Geek City:
Unix under the Hood of the Mac OS X
Peter Roll
Sun City TX Computer Club
Advanced Technology SIG
March 18, 2003
Summary: topics to be covered
Unix ....
|
1. Where it came from and how it got in under the Mac operating system (a little history...)
- Developed by computer scientists at Bell Labs in 1969, for minicomputers (new) for basic science and engineering research; handled numerical calculations, text manipulation, and all sorts of symbol-processing.
- UC Berkeley Computer Science Department extended and developed a new dialect of Unix during the 1970's, which came to be called the Berkeley Software Distribution (BSD Unix).
- Government agencies, the computer industry, and foreign governments wanted a standard version of Unix that would always produce identical results for calculations.
- Computer scientists representing the profession and these groups defined the Posix standard for Unix; the Berkeley Computer Science Department made its BSD Unix the first implementation of Posix.
- In the meantime, many computer manufacturers devised their own proprietary operating systems and versions of Unix, and the Posix standard has largely been forgotten.
- When Steve Jobs was fired as President of Apple Computer in 1986, he founded the Next Computer company.
- Next developed a computer system using Motorola processors and the NextStep operating system based on BSD Unix with an advanced graphical user interface and application development system.
- Later, Next ported the NextStep OS to run on standard Intel-based PC computers, thus enlarging their potential market.
- By the time Apple purchased Next in 1997, Apple had begun allowing 3rd parties to build and sell Mac-OS-based computers and had started a project, code-named Copland, to develop a new operating system eliminating some of the limitations built into the original Mac OS.
- Shortly after Apple purchased Next, Steve Jobs was named Interim President; his two major actions were to discontinue allowing Mac clones to be sold; and to initiate a review of the Copland project.
- Jobs and the senior technical staff brought over from Next concluded that the Copland project would fail.
- They developed an alternative OS strategy based on the NextStep approach, using BSD Unix as the foundation of the new OS and building an entirely new graphical user interface on top of it.
- The most difficult problem in developing the new OS (Copland or NextStep-based) was to allow old Mac proglrams to continue to function under the new OS, knowing this would be required while users adapted and accepted the new OS and developers rewrote their application programs.
- The solution to this problem was to allow old Mac OS to run under the new OS in so-called "classic mode," thus preserving the look-and-feel of the old OS and the functionality of the old programs.
Why Unix? What does it do that other PC OS's didn't do (Windows and Mac)?
Pre-emptive
multitasking and protected memory:
prevents one program or process from interfering with memory utilization of
another, thus preventing crashes and simplifying application program design.
Multiprocessor support: allows use of two or more processors by
the same task, thus making the computer faster.
Scalability: work the same way on the smallest and largest
systems available, with minimum ormaximum feature sets, all sorts of
peripherals, protected memory, multiprocessing, threaded processes; from the
smallest, most primitive micros to parallel-processing supercomputers
with hundreds of processors.
2.
How it's put together (a little architecture...)
... with apologies to the Computer Science profession ...
... and with apologies to Apple Computer Corp. ...
Some important characteristics of Unix operating systems:
- settings controlled by small text-based files
- settings files created and changed with simple text editor
- highly-coded text,
- so its easy to read and change (for anybody who knows the code!)
- easy to learn (for those who learn codes easily!)
- and it led to a weird jargon, including the word Geek
- and ... the most important characteristics of
- preemptive multitasking,
- protected memory,
- multiprocessor support
- scalability
3.
How it works (scratching the surface just a little...)
a. Important notes:
- Unix is case-sensitive
- not consistently, but when you least expect it and when it is most annoying or damaging
- convention: always use lower-case characters
b. Anatomy of a Terminal window, on opening (login):
|
Last login: Sun Mar 16 15:03:06 on ttyp1 |
Date, time, device |
c. Some definitions:
|
Unix directory |
a folder in Mac or Windows lingo |
|
Active directory |
the one that all the action will take place in at any given time |
|
root directory |
at the root or top level of the hard disk |
|
root directory |
/ |
|
active user account home directory |
~ |
|
pathnames in the file |
|
|
full pathname, e.g. |
/Users/proll/Documents |
|
pathname relative to active directory |
/Documents |
|
pathname relative to active user home directory |
~/Documents |
|
down one level in file system hierarchy |
/dirname |
|
up one level in the file system hierarchy (parent directory) |
../ |
|
change active directory command |
cd pathname (note the space as a delimiter!) |
d. The Unix File system
The file system under Mac OS X (column view, similar to Windows Explorer
-- shows relative position of files and folders):
The actual file structure under Unix contains much more at the root level
than is shown in the OSX finder!
|
[Peter-Rolls-Computer:~]
proll% ls |
What's found in this Terminal window:
- initial active directory is active user's home directory (~)
- ls is the shell command to list the contents of the active directory
- cd / changes the active directory to root
- ls lists the contents of the root directory; note that there are several files listed that are missing from the OS X finder window -- these Unix directories are unneeded in OS X and they are hidden, visible only in the Terminal window
- cd ~/documents changes the active directory to the Documents directory in the active user's home directory
- note that the case of the first letter of the word directory doesn't make any difference!
- ls lists the files and directories in the active user's Documents director
Some notes on the File system, Unix
and OS X:
/Users/proll/documents/Compclub is
the full path to my Computer Club folder; and that
~/Documents/Compclub is exactly the same path.
All info for a given user (settings, documents, etc.) is stored in the User
Account Home directory (or folder) (similar to the Documents and Settings
folder in Windows XP).
In the directory /Users/proll/ (same as ~/)
- the Documents directory-folder contains all user documents and other data (but you have to keep it this way!)
- ~/ Library directory-folder contains preferences or settings applicable only to the active user account
- the /Library directory-folder contains preferences or settings applicable to all user accounts
Applications
available for use by all user accounts are stored in the root /Applications
directory-folder
Appllications available for use only by a given user are stored within the
user's home directory-folder, ~/Applications
e. A few of the Unix Services:
(1) The Unix Shell: the tcsh shell is default for OS X
- but many other shells are available
- all shells are pretty similar -- they work the same way but have minor differences
- you can install other shells on OS X if you wish
(2) Some shell commands (Unix utility programs):
General format of shell commands: commandname options arguments
· Note that the spaces are essential delimiters
· options are of the format -x, where x is a code letter for an option
How do you find out what the commands do and what the options are?
· type the command man commandname
· this displays the Unix manual page for the specified command -- try it!
(3) Some commands or services we've already seen (above):
· ls
· cd
· man
· ls -la (list showing details (l) and hidden files (a))
|
Last login: Sun
Mar 16 16:33:30 on ttyp1 |
Some other useful commands:
Finding things on your hard disk: locate pattern
- pattern is a string of characters that can be contained in a filename or directoryname; the command will find all files and directories with that string in its name;
- a database of file- and directorynames
must be created before the locate command will work; this database is
created by the command
sudo /usr/libexec/locate.updatedb (note: this took about 5 minutes to complete on my computer); - use the man locate command to find out more.
Printing and Piping:
enscript filename: converts a file to postscript for printing to a
postscript printer (most laser printers)
atprint filename: prints a file to an AppleTalk printer; this command
must be set up first with the commands
- atlookup to find all of the AppleTalk devices connected to the computer, followed by the superu command
- sudo at_cho_prn to select the device you want to use to print (lyou need the superuser or root password for this one).
If the AppleTalk printer is a postscript printer, then you must convert it to postscript before sending to the printer. The way to do this is to Unix's piping capability: the pipe symbol | will pipe the output of one command into the input of the next; e.g., to print the manual page for the locate command,
man locate | enscript | atprint
Shell scripting, aka shell programming: the Unix alias:
|
[Peter-Rolls-Computer:~] proll% ls |
Aliases can be saved to the /bin/.cshrc text file so that they will always be active. An alias is a little shell program; you can construct some very complex programs this way!!
4. What you can do with Unix if you're not a Geek:
normal applications software available
MS Office replacements:
- file compatibility with MS Word, Excel, PowerPoint (Open and Save as...)
- usually run in the X11window, so you need to install X11, too
- available for online download, often at no cost (but 1xx MB, so it takes a while), with X11 and everything else you need
- usually available on CD for $40-50, with X11 and everything else you need
- Examples:
- OpenOffice
- ThinkFree Office (written in Java, so it runs on every platform!)
Browsers:
- Netscape
- Mozilla
- Lynx (text-only, so it's fast, if nothing else)
- others....
Utilities: thousands of these
One example: CarbonCopyCloner, by Mike Bombich
- a script invoking several pre-existing Unix programs to make a bootable copy of a hard disk and to back up all or parts of a hard disk to a variety of media (CD-R, a 2nd HD, etc.)
- downloadable giftware (pay the author what you want if it's been usefult to you)
- simple -- it just works
- no comparable simple program for Windows
The
Good News: thousands of programs available
at no cost, downloadable
The Bad News: most of them are designed for other Geeks, rather
than ordinary users,
but if there's something usable for just about every purpose if you are
willing to look and tolerate a little geekiness.
5. The Geek's Business Model: the economics of Unix
The open-source movement -- an integral
part of Unix:
From the Apple Darwin
FAQ page:
Q. What is open source?
Open source is a term for the historical development model used by the
Internet community to facilitate distributed development of complex,
high-quality software. The basic principle is to involve as many people as
possible in writing and debugging code, by publishing the source code and
encouraging the formation of a large community of developers who will submit
modifications and enhancements. Community efforts such as BSD, Linux, Sendmail,
Apache, and Perl embody the spirit and power of the open source model.
Q. Why is Apple opening up its source?
We believe the open source model is the most effective form of development for
certain types of software. By pooling expertise with the open source
development community, we expect to improve the quality, performance and
feature set of our software.
Secondly, we realize many developers enjoy working with open source software,
and we want to provide them the opportunity to use that kind of environment
while delivering solutions for Apple customers.
The open-source movement is
- Diverse; based on several rather different kinds of open-source licensing:
- Open Software Foundation; the GNU license -- copyright; use requires that all derivative works go into public domain and be distributed;Free Software Foundation's General Public License (GPL),
- BSD license
- Apache license,
- Netscape and Mozilla Public Licenses
- Sun's Community Source License.
- Apple Public Source License
- Based on a fundamental difference between the economics of goods and services and the economics of information:
- goods and services: can be pounit value is reduced or eliminated by consumption
- information: value is increased by use and by the number of people using it; value is created by the consumers
- may require new business models and a new form of economics that is not yet understood or even much studied
- Full of private and corporate ideological agendas, most of which have little to do with the realities of the world and how the future is likely to develop
The results of this information and
communications revolution and the surviving business and economic models
will become clear only after decades of evolution -- not in our lifetime.
What better name than Darwin for an operating system that grew out of the beginnings of
this revolution?
6. A Few
References: Unix under Mac OS X
Taylor and
Peek, Learining Unix for Mac OS X; O'Reilly, Sebastopol, CA, 2002; 126 pgs.
O'Reilly is the definitive publisher of reference and textbooks on alll
varieties of the Unix OS; see their website
for many more useful references
Listing of Unix & Open-Source programs that will run on OSX Macs: http://www.apple.com/downloads/macosx/unix_open_source/
Apple's Open-source Darwin home page; explains briefly the concept
behind Apple's open-source approach and the architecture underneath OSX:
http://developer.apple.com/darwin/
The Fink Project " ... bringing the full world of Unix
Open Source software to Darwin and Mac OS X . We modify Unix software so that
it compiles and runs on Mac OS X ("port" it) and make it available
for download as a coherent distribution. Fink uses Debian tools like dpkg and
apt-get to provide powerful binary package management. You can choose whether
you want to download precompiled binary packages or build everything from
source." http://fink.sourceforge.net/
SourceForge.net: " ... the world's largest
Open Source software development website, with the largest
repository of Open Source code and applications available on the Internet.
SourceForge.net provides free services to Open Source developers." http://sourceforge.net/