IT 244: Introduction to Linux/Unix
Class 16 Exercise, Tuesday, April 12th

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!)

• Go to your ex directory

      cd  ~/it244/ex

• Create an ex16 directory
  

      mkdir  ex16

• Go to your ex16 directory
  

      cd  ex16

Start Up a script Session

Execute the script command, using the --flush option

    script --flush

More Practice with Background Jobs

• Copy bother.sh from my course_files/it244_files directory
  

      cp  ~ckelly/course_files/it244_files/bother.sh  .

• Make sure the copy operation worked
  

      ls

• Run bother.sh in the background redirecting its output
  

      ./bother.sh > /dev/null & 

• Run jobs
  

      jobs

• Run ps
  

      ps

• Bring the job to the foreground
  

      fg

  Notice that you do not have a prompt.
  
  That is because bother.sh is running in the foreground.
  
  You can't see that becasue it's output is redirected to /dev/null.
  
  Right now you can't run a command, because you do not have a prompt.
  
  But you can suspend the current foreground job using Control Z .
  
  
• Suspend the job
  

      Control Z

  Now you get your prompt back.
  
  
• Run jobs
  

      jobs

  Notice that the bother.sh process still exists.
  
  But it is in a state of suspended animation.
  
  So it is nothing doing anything at the moment.
  
  
• Send the job back to the background
  

      bg

• Run jobs
  

      jobs

  Notice that .bother.sh is running again.
  
  
• Run ps
  

      ps

• Kill the job using the process ID of bother.sh
  

      kill PROCESS_ID

  PROCESS_ID is the PID number of the bother.sh process.
  
  
• Run jobs
  

      jobs

  The job has been terminated

Built-in Commands

• Find the file that will be run when you use ls
  

      which ls

  You get an absolute pathname, so ls is not a built-in.
  
  
• Find the file that will be run when you use cat
  

      which cat

  cat is also not a built-in.
  
  
• Find the file that will be run when you use bg
  

      which bg

  which returns nothing because bg is a built-in command.
  
  This means the code for this command is contained within the shell itself.
  
  
• Find the file that will be run when you use fg
  

      which fg

  fg is also a built-in command.

bash Startup Files

• Go to your home directory
  

      cd

• Make sure you are in your home directory
  

      pwd

• Look for any bash startup files
  

      ls .bash*

  Unless you have created .bashrc or .bash_profile, you should see only .bash_history.
  
  
• Open up a second login session, while leaving your first login session going.
  
  • You will use this second login session for file editing.
  • This is so that your use of nano does not interfere with the script session in your first session.
  • Make sure that you keep track of what is to be done in which login window!
• In your SECOND login window: Create a .bash_profile startup file
  

      nano .bash_profile

• In your SECOND login window: Enter the following line:
  

      ex=~/it244/ex

  There must not be any spaces on either side of the  = .
  
  You have just created the variable ex with the value of ~/it244/ex.
  
  
• In your SECOND login window: Save your changes and quit nano
  
  
• Back in your FIRST login window: Try to use this new variable
  

      echo $ex

  echo prints a blank line, because .bash_profile ran when you first logged in.
  
  When .bash_profile ran, ex was not defined in .bash_profile.
  
  It has not been run again since you made the changes.
  
  
• Run .bash_profile in your current shell
  

      source .bash_profile

• Now try to use the new variable
  

      echo $ex

• Use this new variable to go to your ex directory inside your it244 directory
  

      cd $ex

• Verify your current location
  

      pwd

Create an Interactive Non-login Shell

• In your FIRST login window: Go back to your home directory
  

      cd

• Also in your SECOND login window: Go back to your home directory
  

      cd

• In your SECOND login window: Create a .bashrc file
  

      nano .bashrc

  Notice that this is a different file than .bash_profile.
  
  
• In your SECOND login window: Enter the following line in the file
  

      PS1='--> '

  Again, there must be no spaces on either side of the  = .
  
  
• In your SECOND login window: Save your changes and quit nano
  
  (You can now close out your second login shell, but NOT the first!)
• Back in your FIRST login window: Create a subshell
  

      bash

  Notice that your prompt has changed.
  
  That is because you changed the prompt variable PS1 in your .bashrc file.
  
  When you created this interactive non-login shell, .bashrc was run.
  
  .bashrc changed the value of PS1, giving you a new prompt.
  
  
• Look at your running processes
  

      ps

  The first bash process is your login shell.
  
  The second is your current shell.
  
  
• Leave the subshell
  

      exit

  Notice that your prompt now has returned to normal.
  
  
• Run ps again
  

      ps

  You have only one bash process running.
  
  This means you are back in your login shell.
  
  

Exit Your script Session

Use the exit command

    exit

You should see a confirmation message confirming that the script session is finished, resulting in a file called typescript, and you will probably also noticed that you are back in the original directory, from where you first ran the script command.