TweetFollow Us on Twitter

Unix Underpinnings on The Mac

Volume Number: 22 (2006)
Issue Number: 1
Column Tag: Programming

Mac In The Shell

Unix Underpinnings on The Mac

by Edward Marczak

What To Use and What to Avoid

"Think Different" is a great campaign, however, it's nice to know - and downright important - that we share some things with others. Coincidentally, I'm sometimes reminded that I need to go back and cover the basics: the bare essentials. What better time to do that than the new year? (even though time is an abstract, it's a useful tool). So, while us Mac users like to run different, think different, be different, we can learn a lot by looking at what we have in common with other Unix systems.

Introduction

Although I don't hear it too much any more, when OS X first shipped, there was a, "OS X is not Unix" current from certain corners of the Web. While OS X certainly does some things differently than a traditional Unix, and continues to do so increasingly (especially under Tiger, which is all I refer to here), that doesn't make it "not Unix." As Apple "Applefies" more of the Unix that does underpin OS X, let's see what keeps us tied to our Unix brethren.

FreeBSD

The Unix conventions and utilities found in OS X are largely based on, and often taken straight from, FreeBSD. In Beta-vs-VHS thinking, perhaps the *BSDs are Beta to Linux's VHS: a loser in mindshare, but certainly technically superior. If you've used Linux, but not any of the BSDs, as a techie, you owe it to yourself to dive in and check it out. If you have a spare PC, or even an unused Mac, sitting around go download or purchase FreeBSD and give it a whirl. It'll also improve your OS X skills. Next time you're putting together a public facing web site on a budget, and are ready to reach for Linux, try FreeBSD instead.

cron

cron is the sub-system that is most likely completely ingrained in a sys-admin's skull. It would almost be impossible to be an effective admin without it. For the uninitiated, cron is a daemon that schedules jobs to run at certain times. You may have heard that cron no longer exists or runs as of Tiger. Nothing could be further from the truth. Apple's new subsystem, launchd, tries to take over all responsibilities for cron...and doesn't really succeed. A clean install of Tiger has no cron jobs installed by default. If you upgraded from Panther, you'll have your cron jobs carried over.

launchd is Apple's new system for managing daemons and 'agents' on a system-wide and per-user basis. It's a one-system-to-rule-them-all kind of thing that currently only half succeeds. I covered launchd in depth in the May 2005 Mac In The Shell column, pointing out both the advantages and disadvantages. If you're just joining us, I'll give you the top three reasons why launchd can't currently replace cron:

    1. cron is way too engrained to go away anytime soon. This leads to...

    2. launchd's reliance on plist files for configuration. As nice as the XML based plist is, there are enough tools out there that can easily update a crontab file thanks to it's plain-text based format.

    3. Flexibility. While launchd can schedule a job to run at a certain time and date, it can't currently match cron's scheduling flexibility. As in "0 8-20/3 * * 1-5 root /path/to/program" which runs the given job every three hours, Monday through Friday only between 8am and 8pm.

In short, cron kicks butt! You certainly need to learn about launchd, but don't be afraid to schedule things with cron. It's not dead yet! If you're looking to learn a bit more about it, cron on OS X was covered in depth in the March 2005 MacTech.

xinetd

Much like cron, xinetd still exists, but is sitting idle. Also like cron, its features have been subsumed by launchd. Unlike the advice I gave for cron, this is a system to abandon on OS X.

xinetd, like inetd before it, and now launchd, all act as "superservers." Originally, every daemon on a system would launch itself, daemonize, deal with source IP checking (maybe), reserve their listening port, etc. Wietse Venema created "tcp-wrappers", inetd, to act as a master listening agent, which could be configured to enable, disable and restrict access to other daemons that needed to listen for outside requests. The request actually comes into the super-server and then, if appropriate, gets passed on to the real daemon to do the work.

Launchd really excels here: from it's deep integration into OS X, through its efficient use of resources, it's the way to go. Use xinetd if you need to wean yourself off due to use on another Unix. However, make sure it's only a transition. Switch to launchd as soon as possible for this!

Networking Tools

While the use of some of these CLI utilities are deprecated under OS X, they all still work. Certainly not deprecated is netstat. netstat shows information about various network related data structures. It's primarily used to show active network sockets. This is one way you can hunt down exactly what's listening to a port (http://www.radiotope.com/writing/?p=8). netstat will also display the routing table when used with the '-r' switch - an important troubleshooting tool.

ifconfig has been the traditional way to view and set information about a network interface. While ifconfig does work, it may not do precisely what you want. It does still work perfectly as a way to view information about an interface. However, to change or set up an interface, ifconfig has been superceded by networksetup. networksetup is as extensive as any other tool, including any GUI, and should be used over ifconfig.

Like other Unicies, OS X sports an /etc/resolve.conf file. The resolver file configures access to DNS servers for applications, including order of name server lookup, their ports and search domains. Unlike other Unicies, OS X will automatically fill in and adjust /etc/resolv.conf based on your network configuration. Other Unices use /etc/resolv.conf as the origin of this information, and you edit it manually there. OS X plops the sum of other sources into /etc/resolv.conf. Don't edit it manually!

ipfw, the IP FireWall, from FreeBSD has also been included in OS X. It's what handles the software firewall behind the scenes. Note, though, that ipfw is a FreeBSD creation. Linux uses iptables, OpenBSD uses pf, and other Unicies tend to have their own solution.

Config Files

Traditionally, Unix has been a system configured by text files. While Apple has introduced non-plain text config systems, such as NetInfo, OS X does tend to respect the traditional text files for compatibility reasons.

/etc/passwd, traditionally the user authentication database, is still present on OS X. /etc/group, used for group association is also present. Both files are ignored by default, but programs that may not know any better are free to read them. You can have the system reference these files normally by selecting the "BSD and Flat Files" option in Directory Access.

/etc/hosts is present and active by default. This is actually really good news. /etc/hosts is a host to IP database that is consulted ahead of DNS. I use hosts on a daily basis as I test web sites that I'm developing on my local machine. This way, each entry can be set up as a name-based virtual host in Apache. Very handy.

Text Processing Utilities

Due to the number of text files used to configure a traditional system, Unix is awash with programming languages and utilities that manipulate text. Thankfully, Apple saw fit to include all of the current choices out of the box.

perl version 5.8.6 is ready for use under OS 10.4.3. This is an especially nice treat seeing Apple listen closely to their developer audience. During the Jaguar days, perl tended to languish a few revisions behind the current release. Additionally, due to some non-standard choices made for 10.1 and 10.2, updating perl was not easy. Thankfully, version 5.8.6 is close to current - close enough that most utilities won't gripe about it. (Current is 5.8.7, but there's always some script that relies on the latest!).

sed, awk and grep are all where you expect them to be. Last month's column introduced sed, and will have a part 2 next month. These three form the triumvirate of power tools for text processing. Additionally, OS X includes 'tr', the translation utility and, of course, sort - one of the oldest text utilities for Unix platforms.

To round out the programming camp, OS X includes, out of the box, Python, ruby and PHP. Kudos to Apple for keeping this diverse base of utilities on the system, developers happy, and switchers comfortable.

Development

You may have noticed that many of the aforementioned utilities, and other products on OS X are open source that started life elsewhere (including Apache, sendmail, Postfix, Cyrus and others). What makes all of this possible, aside from the source code, is having development tools loaded up. Like some other Unicies, OS X sports gcc, the GNU C compiler. There's a link from 'cc' to the current 'gcc' that acts as a compatibility layer - most Unicies had run their C compiler simply as 'cc'. Most open source software that I've had the pleasure of working with compiles cleanly on OS X. This includes the recently released MySQL 5.

Additionally, the GNU Debugger, gdb, is on the system and ready for use. Interestingly, XCode is partially just a big, convenient front-end to gcc and gdb. Choosing to use these development tools certainly makes switchers feel right at home. Of course, once you get deep into OS X development, there are some great utilities that let you get deeper into the system (like CHUD and Shark).

Mail Systems

Thanks to the open development tools and open source software mentioned in the previous section, the mail systems bundled with OS X are the same ones you can find running on many other Unix platforms. The first huge win is Postfix. Up through OS X 10.2, sendmail was the default MTA. 10.3 brought the switch to Postfix. Written from the ground up with security in mind, Postfix is also an incredible performer. While there are many MTAs in use, including the venerable sendmail (and exim and qmail...) they all operate the same no matter the platform - save Apple's extensions that hook into OS X's authentication methods, which you can find the changes of on Apple's developer site (http://developer.apple.com/darwin).

A popular and powerful POP and IMAP server is Cyrus, from Carnegie Mellon University. Also introduced to OS X as of 10.3, Cyrus has been modified by Apple to work with their custom authentication schemes.

I covered troubleshooting Cyrus/Postfix and DNS as it relates to e-mail in the July and August Mac in the Shell MacTech columns. An upcoming column will get into the details of administering a Tiger based mail system.

Permissions

Yes, Tiger brings us ACLs, however, I find that most people don't know about them, or don't feel comfortable using them (even though I covered them in the May 2005 issue of MacTech!). This keeps us relying on POSIX permissions. Well, welcome to the club! Every Unix out there uses the same set of permissions - even though they may also have something that is more flexible. Of course, sometime with flexibility comes complexity, so, the more basic POSIX permissions will be around for a good long time. Like cron, they're ingrained in the brains of sysadmins everywhere (and, of course, you can find an in-depth tutorial in a prepubescent Mac in the Shell dating February 2005).

Number 1

The number one thing we have in common with other Unix users is Love! OK, maybe not love....but community! Mac culture really is a perfect fit into the Unix world where people tend to be passionate about the tools they use and the platforms they run them on.

Fin

Apple is adding a lot with the systems they've created for OS X. Of course, it's also fantastic to be able to leverage the history that Unix brings. While I wish everyone a very happy New Year, I'll remind you again: it's a great time to assess what you know, what you want to know, and what you need to learn. When you're summing that up, don't forget one of the best systems that OS X inherits from Unix: man.

Enjoy!


Ed Marczak owns and operates Radiotope, a technology consulting company. If you're reading this while at MacWorld Expo, and it's Wednesday, come see Ed present, "From the Chime to the Desktop" and learn all about launchd and the Mac boot sequence. Always more tech tips at http://www.radiotope.com

 
AAPL
$102.47
Apple Inc.
+2.71
MSFT
$44.88
Microsoft Corpora
+0.80
GOOG
$526.54
Google Inc.
+5.70

MacTech Search:
Community Search:

Software Updates via MacUpdate

RapidWeaver 6.0 - Create template-based...
RapidWeaver is a next-generation Web design application to help you easily create professional-looking Web sites in minutes. No knowledge of complex code is required, RapidWeaver will take care of... Read more
NTFS 12.0.39 - Provides full read and wr...
Paragon NTFS breaks down the barriers between Windows and OS X. Paragon NTFS effectively solves the communication problems between the Mac system and NTFS, providing full read and write access to... Read more
RestoreMeNot 2.0.3 - Disable window rest...
RestoreMeNot provides a simple way to disable the window restoration for individual applications so that you can fine-tune this behavior to suit your needs. Please note that RestoreMeNot is designed... Read more
Macgo Blu-ray Player 2.10.9.1750 - Blu-r...
Macgo Mac Blu-ray Player can bring you the most unforgettable Blu-ray experience on your Mac. Overview Macgo Mac Blu-ray Player can satisfy just about every need you could possibly have in a Blu-ray... Read more
Apple iOS 8.1 - The latest version of Ap...
The latest version of iOS can be downloaded through iTunes. Apple iOS 8 comes with big updates to apps you use every day, like Messages and Photos. A whole new way to share content with your family.... Read more
TechTool Pro 7.0.5 - Hard drive and syst...
TechTool Pro is now 7, and this is the most advanced version of the acclaimed Macintosh troubleshooting utility created in its 20-year history. Micromat has redeveloped TechTool Pro 7 to be fully 64... Read more
PDFKey Pro 4.0.2 - Edit and print passwo...
PDFKey Pro can unlock PDF documents protected for printing and copying when you've forgotten your password. It can now also protect your PDF files with a password to prevent unauthorized access and/... Read more
Yasu 2.9.1 - System maintenance app; per...
Yasu was originally created with System Administrators who service large groups of workstations in mind, Yasu (Yet Another System Utility) was made to do a specific group of maintenance tasks... Read more
Hazel 3.3 - Create rules for organizing...
Hazel is your personal housekeeper, organizing and cleaning folders based on rules you define. Hazel can also manage your trash and uninstall your applications. Organize your files using a... Read more
Autopano Giga 3.7 - Stitch multiple imag...
Autopano Giga allows you to stitch 2, 20, or 2,000 images. Version 3.0 integrates impressive new features that will definitely make you adopt Autopano Pro or Autopano Giga: Choose between 9... Read more

Latest Forum Discussions

See All

Fiete – A Day on a Farm Review
Fiete – A Day on a Farm Review By Amy Solomon on October 21st, 2014 Our Rating: :: A MEMORABLE EXPERIENCEUniversal App - Designed for iPhone and iPad Fiete – A day on a farm in an interactive app for young children full of... | Read more »
Tilt to Live: Gauntlet’s Revenge is Almo...
Tilt to Live: Gauntlet’s Revenge is Almost Here Posted by Jessica Fisher on October 21st, 2014 [ permalink ] One Man Left has announced the official release date of Tilt to Live: Gauntlet’s Re | Read more »
Sago Mini Monsters Celebrates Halloween...
Sago Mini Monsters Celebrates Halloween with Fun Costumes and Special Treats. Posted by Jessica Fisher on October 21st, 2014 [ permal | Read more »
Inferno 2 Review
Inferno 2 Review By Andrew Fisher on October 21st, 2014 Our Rating: :: TWIN STICK GOODNESSUniversal App - Designed for iPhone and iPad With tight controls and awesome, stark visuals, Inferno 2 is loads of fun.   | Read more »
Clips Review
Clips Review By Jennifer Allen on October 21st, 2014 Our Rating: :: CONVENIENT PASTINGUniversal App - Designed for iPhone and iPad Making copying and pasting more powerful than usual, Clips is a great way to move stuff around.   | Read more »
MonSense Review
MonSense Review By Jennifer Allen on October 21st, 2014 Our Rating: :: ORGANIZED FINANCESiPhone App - Designed for the iPhone, compatible with the iPad Organize your finances with the quick and easy to use, MonSense.   | Read more »
This Week at 148Apps: October 13-17, 201...
Expert App Reviewers   So little time and so very many apps. What’s a poor iPhone/iPad lover to do? Fortunately, 148Apps is here to give you the rundown on the latest and greatest releases. And we even have a tremendous back catalog of reviews; just... | Read more »
Angry Birds Transformers Review
Angry Birds Transformers Review By Jennifer Allen on October 20th, 2014 Our Rating: :: TRANSFORMED BIRDSUniversal App - Designed for iPhone and iPad Transformed in a way you wouldn’t expect, Angry Birds Transformers is a quite... | Read more »
GAMEVIL Announces the Upcoming Launch of...
GAMEVIL Announces the Upcoming Launch of Mark of the Dragon Posted by Jessica Fisher on October 20th, 2014 [ permalink ] Mark of the Dragon, by GAMEVIL, put | Read more »
Interview With the Angry Birds Transform...
Angry Birds Transformers recently transformed and rolled out worldwide. This run-and-gun title is a hit with young Transformers fans, but the ample references to classic Transformers fandom has also earned it a place in the hearts of long-time... | Read more »

Price Scanner via MacPrices.net

Select MacBook Airs $100 off MSRP, free shipp...
B&H Photo has 2014 a couple of MacBook Airs on sale for $100 off MSRP. Shipping is free, and B&H charges NY sales tax only. They also include free copies of Parallels Desktop and LoJack for... Read more
13-inch 2.5GHz MacBook Pro on sale for $100 o...
B&H Photo has the 13″ 2.5GHz MacBook Pro on sale for $999.99 including free shipping plus NY sales tax only. Their price is $100 off MSRP. Read more
Strong iPhone, Mac And App Store Sales Drive...
Apple on Monday announced financial results for its fiscal 2014 fourth quarter ended September 27, 2014. The Company posted quarterly revenue of $42.1 billion and quarterly net profit of $8.5 billion... Read more
Apple Posts How-To For OS X Recovery
OS X 10.7 Lion and later include OS X Recovery. This feature includes all of the tools you need to reinstall OS X, repair your disk, and even restore from a Time Machine backup. OS X Recovery... Read more
Mac OS X Versions (Builds) Supported By Vario...
Apple Support has posted a handy resource explaining which Mac OS X versions (builds) originally shipped with or are available for your computer via retail discs, downloads, or Software Update. Apple... Read more
Deals on 2011 13-inch MacBook Airs, from $649
Daily Steals has the Mid-2011 13″ 1.7GHz i5 MacBook Air (4GB/128GB) available for $699 with a 90 day warranty. The Mid-2011 13″ 1.7GHz i5 MacBook Air (4GB/128GB SSD) is available for $649 at Other... Read more
2013 15-inch 2.0GHz Retina MacBook Pro availa...
B&H Photo has leftover previous-generation 15″ 2.0GHz Retina MacBook Pros now available for $1599 including free shipping plus NY sales tax only. Their price is $400 off original MSRP. B&H... Read more
Updated iPad Prices
We’ve updated our iPad Air Price Tracker and our iPad mini Price Tracker with the latest information on prices and availability from Apple and other resellers, including the new iPad Air 2 and the... Read more
Apple Pay Available to Millions of Visa Cardh...
Visa Inc. brings secure, convenient payments to iPad Air 2 and iPad mini 3as well as iPhone 6 and 6 Plus. Starting October 20th, eligible Visa cardholders in the U.S. will be able to use Apple Pay,... Read more
Textkraft Pocket – the missing TextEdit for i...
infovole GmbH has announced the release and immediate availability of Textkraft Pocket 1.0, a professional text editor and note taking app for Apple’s iPhone. In March 2014 rumors were all about... Read more

Jobs Board

Senior Event Manager, *Apple* Retail Market...
…This senior level position is responsible for leading and imagining the Apple Retail Team's global event strategy. Delivering an overarching brand story; in-store, Read more
*Apple* Solutions Consultant (ASC) - Apple (...
**Job Summary** The ASC is an Apple employee who serves as an Apple brand ambassador and influencer in a Reseller's store. The ASC's role is to grow Apple Read more
Project Manager / Business Analyst, WW *Appl...
…a senior project manager / business analyst to work within our Worldwide Apple Fulfillment Operations and the Business Process Re-engineering team. This role will work Read more
*Apple* Retail - Multiple Positions (US) - A...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
Position Opening at *Apple* - Apple (United...
…customers purchase our products, you're the one who helps them get more out of their new Apple technology. Your day in the Apple Store is filled with a range of Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.