Tutorial 19 - UNIX 3

1. Log onto a UNIX workstation

2. Get the Date and Time

To check the current date and time, use the date command.

Alternatively a clock can be displayed. Run the xclock program by typing the command xclock.

3. Running Applications in the Background

Try and type something in the terminal window while the clock is displayed. The commands are ignored for the moment as the terminal (shell) is tied up running the current command - the clock. Close the clock. The commands typed in while the clock was running are now executed, and the terminal window will now accept commands.

This time run the clock in the background by placing an ampersand (&) after the command (e.g. xclock&). This runs xclock as a background process, and doesn't tie up the terminal window. Try typing some commands to confirm this.

Similarly when you use applications such as nedit, firefox etc, type the command then an ampersand, so that they run in the background. e.g. nedit& or nedit filename& or firefox&

Note: you can always open multiple Terminal windows as well, for example you might want to work in different directories at once etc.

4. Printing

Change directory to the directory containing HelloToMe.java from the last tutorial.

Running nedit in the background, open HelloToMe.java.

Obtaining a printout is the same as for the PC labs. You student card is needed to pay for the printout. If you send something to the printer and decide not to print it, it doesn't matter, it will disappear from the print queue in time.

From within nedit print the file to the printer itlab3.

Exit nedit.

Printing the file HelloToMe.java to the printer itlab3 using a2ps, specifying 1 page per sheet and portrait page layout. 

5. Check for Other Users

As you are already logged in to a UNIX workstation you can remote login to another UNIX computer using ssh (ssh is a secure remote login program unlike rlogin). Pick a UNIX workstation to remotely log into that already has someone logged into it e.g. ask the person next to you what indy they are using (the indy name is specified at the top of the terminal window) or check the map on the notice board at the front of the classroom (if available). e.g. to remote login to indyc, type

    ssh indyf

or

    ssh indyf.bendigo.latrobe.edu.au

Then type in your username and password.

Check who else is using the workstation.

The who command shows information on the users using the system. Try it. It should look something like:

tim     ttyq0 May 4 22:43 (whitfort.bendigo.latrobe.edu.au:0.0)
afsmith ttyq2 May 7 13:15 (:0.0)

Description

tim           Username
ttyq0         Terminal line
May 4 22:43   Date and time logged in 
(whitfort.bendigo.latrobe.edu.au:0.0)  The computer user is logged in from. 

In the above example the user afsmith is sitting at the Unix workstation.

For more information on what users are doing on the system you have logged into, use the w command. Try it. It should look something like:

 1:59pm up 6 days, 23:01, 2 users, load average: 0.02, 0.04, 0.00
User    tty from           login@  idle JCPU PCPU what
tim     q0  whitfort.bendi Sun10pm      3:38      w
afsmith q3 :0.0            1:15pm  1      22      nedit Page1.html

Description

The first line describes statistics on the system e.g. the current time is 1:59pm, the system has been up (on) for 6 days, it has 2 users etc.
The first 4 columns are similar to those described in who. The idle column shows the time (as minutes, or hours:minutes) since there was any user input, the JCPU column shows the total CPU time (as seconds, or minutes:seconds) of all jobs run by the user, PCPU column shows the CPU time (as seconds, or minutes:seconds) taken by the current job, and the what column shows what the users are doing e.g. what they are running.

Log off the remote workstation

• Logoff the remote workstation by typing one of the following: exit, logout or Ctrl+D
• The message "Connection to indy? closed." should be displayed if you have successfully logged off

6. Editing Commands

• The left and right the arrow keys can be used to move the cursor within the current command to modify it.
• The up and down arrow keys allow you to scroll through previous commands. These commands can be re-executed, or modified and executed.
• Clicking on the right mouse button displays a menu that can be used to cut and paste between windows or commands
• The history command shows the commands executed in sequence at the terminal. The commands are numbered and can be executed by number e.g. !34 executes command number 34.
• !! re-executes the previous command
• Alternatively the command to be executed can be specified in terms of how far back it was e.g.!-1 is the last command, !-2 the command before that etc.

Type the following commands

    history
    pwd
    du -s

Re-execute the pwd command. By specifying ! and how many commands ago it was.

7. Startup Files - .login

Check if you have any start-up files, first use ls -a check if you have a .login file, and a .cshrc file..

If the files exist, view them.

We will make a few adjustments to your .login file

• Open the file in an editor. (If you don't have a .login file use the same command) eg.:

nedit .login&
• Set the default file permissions for new files so the user has read, write and execute permissions and group and other have none.
  umask 077
• Exit nedit saving your changes.
• These changes are not immediately invoked. There are two methods.
  • source .login
  • or log off and log on again 
• Use one of the above methods to execute your .login file

8. Startup Files - .cshrc

Make the following changes to your .cshrc file

• Type the following in the file .cshrc
  alias home 'cd $HOME'
  alias cdwww 'cd $HOME/public_html'
  alias dir 'ls -al | less'
  This gives you the equivalent of three extra commands - What are they?
  Personally I think at this stage it is a good idea to use the Unix commands rather than using aliases.
• Exit nedit saving your changes.
• These changes are not immediately invoked. There are two methods. Try one:
• source .cshrc
• or close all terminal windows and reopen them
• Try each of your new commands
• If you forget what they are just enter the command: alias (try this)

9. File Modes (Permissions)

• Ensure you are in your home directory
  Enter the pwd command to confirm you are.
• Create a new directory called mytmp attached to your home directory. Then change directory to it:
• Copy all the files from /Users/tjwhitfort/Public to the current directory:
• Enter the ls -l command to see who owns those files and view their permissions.
• Take away your read and write permissions from the lect17.txt file:

chmod u-rw lect17.txt
• View a file listing again that shows the permissions to ensure your change worked
• Use the cat command to view the contents of lect17.txt

Funny - now you cannot read it but the rest of the world should be able to!
• Give yourself read permission for lect17.txt again
• Ensure your group has write permission to your lect17.txt file
• If the student next to you is in your group you should be able to edit their lect17.txt - Try it!

If not in your group alter your other write permission for lect17.txt
(You will have to find out the full pathname of their lect17.txt)
• Change directory back to your home directory:

cd
• Remove your mytmp directory:

rmdir mytmp       (didn't work! - Why not?)
• Delete all files from your mytmp directory:
• Now remove the mytmp directory

10. Protecting your Files (more on permissions)

If you haven't already done so run your .login file so that the umask command within is applied to new files. See the lecture for more information on permissions.

Change the protection on all of your files so that only you can access them

• Make sure you are in your home directory
• Change the permission on all of your files and directories including subdirectories
  • chmod  -R  go-rwx  *
• Check the permission on all files
  • ls  -al
• Restore read and execute access on any directories that you want to be public, such as public_html e.g.
  • chmod  go+rx  public_html
• Change directory into the public directory changed above and change the permissions so that everyone can read the files, e.g public_html.
  • cd  public_html
  • chmod  go+r  *
• Check the permission on all files to ensure that they have the desired permissions

Any new files created in directories that you want to be public will need to have their permissions changed explicitly, as the default permissions now stop group or other access. For example if you create a new web page in public_html called myholidays.html, then you need to provide group and other read access e.g. chmod go+r myholidays.html.

11. Special Files

All users have an entry in the password file. The password file can be viewed, but the passwords are encrypted or not shown.

Change directory to: /etc.

Do a long format listing for the file passwd. e.g. ls -l passwd.
Everyone has read access to the file.
Use less to view the file passwd.

There are would normally be many thousands of entries in the file (username and passwords are now held at Bundoora). Trying to locate an entry can be difficult.

grep can be used to find text within a file or files.

Use grep to find your "ice" in the passwd file, its format is: grep "stringtofind" filename

Use grep to find occurrences of "unix" in /Users/tjwhitfort/Public/lect17.txt

12. Standard Input Output

Output from a command can be redirected to a file. For example to save the output from a ls command, use > and specify the file the output is to go to. e.g.

ls > myfilelist

Try the above command. View the contents of the file.

The output from one command can be used as input to another command (piped). The pipe symbol (|) is placed between the commands.

In the following example the output of the ls command is used as input to the less command. Try it.

ls /etc/passwd | less

The following command finds occurrences of  "z" in the passwd file and sends the output to less so that it can be viewed a screen at a time. The output from grep is treated as input to less. Try it.

grep "z" /etc/passwd | less

Write a command to find all occurrences of "smith" in the password file.

The following command makes displays a sorted copy of the passwd file, sorting on its first field (username), displaying the output a screen at a time. Try it.

sort -k1 /etc/passwd | less

13. Script

Script records everything output to your shell window to a file. If a file name is not specified, the file typescript is used. Script is useful for keeping a record of program runs, output of commands etc. To end recording (exit script) press Ctrl+D.

Format

script [-a ] [filename]

Options

-a  Append to the end of the file

Example running script and typing the commands ls -1 and who. Use Crl+D to end script.

indyk> script
Script started, file is typescript
indyk> ls -l
drwx------ 2  tim  itstaff     9  May 4  20:24  ProgEnv
-rw-r--r-- 1  tim  itstaff    77  Apr 30 10:00  geelong.txt
drwxr-xr-x 5  tim  1234     4096  Apr 30 10:14  public_html
indyk> who
tim     ttyq0 May 4 22:43 (whitfort.bendigo.latrobe.edu.au:0.0)
afsmith ttyq2 May 7 13:15 (:0.0)
<Crtl+D>Script done, file is typescript

View the contents of the typescript file

indyk> less typescript
indyk> script
Script started on Wed May  7 11:32:08 2003
indyk> ls -l
drwx------ 2  tim  itstaff     9  May 4  20:24  ProgEnv
-rw-r--r-- 1  tim  itstaff    77  Apr 30 10:00  geelong.txt
drwxr-xr-x 5  tim  1234     4096  Apr 30 10:14  public_html
indyk> who
tim     ttyq0 May 4 22:43 (whitfort.bendigo.latrobe.edu.au:0.0)
afsmith ttyq2 May 7 13:15 (:0.0)
script done on Wed May  7 11:32:21 2003

Run script, recording the session to the file tut19script.txt. Try a few commands. End script (Ctrl+D). View the file tut19script.txt.

14. Log off