Lecture 01/21/2003



 Introduction to the Course  




Instructor:  Alexei Kotelnikov
TA: Amit Freeman

Recitation TA:
     Malik Khan 
     Lucas Machado 
     Paul Arias 
     Diane Palla 
    



Objectives of the course 






Course agenda
 




Textbook and online materials




Class schedule to be decided



Lecture in EIT Lab (D-110):




		
Period


		
		
Time

		
		
Monday

		
		
Tuesday

		

		
Wednesday

		
		
Thursday

		
		
Friday



	

		1

		8:10-09:30
		
-

		
-

		
-

		
-

		
-


	

	

		2
		9:50-11:10
		
-

		
-

		
-

		
-

		
-

	

	

		3
		11:30-12:50
		
-

		
-

		
Lecture

		
-

		
-

	

	

		4

		1:10-2:30
		
-

		
-

		
-

		
-

		
-


	

	

		5
		2:50-4:10
		
-

		
-

		
-

		
-

		
-

	

	

		6
		4:30-5:50
		
-

		
-

		
-

		
-

		
-

	

	

		7

		6:10-7:30
		
-

		
-

		
-

		
-

		
-

	

	

		8
		7:40-9:00
		
-

		
-

		
-

		
-

		
-

	

	


		9
		9:10-10:30
		
-

		
-

		
-

		
-

		
-

	







Practical sessions in Unisys Lab:(D-112):




		
Period


		
		
Time

		
		
Monday

		
		
Tuesday

		

		
Wednesday

		
		
Thursday

		
		
Friday



	

		1

		8:10-09:30
		
-

		
L

		
-

		
L

		
-


	

	

		2
		9:50-11:10
		
-

		
M

		
-

		
L

		
-

	

	

		3
		11:30-12:50
		
L

		
M,D

		
-

		
-

		
D

	

	

		4

		1:10-2:30
		
L,D

		
M,D

		
L

		
L,D

		
L,D


	

	

		5
		2:50-4:10
		
L,D

		
M,D

		
D

		
D

		
L

	

	

		6
		4:30-5:50
		
-

		
P,D

		
L

		
P,D

		
L,D

	

	

		7

		6:10-7:30
		
L

		
L,D

		
L

		
L,D

		
L,D

	

	

		8
		7:40-9:00
		
L

		
L,D

		
L

		
L,D

		
L,D

	

	


		9
		9:10-10:30
		
L

		
L,D

		
L

		
L,D

		
L,D

	











Unisys Laboratory, D-112

Please use only the following machines:



The unisys lab machines are on a private network; to access them from the outside,
you need to ssh to capone.rutgers.edu first, then ssh to the machines. 
  








Unix/Linux history




Modern Linux Applications






























Practical work; to be done in Unisys lab by 01/28/2003



Creating user account for yourself




First, you need to login as root to one of the desktop stations (they are 
 labeled as unisys01, unisys02, ... unisys18 on the monitor left corner);
root password is written on the board. Create account for yourself running
command useradd, for example, useradd joe; if the command is not found, run 
whereis useradd, then use the full path to the command;
 assigne a new password, passwd joe; logout and login again as yourself;
check in what directory you are, pwd; see what files
you got in the home directory, ls -la; become superuser, su; run command
useradd -D, see the output and compare it with your user settings in 
/etc/passwd, /etc/shadow and /etc/group and content of your home directory. 
Use command less to browse those files.

Read 
  • Chapter 14, User accounts and Ownerships
    • 




    
Practicing with Unix Commands


    


    

    
System Command Exercises from the Book- Chapter 4
    


    




    
I. Preface: brief introduction into Unix commands. 



    
Unix system is based on files: commands, programs, configuration files,
 documents, etc.

    
Files in Unix have ownership (user, group, and others)
 and attributes:
 
    


    
The files ownership and attributes can be listed with command ls -l.
The ownership can be changed with command chown, the attributes can
 be modified with chmod.
 
    

Executable system files are called system commands. Note, file names and
 commands in Unix are case sensitive. Do not create files
 with the names similar to the system commands, for example,
 "test", "file".
 
    
When you login to a system, you get the shell, which provides you
 with ability to execute commands interactively. You can also assemble
 commands into so called shell scripts. 
    
You can read about the main Unix commands in Chapter. 4 and
 shell scripting in Chapter 7. Information about various commands, their
 options and parameters can be obtained via command
 man command_name (man pages) and
 info command_name
    

If the command you want to run is located in one of the directories
 listed in the PATH environmant variable, you just need to type its name and
 press Enter key, otherwise, use the absolute or relative pathname, as
 discussed in Section 4.6. You can use the
 Tab key to complete typing the
 command. For example, type "dme" and press the  Tab key to get "dmesg".
 
    
Running commands are called processes. Each running process has
 a user ID, UID,  process ID, PID, and process parent ID, PPID.
 
    

 Processes can be viewed with command ps.
To see all running processes in the system, use ps -ef
 or ps -aux.
 
    

Usually, the processes you start run with your UID. However, if there is
 the SETUID bit set in a command file, the process would run with UID of
 the file owner regardless of whoever starts it.
  
    
Most of the Unix system processes have three data streams: 
    

    
Usually, the standard output and
 standard error are directed to the scren of your monitor; the standard
input is read from a keyboard. It is possible to redirect the standard
 output and error into files: command 1>stdo.out 2>stderr.out. For example,


If you need to discard the stream, you can re-direct it to /dev/null:

It is also possible to re-direct the standart output of one process into
 the standard input of the other using pipes "|": command_1 | command_2.
For example:





    
II. Exercises with some system commands in Chapter 4.

    
    Try to use the Tab key for command name completion.
    If you have any problems or questions during the exercises,
    ask the instructor or TA for help.
 
    

    Directory Manipulation, Sec. 4.5
   
    
Standard Linux directory structure. The subdirectories of / :

            
    

Each of the directories above has its own subdirectories tree.
When you login into the system, you automatically get into
 /home/your-name directory.
 
    

1. Determine the directory you are in: 
    
   
    
 
    
2. Go to some other directory, for example, /etc: 
    
  
    
  
    

3. Go to your home directory: 
    
   
    

4. Go back-and-forth between directories and check where you are: 
    
  

5. Create a new directory above your home directory: 
    
   

6. Go to the new directory and check where you are: 
    
   

7. Go one step back to the parent directory and check where you are:
   

8. Remove the new directory:  
    
   

9. Create a new directory above your home directory with subdirectories.
Try the following:  
    
    

Does it work?

    
Try the following: 
    
    

10. Create a few files in Newdir/one: 
    
    

11. Go back into the original directory and try to delete Newdir:   
    
    
Does it work ?
    
Try the following:
 

12. Repeat step #10; Copy the directory with its tree into another
 directory:   
    
 


    Some Basics Commands, Section 4.9
    
    

The commands are listed in alphabetical order. 
    
Read the section and try to run the following commands as follows:

    

   Compressed files, Section 4.13

   


    
  Searching for files, Section 4.14

   
    

                                               
    
Become root and update the database:        
    

    


As a user, run the following commands:  
    

 
    

  Searching Within files, Section 4.15

    

    

You may see a lot of output from the standard error coming onto your screen.
To suppress the standard error, you can re-direct it to /dev/null
:

    


    
Try also re-direction of the standard output into a file:


    

 
    


  Copy to MS-DOS and Windows Formatted floppy disks, Section 4.16
  
    

Ask the instructor or TA for a formatted PC floppy and
  complete Section 4.16 exercise. Try also commands mdeltree
   and mformat.

 
    

  Archives and Backups,  Section 4.17.
    

Create a new directory with subdirectories above your home directory,
 then tar and gzip it. For example,

 
    

    

To tar and gzip file with one command, try the following:

    

  Complete exercises in Sections 4.18 and 4.19 
 
    
If you don't understand why it is unsecure having "." in your path, ask
the instructor or TA to explain it to you.



    
III. Process ID; SETUID; sticky bit

    


 SETUID files

A) Login as yourself; copy /bin/sleep into your home directory
cp /bin/sleep
run ls -l on it and see who is its owner; run chmod 4755 sleep; become root, su; type whoami;
run command ./sleep 20 & ; run ps -aux | grep sleep and see who is the owner of the process ./sleep

B) Login as yourself and create a simple shell script, for example, ex1.x file:

#!/bin/bash

sleep 30

Then, chmod 4755 ex1.x; become root and execute the file:
 ./ex1.x ; run ps -aux | grep ex1.x to see who the process belongs to.

C) Login as yourself and chmod 0755 ex1.x; then become a superuser and run the following command:
su your_user_name -c "./ex1.x &"
Where for your_user_name you substitute your user name.
Then run ps -aux | grep ex1.x 
Who is the owner of the process?


Sticky bit

Login as root; cd /tmp
create directory temp, mkdir temp; give it a world writable permissions, chmod 777 temp; 
go there, cd temp; create an empty file, touch ex3; login as yourself; cd /tmp/temp; 
remove the file ex3, rm ex3.

As root, chmod 1777 temp go there, cd temp; create an empty file, touch ex3; 
login as yourself; cd /tmp/temp; remove the file ex3, rm ex3.

Unremovable (immune) files

Login as root; cd /tmp; create a new file, touch ex4; change its attributes,chattr +i ex4;
try to remove the file, rm ex4; run lsattr ex4.
What do you see? Note, chattr works with ext2 (native linux) file system only.