“Dilbert” by, Scott Adams, Sep 30, 1994.
Basics of the Unix/Linux
Environment
Unix Philosophy and Account Information
Unix Philosophy
According to Doug McIlroy
 Make each program do one thing well.
 So, to do a new job, build afresh rather than complicate
old programs by adding new features (otherwise known as
“bells and whistles”).
 Machine shop vs. appliance (gives you the tools and you to
make appliance)
implications
 Typical question from you all:
Can UNIX do this?
 Typical answer from a professor:
NO, but YOU can write a program!
Unix enthusiasts think this is the answer the average user
wants to hear!
 Unix put lots of single minded programs in a row (with
pipes “|” ) to do what you need.
 Don’t use temporary/intermediate files – use pipe
 In other words, Unix prefers to take input from previous
program and send output to next program
 Write programs that do one thing and do it well.
(lean and mean)
 Write programs to work together.
(pipes)
Accessing unix from Sun lab
 Sit down
 If the screen is dark – hit any key (the shift key is the
“safest” as it does not actually send anything to the
computer) or move the mouse to “wake it up”.
 Type your CERI/UoM user id (uuid)
 Type your CERI unix password
*Note that unix machines are case sensitive
The % is the “prompt” from the shell that says it is ready
read input. There is also usually a flashing cursor after
the prompt.
Commands we will enter are shown in italics.
<CR> is Carriage Return/Enter.
This activity occurs in the terminal window
User ID
 User ID: usually a short derivative of your name and
the beginning of your email.
 Your CERI and UoM user ids are the same
User ID’s on the UM system can only be a maximum of 8 characters
due to the limitations of early computers. Unix is full of such
anachronisms.
User ID’s are formed using an algorithm. Take first initial (and
maybe middle) and full last name, if that is more than 8
characters, start removing vowels from the back, if still longer
than 8 characters, start removing consonants from the back.
User Passwords
 Password: a complicated combination of upper and
lower case characters, symbols, and numbers that
allows access to the account.
 Your CERI Unix password is unique to the Sun system
 Your UoM Outlook email, Spectrum, Tiger labs, and CERI
PC lab password is the same because it is all accessing
your primary UoM account.
 If you need/use the non-Sun systems (Unix machines in
the GPS lab, a faculty member’s Apple, etc.) you will have
a unique username/password for each of them.
Passwords
 Do not share your password!!!!
 Do not leave your password sitting around on a postit note.
 Do not email your password.
 If you forget your password, you have to visit the
system administrator and (humbly) ask for a new
one. There is no way for anyone (except hackers) to
figure it out.
Changing your password
 Unix passwords can be easily changed using the passwd command
%passwd
for CERI password changes
%passwd –r nis
Changing password for hdeshon
Old password: type in old password
New password: type in new password
Re-type new password: type in new password again
What not to use for your password:
- Your name, address, phone number, or anything that
is common knowledge, or can be easily guessed,
about you.
- Common words.
Password guessing programs don’t get tired and can
try 1000’s of permutations of passwords based on
the above.
What to use for your password:
- Something you will not forget.
- Mix in numbers and special characters (1, 2, 3 ,
!, @, #, $, %, etc.).
- Should be at least 6 characters long (some
systems require longer ones).
- (don’t use items from “do not use” list with “1”
substituted for “i”, “0” substituted or “o”, etc.,
the password guessers will try these.)
Accessing unix via SSH
 SSH: secure shell login is the preferred way to
remotely log on to the CERI unix system; do not use
telnet
 SSH is secure, easy and with X-tunneling enabled,
you can view graphics just as if you were sitting at
the remote machine
 Machines at CERI accept ssh access from all local
Internet providers and other CERI and UoM
addresses
 If you want access from out of town, you will have to
send Bob Debula the IP address of the out-ofMemphis computer
Accessing Suns via SSH
Mac or Sun machine
1: open an X11 or Terminal window
2a: mac% ssh -Y hdeshon@enigma.ceri.memphis.edu
2b: sun% ssh -X hdeshon@enigma.ceri.memphis.edu
3: type CERI unix password at prompt
PC
1: open the SSH application from the desktop or applications folder
2: enable X11 tunneling via the Settings menu (only do once)
3: click on Quick Connect
4: type in CERI host name and uuid, then password at prompt
Accessing Suns via Exceed
 The PCs in the long building have a special terminal
emulator program, called Exceed, for remote ssh
access to the unix machines.
 Once you choose a unix machine via Exceed, the PC
screen looks like the unix terminal and regular unix
log-in applies
 Directions for Exceed setup can be found at
 http://www.ceri.memphis.edu/people/mwithers/CERIComputing/Exceed/sshexceed.
html
Directories
Hierarchical file system which looks like upside down tree
Starts at top with “/”, called “root”.
Uses “/” to separate directories
(known as folders on
Apple/Windows)
Top Level
Directories
Home directories
Home
Directory
/gaia/home/hdeshon
Subdirectories
bin/
tomoDD*
Projects/
db2hdd*
SUMATRA/
Up the directory structure
or moving backward through the path
/gaia/home/hdeshon
bin/
tomoDD*
Projects/
db2hdd*
Down the directory structure
or moving forward in the path
SUMATRA/
Moving around directories
 pwd: prints path name of current directory
% pwd
%/gaia/home/hdeshon [this is what would appear if I had just logged
on]
 cd: change directory
% cd Projects
% cd automatically cd into your home directory
% cd ~/bin cd into your-home-directory/bin
. and ..
 The “.” signifies the current or working directory
% cd . No change in location
 The “..” signifies the directory directly above you (up) in
the directory structure (tree)
% cd .. cd back one directory
% cd ../../scratch/200GB/hdeshon
cd back two directories then forward three into scratch
subdirectory hdeshon
Listing directory contents
 ls: lists files and subdirectories of the specified path
% ls /gaia/home/hdeshon
bin
src
suma.new.res
% ls list everything in the current directory
% ls ~/bin list your-home-directory/bin
Flags & manual pages
 Almost all unix commands have a list of flags that can
be specified to modify the default behavior
% ls –F
-F in this case is one flag option for ls
 The potential flags are listed within each command’s
manual page
 To view a manual page, use the man command
% man pwd
PWD(1)
BSD General Commands Manual
PWD(1)
NAME
pwd -- return working directory name
SYNOPSIS
pwd [-LP]
DESCRIPTION
pwd writes the absolute pathname of the current working directory to the standard output.
The pwd utility exits 0 on success, and >0 if an error occurs.
The following options are available:
-L
Print the logical path to the current working directory, as defined by the shell in the
environment variable PWD.
-P
Print the physical path to the current working directory, with symbolic links in the path
resolved. This is
the default.
ls continued
% ls -F list directories with ‘/’ & executables with ‘*’
% ls –alF list entries beginning with ‘.’ & show in long format
-rwx------ 1 hdeshon hdeshon
1201 Jul 10 15:03 .tcshrc*
drwx------ 1 hdeshon hdeshon
16384 Aug 1 13:50 bin/
-rw------- 1 hdeshon hdeshon 186668405 Jul 31 2007
suma.new.res
From my mac….
%cd /Applications
%ls -F
Absoft10/
Adobe Acrobat 8 Professional/ Macs have many directories with
spaces in the name
 Spaces on Unix are somewhat of a problem as Unix does not
handle spaces and special characters well because they mean
something special in the shell.
!@#$%^&*()_+|?><`[]{}\’”:;
 The problem with spaces is that the command interpreter of the
shell parses (breaks) the command line up into tokens (individual
items) based on the spaces. So our file name gets broken into 4
small distinct character strings (“Adobe”, “SVG”, “3.0”, and
“Installer”) which causes confusion.
 So we have to “protect” the spaces from the interpreter. This is
done with quotes. We refer to this file using
%ls “Adobe SVG 3.0 Installer”
or
%ls ‘Adobe SVG 3.0 Installer‘