Transcript Week 1 Power Point Slides

Why UNIX?
• Superior Initial Design
– Multi-user, Multiprogramming, Protected mode, Many Support
many Devices
– Written to optimize the use of memory and maximize efficiency
– Remained consistent to its original design
– Not driven by profit motives
– Source code compatible across platforms
• Other Operating Systems
– IBM MVS: initially designed for a batch punch card environment
with proprietary monitors
– DOS: initially ran on very single user, limited memory computers.
Multiprogramming was added on as an afterthought.
UNIX downside: Geared for power users using a command line interface
OS Benchmarks (A bit dated)
OS
Loop
Write
Seek
Read
FreeBSD
3.0
21
7.3
17.8
Linux
3.0
14
16.3
18.2
SCO (Unix) 2.4
34
16.6
24.5
Window 3.1 6.2
190.4
26.6
56.8
Linux
15.97
11.98
13.95
125.94
11.79
47.45
3.0
Window 95 6.65
Why C
• Fast
– Designed to produce code nearly as fast as assembly
code.
– Designed to be able to support Operating System
development.
• Portable
– Recompiling will cause code to work across platforms
– POSIX provides a standard OS interface
• Powerful: Able to perform low level functions
• Small: C code is smaller than other high level languages
• Popular: C is a very popular programming language
Downside: With power comes danger. You have to know what you are doing
Downside: Not object oriented. You have to be disciplined
Language Comparisons
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Assembly – small, fast, not portable
C – almost as small and fast, portable
Fortran, Pascal – Slower, specific purpose
C++, PL1 – Complex, larger and slower
Java, Basic – Byte oriented, even slower
Scripting languages – interpreted, slow
Memory Use Example
C
Executable
Memory
3811
820kb
C++ 18033
1052 kb
Note: JIT technology makes byte code languages more speed competitive
History
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1960s was the era of batch processing
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Multics attempt at an OS
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Punch cards, paper tape, Magnetic tape
System operators
general purpose, multi user, time sharing
project died: technology of the time could not support the effort
1969 – AT&T Bell Labs (Ken Thompson) writes first
version of Unix in BCPL
1972 – Dennis Ritchie creates "C", UNIX written in C
1984 – Richard Stallman starts the free Software
Foundation (FSF) with goal to develop a free version of
UNIX (GNU – Not Unix)
1991 – Linus Torvalds writes Linux Kernel (GNU+ Kernel)
2000 – User Friendly UNIX (Mac OS X) interface
Academia likes UNIX based systems; they are free
"Pigs get fat, Hogs get slaughtered"
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AT&T develops UNIX at Bell Labs
Berkeley gets a copy and makes enhancements
AT&T commercializes UNIX and makes it proprietary
Richard Stallman was an AI researcher at MIT
– He objected to the trend towards proprietary software.
– He formed GNU (GNU's not UNIX)
– GNU to replace the UNIX shells and utilities
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Berkeley objected to AT&T licenses, and developed BSD
Andrew Tananbaum created Minimal Unix (MINIX)
Linus Torvalds (CS student) coded the Linux kernel
Open source produces lots of high quality software
No open source movement implies no Internet
UNIX Structure
• The Kernel is the part of
the OS always in memory
• Includes
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File system
Device manager
memory management
process scheduler
well defined interface
• GUI: Point and click
(many wrappers to the XWindow interface)
• Shells: command line
Users
GUI's
Shells
Kernel
Hardware
Shells
• A command-line interface that allows users to
directly access operating system capabilities
• There are more than one shells possible in
UNIX: csh, bash, tsch, ksh, etc
• Text only commands, without using the mouse.
“Finger never leaves keyboard.”
• Groups of commands can be strung together in
unique ways to make difficult tasks possible,
without creating specialized programs
Comparison between shells
• sh (bourne shell)
– small
– good scripting capability
– popular with system
administrators
• csh (c-shell)
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extends sh
uses a c-like syntax
created by Bill Joy
popular with UNIX
users
• bash
– "bourne-again" shell
– extends sh with some
features form csh
– The linux default
– We will use bash
• tcsh
– extension of csh
Where do we find a UNIX
• Virtual “Linux” servers provided by IT
– Log In (Putty program) creating a secure shell (SSH)
with your standard username/password
– See a shell prompt (>, &, $, etc.)
– Type your command
– The shell will execute the command and return with
another prompt
• Mac/OS provides a UNIX-like system
• You can install LINUX on windows systems
using a dual boot
• You can install CYGWIN on a windows system
The Shell language
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Remember
– Shell commands are case sensitive
– The general form of commands are
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Syntax: <cmdName> [-flags] [args]
Note: <> indicates something that is required, [] indicates
something that is optional
Example: >echo –n I love UNIX
1. > is the shell prompt
2. echo is a UNIX command
3. -n is a flag
4. I love UNIX are three arguments (space separators).
5. This command outputs the arguments: I love UNIX
6. The –n inhibits a new line after the output
Display prompt  Enter command from command line  execute/process command
Some basic commands
>clear
clears the screen
>who
lists the users currently logged in
>logout or >exit (Exit is recursive)
exit the shell, and wait for another log in
>echo whatever I want
outputs the data to the right
>man <manName>
display UNIX manual for the command, manName
Note: Use ctrl c to abort commands (abbreviation ^c)
Shell Variables
• Example: $<varName>
• The shell has some built in variables
$TERM represents the terminal type
$SHELL represents which shell is active
$USER user name
$PATH places to look for executables
• What do you suppose the following does?
>echo I have a $TERM with $SHELL shell
• Printenv outputs environment variables, set
outputs environment and shell variables
Environment variables: those common to all shells
The File System
• The file system is a hierarchical tree structure of
regular files and directories (folders)
• Within the file system, there are individual files
for programs and data, and directories that
contain other files
• Directory Examples
– The root directory is / (analogous to c: on Windows)
– A users home directory is ~
– /faculty/harveyd/public_html/classes/cs367/ppt
Important: File names are case sensitive. Name only with numbers, letters,
and underscores. Punctuation characters can conflict with shell commands
Explore Linux (partial directory list)
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/root : super user’s home directory
/ : system root directory (like Window’s c: )
/tmp : temporary sharable files available to all users
/bin : executables required for kernel
/sbin : executables requiring super user access
/etc : system configuration files
/var : system changeable files
/opt : optional installs
/home : contains all user’s home directories
/mnt or /media : mount points
/dev : system devices
/boot : contains linux kernel
/usr/bin : applications coming with distribution
/usr/sbin : applications installed later
File Commands
>cd
Change directory
Example using 'absolute' pathnames (cumbersome)
/faculty/harveyd/public_html or ~/dir1/dir2/dir3
Example using relative pathnames
>cd ~ (go to the users home directory)
>cd public_html (public_html directory relative to working directory)
>cd .. (change to parent directory above the working directory)
>pwd
Displays the 'absolute' pathname from the root with '/' separators
Note: >cd . refers to the current y
Note: The shell variable $PWD contains what pwd displays
more/ less and cat commands
Command
Action
Space or f or
page down
Go forward
one page
b or page up
Go back one
page
Explanation: more is a
program that displays one
page at a time and then waits
for you to enter a command
Explanation: less is an
enhancement to more (“less is
more”)
/keyword
Find first page
with keyword
/ or n
Find next
occurrence of
keyword
Up or down
arrows
Move up or
down one line
Note: The man command
uses more commands, and
displays a page at a time
return
Go forward
one line
q
Quit
>cat <filename>
Display the contents of the file
Problem: too much to display
Solution: >more fileName
List contents of a directory
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List all files that match the pattern
>ls <pattern> … <pattern>
A pattern can be: a combination of letters, asterisks, and
question marks.
– Asterisks mean any sequence of characters
– ? is any single character
– Example: *cat?dog* refers to any file name having the word cat
separated by one character frm the word dog anywhere in the
file name
– [abc] means any single character between the brackets (but
cannot use / or . characters in the list.
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Flags (refer to the man command for a complete list
>ls –l lists files in a long format
>ls –a lists all files including hidden ones (starting with a period)
>ls –al or ls –a –l lists files combining the flags
man <anycommand> gives information how to use it
File links
• Hard link (ln myFile myLink)
– Points directory to the file’s data
– We can delete either the file or the link
– The actual data is removed when the last link is
removed
– It is illegal to link to directories
• Symbolic links (ln –s myfile mySymbolicLink)
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References file’s directory entry by name
myfile does not even need to exist (link broken)
Deleting a link, never deletes the file
Equivalent to Windows shortcuts
Circular links cause errors when access is attempted
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Additional Commands
Rename file: >mv <oldName> <newName>
Copy file: >cp <file> .. <file> <destination>
Secure copy to remote computer:
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scp <file>...<file><destination
Example: scp cat.c [email protected]:drop
Delete file: >rm <file> .. <file>
Make a directory: >mkdir <directory>
Execute allowed as superuser: >sudo command
Which version of a command: >which <command>
Type of command : >type <command>
Who’s logged in: >whoami
Detailed documentation: >man <command>
Brief description: >whatis <command>
Description of shell built-in commands: info <command>
Note: Most commands have many flags. For example –r is
often used to access all subdirectories (ex: rm –r <dir>
More on flags
• cp –vfirl or rm –rifv --help
– Note that we can string multiple flags together
– v = verbose, f = force, i = interactive, r = recursive, l =
link instead of copy
– Most also have long english type versions preceded
by double dashes. For example: cp –recursive
• ls –dlaRr
– d = directory (not contents), l = long form, a = all files,
R = recursive, r = reverse order
• mkdir –p (create parent directories if not found)
• man –k term (same as apropos) to find all
entries related to term