Title

INTRODUCTION TO UNIX

Joel Jaeggli (joelja@darkwing.uoregon.edu)
Joe St Sauver (joe@oregon.uoregon.edu)
University Computing Center
July 11, 1997

Our Goals for Today

Give you some background to help you understand why Unix is the way it is.
Help you understand any peculiarities of our local environment.
Help you become minimally functional
Give you the foundation for developing greater understanding in the months ahead
Will you ``know it all'' after one brief session? No... but you will at least have a taste of different areas that you may want/need to explore in greater depth.

The Unix ``Philosophy''

Unix tends to use terse commands from the days back when we used slow teletypes.
Unix commands do one thing (only), but those commands do that one thing very well.
Simple Unix commands are chained together to accomplish complicated tasks.
If a Unix command works OK, say nothing.
If the user asks to do it, DO IT, no questions asked (aka ``we're all big boys and we never make mistakes, so just do it'')
understanding Unix is a lifelong project.

The Different Flavors of Unix

Unix has evolved over a long period of time (and continues to evolve today); this has been facilitated by the distribution of source code for the Unix operating system.
The existence of different ``flavors'' of Unix means that some commands may not work on some systems, or they may take different arguments or return different output.
A recent trend is the reconcilliation of the various flavors of Unix (not there yet).

Logging In.

At the Login: prompt, enter your username
At the password: prompt enter your password (it won't echo on the screen)
Note that your username and password are case sensitive (JSmith is not the same as jSmiTH); be sure to enter it just as it appears on your account authorization form

The C Shell

Unix offers different command line working environment; all the UO systems use the C shell by default.
The C shell remembers commands you've entered; for example:
- ```
 % !!             
```
  (redo the last command)
- ```
 % ^smith^smythe  
```
  (redo last command changing smith to smythe)
- ```
 % history        
```
  (see old commands I've done)
- ```
 % !5             
```
  (redo command number 5)
Other shell tricks:
- The | command (pipe) can be used to send the output of one command to the input of another command; for examplle:
  % ls -la|more
  would break up a long dir listing into readable chunks.
- The > command would send the output of a command to a file.
  ls -la > foo.txt
  would create a file foo.txt which contained the output of the ls -la command.
- If you want to abort a program you're running, you can hit CRTL-c which will tell the program to stop.
- CRTL-z will suspend the currently running process and put you back at the % prompt.
- If you want the process to continue you can type fg or bg to put it to the background type bg, fg and bg have many more options which their respective man pages describe.
- To run a command in the background put an & at the end of the command.
The C shell is able to do much more...
For more information see % man csh or the Unix C Shell Field Guide

Understanding Unix Files

Under Unix, files are just a stream of bytes (Unix files aren't made of records the way VMS files are, for example)
Each file has a unique number associated with it (known as an <``inode'')
Each inode has one (or more) filename(s) associated with it.
Filenames (like everything in Unix) are case sensitive.
Try to use comparatively short filenames comprised of normal lowercase characters:
fall97.dat NOT FaLL-1997-datum-forms.dat

There are standard file extensions you should strive to use where applicable...

File Type:          File extension
-----------------------------------
Data file            .dat
Text file            .txt
Web document         .html
C source             .c
Fortran source       .f
Object file          .o
etc.

Unix accepts wildcards:
* --> ``match any zero or more characters''
? --> ``match exactly one character''
For example:
form*
matches form, form1, format, formula, etc.

What Files Do I Have On My Account?

```
% ls             
```
(list status of my files)
```
% ls -l          
```
(...including sizes and dates)
```
% ls -la         
```
(...including hidden files)
```
% ls -laR        
```
(...including subdirectories)
```
% ls -l | more   
```
(... and pause to let me read what's scrolling by)
You have a finite amount of space for files (your ``disk quota'')
To see how much space you have, do:
% quota -v

Renaming/Copying/Deleting/Printing Files

Rename a file:
% mv old.txt new.txt
Copy a file:
% cp foo.txt bar.txt
Delete a file:
% rm bar.txt
Print a file:
% lpr foo.txt
If you print a file with ``lpr'' you are printing it (by default) to the text-only line printer in the CC machine room, NOT to a local laser or dot matrix printer.
Pick up your printouts in the CC lobby.
View a file:
% more foo.txt
more and less are two very useful tools for viewing files in your directories. more and less break files up into screen size chunks so that you can view them try typing:
% less foo.txt

Using Subdirectories

Make a directory:
% mkdir research
To move a file into the directory, say:
% mv klamath.dat research/.
To move down into that directory:
% cd research
To go up one level, say:
% cd ..
To go back to your default directory:
% cd $HOME (note capitalization!) or cd ~/
To find out where you are:
% pwd

File and Directory Protections

Unix emerged from a collaborative and trusting environment where sharing data,programs and documents was routine.
Today, on larger systems like UO's, you will want to limit who can read, change or remove your files.
There are only three basic categories of people on a unix host (remember ``UGO'' cars)
u (you)
g (``g''roup, i.e., everyone in your dept)
o (``o''ther, i.e., everyone on the box)
a is shorthand for u and g and o.
Files that you want to protect from being read by others (examples: homework solutions, tests, confidential data, etc.) should be protected with the command:
% chmod go-rwx answers.txt
When you look at that file with the ls -l command, it should look like:
```
% ls -l answers.txt

-rwx------ <etc> answers.txt
    ^^^^^^ there MUST be six dashes here
```
Files that you WANT others to be able to read but not change (sample data for students to use in a homework exercise, for example) should be protected with:
% chmod go-w sample.dat
% chmod a+r sample.dat
When you look at that file with the ls -l command, it should look like:
% ls -l answers.txt
```
-rwxr--r-- <etc> answers.txt
    ^  ^ there MUST be r's here.
```
A final note on protections: just as you can protect file contents, you can also allow (or disallow) discovery of the names of files in your directory. For example, assume you are looking around for a new job, and have a file called likely-new-job-prospects.txt in your directory. If you don't want random people to see that filename, remove read protections from your directory:
% chmod go-r ~jsmith
Note that the system manager (``root'') will ALWAYS be able to access a file/directory.
Don't store secret stuff on a shared box.

X Windows
- The X Window System is a graphical user interface to Unix (the equivalent of what Windows 3.11 was to DOS)
- You need to either use an X terminal (such as those in the Science Library), or run an X Window emulator on your PC or Mac (such as Hummingbird eXceed, a commercial product), or use a Unix desktop box (such as a Sun Sparc, SGI Indy, DEC Alpha, or Linux running on a Pentium). X Windows is NOT the same as other windowing systems such as the Macintosh's graphical user interface, Windows/95, or other GUIs you may be familiar with.
- If you are working from an X terminal, you can run Netscape and use othergraphical programs.
- You can select which of several desktop environments you'd like to use at the time you login; the most common choices are CDE (``Common Desktop Environment'') or Motif, but some hosts support other choices such as fvwm as well.
- See the seperate handouts available for X Windows.
joelja@darkwing.uoregon.edu