IT 244: Introduction to Linux/Unix

IT 244: Introduction to Linux/Unix
Class 3

Microphone

Trouble? Questions?

Has anyone had any trouble doing something for this class or have any questions?

Readings

If you have the textbook you should read chapter 2, Getting Started.

Homework 2

I have posted homework 2.

As usual, it will be due this coming Sunday at 11:59 PM.

Let's take a look at the assignment

Today's Class

In today's class I will cover some basics of the command line.

I will also show you and editior that can be used to create scripts.

And I will cover the script command that you will need for homework 2.

General Advice

Do You Have Enough Time to Do the Work for This Course?

Many of you work, either part or full time
This cuts down on the time you have to study
Technical courses are filled with details where accuracy is very important
They also introduce concepts which may take some time to fully understand
Such courses require a significant amount of study time ...
to learn the material and do well in class
This studying should not be done on one day ...
but spread out over the days of the week
You should not be taking this course ...
if you can't study several hours a week for it
Too many students rush to finish a degree ...
without doing the work to really learn the material
These people are setting themselves up for professional failure
If you try to do too much ...
you may end up accomplishing too little
Today is the last day of Add/Drop ...
when dropping the class won't mean losing money
Be honest with yourself
Looking at all your other commitments ...
do you have enough time for the work I will demand of you?

Course Work

Class Quizzes

From now on, each class will have a Class Quiz
The Class Quiz is ungraded
It is designed to help you remember the material covered in class
Here is how it works
Go to the listing of Class Quizzes you will find here
Click on the link for the day's quiz
Get a blank piece of paper
Write the answers to the questions on the paper
Go to the listing of Class Quiz Answers you will find here
Check your answers
Do not give me the paper with your answers
Class quizzes are not graded
They are designed to help you learn the material covered in class

First Graded Quiz

The first Graded Quiz will be given on Tuesday next week
I will pass out the exam papers after my lecture
Questions on the Graded Quiz come from the Class Quizes
Usually the quizzes from the previous week
Unless I tell you otherwise ...
you should expect a Graded Quiz each week on Tuesday
You will be able to see your scores on Gradescope

Home and it244 Directories

When you first log in, you will be in your home directory
This directory belongs to your account ...
and no other account can make changes to it
The name of this directory is your Unix account name
If you registered for this class, you should see a it244 entry here
It looks like a directory ...
but it is really something called a link
We'll discuss links in a future class
If you use cd to enter it244 ...
you will be inside your IT 244 class directory
In Class Exercise 2 your were told to create two directories
An hw directory for homework scripts
And an ex for Class Exercises
For each new assignment you must create a new directory inside either hw pathname ex
So today you will create an ex3 directory inside your ex directory
The files you create for this exercise should be created in this directory

Tips and Examples

Some Skills Only Come With Work

This course requires you to learn and understand a number of concepts
You will find a list of them here
You must know them on a deep and fundamental level ...
so that you can use them to accomplish a task
It is not enough to memorize a definition ...
though that is a first step
Each of these concepts is a tool
And the best way to learn a tool is to use it
That is why there are so many assignments in this class
You will be writing small scripts for this course
When you write them, think of the concepts you are learning
And what other things you can do with them
You might want to play around with a concept
Write a little something of your own ...
to better see how it works
Understanding comes with effort
The more you work with a concept ...
the more you can do with it

Class Exercises

There is a Class Exercise for every class ...
except the review sessions for the Midterm and Final exams
Each Class Exercise must be in a separate directory inside the ex directory
The ex directory must be inside your it244 directory
If you do not finish the script in class, you can finish it later
All Class Exercises must be finished by the following Sunday at 11:59 PM
I check your Class Exercises 4 times a week
The last check is on the weekend after they are due
If there is a problem with your script, or it is missing ...
I will send an email to your UMB email address
If the exercise is not complete or it has an error you will lose points
I have have written test scripts for each of the Class Exercises
I use these scripts to test your code
You can run these scripts to test what you have written
But you have to connect to pe15.cs.umb.edu to do this
At the bottom of every Class Exercise is the command you can run to test your script
When you run this command you will be asked for your username
After you enter this and hit Enter or Return, the test will run

Here is how it looks for Class Exercise 2

$ ~ghoffman/it244_test/ex02.sh
Unix username: ghoffman
ex  hw
ex2.sh
ghoffman 		 Glenn Hoffman
Class Exercise 2

When testing future Class Exercises you will see something like this

++++++++++++++++++++++++++++++++++++++++++++++++++
Error check
--------------------------------------------------
--------------------------------------------------

If you see nothing between the two lines of dashes, ---- ...
your script has no Unix errors
If the output of your script is missing something or produces incorrect output ...
you will hear a beep ...
and see an error message

Getting Help

This course makes you do things that you may not have done before
Whenever you do something new there is always a good chance you will make a mistake
When this happens, the first thing you should do is reread the instructions
Mistakes often happen when we read too fast
If you cannot fix the problem in a reasonable amount of time, ask for help
There are a number of ways you can do this
- Post a question in the class discussion area
- Email the Class Assistant
- Ask other students in the class
- Come to Zoom Office Hours
DO NOT EMAIL ME with your question
I have close to 100 student each semester
With that workload I must be very careful how I spend my time
I would rather respond to your question on Piazza than in an email
Only one student will see an email response
But an answer on Piazza can be seen by the entire class
Only send me an email when you have an issue that affects you and you alone
Like being out of the country due to a family emergency

Describing a Problem

You can't get help with a problem unless you describe it well
Statements like the following are useless when asking for help
- It does not work
- I get an error when I run the code
You have to describe the specific circumstances that caused the problem
The best way to do this is with the actual text from the ssh client window
Copy both what you typed, and what happened after you hit Enter

Something like this

it244gh@itserver6:~/it244/ex$ mkdr ex2
No command 'mkdr' found, did you mean:
 Command 'mkdir' from package 'coreutils' (main)
mkdr: command not found
it244gh@itserver6:~/it244/ex$

Don't Use Screenshots in Piazza

Many students paste screenshots of code into Piazza
This is not a good idea
I have a hard time reading some of the screen shots
And I can't copy the code onto pe15 to test it
Instead, tell me the name of your script on pe15.cs.umb.edu
This way I can run the code myself ...
and use various debugging techniques

Login Failure

If you enter the wrong password when connecting to pe15 ...
you will be blocked from logging in for 10 minutes
Wait 10 minutes and try again
If you have forgotten or misremembered your password, you can change it
Go to https://portal.cs.umb.edu/password/
If you have trouble with your account send an email to operator@cs.umb.edu

Review

Operating Systems

The operating system is the software that allows you to use a computer
Without an operating system, a computer is a dead piece of metal

Here is now the textbook defines an operating system

An operating system is the low-level software that schedules tasks, 
allocates storage, and handles the interfaces to peripheral hardware, 
such as printers, disk drives, the screen, keyboard, and mouse

Windows and MacOs are operating systems
As are Android and iOS for phones

Components of the Operating System

There are three components of an operating system
- Kernel
- Shell
- Utilities
The kernel runs the operating system
It gets it's own chunk of memory ...
that no other program can use
The kernel is always running
The kernel also allows programs to talk to the hardware
No program can use any piece of hardware without going through the kernel
The shell is a special program that gives you the command line
You use the shell to run other programs
Utilities are programs that allow you to use and manage computer resources

Shells

The shell is the program that gives you the command line
You use the command line to run programs
Modern shells provide a number of features that make them easier to use
Down through the years there have been a number of different Unix shells
Today, the two most commonly used shells are the TC shell and Bash
We will be using Bash in this course

Unix Commands

Unix commands are programs
To run a Unix command type the program name on the command line ...
and hit Enter or Return
Sometimes you want that command to work on something like a file or directory
To do this, you type the name of the file or directory after the command
This is called an argument
Some commands have options which appear right after the command
Options change the way a command works
For example the ls command lists the contents of a directory
```
$ ls
foo.txt  it244  work
```

When ls is used with the -l (for long) option, you get more information

$ ls -l
total 3
-rw-r--r-- 1 it244gh libuuid  16 2012-06-26 16:19 foo.txt
lrwxrwxrwx 1 it244gh libuuid  34 2012-02-07 09:46 it244 -> /courses/it244/s19/ghoffman/it244gh
drwxr-xr-x 2 it244gh libuuid 512 2012-06-27 11:08 work

If ls is given the name of a directory as an argument ...

it will list the contents of that directory

$ ls html
it116_html  it117_html  it244_html

Attendance

New Material

The Command Line

In this course we will be using the command line
In other words, we will be talking to the shell
On the command line, you do your work by typing commands
You have to be careful what you type
If you make a mistake of even one character ...
the command will not work
This is not the way most of you have interacted with computers
You are used to a Graphical User Inteface
GUIs use windows, icons, menus and buttons to make it easy to work with a computer
The command line is NOT a user friendly environment
I sometimes call it user hostile
So why do we study the command line?
Because the command line has more power
Programs written with a GUI take time to create and maintain
They will never have all the features of the command line
Most Linux/Unix server installations never install a GUI
A GUI uses system resources that are better spent on other things
The commands you type at the command line can be put into text files
These files are called shell scripts
Instead of typing the commands, you can simply run the shell script
This makes it easy to automate routine tasks

The Unix `script` Command

Sometimes it is useful to keep a record of your Unix session
For example, when you are running software to install a program
When you run an installer you usually answer a number of questions
It's good to have a record of your answers and how the machine reponded ...
if you run into trouble later
Unix provides the script command to keep a record of a shell session
When you run script, Unix creates a new shell session
Then everything that appears on the screen is stored in a text file
Everything you type ...
and everything the machine prints in response
If you run script with no argument ...
the name of the text file will be typescript
This file will be created in the directory you were in when you ran script
To end the script session, type exit at the command line
script does not save anything to disk until you type exit
If you want to add to the bottom of an existing typescript file run
```
script -a 
```
If you don't, you will lose what was in the original file
It will be overwritten with the text from the new session
When you end a script session you will be back in the original directory
This will happen even if you changed directories in your script session

The Editor Used in This Class

Unix can be customized in many ways
These customizations are done by editing text files
This means you need to know how to use a Unix text editor
A text editor creates a file that only contains characters
It does not contain formatting information like bold or italic
Most Unix system administrators use the vim text editor
vim is an updated version of the vi editor
The textbook devotes an entire chapter to vim and another chapter to emacs
emacs is preferred by programmers
I don't want to spend class time teaching you either editor
The only way to learn an editor is to use it
Both vim and emacs have many features
So using them can be very confusing at first
Today I'll show you nano, a simple text editor
Today's Class Exercise will give you some practice with nano
You are free you use any Unix text editor in this class
Do not use a word processor, such as Microsoft Word
These programs create files with non-printing format characters
Such files are useless on Unix

The `nano` Text Editor

nano is a simple text editor created as part of the GNU project
In nano you give a command by holding down the Control key ...
while pressing a letter
You can move to the beginning of a line of text by pressing Control A
Control E will move the text insertion point to the end of the line
The Control key is a modifier key like the Shift key
You hold down the Shift key to capitalize a letter
You hold Control key while pressing a letter to make something happen
When I write "Control A" it does not mean hold down the Shift key and the Control key
I mean hold down the Control key while pressing the A key
Some of the basic nano commands appear at the bottom of the window
The ^ in this list of commands stands for the Control key
So ^O means Control O
The nano feature set is limited
You can only work with one file at a time
You can search for text ...
but there is no search and replace feature
nano does have a limited cut and paste feature
If you press Control K the entire line will disappear
You can then go to another line and hit Control U
The line will be pasted back at that point
When you want to save a file you hit Control O
The name of the file will appear at the bottom of the screen
You need to hit Enter to accept that name and complete the save process
Control X will quit nano
I have created a web page with instructions for using nano here
There is also a link to it on the class web page

Retrieving Your Last Command

What do you do when the command does not work?
You need to run it again, fixing your mistake
But if you try to type in the command all over again ...
you could make a different mistake
Fortunately, Bash can help
Bash remembers your previous command lines and lets you run them again
This feature allows you to retrieve the last command you typed
You use this feature by pressing the Up and Down arrow keys
To retrieve the last command, simply hit the Up arrow
To retrieve the next to last command, hit the Up arrow twice
You can use the Down arrow to go in the opposite direction
Get in the habit of using this history feature
It can save you a lot of typing

Correcting Mistakes on the Command Line

The command line is not a user friendly environment
There are no menus
You have to remember the names of all commands
This is one reason Unix command names tend to be short
If you misspell a command, Unix responds with a cryptic error message
Fortunately, Unix provides command line editing
This means you can change what appears on the command line before you run it
Control A moves to the beginning of the command line
Control E moves to the end of the command line
Control U removes all text from your current position to the beginning of the line
Control K removes all text from your current position to the end of the line
Any text deleted by using Control U or Control K is stored in memory
You can paste it back on the command line using Control Y
The Right and Left arrow keys move the text insertion point back and forth
Today's class exercise will let you practice these features

Stopping a Running Program

Most commands run quickly
But some programs, like a compiler, can take a long time to finish
Every once in a while you run a command that never seems to finish
When you need to abort a running program use Control C
This will work on most Unix systems

Using Options with Unix Commands

Most Unix commands have options which modify their behavior
These options appear after the command
You must type a space before entering the option
Before the GNU project, most options used a single letter ...
and were preceded by a single dash
Most GNU utilities also have options which consist of words ...
preceded by two dashes

Often, commands will support both option formats

$ cat --help
Usage: cat [OPTION]... [FILE]...
Concatenate FILE(s), or standard input, to standard output.

-A, --show-all           equivalent to -vET
-b, --number-nonblank    number nonempty output lines
...

Getting Help with Unix Commands

Most Unix commands have a help option, --help
This option will provide a brief description of the command

It will also provide a list of options

$ ls --help
Usage: ls [OPTION]... [FILE]...
List information about the FILEs (the current directory by default).
Sort entries alphabetically if none of -cftuvSUX nor --sort.

Mandatory arguments to long options are mandatory for short options too.
  -a, --all                  do not ignore entries starting with .
  -A, --almost-all           do not list implied . and ..
  ...

The System Manual

Unix comes with two extensive documentation systems
The first system consist of the man pages
man as in a manual of instructions
To use this system type man followed by the name of the Unix command
```
$ man ls
```
The man pages are usually several screens in length
Hit the Enter key to move down one line
Or hit the Space bar to move to the next screen
To exit, type q
You can move up and down through the man pages using the Up and Down arrow keys
The man pages are often very technical
They can be quite intimidating
But you don't have to read all of the page
You only have to read enough to answer your question
I usually read the first few lines which show the arguments expected
Then I skim down the list of options
Learn the art of reading just enough to get the job done
A dear friend of mine called this "guerrilla reading"
Go in
Get what you need
And get out

The `info` System

Linux also provides an entirely different documentation system
This system is menu-based and was created by the GNU project
To enter this system use the info command
You can follow info with the name of a command
If you don't give an argument to info you will see an introductory section
The Up and Down arrow keys will move up and down one line at a time
The Space bar moves you down one screenful
The info system uses links which are indicated by an asterisk, *
To use a link, move down to a line with an asterisk and hit Enter
This will take you to a new page
To return to where you were, type l (the letter "el") for "last"
Type h for help
When you are done with the help page type l (el)
To leave the info system type q
info is better than man for commands created by the GNU project

Searching for a Keyword with `apropos`

man pages are useful, but you must know the name of the command
What if you know there is a command but you don't know its name?
apropos was created to help with this problem

Follow apropos with a key word and it will give you a list of man page topics

$ apropos who
btrfs-filesystem (8) - command group that primarily does work on the whole fi...
ldapwhoami (1)       - LDAP who am i? tool
Text::BibTeX::File (3pm) - interface to whole BibTeX files
w (1)                - Show who is logged on and what they are doing.
who (1)              - show who is logged on
whoami (1)           - print effective user name
whois (1)            - client for the whois directory service
whois.conf (5)       - alternative WHOIS servers list for whois client
whom (1mh)           - show to whom an nmh message would be sent

Getting Help from the Internet

The Internet is also a very good source of information about Linux
If you get a strange error message, try typing it into an internet search engine ...
like Google or DuckDuckGo
There is a large amount of Linux documentation on the web
One place to start is the Linux Documentation Project which you will find at www.tldp.org

Using `script` in Homework 2

Homework 2 is your first homework assignment using Unix
The assignment must be done on pe15.cs.umb.edu
You need to create a text file using nano or some other Unix text editor
You will also be asked to run script and do 12 things
I will look at the typescript file you create ...
to see if you have completed the work correctly
Your script session does not have to be perfect
If you make a mistake while running script simply try again
The best thing to do is to practice the commands before you use script
When you have a list of commands that work ...
you can then run them in a script session
Be sure to check your work

General Advice

Course Work

Tips and Examples

Review

New Material

Trouble? Questions?

Readings

Homework 2

Today's Class

General Advice

Do You Have Enough Time to Do the Work for This Course?

Course Work

Class Quizzes

First Graded Quiz

Home and it244 Directories

Tips and Examples

Some Skills Only Come With Work

Class Exercises

Getting Help

Describing a Problem

Don't Use Screenshots in Piazza

Login Failure

Review

Operating Systems

Components of the Operating System

Shells

Unix Commands

Attendance

New Material

The Command Line

The Unix script Command

The Editor Used in This Class

The nano Text Editor

Retrieving Your Last Command

Correcting Mistakes on the Command Line

Stopping a Running Program

Using Options with Unix Commands

Getting Help with Unix Commands

The System Manual

The info System

Searching for a Keyword with apropos

Getting Help from the Internet

Using script in Homework 2

Class Exercise

Class Quiz

The Unix `script` Command

The `nano` Text Editor

The `info` System

Searching for a Keyword with `apropos`

Using `script` in Homework 2