IT 244: Introduction to Linux/Unix
Class 9 Exercise, Thursday, March 4th

Log in to pe15

• Run the ssh client
  

  Use the values in the table below to connect to pe15.

  ssh configuration parameter	value
  protocol	ssh
  ssh version	2
  ssh port	22
  host	pe15.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

Create a typescript File

• Make sure you are in your ex09 directory
  

      pwd

  If the result of running this command is not

      ~YOUR_UNIX_USERNAME/it244/ex/ex09

  where YOUR_UNIX_USERNAME is the name you created for your Unix account, see me.
• Run the script command
  

      script --flush

  This will create a typescript file in your ex08 directory.
  
  You must perform the remaining steps in this exercise while script is still running.
  
  If you make a mistake, simply try again.
  
  Do not exit the script session until you have finished all the steps in this exercise.

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

Practice with Permissions

• Go to your ex09 directory
  

      cd ~/it244/ex/ex09

• Make sure you are in the right directory
  

      pwd

• In a SEPARATE CLI window (same directory): Use nano to create the file 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.
  
  
• In a SEPARATE CLI window (same directory): 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

• In a SEPARATE CLI window (same directory): 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.
  
  
• In a SEPARATE CLI window (same directory): 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

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

End your script Session

• Exit from your script session
  

      exit

  You need to do this or the typescript file will never be created
• Look at the contents of the typescript file
  

      cat  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

• Write into this file the commands from the previous section
  
  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.