IT 244: Introduction to Linux/Unix - Class 6 Exercise, Thursday, February 13th

IT 244: Introduction to Linux/Unix
Class 6 Exercise, Thursday, February 13th

When finished: Remember to check with instructor to make sure you are recorded as having completed the class exercise!

Logging in to users

Run the ssh client
Use the values in the table below to connect to the virtual machine we'll be using in this class.

In the value for "host" listed below, the first part of the string, "users", specifies the machine, on the Unix network, that you will connect to.

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.

Confirm that you are connected
You should see the following:

        Welcome to Ubuntu 16.04.6 LTS (GNU/Linux 4.4.0-171-generic x86_64)

Learn More About the Machine to Which You Are Connected
The uname command displays information about the machine you are using.
```
    uname -a
```
When used with the -a option, uname displays more information than just the name of the machine.

Your Shell

Determine Your Current Shell
The easiest way to determine your current shell is to use the ps (process status) command.
```
    ps
```
The ps command shows all your running processes, including your shell, bash.

Explore Your Home Directory

Learn Your Current Location
At every point in your Unix session, you are working inside some directory.

When you log in, you will be in your home directory.

You can create subdirectories inside your home directory, and customize your environment through special files located here.

To determine your current location, you will use the pwd command, which stands for "print working directory".
```
    pwd
```
Notice that your home directory has the same name as your username, and is located inside /home.

This is true for all users.
Look at the Contents of Your Home Directory
The ls command (for "list"), when used with no arguments will display the contents of your current directory.
```
    ls
```
You should see at least one directory - it244. This is where you will submit your homework assignments.
Look at Your "Invisible" files
ls, when used without the proper option, ls will not show files whose first character is a ".".

These special files are used to change features of your Unix environment.

To see these files, you need to use ls with the -a option:
```
    ls -a
```
Forward Your Unix Account Emails to Another Email Address
You can forward the emails sent to your Unix email account by creating a .forward file.

The .forward file contains the email address you want your Unix email to be forwarded to.

To do this, we will use a Unix trick.

Since I haven't introduced you to a Unix text editor yet, we'll use the cat command instead.

Later, when we talk about redirecting the input and output of a command, you'll understand why this works.

Where I have written "Control D" below, you should hold down the Control key while pressing the key for the letter "D".

Where I have written YOUR_EMAIL_ADDRESS, enter your UMass Boston e-mail address. Where you see [Enter], that means to press the Enter key.
```
    cat > .forward [Enter]
    YOUR_EMAIL_ADDRESS [Enter]
```
Press Ctrl-d and then press the Enter key
View the Contents of the file you just created.
```
    cat .forward
```
If you make a mistake, simply repeat the procedure.

The file contents will be overwritten by the new text you enter.
Test your .forward file
Send an email to YOUR_UNIX_USERNAME@cs.umb.edu

If forwarding is working, then you should see this message in your email account after a minute or two. If you get an error message, or nothing happens, then don't worry about it.

Create ex and ex6 Directories

Make sure you are in your home directory
```
    cd
```
If your it244 directory was created and it now exists, then go into it. (Otherwise, we'll need to help you set it up.)
```
    cd  it244
```
Create an ex directory
```
    mkdir  ex
```
Go to your ex directory
```
    cd  ex
```
Create an ex6 directory
```
    mkdir  ex6
```
Go to your ex6 directory
```
    cd ex6
```

nano

Run nano creating a text file named today.txt
```
    nano  today.txt
```
Practice with nano
Write a few sentences about what you did today.

Use as many of the nano commands, which you see at the bottom of the page, as you can.

The ^ character you see before each letter in the help menu at the bottom of the page tells you to hold down the Control key as you type the letter of the command.

Some important commands do not appear in the menu.

Control A will take you to the beginning of the line, Control E will take you to the end of the line, and Control K will delete the current line.

When you use Control K, the line you deleted is placed in a buffer.

You can get this line back, pasting it in your current position in the file. using Control U.
Save the file
```
    Control O
```
After typing this command, the file name will appear at the bottom of the screen.

Hit Enter, to indicate that this is the correct file name.
Quit nano
```
    Contrl X
```
Look at the contents of the file
```
    cat today.txt
```

script

Run script
```
    script --flush
```
Move to your home directory
```
    cd
```
If you run cd without any arguments, it will take you to your home directory.
Determine your current location
```
    pwd
```
You should be in
```
    /home/YOUR_UNIX_ID
```
List the contents of your home directory
```
    ls
```
Quit script
```
    exit
```
Determine your current location
```
    pwd
```
You should be in
```
    /home/YOUR_UNIX_ID/it244/ex/ex6
```
When you run script, a sub-process is generated which contains a new instance of the Bash shell.

Any changes you make to your environment, such as your current location, disappear when you exit script.

Since you started script in your ex6 directory, that is where you will return when you exit.

Any files you created or changed while you were using script will remain as you left them in your script session since they are part of the file system, not your environment.
Look at the typescript file
```
    cat typescript
```
Run script again, adding you new session to typescript
```
    script -a
```
Look at the value of the SHELL variable
```
    echo $SHELL
```
Pay attention to capitalization. Unix is case sensitive.
Quit script
```
    exit
```
Look at the typescript file
```
    cat typescript
```
You should see the echo command you just invoked, along with its results.

Stopping the Execution of a Command

Run a command that cannot finish

To see how this works, we'll try to run ssh using an account on users that doesn't exist.
```
    ssh foo@users.cs.umb.edu
```
If you get a message saying the authenticity of host cannot be established, type "yes".

No password you can enter will allow this command to complete, because you are trying to log into an account that does not exist.
Abort the program
```
    Control C
```
This is the only way you can get out.

Command Line Editing Practice

Type something at the command line
```
    foo bar bletch
```
Move to the beginning of the command line
```
    Control A
```
Move to the end of the command line
```
    Control E
```
Clear the command line
```
    Control U
```

Use the History Feature

Retrieve the last command
```
    ⇑
```
Retrieve the command before that
```
    ⇑
```
Return to the last command
```
    ⇓
```

Look at a man Page

Run man on ls
```
    man ls
```
Scroll down one screen
```
    Space
```
Scroll down one line
```
    Enter
```
Scroll up one line
```
    ⇑
```
Scroll down one line
```
    ⇓
```
Quit man
```
    q
```

Experiment with apropos

Run apropos on the word "link"
```
    apropos link
```

Use info

Run the info command on the word "link"
```
    info link
```
Display the help menu
```
    h
```
Close the help menu
```
    x
```
Quit info
```
    q
```
Run info without an argument
```
    info
```
You should see the first page of the info system.
Look at the file permission entry
```
    m
```
At the bottom of the screen, you should see the following prompt
```
    Menu item:
```
Enter the "File" then hit the Tab key, then press Enter.
Go to the previous node
```
    p
```
You should see the entry for "Numeric operations"
Return to the File permissions node
```
    n
```
Look at the "Mode Structure" Link

Keep hitting the down arrow until you are on the line with an * and the words "Mode Structure"

Hit Enter

You should see the "Mode Structure" page
Quit info
```
q
```

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.