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Take Control of Permissions in Snow Leopard
Solve quirky problems, increase privacy, and share files better!
Permissions problems got you down? Turn to Unix expert Brian Tanaka's unique guide to the permissions in Mac OS X 10.6 Snow Leopard that control access to your files, folders, and disks. You'll learn how to keep files private, when to set Ignore Permissions, what happens when you repair permissions, how to delete stuck files, and the best ways to solve permissions-related problems. Advanced concepts include the sticky bit, Snow Leopard's increasingly important access control lists (ACLs), bit masks, and symbolic versus absolute ways to set permissions. The book covers how to take control of permissions via the Finder, with the Mac utility FileXaminer, and using the Unix command line.
- More Info
- Contents & Intro
- What’s New
- FAQ
- Blog
Read this book to learn the answers to questions like:
- Why do so many problem-solving sites suggest that I repair permissions?
- Why can't I always access my own files when I boot from an external drive?
- What should I do if someone tells me to "set the permissions to -rw-r--r--"?
- What are promiscuous permissions, and should I inform the vice squad?
- What's new about access control lists (ACLs) in Snow Leopard?
- What are the default permissions for copied files?
- Without the NetInfo database, how do I edit account settings like numeric UID?
- How do I work with account groups from System Preferences?
Book Info
iPad & KindleAn EPUB is available to purchasers of this ebook; log in to your account to download it. More info... A Mobipocket file is available to purchasers of this ebook; log in to your account to download it. More info... |
About the AuthorBrian Tanaka has worked for a variety of companies including the Well, SGI, Intuit, Nintendo, and RealNetworks. Today, his own company, Martingale-Oak LLC, provides Unix and open source technologies consulting. His articles have appeared in Linux Journal and Sysadmin Magazine. |
Book Reviews
Reviews of Previous EditionsAuthor Interviews
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Table of Contents
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Read Me FirstThis book helps you control the often-perplexing world of permissions in Mac OS X 10.6 Snow Leopard. It explains how permissions work, how to resolve common problems, and how to best control access to your files in a variety of situations. This book was written by Brian Tanaka, edited by Geoff Duncan, and published by TidBITS Publishing Inc. |
Introduction
Even if you don’t know a thing about permissions, if you’re using Mac OS X, you’re using them right now. Every file and folder on your computer carries permissions from the moment it’s created until the moment it’s deleted. Because permissions are literally everywhere on your computer and because they control who can access what, it’s tremendously advantageous to understand them. You’ll have better control over your Mac, and you’ll be able to share items and access shared items with greater ease.
Problems arising from improperly set permissions are common and can be frustrating: sharing files among users on one computer can be problematic if you don’t understand permissions, and sharing items on a network raises yet another set of potential problems.
In this book I teach you how to prevent and fix permissions problems with ease—and much more. You’ll learn how to interpret and manipulate permissions with the Info window in the Finder, Disk Utility, third-party tools, and Unix commands. You’ll learn how accounts and groups work (and how permissions control them), how default permissions work, how to repair permissions, and how to ignore permissions on an attached volume.
Equipped with this expertise, you’ll be able to handle permissions problems when sharing files locally or across networks, booting from multiple volumes, exchanging files with other users, running FTP and Web servers, and much more.
Permissions Quick Start
The first sections of this book teach the basics of permissions and how to set them. The remaining sections explore more advanced techniques and concepts that help you solve problems.
Learn about permissions:
- Find out what permissions are, and why you need them. See About Permissions.
- Permissions are composed of simple interrelated parts. Discover how they work together. See The Anatomy of Permissions.
- If you already know a bit about permissions and want an overview of what's new in Snow Leopard, read What's New.
Set permissions:
- There's more than one way to set permissions. See Choose a Method of Setting Permissions.
- Learn to Set Permissions Using the Info Window and to Set Permissions Using FileXaminer. And, if you need more fine-grained tools for controlling permissions, read Use Access Control Lists.
- To solve a permissions-related problem, see Problems and Solutions (next page), for a quick index to helpful info.
- If you enjoy working in Unix or need the fine-grained control that Unix can provide, Learn Advanced Unix Techniques.
Delve deeper into permissions:
- Discover how your Mac assigns default permissions in Understand Default Permissions, and increase your permissions IQ by reading Work with User Names, UIDs, and GIDs.
- Learn to use two important Mac OS X features in Understand Ignore Ownership and Repair Permissions with Disk Utility.
- Unix commands empower you to do things you can't do from the graphical user interface, which you'll see when you Learn Advanced Unix Techniques.
Problems and Solutions
I discuss a variety of common problems in Appendix A: Fixes For Common Problems, but you will find help with solving other problems throughout the book. The sections listed below contain info that will help you with specific problems:
- I'm having trouble with The Shared Folder.
- The Info window doesn't show permissions settings I know exist. See Set Permissions Using FileXaminer and Learn Advanced Unix Techniques.
- I don't own my own files! See Work with User Names, UIDs, and GIDs.
- I am concerned about the privacy of files and folders that I created and saved in my user account, and I want to make sure that others on the computer cannot access them in any way. Read The Case of the Promiscuous Folder.
- When do I use Ignore Ownership on This Volume? See Understand Ignore Ownership.
- Everyone tells me to use Repair Permissions but I don't understand what it does. Learn the real story in Repair Permissions with Disk Utility.
- I can see why understanding octal is useful when setting permissions, but I can't seem to get my head around it. See Appendix B: Converting to Octal.
- When I copy or create items, I can't predict what the permissions will be. It's driving me batty! Find help in Understand Default Permissions.
What's New in the Snow Leopard Edition
This book is a complete, Mac OS X 10.6 Snow Leopard-specific update to Take Control of Permissions in Leopard. Whereas that book covered all versions of Mac OS X up to and including 10.5 Leopard, this book focuses tightly on Snow Leopard.
Changes in this edition include:
- Of the three third-party tools that I recommended in earlier editions of this book (FileXaminer, Super Get Info, and XRay), only FileXaminer remains available for Snow Leopard. See Set Permissions Using FileXaminer .
- ACLs are on by default in Snow Leopard. Therefore, we no longer need to test whether or not ACLs are on. Furthermore, we previously used fsacltl to test ACL status, but fsacltl has been removed from Mac OS X. See Use Access Control Lists.
- In Leopard, a umask in /etc/launchd.conf did not work, contrary to Apple's documentation. In Snow Leopard, it does work, but the warning from the last edition to avoid using this technique still stands. See Understand Default Permissions.
- In Snow Leopard, a umask in ~/.launchd.conf doesn't work, contrary to Apple's documentation. Unfortunately, that means there is no way in Snow Leopard to set default permissions on files and folders created by the Finder or Mac OS X applications on an account-by-account basis. Read Understand Default Permissions.
- Many of the default permissions (and ACLs) that result from the copy operations described in "Permissions on Copied Items" have changed. I have updated the tables accordingly. For example, when copying a file to another user's Drop Box, unlike in Mac OS X versions prior to Snow Leopard, the ACLs on the resulting file are such that the receiving user can edit the file, and more interestingly, after saving, the file ownership switches to the receiving user's account. See Permissions on Copied Items.
Q: Do you have an ebook that covers permissions in older versions of Mac OS X?
A: Yes, we do. See Take Control of Permissions in Mac OS X, which covers permissions in Mac OS X 10.4 Tiger and earlier, and Take Control of Permissions in Leopard, which adds Leopard-specific details.
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Update Plans
January 2012 -- Although we might reconsider at some later date, at this time, we have no plans to update this ebook.
—Adam Engst
Manage File, Folder, and Disk Permissions in Snow Leopard
April 30, 2010 --
If you like to go under the hood of Mac OS X, or if you've been forced to by quirky problems, check out our latest ebook, freshly revised for Snow Leopard: Take Control of Permissions in Snow Leopard. Written by Unix guru and Mac aficionado Brian Tanaka (and edited by Geoff Duncan), the 91-page ebook mixes practical how-to details and troubleshooting tips with just the right amount of theory as it explains permissions in relation to how you keep your files private, copy files to and from servers effectively, set the Ignore Permissions option for external disks, repair default permissions, and delete those files that just won't die.
For those who want to learn advanced concepts, the $10 ebook delves into topics like the sticky bit, symbolic versus absolute ways to set permissions, and how to work with bit masks. Of course, Brian looks at what's new with permissions in Mac OS X 10.6 Snow Leopard, including the increased use of access control lists, changes to the way umask works, and which permissions a copied file ends up with.
Don't worry if you're not accustomed to using the Unix command line in Terminal, since Brian provides clear instructions for that, along with how to manage permissions from the Finder's Get Info and Inspector windows, and with a third-party utility, FileXaminer. (And of course, if you do want to become more familiar with the command line, we strongly recommend Joe Kissell's Take Control of the Mac Command Line with Terminal, which provides a friendly and thorough introduction.)
—Adam Engst
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