TweetFollow Us on Twitter

The Process Tree

Volume Number: 19 (2003)
Issue Number: 8
Column Tag: Programming

Section 7

The Process Tree

by Rich Morin

Which processes do what

The initial design of Unix (by Ken Thompson, Dennis Ritchie, et al) was based on the idea that large jobs could be done by lots of little programs, working together. Part of the reason for this was that the available hardware had only minuscule amounts of RAM. Another part was the designers' dislike of large, monolithic programs.

Mac OS X inherits this modular approach. Most of its programs aren't "little", especially by the standards of early Unix, but there are certainly lots of them. On my freshly-booted desktop machine, I found 62:

% ps -ax | wc -l
      62

The command-line options (-ax) tell ps to show all processes, even if they belong to another user or have no controlling terminal. Using another of ps's many options, we can take a detailed look, concentrating on the commands and their parentage. Stretch a Terminal window really wide, then try:

% ps -axo pid,ppid,tt,user,command
  PID  PPID  TT  USER COMMAND
    1     0  ??  root /sbin/init
    2     1  ??  root /sbin/mach_init
   51     1  ??  root kextd
71     1  ??  root update
...
  539   536 std  root login -pf rdm
  540   539 std  rdm  -tcsh (tcsh)
1506   540 std  root ps -axo pid ppid tt user command
 674   536  p2  root login -pf rdm
 675   674  p2  rdm  -tcsh (tcsh)

The PID (Process ID) and PPID (Parent Process ID) columns allow us to guess at the "genealogy" of each process. If a process has PPID 1, for instance, its "parent" has PID 1. Note, however, that a PPID of 1 may also mean that the original parent process has terminated.

The TT ("terminal"; originally from teletype) column tells us the identity of the controlling terminal ("??" for none). Because most OSX applications have no controlling terminal, this field is insufficient to distinguish apps from background processes.

Fortunately, the USER (username) and COMMAND columns help to clear this up. Apps generally run with the username of the logged-in user; in addition, most apps have long path names which include directories such as "Applications". Also, the names of BSD-derived daemons often end in "d" (e.g., configd, cupsd).

If you're seriously interested in looking at processes (e.g., to figure out which one is bogging down your system :-), you should also investigate pstat(1), top(1), vm_stat(1). Apple's Process Viewer utility is also handy, but note that it may not report information in a manner that is consistent with the command-line tools. For example, it shows a process named "Window Manager", which ps(1) and top(1) do not list...

Background processes

When OSX starts up, it initiates a number of background processes (commonly referred to as "daemons", after the "attendant spirits" found in Greek mythology). Because these daemons have low Process IDs, they appear at the start of the listing.

Note: Although OSX uses a 32-bit value (pid_t) for process IDs, it "wraps" the IDs at ~32K, so a ps(1) listing taken from a long-running (and/or busy) system may show other processes with low IDs. Interestingly, FreeBSD does not seem to limit IDs in this manner.

Most daemons are started up by init(8), as part of the system start-up process. This accounts for the long list of processes whose PPID is 1. Scattered in this list, however, you may see a few processes with PPIDs of 2, indicating that they are children of mach_init(8). Finally, some applications (e.g., iChat) and daemons (e.g., loginwindow, WindowServer) start up their own daemons.

Here's an annotated list of some background processes that show up on my machine. Lacking any other organizing rationale, I'll use alphabetical order. If nothing else, that will make the list easy to navigate (:-):

    AppleFileServer - personal file sharing server; supports AppleTalk Filing Protocol (AFP) over Internet Protocol (IP).

    ATSServer - Apple Type Solution server; enables system-wide font management.

    autodiskmount(8) - checks and mounts disk-based file systems.

    automount - automatically mounts and unmounts network (NFS and AFP) file systems. See amd(8) for information on the traditional (NFS-only) variant of this daemon.

    configd - maintains dynamic configuration information about the computer and its environment (e.g. network).

    coreservicesd - core services daemon.

    crashreporterd - logs information about program crashes.

    cron(8) - executes scheduled commands. See also crontab(1,5).

    cupsd(8) - Common Unix Printing System daemon. Run "apropos cups" to see an extensive list of man pages.

    DirectoryService - directory server for Apple's Open Directory architecture.

    dynamic_pager - assists the kernel with managing swap files for virtual memory.

    httpd(8) - Apache hypertext transfer protocol server; may be replicated, for performance. Run "apropos http" to see an extensive list of man pages.

    inetd(8) - internet "super-server"; listens for connections on certain internet sockets. When a connection is found on one of its sockets, it decides what service the socket corresponds to, and invokes a program to service the request.

    kextd(8) - handles requests from the kernel to load kernel extensions (kexts).

    loginwindow - handles miscellaneous process- and session-monitoring functions (e.g., login, logout, restart, shutdown, and restarting of the Dock and Finder).

    lookupd(8) - caches directory service information (e.g., user accounts, groups, printers, e-mail aliases and distribution lists, computer names, Internet addresses).

    mDNSResponder - multicast-DNS responder; advertises network services (such as AFP file sharing) provided by this computer (part of Rendezvous).

    netinfod(8) - serves NetInfo information to the network. Run "apropos netinfo" to see an extensive list of man pages.

    nfsiod(8) - typically, several copies of this daemon will be running on any NFS client machine, servicing asynchronous I/O requests. This daemon improves NFS performance, but it is not required for correct operation. Run "apropos nfs" to see an extensive list of man pages (but ignore the bogus hits for config(5) and confstr(3) :-).

    ntpd(8:FreeBSD) - Network Time Protocol (NTP) daemon; sets and maintains the system time of day in synchronism with Internet standard time servers.

    pbs - pasteboard server (similar to the Clipboard in Mac OS 9); enables the exchange of data between applications. It is also the data-transfer mechanism used in dragging operations. (started by loginwindow).

    SecurityServer - oversees system authorization, authentication, and keychain access.

    slpd - Service Location Protocol (SLP) responder; advertises network services (such as AFP file sharing) provided by this computer.

    sshd(8) - with ssh(1), replaces rlogin(1) and rsh(1), providing secure encrypted communications between two untrusted hosts over an insecure network. Run "apropos ssh" to see an extensive list of man pages.

    syslogd(8) - reads and logs messages to the system console, log files, other machines, and/or users as specified by syslog.conf(5), its configuration file. See also syslog(3).

    SystemUIServer - displays items on the right-hand end of the menu bar; loads menu and dock extras as plug-ins (started by WindowServer).

    update(8) - helps protect the integrity of disk volumes by flushing volatile cached file system data to disk at thirty second intervals.

    WindowServer - responsible for rudimentary screen displays, window compositing and management, event routing, and cursor management. It coordinates low-level windowing behavior and enforces a fundamental uniformity in what appears on the screen.

Interactive Processes

Most apps are children of the WindowServer daemon. Their names should be quite familiar: Dock, Finder, iChat, Preview, Terminal. As noted above, some apps start up their own daemons. For example, iChat starts up iChatAgent (probably to handle communications).

The lineage for command-line programs is a bit more complex. Assuming that you're using Terminal, it should look something like this:

PID PPID  TT  USER COMMAND
173    1  ??  rdm  .../WindowServer ...
536  173  ??  rdm  .../Terminal ...
539  536  p1  root login -pf rdm
540  539  p1  rdm  -tcsh (tcsh)
873  540  p1  root top

As these lines show, init(8) started up WindowServer, which started up the Terminal. Then, to generate an interactive shell window, Terminal started up login, which started up tcsh(1). Finally, I ran top(1) from the command line.

Careful Reader will notice that the username for login and top is root, rather than rdm. Because these processes need to do some things which a normal user is not allowed to do, they have been created as setuid(2) executables:

% ls -l /usr/bin/{login,top}
-r-sr-xr-x 1 root wheel ... /usr/bin/login
-r-sr-xr-x 1 root wheel ... /usr/bin/top

Further Reading

In a traditional BSD system, the first place to look for information on commands and daemons would be the manual. Unfortunately, many OSX commands and daemons do not have accompanying manual pages. Even when man pages are present, they may not be up-to-date, let alone customized to reflect changes which Apple has made, other documentation it has developed, etc.

A comprehensive attack on this problem has been suggested by parties inside and outside of Apple, but (AFAIK) no significant effort has been made as yet. If you would like better manual pages, let ADC (etc.) know!

In the meanwhile, here are some places where I found useful information for this section:

http://www.westwind.com/reference/OS-X/background-processes.html

http://developer.apple.com/techpubs/macosx/Essentials/SystemOverview/ BootingLogin/chapter_4_section_5.html


Rich Morin has been using computers since 1970, Unix since 1983, and Mac-based Unix since 1986 (when he helped Apple create A/UX 1.0). When he isn't writing this column, Rich runs Prime Time Freeware (www.ptf.com), a publisher of books and CD-ROMs for the Free and Open Source software community. Feel free to write to Rich at rdm@ptf.com.

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

coconutBattery 3.6.3 - Displays info abo...
With coconutBattery you're always aware of your current battery health. It shows you live information about your battery such as how often it was charged and how is the current maximum capacity in... Read more
Little Snitch 4.0.2 - Alerts you about o...
Little Snitch gives you control over your private outgoing data. Track background activity As soon as your computer connects to the Internet, applications often have permission to send any... Read more
VueScan 9.5.82 - Scanner software with a...
VueScan is a scanning program that works with most high-quality flatbed and film scanners to produce scans that have excellent color fidelity and color balance. VueScan is easy to use, and has... Read more
Postbox 5.0.17 - Powerful and flexible e...
Postbox is a new email application that helps you organize your work life and get stuff done. It has all the elegance and simplicity of Apple Mail, but with more power and flexibility to manage even... Read more
CleanMyMac 3.8.6 - $39.95
CleanMyMac makes space for the things you love. Sporting a range of ingenious new features, CleanMyMac lets you safely and intelligently scan and clean your entire system, delete large, unused files... Read more
Default Folder X 5.1.6b3 - Enhances Open...
Default Folder X attaches a toolbar to the right side of the Open and Save dialogs in any OS X-native application. The toolbar gives you fast access to various folders and commands. You just click on... Read more
Amazon Chime 4.6.5852 - Amazon-based com...
Amazon Chime is a communications service that transforms online meetings with a secure, easy-to-use application that you can trust. Amazon Chime works seamlessly across your devices so that you can... Read more
VOX 2.8.30 - Music player that supports...
VOX just sounds better! The beauty is in its simplicity, yet behind the minimal exterior lies a powerful music player with a ton of features and support for all audio formats you should ever need.... Read more
iFFmpeg 6.4.3 - Convert multimedia files...
iFFmpeg is a comprehensive media tool to convert movie, audio and media files between formats. The FFmpeg command line instructions can be very hard to master/understand, so iFFmpeg does all the hard... Read more
Alfred 3.4.1 - Quick launcher for apps a...
Alfred is an award-winning productivity application for OS X. Alfred saves you time when you search for files online or on your Mac. Be more productive with hotkeys, keywords, and file actions at... Read more

War Wings beginner's guide - how to...
War Wings is the newest project from well-established game maker Miniclip. It's a World War II aerial dogfighting game with loads of different airplane models to unlock and battle. The game offers plenty of single player and multiplayer action. We... | Read more »
How to win every 2v2 battle in Clash Roy...
2v2 is coming back to Clash Royale in a big way. Although it's only been available for temporary periods of time, 2v2 has seen a hugely positive fan response, with players clamoring for more team-based gameplay. Soon we'll get yet another taste of... | Read more »
Roll to Win with Game of Dice’s new upda...
Joycity’s hit Game of Dice gets a big new update this week, introducing new maps, mechanics, and even costumes. The update sets players loose on an exciting new map, The Cursed Tower, that allows folks to use special Runes mid-match. If you feel... | Read more »
Bottom of the 9th (Games)
Bottom of the 9th 1.0.1 Device: iOS iPhone Category: Games Price: $4.99, Version: 1.0.1 (iTunes) Description: Play the most exciting moment of baseball in this fast-paced dice and card game! | Read more »
The best apps for viewing the solar ecli...
If you somehow missed the news, many parts of the United States will be witness to a total solar eclipse on August 21 for the first time in over 90 years. It'll be possible to see the eclipse in at least some capacity throughout the continental U... | Read more »
The 5 best mobile survival games
Games like ARK: Survival Evolved and Conan Exiles have taken the world of gaming by storm. The market is now flooded with hardcore survival games that send players off into the game's world with nothing but maybe the clothes on their back. Never... | Read more »
Portal Walk (Games)
Portal Walk 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: Portal Walk is adventure and relaxing platform game about Eugene. Eugene stuck between worlds and trying to find way back home.... | Read more »
Technobabylon (Games)
Technobabylon 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: City of Newton, 2087. Genetic engineering is the norm, the addictive Trance has replaced almost any need for human interaction,... | Read more »
5 reasons why 2v2 is the best mode in Cl...
Supercell has been teasing fans with 2v2 windows that allow players to team up for limited periods of time. The Summer of 2v2 was just this past July, but players are already clamoring for more of that sweet, sweet team-based action. The fans have... | Read more »
The best deals on the App Store this wee...
It seems like the week's only just started, and yet here we are with a huge pile of discounted games to sort through. There are some real doozies on sale this week. We're talking some truly stellar titles. Let's take a look at four of the best... | Read more »

Price Scanner via MacPrices.net

Back To School With The Edge Desk All-in-one...
Back to school is just around the corner, and the ergonomically correct Edge Desk all-in-one portable kneeling desk is ideal for students living in dorms and small apartments, Edge Desk features:... Read more
Norton Core Secure Wi-Fi Router Now Available...
First introduced at the 2017 Consumer Electronics Show (CES), Norton Core, a secure, high-performance Wi-Fi router, fundamentally changed the concept of Wi-Fi routers by making security the primary... Read more
ViewSonic Adds New 27-inch 4K UHD Monitor to...
ViewSonic Corp. has introduced the VP2785-4K, a 27-inch 4K UHD (3840×2160) monitor that delivers precise and consistent color representation and performance to ensure incredible image quality. Built... Read more
Apple now offering Certified Refurbished 2017...
Apple is now offering Certified Refurbished 2017 27″ iMacs for up to $350 off original MSRP. Apple’s one-year warranty is standard, and shipping is free. The following models are available: – 27″ 3.... Read more
13-inch 2.3GHz MacBook Pros on sale for $100...
Amazon has the new 2017 13″ 2.3GHz MacBook Pros on sale today for $100 off MSRP, each including free shipping: – 13″ 2.3GHz/128GB Space Gray MacBook Pro (MPXQ2LL/A): $1199.99 $100 off MSRP – 13″ 2.... Read more
Clearance 2016 13-inch MacBook Airs available...
B&H Photo has clearance 2016 13″ MacBook Airs available for up to $200 off original MSRP. Shipping is free, and B&H charges NY & NJ sales tax only: – 13″ 1.6GHz/128GB MacBook Air (MMGF2LL... Read more
Clearance 21-inch and 27-inch iMacs available...
B&H Photo has clearance 21″ and 27″ Apple iMacs available for up to $500 off original MSRP, each including free shipping plus NY & NJ sales tax only: – 27″ 3.3GHz iMac 5K: $1799 $500 off... Read more
New iOS 11 Productivity Features Welcome But...
The iOS community is in late summer holding mode awaiting the September arrival of the iPhone 8 and iOS 11. iOS 11 public betas have been available for months — number six was released this week —... Read more
Samsung Electronics Launches New Portable SSD...
Samsung Electronics America, Inc. has announced the launch of Samsung Portable SSD T5 – its newest portable solid state drive (PSSD) that raises the bar for the performance of external memory... Read more
TrendForce Reports YoY Gain of 3.6% for 2Q17...
Market research firm TrendForce reports that the global notebook shipments for this second quarter registered a sequential quarterly increase of 5.7% and a year-on-year increase of 3.6%, totaling 39.... Read more

Jobs Board

Business Development Manager - *Apple* Medi...
Job Summary Apple Music is a single, intuitive app that...- all in one place. You can stream any Apple Music song, playlist or album, and download it Read more
Development Operations and Site Reliability E...
Development Operations and Site Reliability Engineer, Apple Payment Gateway Job Number: 57572631 Santa Clara Valley, California, United States Posted: Jul. 27, 2017 Read more
Frameworks Engineering Manager, *Apple* Wat...
Frameworks Engineering Manager, Apple Watch Job Number: 41632321 Santa Clara Valley, California, United States Posted: Jun. 15, 2017 Weekly Hours: 40.00 Job Summary Read more
Program Manager, *Apple* Pay Business Opera...
…Manager to deliver and sustain a seamless user and support experience for Apple Pay Cash, the upcoming person-to-person payments feature in iMessage. On the Business Read more
Sr. Software Engineer, Core Services, *Apple...
…You will be part of the server team that powers various features within the Apple client applications - iTunes, App Store, iBooks, Podcast, Apple Music etc. You Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.