Transcript Electronic Engineer

CIS 14A - Operating Systems
(UNIX)
Markus Geissler, MBA
Nghiep Nguyen, MSEE
About the Instructor...

Nghiep Nguyen, MSEE
-Sacramento High School, 1983
- AA in Math and Science
Sacramento City College, 1985
-BS in Electrical Electronics Engineering
UC Davis, 1987
-MS in Electrical Electronics
Engineering
CSUS, 1993
Experience
- Electronic Engineer, 87 - 90
Sacramento Army Depot
Write Test Program Sets for Unit Under
Test for Tomahawk Computer.
- Software Engineer, 90 - 95
McClellan Air Force Base
Operational Flight Program for A-10
Experience
- Electronic Engineer, 95 -96
Tinker Air Force Base
B-2 Stealth Bomber
- Software Engineer, 96 - 98
McClellan Air Force Base
A-10 aircraft
Experience
- Associate Programmer 1/98 - 10/98
P.O.S.T: Work with PowerBuilder, SQL
- Associate Systems Software: 10 - 11/98
F.T.B: Sybase DBA
- Systems Software Specialist, 11/98 to
Present
Legislative Data Center
Unix (Sun Solaris) System Administrator
Experience


Adjunct Faculty: 8/97 to Present
Cosumnes River College
Unix, Internet, HTML
Java, Visual Basic
Visitor Lecturer: 8/02 – 6/03
California State University, Sacramento
Visual Basic, Java
Office Hours




None
E-mail: [email protected]
Work: [email protected]
Web site:
http://www.geocities.com/nghiep_nguyen
Textbook(s)

Required
– UNIX System V - A Practical Guide (Third
Edition)
• by Mark G. Sobell
• Addison-Wesley Publishing Company

Strongly recommended
– CIS 14A Lecture Slides
• By Markus Geissler
• Download from website
Reverse Flows of Knowledge

Examinations
– Hands-on in Classroom
– One make-up exam per person at the
instructor’s convenience
• No more than 90% possible on makeup exams

Homework projects
Other Resources

UNIX Utility Program Reference
– Back of textbook (starting on p. 521)
Things You Should Know Before
Starting This Course

A basic understanding of the
components of a computer system
– CIS 1
UNIX

What exactly is UNIX?
– Computer Operating System
– large set of utility programs
•
•
•
•
general user
programmer
communication
administrative commands
Operating System

Definition:
An operating system (OS) is a set of
instructions that manages all computer
operations and provides an interface
between user(s) and system resources.
UNIX

Computer operating system (OS)
– Large set of utility programs
– Based on C programming language
– Used in enterprise networks
Application
Monitor
Keyboard
Disk Drive
Operating
System
Mouse
Printer
What Can UNIX Do For You?
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
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
General user applications
Programming environment
Typesetting tasks
Communication applications
Administration commands
The Inner Workings of a
Computer - Summary




Central Processing Unit
Memory
Storage
I/O
Central Processing Unit (CPU)

“Brain” of the computer
– Executes instructions from programs and
processes
– Manufacturers include
•
•
•
•
•
Intel
Advanced Micro Devices (AMD)
Cyrix
Motorola
Sun Microsystems
Memory

RAM (Random Access Memory)
– Volatile
• Information disappears when electrical power
to RAM is interrupted
• Capacity measured in Megabytes (MB)
• Access speed measured in Nanoseconds (ns)
– Holds data before and after CPU
processes them
• Program instructions
• Application data
Storage

Hard disk
– Installed inside computer’s case

Floppy/ZIP®/JAZ®/SyQuest® disks
– Portable; require disk drive

Disks are typically non-volatile
– Data called into memory when needed
• Capacity measured in Gigabytes (GB)

Magnetic Tape
– Largely used for data backup
Input/Output (I/O)

Reads input from a device into memory
– Keyboard
– Mouse

Writes output from memory to devices
– Monitor
– Printer

Disk drives are input and output devices
– long term storage devices
UNIX Facts

Created in 1969
– by Kent Thompson
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
Based on C language
AT&T (Bell Labs) shared UNIX with
colleges and universities
– Colleges made enhancements
– Berkeley Software Distribution (BSD)

See Introduction to UNIX
– by Fiamingo, DeBula and Condron
Linux

Compact version of UNIX for PC
– Created by Linus Thorvald

Not yet standardized
– Supported by a large, active user
community

Free versions available on the Internet
– approx. $50 for RedHat Linux
Major UNIX Components


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Kernel
Shell
File System
Shell & Utilities
Kernel
Hardware
Kernel

Core of UNIX OS
– Manages hardware, memory and file
system resources
– Controls transmission of information
between user application and CPU
– Stores information about the arrangement
of the computer system and the network
Shell
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
Interface between user and OS
Korn shell
– Most robust features

Bourne shell
– Subset of Korn shell

C shell
– Not related to other two shells
– Most widely used in SunOS
UNIX OS Components

Shell
– Shell program are interpreted, not
compiled
• commands are read and executed one by one
• compiled program is read and converted to a
machine language then execute all at once
• slower than compiled language such as C

Three types of Shells: Korn, Bourne,
and C
Shell History

Bourn -- Steve Bourne at AT&T Bell
Labs
– Original UNIX shell -- compactness &
speed
– lack features for interactive use

C -- Bill Joy (SUNW)
– friendly features for users
– larger and slower than Bourne
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Korn -- David Korn of AT&T Bell Labs
File System


Organizes data on disk in a hierarchical
structure of directories
File
– Program or data
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Directory/folder
– Similar to file drawer
• Each disk has root directory

Subdirectory
– Directory/folder within other directory
File System Structure

Root (/)
– /etc : system administration files
– /usr : executable commands, s.a. utilities
– /opt : third-party software
– /export/home or /home : user’s home
directory
Multitasking OS

Used to approach 100% of computer
resource utilization while increase user
productivity
– Reduced cost per user
• Time slicing
– Users can run multiple processes
• Increases user productivity

UNIX refers to task as “process”
– Usually maximum of 25 concurrent
processes per user session
Multi-User OS

Supports 1 - 2000 users
– Users share system resources


To approach 100 percent in computer
resource utilization while reducing the
cost per user
Share system resources
Interactive Mode
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
Immediate response to keyboard or
mouse input
“No news is good news”
– Display returns shell prompt after
commands are issued
• Different shells have different prompts
– Detailed feedback only when errors made
Networking Terms

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Host - a computer system
Host Name - a unique name for a
system
IP address - a number used by
networking
Network
– connects machines to enable comm.
between users on other systems.

Server provides resources to one or
More Terms
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Client is a machine that uses services
from one or more servers on a network
NFS (Network File System) enables
files to be shared across the network.
NIS (Network Information Services)
enables system administration functions
to be centralized on a server.
Client-Server
Network

Connects computers to enable
communication between users on
multiple systems
Clients vs. Servers

Server
– Provides resources to one or more clients
on the network
– Usually requires more powerful equipment
than clients

Client
– Computer that uses services from one or
more servers

Front end vs. back end
Set Up

User Account
– must have it set up before a user can log in
– contains essential user account info
• User name identifies a user to the system
– is created by System Administrator.

Bring your class registration/schedule to
the computer lab. The lab assistant will
set up the Unix account for you
Logging into CRC’s LAN

Login name
– First four letters of your last name
– Last four digits of student ID number

Initial password: new2lan
– Change password right away
Password Security
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
Do not choose a password that can be
related to you!
Use a password that does not resemble
a word in the dictionary
– Case sensitivity
Password Guidelines
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
No less than six characters
Must contain at least two alphabetic
characters and at one numeric or
special character
– can have spaces, avoid special characters

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Cannot be login name or reverse
New password must differ from old
password by at least three characters
Accessing CRC’s UNIX Box

From Windows 95 or Windows NT
– Connect to Internet via your ISP
– Start, Run…
– TELNET 165.196.137.125
or
TELNET cosumn.crc.losrios.cc.ca.us
User Account
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

Required for user login
Identifies user to the system
Contains essential user account info
– Special environment settings for user
– Mail file
Logging into CRC’s UNIX Box

Log into system
– Initial username is same as for CRC’s LAN
– Initial password: new2mini
– Password will not display when typed
– Connection times out if you take too long

Use exit command at the $ prompt to
log out
– Also possible to disconnect within TELNET
application
Entering UNIX Commands


Type commands with keyboard
To correct a typing error, use Delete key
– NOT the Backspace key

Press Enter key to send command to
kernel
Changing Your Password

Use passwd command at $ prompt to
change your password
– Type old password first
– Type new password twice
• Password will not be displayed when typed
• Password has to have at least one number in it
• Suggestion: Use same password as LAN
account and add a number, if necessary
Getting Help in UNIX


Use man command
Include command about which you want
help
– man ls
– Use man ls | more to display one page at a
time
• “Pipe” character
– Use Ctrl-C to interrupt file display
• If file is too long for one screen
Logging a TELNET Session


Record all activity within a session
In TELNET utility
– Choose Terminal, Start Logging…
• Specify filename to which to log
– Local drive
– Network drive (U: drive in CRC lab)
» Up to 5 MB of space
– Choose Terminal, Stop Logging to stop
writing to log file
The script Command

Logs commands entered and results
displayed
– If no filename specified, script logs to file
typescript

Type exit to stop logging and close the
log file
Printing Log Files


Type lp filename to print to CRC lab
FTP file to home computer and print to
local printer
– Printing from DOS Editor may be easier
than from Notepad
• Potential problems with line breaks
• Turn off Word Wrap
UNIX Commands

Command line format
– command [ - option(s) argument(s)]



Options modify the command
Arguments tell the computer to what to
apply the command
Example
– cd [directory_name]
– ls [aFIR] [pathname]
Command Syntax

Command Line Format
– command [option(s)] [argument(s)]
– case sensitive
– blank space does matter since it is the
delimiter for the shell
– do not necessary require all three parts
– 256 characters can be entered on a single
command line
Commands
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passwd
ls
cd
pwd
cp
rm
mv
Commands
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cat
more
man
mkdir
rmdir
date
echo
Commands
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cal
head
tail
wc
grep
find
Commands
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cd [ directory_name]
pwd
ls [ -aFlRt] [pathname]
man command
Commands
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pwd -- present working directory
cd -- change directory
mkdir -- create a new directory
ls -- diplays contents of your directory
– l -- stands for long information
– F -- File type option
– a -- display all files (including customization
files)
– R -- display recursively all directories/sub-
Commands

ls -F will display the following symbols
next the listing of files:
/
for directory
*
executable file, shell script
@
symbolic link
none text file (ASCII)
Commands
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rmdir - remove directory
head -n --- displays the first n lines
tail -n -- displays the last n lines
wc -- word count command to display
numbers of lines, words, characters
diff -- to display the differences between
two files.
Commands

grep -- search for a pattern in a file or
files
The cal Command


Displays a calendar on the screen
Syntax: cal [ [month] year]
– Month from 1-12
– Year from 1 to 9999 (!)

Example: cal 1999
– Displays the calendar for 1999
– Eastern and Western calendars were
combined in 1752
• Check out September 1752!
The who Command

Lists current system users
– Syntax: who
– Example: who | sort -r
• Sorts users in reverse order
– Example: who | grep geisslm
• Allows you to check whether or not user
geisslm is logged-in
– More details on examples later
Directory Structure
/
/home
/dev
/usr
/bin
/cis14a
/user A
/user B
/home
Path

Absolute path
– Type pwd at $ prompt
• Present working directory
• /usr/cis14a/user B/home
– To change to directory, type
cd /usr/cis14a/user B/home

Relative path
– From /usr/cis14a/user B directory, type
cd home
File Path


absolute path -- Starts with / (stands for
root directory) and go to where you
want to go
relative path -- start from where you are
and move to sub-directory or parent
directory
The cd Command


Navigate directory structure
Type cd .. at $ prompt to change to
parent directory
– Directory above current directory

Type cd without attributes to change to
home directory
Special Directory Names


. represents current directory
.. represents parent directory
– “Above” current directory in directory tree

Combine .. and “sibling” subdirectory
name to move to “sibling” subdirectory
– To change from /usr/cis14a/user B
directory to /usr/cis14a/user A, type
cd ../user A
The ls Command



List the contents of current directory
Type ls at $ prompt
Directory entry types
– - (hyphen) for file
– d for directory
ls Command Options
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Directory entry type
User/group/other (world) permissions
Number of links
Owner name
Owner group
File size in bytes/blocks
Date of file creation/last access
Filename/directory name
ls Command Options

ls -l lists details about contents
– Long version


ls -F shows slash (/) after directory
name listing
ls -R lists contents of entire tree
(including subdirectories)
– Recursive
More ls Command Options
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ls -r lists contents in reverse order
ls -l (filenames) to list specific files
ls -a displays all contents, including
hidden
ls -s lists size of file/directory in blocks
– 1 block = 512 bytes

ls -i displays system’s item number for
each directory entry
More ls Command Options

ls [directory name] lists contents of
other directory
Combining ls Command Options

Possible to combine ls command
options
– ls -a -F is the same as
– ls -aF

| more option
– Say “pipe more”
– Lists one screen at a time
• Example: ls -R |more
• More on “piping” later
UNIX Filenames

At least one character long
– Maximum length: 255 characters

Case-sensitive!
– Uppercase and lowercase characters are
distinct
• Unlike DOS or Windows 9x
Special Characters in UNIX

Filenames cannot contain certain
“special characters”
– Special meaning to the shell

Examples
–&;|*?‘“`[]()$<>{}^#/\
– see p. 38 in Sobell textbook for list
UNIX Wildcards

Wildcards replace characters
– * replaces zero, one or more characters
– ? replaces one character
– [ ] match one of the choices inside brackets
– { } match each of the choices inside braces

Example: ls ?h*e
– Returns ah123e, bhe, 1h23e, etc.

Example: ls t[aeiou1-3]p
– Returns tap, tep, tip, top, tup, t1p, t2p, t3p
Creating a Directory

Type mkdir command at $ prompt
– Example: mkdir reports

Possible to create multiple directories
with one command
– Use space as delimiter
– Example: mkdir memos letters
Clearing the Screen

Use clear or cls command to clear
screen
– Clears screen buffer
– $ prompt only will appear at top of screen
More mkdir Command Options

mkdir -p cis14a/hw1
– Creates cis14a directory as well as hw1
subdirectory below cis14a directory

Use -p option to create multiple
subdirectories at multiple levels at the
same time
– Example: mkdir -p cis14a/hw2 cis14b
The rmdir and rm Commands

Use rmdir to remove a directory
– Current directory must be parent of
directory to be deleted unless absolute or
other relative path is specified

If directory is not empty, use rm
command
– rm -r hw1 for recursive remove
– rm -ir hw1 for interactive recursive remove
• System will prompt for confirmation
The cat and more Commands

cat [filename]
– Displays contents of file

more [filename]
– Displays contents of file in segments
– Press Enter key to display one line at a
time
– Press Spacebar to display one screen at a
time

Similar to pg [filename]
Ctrl Commands
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Ctrl-c interrupts current activity
Ctrl-u erases current command line
Ctrl-w erases word in current command
line
Ctrl-s stops scrolling screen output
Ctrl-q restarts scrolling screen output
Other commands can be customized for
user by administrator
The head and tail Commands

head [-n] filename
– Displays top portion of file
– head -5 hw1 displays first 5 lines of file
hw1

tail [-n] filename
– Displays bottom portion of file
– tail -10 mbox displays last 10 lines of file
mbox
UNIX Editors


Use editor to create and edit files
Several editors available
– vi - most commonly used
– pico - not included in SVR4
• Not available at CRC
– emacs - not included in SVR4
• Not available at CRC
Visual Editor (vi)

Type vi at $ prompt to start editor
– vi [filename] to edit existing file (p. 212)

Three modes (p. 183)
– Command mode
• Hit Esc key to access command mode
– Input (Text) mode
– Last-line mode ([shift]&[colon] keys)
Accessing vi’s Insert Mode

From command prompt, press
– i to insert text before cursor
– I to insert text at beginning of line
– a to append text after cursor
– A to append text at end of line
– o to open new line below cursor
– O to open new line above cursor
• Page 214
Accessing vi’s Last-Line Mode

From command mode, press : (colon)
– Necessary to save file and exit vi
vi Cursor Movements

Command mode
– j or  moves cursor down one line
– k or  moves cursor up one line
– l or  moves cursor to the right
– h or  moves cursor to the left
– Ctrl-D moves down one half screen
– Ctrl-U moves up one half screen
– Ctrl-F moves forward one screen
– Ctrl-B moves backward one screen
More vi Cursor Movements

Command mode
– w moves to next word
– $ moves to end of line
– G moves to last line
– Many more...
vi Commands
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dd - delete one line to buffer
ndd - delete n lines
x - delete one character
dw - delete one word to buffer
d$ - delete to end of line to buffer
d0 - delete to beginning of line to buffer
Command Mode

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u -- undo a last command/change
. -- do last change again
Copy Text
yy - yank a copy of a line to buffer
nyy - yank a copy of n line to buffer
yw - yank a copy of a word to buffer
Past Text
p -- put buffer after a cursor
P -- put buffer before a cursor
Command Mode


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
cw -- change a word
ncw -- change n words
c$ -- change to end of a line
r -- replace one character
R -- replace the text (type over)
Last-Line Mode Commands

set showmode indicates Insert Mode
or Command Mode
– At bottom right of screen




set nu displays line numbers
set nonu turns off line number display
set list displays invisible characters
set ic specifies that pattern search
should ignore case
Searching File Contents


Access vi’s command mode
/[string] finds next occurrence of string
– /^[string] searches for string at the
beginning of a line
– /\>[string] searches for string at end of
word
• More examples on p. 197 of textbook
Last - line Mode

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

To turn off an option, put a “no” infront of
the variable, i.e.,
set nu
set nonu -- to turn it off
Search for text
/text -- go forward to the first occurence
of text
?text -- go backward to previous
occurence of test
Moving and Deleting Lines




:3,8d deletes lines 3 to 8
:4,9m 12 moves lines 4-9 to line 12
:2,5t 13 copies lines 2-5 to line 13
:5,9w filename writes lines 5-9 to
filename
File Management Summary



Copying
Renaming
Moving
The cp Command

Create an exact copy of another file
– With the same name in a different directory
• Possible to specify target directory only
– With a different name in the same directory

Syntax: cp [source] … [target]
– Example: cp misc ./w1/misc
• Copies file misc to subfolder w1 with the same
name
More About the cp Command

Example: cp w2/* w4
– Copies all files from w2 directory to w4
directory
– Does NOT copy subdirectories under w2

cp -r w2/* w4 also copies subdirectories
– Recursive
– Lowercase “R”!
Copying Multiple Files

Example: cp test test.out w3
– Copies files test and test.out to w3
directory
• w3 directory must exist
The mv Command

Moves and/or renames a file
– Original file will disappear
• Different from cp command

Example: mv test exam
– Renames file test to file exam

Example: mv exam w4
– Moves file exam to directory w4
• w4 directory must exist
• mv command will not create it
Commands For Analyzing And
Manipulating Files

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


sort - sort file contents
grep - search file for a pattern
diff - point out differences between files
comm - details file differences
wc - counts words, lines and letters in
file
compress - reduce file size to conserve
disk space
The sort Command


Sort information within files and/or
merge different files
Example: sort [filename]
– Sorts [filename] alphabetically by first word

Example: sort -f +2 [filename]
– Sorts [filename] alphabetically by third
word while ignoring case-sensitivity
The grep Command




Global regular expression pattern
Find text patterns in files
Syntax: grep [options] pattern [filelist]
Example: grep echo test1
– Finds pattern echo in file test1 and displays
lines matching pattern
More grep Command Examples

Example: grep -c echo test1
– Displays line count of lines matching
pattern

Example: grep -l echo
– Displays name of file that contains one or
more matches
The diff Command



Shows lines that are different between
two files
Syntax: diff [filename1] [filename2]
Example: diff t1 t2
– Lists line and column number
– Lists different text patterns
The comm Command

Displays line-by-line comparison of
sorted files
– Files must be sorted!


Syntax: comm [filename] [filename] …
Example: comm file1 file2
– Results displayed in three columns
• file1 unique text patterns
• file2 unique text patterns
• common text patterns
The wc Command


“Word Count”
Display number of
– Lines
– Words
– Characters


Syntax: wc [options] [file-list]
Example: wc -lw memo
– Displays the number of lines and words
contained in the file memo
The compress Command

Compresses files to reduce amount of
space required on disk
– Similar to ZIP utility in DOS/Windows
– Compressed file cannot be
viewed/executed until decompressed

Syntax: compress [filename]
– Results in file filename.Z

Example: compress -v text
– -v option displays compression ratio
Limiting Access to Resources

Use permissions
– Not available in DOS
• Usually available only on network operating
systems (NOS)

Who can change permissions?
– Owner of file or directory
– Administrator
Cis-14A: Misc

Printing
– lp (after using script command)
– File Transfer Protocol (FTP)
• Open Dos Command window
• ftp 165.196.137.125 to log in
– Telnet Preference menu
• Name your file, and location
• start logging, do work, and stop logging
• Use word processor to print your file
Cis-14A: Misc


Turn in assignments 1 and 2
File Structure
– Tree structure
– Directory, and Files
– File names
• Extension
– Absolute and Relative Path
– cd, mkdir, rmdir, rm, cp, mv

Midterm 1
File Structure


Pyramid structure, inverted tree
Each directory -- a subject
– a folder
– can be divided into smaller directories for
more clarity or easy to use
– sub-directory(ies) and/or file(s)
– the end of a path
File Structure

File Name
– 14 chars, some has up to 255 chars
– A-Z, a-z
–0-9
– underscore (_)
– period (.)
– comma(,)
File Structure

Filename Extension
– usually after period (filename.ext)
– can use more than one period
– meaningful
• .ext, .c, .txt, .990206
– Invisible Filename
• start with a period (.filename)
• ls -a
File Structure


Absolute and Relative Paths
Commands that work with directory
– Change or go
– create, delete
– rename
– copy
– empty, or non-empty
File Structure

Standard Unix Directories : / -- root
– /home, /export/home
– /usr -- system information
• /usr/bin
• /usr/sbin
– /etc
– /var -- files that vary as system runs
– /tmp
– /dev
File Structure

File or Directory Permission
–r
–w
–x

ls -l
read from the file
write to the file
execute the file
File Structure

chmod mode filename
– mode
• who
• op
• permission

File owner or root can change
permission of a file
File Structure

Symbolic
– chmod u+x,g+w,o+r

Numberic
–r=4
–w=2
– x=1
• rwx=7
• rw-=6
File Structure

Links
– ln -- link command
– ln associate_file destination
– hard link
– soft link
– ls -i
File Structure

Question
????
BREAK
Redirection



Standard Input
Standard Output
Redirect Output
– cat > test
– cntl-d to end

Redirect Input
– command [arg] < filename
Redirection

Appending
– Use command >>

Examples
Pipes





command_a [arg] | command_b [arg]
command_a > temp
command_b < temp
rm temp
Examples
Filter

Processes an input stream of data to
produce an output stream of data
– who | sort | lp
– who | tee test | grep user
Metacharacters




*
?
[,,,]
{...}
UNIX/NFS Permissions

NFS file permissions
– Read (r)
– Write (w)
– Execute (x)

Permissions listed in sequence of
– User
– Group
– World (all other users on system)
File Permissions vs. Directory
Permissions
Permission
Read
r
Write
w
Execute x
File
display/
copy
modify
execute
Directory
list content
files add/delete
control directory
access
Default Permissions

Default permissions after creation
File:
rw-r--r--
Directory: rwxr-xr-x
The chmod Command

Change permissions
– Syntax: chmod opcode filename

Example: chmod u+w test
– Gives you permission to write to file test
– Does not influence existing permissions

Example: chmod g+r test
– Gives your group permission to read file
test
– Does not influence existing permissions
chmod Permission Categories




u - user
g - group
o - others (world)
a - all
Taking Permissions Away

chmod g-x
– Takes execute permission away from
group
– Does not change r and w permissions
Absolute Permissions

chmod o=x
– Assigns execute permission to others

Example: chmod a=x test
– Sets permissions to execute ONLY
– r and w permissions are eliminated
Setting Permissions Using
Symbolic vs. Numeric Mode

Symbolic mode
– rwx rwx rwx
– Example: chmod u+r test

Numeric mode
– 421 421 421
– Example: chmod 700 text
• Possible to set absolute permissions only
Redirecting Screen Output

Prevent output from echoing to screen
– Is sent to file/printer instead
– Example: ls > test.out
• Sends ls listing to file test.out

Caution: Existing file will be overwritten
without warning!
– Use >> option to append existing file
– Example: ls >> test.out
Capturing Keystrokes

Record keystrokes
– Use cat command
– Syntax: cat > filename
• Type text to capture to file
• Press Ctrl-D to stop capturing and write to
specified file
– Example: cat > test.out
Piping

Use the | (pipe) character
– Modifies or redirects previous command in
line
– Example: man ls | more
• Displays help for the ls command one screenful
at a time
– Example: who | sort | lp
• Sends a sorted list of currently logged-in users
to the printer
• Note: lp command must be last command
Communicating in UNIX

Real-time communication
– write
– talk

E-mail communication
– mailx
The write Command

Send instant message to other user on
UNIX system
– Similar to “chatting”
– Recipient must permit messaging
• Type mesg y at $ prompt
– Example: write geisslm
• Opens write session with user geisslm
• End conversation with “oo” (over and out)
• Press Ctrl-C to end transmission
The talk Command

Similar to write command
– Divides user screen into two windows
– Statements displayed in opposite window
on other end of communication
My “talking” appears here
Your “talking” appears here
The mailx Command

Send electronic mail from UNIX system
– Syntax: mailx [username]
• Type subject line
• Type message
• Press Ctrl-D to send message
– Example: mailx geisslm
• Type subject line and message
– Example: mailx geisslm < message.fil
• Sends file message.fil to user geisslm
Using mailx Interactively

Many options available
– Type ? at ? prompt to view list of available
options
– Example: t 2
• Types second message on screen
– Example: delete 3 (or d 3)
• Deletes message number 3 from message list
– Example: h
• Displays list of message headers
Mail Message Listing

Message type
– N - new message
– R - read message
– O - old message




Sender
Date and time
Size
Subject
Changing Message Options

Possible to change options while typing
message text
– Use ~ (tilde) character options
• Be sure to specify option after issuing
command
• Otherwise information may be missing

Specify in mailx command line
– mailx -s “E-mail test” geisslm < test.doc
• Sends file test.doc to user geisslm with subject
“E-mail test”
More About mailx

Replying
– r replies to all recipients of original
message
– R replies to sender of message ONLY
Exiting mailx Input Mode


quit command processes messages
exit command leaves mailbox
“untouched”
Aliasing

Alias
– For one username
– For multiple usernames
• Distribution list
– Example: alias entry in .mailrc file
• .mailrc is UNIX customization file
• Entry: alias users user1 user2
– Mail sent to alias users is forwarded to user1 and
user2
– Create current-session alias at $ prompt
Alias Advantages

Issue multiple commands through one
alias
– Example: alias home=‘clear;cd;pwd;ls’
• Clears the screen, changes to home directory,
displays current directory and its contents

“Rename” UNIX commands to DOS
commands
– Example: alias dir=‘ls -l’
• Possible to issue DOS-like dir command to
view contents of current directory
Removing Aliases

Use unalias command to remove
alias(es)
– Example: unalias test
• Removes test alias in current session
That’s All, Folks!


Course Review
Final Exam