IT 244: Introduction to Linux/Unix - Class 9 Exercise, Thursday, February 27th

IT 244: Introduction to Linux/Unix
Class 9 Exercise, Thursday, February 27th

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!)

Make sure you are in your home directory
```
    cd
```
Go to your it244 directory
```
    cd  it244
```
Go to your ex directory
```
    cd  ex
```
Create an ex09 directory
```
    mkdir  ex09
```
Go to your ex09 directory
```
    cd  ex09
```

Start Up a Script Session

Execute the script command, using the --flush option

    script --flush

Hidden Files

Return to your home directory
```
    cd
```
Confirm that you are in your home directory
```
    pwd
```
Look at your hidden files
```
    ls  -a
```
These files configure various settings in your Unix environment.

Startup Files

Go to my home directory
```
    cd  ~ckelly
```
Look at my "invisible" files
```
    ls  -a
```
Look at the contents of my .bash_profile file
```
    cat  .bash_profile
```
This file runs other files that customize my Unix environment.
Look at the contents of some of the other files
```
    cat  .bashrc
```
What you see here may not mean much to you now.

But it will later in this course.

Absolute Pathnames

Go to my course_files/it244_files directory using an absolute pathname
```
    cd  /home/ckelly/course_files/it244_files
```
You can use this pathname anywhere in the filesystem and will always refer to the same directory.
Determine your location
```
    pwd
```
Notice that pwd always returns the absolute pathname of your current directory.
Go to my home directory using an absolute pathname
```
    cd  /home/ckelly
```
Verify that you are in my home directory
```
    pwd
```

Tilde ~

Return to your home directory using tilde ~
```
    cd  ~
```
Determine your current location
```
    pwd
```
You should be in /home/YOUR_UNIX_ID
Go to my home directory using tilde ~
```
    cd  ~ckelly
```
Determine your current location
```
    pwd
```
You should be in /home/ckelly
Go to your it244 directory using tilde ~
```
    cd  ~/it244
```
Determine your current location
```
    pwd
```
You should be in /home/YOUR_UNIX_ID/it244.

Notice that, although short, ~/it244 is an absolute pathname and can be used anywhere within this filesystem.

The . in a Directory

Go to your ex09 directory in your it244/ex directory using tilde ~
```
    cd  ~/it244/ex/ex09
```
Look at the entire contents of your ex09 directory
```
    ls  -a
```
Notice that you have a . and a .. entry.

The . stands for your current directory.
Create a file named foo.txt
```
    touch  foo.txt
```
Create a test directory
```
    mkdir  test
```
Enter the test directory
```
    cd  test
```
Determine your current location
```
    pwd
```
Copy foo.txt from the parent directory into your current directory
```
    cp  ../foo.txt  .
```
You use . to specify the current directory and .. to specify the parent directory.
Check that the copy operation worked
```
    ls
```
Make sure you are in your test directory
```
    pwd
```
Remove everything from your test directory
```
    rm *
```
Go back to your ex09 diretory
```
    cd ..
```
Remove the test directory
```
    rmdir  test
```

Relative Pathnames in the Current Directory

Go to the course_files/it244_files directory in my home directory
```
    cd  ~ckelly/course_files/it244_files
```
Check your location
```
    pwd
```
List the contents of this directory
```
    ls
```
Display the contents of fruit.txt
```
    cat  fruit.txt
```
Since fruit.txt is in your new current directory, its pathname is simply the filename.

Relative Pathnames in a Subdirectory

List the content of the current directory
```
    ls
```
List the contents of the dir1 directory using a relative pathname
```
    ls  dir1
```
List the contents of the dir2 directory using a relative pathname
```
    ls  dir1/dir2
```
Display the contents of foo.txt inside dir2 using a relative pathname
```
    cat  dir1/dir2/foo.txt
```

Relative Pathnames above the Current Directory

Go to the dir1/dir2 directory using a relative pathname
```
    cd  dir1/dir2
```
Display your current location
```
    pwd
```
Display the contents of the course_files/it244_files directory using a relative pathname
```
    ls  ../../
```
Display the contents of the root directory using a relative pathname
```
    ls  ../../../../../..
```

Relative Pathnames neither Above nor Below your Current Directory

Look at the contents of my home directory using a relative pathname
```
    ls  ../../../..
```
Look at the contents of my class notes directory for this course
```
    ls  ../../../../public_html/teaching/it244/
```

Look at the first 10 lines of my notes for today's class

    head  ../../../../public_html/teaching/common/exercises/linux/intro/exercise_08.html

Look at the Permissions of Files in a Directory

Go to your home directory
```
    cd
```
Make sure you are in your home directory
```
    pwd
```
Look at the permissions assigned to the contents of your home directory
```
    ls -l
```
Go to my home directory
```
    cd ~ckelly
```
Make sure you are in my home directory
```
    pwd
```
Look at the permissions assigned to the contents of my home directory
```
    ls -l
```

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

Practice with Permissions

Go to your ex09 directory
```
    cd ~/it244/ex/ex09
```
Make sure you are in the right directory
```
    pwd
```
Use nano to create the file name.txt
```
    nano name.txt
```
Enter your name in this file and hit Enter

Then save the file (Control O) and exit (Control X) nano.
Look at the permissions on this file
```
    ls -l name.txt
```
You have read and write permission on this file
Display the contents of name.txt
```
    cat name.txt
```
You have read permission so you can run cat on it.
Open name.txt with nano
```
    nano name.txt
```
You can only open the file if you have read permission.
Add the city in which you live under your name and hit Enter again

Then save the file (Control O) and exit (Control X) nano.
Display the content of the file again
```
    cat name.txt
```
You have write permission so you were able to change the file.
Remove write permission from this file
```
    chmod 400 name.txt
```
Look at the permissions for this file
```
    ls -l name.txt
```
You are the only one who has any permissions on this file.

And all you can do it read it.
Display the contents of this file
```
    cat name.txt
```
Open the file with nano
```
    nano name.txt
```
Try to add Massachusetts as the third line of this file

Try to save (Control O) and (Control X) quit.

You can't because you do not have write privileges.

Quit nano

    Control X

When asked the following, press "N".

    Save modified buffer (ANSWERING "No" WILL DESTROY CHANGES) ?

Look at the contents of this file
```
    cat name.txt
```
Nothing has changed.
Remove all privileges from this file
```
    chmod 000 name.txt
```
Look at the permissions for this file
```
    ls -l name.txt
```
Try to display the contents of the file
```
    cat name.txt
```
You can't.
Try to open the file with nano
```
    nano name.txt
```
You can't.
Quit nano
```
    Control X
```
Restore the original privileges
```
    chmod 644 name.txt
```
Look at the permissions for this file
```
    ls -l name.txt
```
Display the contents of this file
```
    cat name.txt
```

Re-Start Your Script Session

Execute the script command, using both the --flush option AND the --append option

    script --flush --append

chmod with Numeric Arguments

Go to your ex09 directory
```
    cd ~/it244/ex/ex09
```
Make sure you are in the right directory
```
    pwd
```
Create a test.txt file
```
    touch test.txt
```
Look at the permissions on your test.txt file
```
    ls -l test.txt
```
Remove read permission for all but the owner of the file
```
    chmod 600 test.txt
```
Look at the permissions on your test.txt file
```
    ls -l test.txt
```
Give read and write permission to everyone
```
    chmod 666 test.txt
```
Look at the permissions on your test.txt file
```
    ls -l test.txt
```
Restore the original permissions
```
    chmod 644 test.txt
```
Look at the permissions on your test.txt file
```
    ls -l test.txt
```
Delete test.txt
```
    rm test.txt
```

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

Bash Script for this Exercise

Go to your ex09 directory
```
    cd ~/it244/ex/ex09
```
Make sure you are in you ex09 directory
```
    pwd
```
Create the script ex09.sh
```
    nano  ex09.sh
```
Add the following line, and then skip two empty lines:
```
    # Exercise 9, First Portion
```
Write into this file the commands you used above, from the sections indicated here.

Include Unix commands from the section Hidden files to the section Relative pathnames neither above nor below your current directory.
Skip two empty lines, add the following line, and then skip two more empty lines:
```
    # Exercise 9, Second Portion
```
Write into this file the commands from the previous sections indicated here

Only enter commands from the section chmod with numeric arguments.
Save this file

Save and quit.
Test the script
```
    bash  ex09.sh
```
Fix any errors you find.

If you have trouble, see me.

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.