MAC OSx and iOS internals useful concepts and commands

Origin of content

Most of this content is from the awesome textbook http://www.amazon.com/Mac-OS-iOS-Internals-Apples/dp/1118057651/ref=sr_1_2?ie=UTF8&qid=1464466126&sr=8-2&keywords=mac+os+x+internals
If you are serious about learning Mac OS X and iOS internal, get a copy of the book and read it. Think of this document as a quick reminder document of userful concepts and commands ###uname Get details of architecture and version history of Darwin
uname -a will give all the info

Architecture

• Darwin - OS core - kernel and UNIX shell enviornment
• Core frameworks - Graphics and Media layer - core frameworks, Open GL, QuickTime
• Application frameworks - Cocoa, Carbon and Java. iOS only Cocoa Touch
• UX - Aqua, Dashboard, Spotlight and accessibility

UX

qlmanage

Quicklook is a way to quickly preview a file without opening it. The utility used is qlmanage
To get thumbnail: qlmanage -t
To get preview: qlmanage -p or press space bar in finder with file selected
To manage quicklook server: qlmanage -m

Spotlight

Quick search technology for OSx and iOS
Magnifying glass icon in Mac or cmd+space
Left swipe on home screen in iOS
To issue search from terminal - mdfind To manage MetaData data database - mdutil To diagnose spotlight - MDdiagnose To list metadata attributes of a file - mdls
To prevent indexing of a directory - create an invisible file .metadata_never_index
this method didn't work, adding .noindex to the folder stopped spotlight search hits

Darwin - The UNIX Core

Shell

Bunch of choices

• sh
• bash
• csh
• tcsh
• zsh

File System

HFS+

• Case preserving but case insensitive in Mac - will show uppercase lowercase differently but commands will work either case
• Case sensitive in HFSX - Default in iOS

UNIX system directories

• /bin - Unix binaries: Common UNIX commands like ls, rm, df
• /sbin - System binaries: binaries for system admin like file system management, network config, etc.
• /usr - User directory: third party software can install here. Contains bin, sbin, lib. /usr/lib is used for shared objects, also contains include/ subdirectory where standard C headers are kept
• /etc - Et Cetera: contains system config files. In OSx, this is a symbolic link to /private/etc
• /dev - BSD device files: contains hardware device representations
• /tmp - temporary directory: used for temp files, it is world writable. In OSx, symbolic link to /private/tmp
• /var - various: used for log files, mail store, print spool. In OSx, symbolic link to /private/var

UNIX directories are invisible to finder. chflags can change an attribute called hidden to make it hidden to the GUI
ls with -O flag will show the hidden attribute
ls -Oal will list hidden directories with attribute showing

OSx specific directories

• /Applications - default base for all applications
• /Developer - If xcode is installed, default installation point for all developer tools
• /Library - Data files, help, documentation for system applications
• /Network - Virtual dir for neighbour node discovery and access
• /System - Used for system files, contains a library subdirectory. Contains frameworks, kernel modules, fonts, etc.
• /Users - Home directory for each user
• /Volumes - Mount point for removable media and network file system
• /Cores - Dir for core dumps. Core dumps are created when a process crashes

To get complete list, run "ls -Oal" from /

Bundles

Standardized heirarchical structure that holds executable code and the resources used by that code
It is used for applications, frameworks, plugins, widgets and even kernel packages

• Contents/
  • CodeResources/
  • Info.plist
  • MacOS/
  • PkgInfo
  • Resources/
  • Version.plist
  • _CodeSignature/
    • CodeResources

Info.plist

plist has 3 formats

• XML: most common
• Binary: known as bplist
• JSON: not very common
  More info using man plist
  Conversion using plutil
  Info.plist entries
  https://developer.apple.com/library/ios/documentation/General/Reference/InfoPlistKeyReference/Articles/AboutInformationPropertyListFiles.html#//apple_ref/doc/uid/TP40009254-SW1
  PkgInfo = CFBundlePackageType + CFBundleSignature

Resources

This directory contains all the resources the applicaiton needs. This can contain any type of file the application might need
I'll add a lot more info about the code signing resources in the Mac OS X code signing project

Frameworks

• Frameworks are libraries that are specific to OS X
• They are closed source as opposed to Darwin libraries
• They also have a bundle format which is slightly different from the bundle format of applications discussed above

Location

• /System/Library/Frameworks: Apple supplied frameworks reside here
• /Library/Frameworks: 3rd party frameworks reside here
• ~/Library/Frameworks: User supplied frameworks reside here

Cocoa

This is the framework used to develop applications for OS X https://en.wikipedia.org/wiki/Cocoa_(API)
Apple is trying to get developers to use Swifthttps://developer.apple.com/swift/ as the primary programming language but objective C is still very much supported. Cocoa API is also accesible through various other programming languages(wiki page linked above has more info)
You can have some fun with speech to text framework https://developer.apple.com/library/mac/documentation/UserExperience/Conceptual/SpeechSynthesisProgrammingGuide/SpeechOverview/SpeechOverview.html

Libraries

• These are the UNIX system libraries that all UNIX folks will be familiar with
• They are stored in /usr/lib directory
• On OS X, they have .dylib extension instead of .so extension
• libc is is libSystem.B.dylib library Apple provides

Widgets

• These are basic web pages that can be presented by dashboard
• They are written just like webpages with html, js and css
• They reside as bundles with .wdgt format in /Library/Widgets directory

BSD and Mach API

• It is also possible to work directly with UNIX and Mach API for application development
• Starting with Leopard(10.5), OS X is a certified UNIX implementation compliant with portable operating system interface(POSIX)
• Mach system calls are also avaiable in the user mode and are negative to keep them distanct from positive POSIX system calls

XNU components

Mach microkernel

• It performs process and thread abstarction
• Manages virtual memory management
• Task scheduling
• Interprocess communication and messaging

BSD system calls

• It provides UNIX process model
• POSIX threading model
• UNIX users and groups
• Network stack

libkern

It is a built in C++ library that allows kernel components to be written in C++(in addition to C and assembly like most kernels are created)

I/O kit

It is a I/O device driver framework that runs in libkern(C++) enviornment