file whose name is your user name in this directory
```
    touch YOUR_UNIX_ID
```
Perform a long listing of the contents of dir1
```
    ls -l
```
Since you have write permissions to this directory, you can create a file in it. Notice that you are the owner of this newly created file.
Return to the dir_permissions directory
```
    cd ..
```
Make sure you are in the right directory
```
    pwd
```
Look at the permissions on dir2
```
    ls -ld dir2
```
Running ls -l on dir2 gives you a long listing of the contents of dir2.

If you want to see the permissions on the directory itself, you must use the -d option.
Look at the contents of the dir2 directory and their permissions
```
    ls -l dir2
```
You have read permission, so you can do this.
Enter dir2
```
    cd dir2
```
You can enter this directory because you have execute permission on it.
Make sure you are in the right directory
```
    pwd
```
Try to create a file in this directory.
```
    touch YOUR_UNIX_ID
```
This command fails because you do not have write permission for this directory.
Return to the dir_permissions directory
```
    cd ..
```
Make sure you are in the right directory
```
    pwd
```
Look at the permissions on dir3
```
    ls -ld dir3
```
Try to list the contents of dir3
```
    ls dir3
```
You can do this because you have read permission on dir3.
Try to cd into this directory
```
    cd dir3
```
This command fails because you do not have execute permission on dir3.
Try to create a file in dir3
```
    touch dir3/YOUR_UNIX_ID
```
This command fails because you do not have write permission on dir3.
Look at the permissions on dir4
```
    ls -ld dir4
```
Try to list the contents of dir4
```
    ls dir4
```
This command fails because you do not have read permission on dir4.
Enter dir4
```
    cd dir4
```
This command succeeds because you have execute permission on dir4.
Confirm that you are in dir4
```
    pwd
```
Try to list the contents of dir4 now that you are inside the directory.
```
    ls
```
Again the command fails because you do not have read permission.
Try to create a file in this directory.
```
    touch YOUR_UNIX_ID
```
This command fails because you do not have write permission for this directory.

Links

Return to your home directory
```
    cd ~
```
Confirm that you are in your home directory
```
    pwd
```
Create a link to the ex10
```
    ln  -s  it244/ex/ex10  ex10
```
List the contents of your home directory along with permissions
```
    ls -l
```
Notice that you have at least two links in your home directory, the it244 link that was created when you applied successfully for this course, and the one you just created.

Notice that the it244 link uses an absolute pathname while the one you just created uses a relative pathname.

Notice that the link you just created references another link, it244.
Enter your ex10 directory using this new link
```
    cd ex10
```
Display your current location
```
    pwd
```
Now show your true location
```
    pwd -P
```
What you think of as your it244 directory is really a link to a directory, named after you Unix ID, in the /courses/it244/f16/ckelly/ directory.
Return to your parent directory
```
    cd ..
```
Show your location
```
    pwd
```
Notice that you jumped back to your it244 directory, ignoring the fact that your ex10 directory was inside your ex driectory.
Tell me when you are finished

There is no shell script for this exercise, but I need to check that you have created the correct link.

Exit Your Script Session

Use the exit command

    exit

You should see a confirmation message confirming that the script is finished, resulting in a file called typescript

When finished:

Remember to check with instructor to make sure you are recorded as having completed the class exercise.
When you are ready, be prepared to show me:
- Your command line interaction -- in other words, scrolling up in the terminal windows, not just running the history command!
- Any other deliverables specified in the instructions, such as scripts or other files.