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

Shimo 4.0 - VPN Client for Mac – for Eve...
Shimo is the most versatile VPN client for OS X and it enables really everybody to master secure network. It supports more protocols than any other VPN application out there! CiscoVPN, AnyConnect,... Read more
Capo 3.3 - Slow down and learn to play y...
Capo lets you slow down your favorite songs so you can hear the notes and learn how they are played. With Capo, you can quickly tab out your songs atop a highly-detailed OpenCL-powered spectrogram... Read more
MacUpdate Desktop 6.0.8 - Search and ins...
MacUpdate Desktop 6 brings seamless 1-click installs and version updates to your Mac. With a free MacUpdate account and MacUpdate Desktop 6, Mac users can now install almost any Mac app on macupdate.... Read more
BitTorrent Sync 2.1.1 - Sync files secur...
BitTorrent Sync allows you to sync unlimited files between your own devices, or share a folder with friends and family to automatically sync anything. File transfers are encrypted. Your information... Read more
Quicksilver 1.3.0 - Application launcher...
Quicksilver is a light, fast and free Mac application that gives you the power to control your Mac with keystrokes alone. Quicksilver allows you to find what you need quickly and easily, then act... Read more
iWatermark Pro 1.72 - Easily add waterma...
iWatermark Pro is the essential watermarking app for professional, business, and personal use. iWatermark, is the number 1 and only watermarking tool available for all 4 platforms iPhone/iPad, Mac,... Read more
RapidWeaver 6.3 - 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
Adobe Photoshop CC 2015 16.0.1 - Profess...
Photoshop CC 2015 is available as part of Adobe Creative Cloud for as little as $19.99/month (or $9.99/month if you're a previous Photoshop customer). Photoshop CS6 is still available for purchase (... Read more
Together 3.4.6 - Store and organize all...
Together helps you organize your Mac, giving you the ability to store, edit and preview your files in a single clean, uncluttered interface. Smart storage. With simple drag-and-drop functionality,... Read more
Monosnap 3.1.0 - Versatile screenshot ut...
Monosnap lets you capture screenshots, share files, and record video and .gifs! Capture: Capture full screen, just part of the screen, or a selected window Make your crop area pixel perfect with... Read more

.Decluster Zero: Bullet Nocturne (Games...
.Decluster Zero: Bullet Nocturne 1.0.1 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0.1 (iTunes) Description: LAUNCH SALE, 40% off for a limited time -- .Decluster is a Guide for Your Bullet-Hell Dream Tonight --... | Read more »
Five Nights at Freddy's 4 has Been...
In keeping with tradition, Five Nights at Freddy's 4 has made its way to the App Store with zero warning fanfare. Honestly I'd be disappointed it if happened any other way at this point. [Read more] | Read more »
Doom & Destiny Advanced (Games)
Doom & Destiny Advanced 2.3.4.0 Device: iOS Universal Category: Games Price: $.99, Version: 2.3.4.0 (iTunes) Description: ---SUPER GIGA LAUNCH DISCOUNT! Get it now for cheap or pay more later!---An additional 143 MB download is... | Read more »
Five Nights at Freddys 4 (Games)
Five Nights at Freddys 4 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: This time, the terror has followed you home. | Read more »
This Week at 148Apps: July 27-31, 2015
Winding Down July With 148Apps How do you know what apps are worth your time and money? Just look to the review team at 148Apps. We sort through the chaos and find the apps you're looking for. The ones we love become Editor’s Choice, standing out... | Read more »
You'll Want to Keep an Eye Out for...
If you're the kind of person who had fun hunting down and completing all the codex puzzles in Assassin's Creed 2, then are you ever in for a treat. The Guides looks like it's going to be a very robust collection of similarily odd, seemingly... | Read more »
Vivid Games has Announced Real Boxing 2...
The original Real Boxing was a pretty impressive bit of fisticuffs, but if the trailer Vivid Games is showing off for GamesCom is any indication Real Boxing 2 is going to be even better. [Read more] | Read more »
PAC-MAN Championship Edition DX - Tips,...
[Read more] | Read more »
Card King: Dragon Wars - Tips, Tricks an...
[Read more] | Read more »
Pac-Man Championship Edition DX has brou...
Bandai Namco has released Pac-Man Championship Edition DX on iOS and Android, which features the classic arcade gameplay that we've all grown to love. Pac-Man Championship Edition DX can be enjoyed in much shorter bursts than the arcade versions... | Read more »

Price Scanner via MacPrices.net

Back to School Time: Outline for iPad Goes Fr...
Sacramento, California based Gorillized Corporation has announced a “Back to School” offer; the iPad version of Outline goes free for August 3-5. Outline is a smart digital notebook for iPad that... Read more
MacBook 12 Retina Pundit’s New Favorite Mac
If you’re eyeing the purchase of a new 12-inch Retina MacBook, but wondering if you can live with a single USB-C port, 2011-level CPU performance, and the unorthodox keyboard, you should find... Read more
15-inch 2.2GHz Retina MacBook Pro on sale for...
Adorama has the 2015 15″ 2.2GHz Retina MacBook Pro on sale for $184 off MSRP including free shipping plus NY & NJ sales tax only: - 15″ 2.2GHz Retina MacBook Pro: $1815 $184 off Adorama will also... Read more
PDF Element Tool Kit For PDF For Windows 10,...
South Surrey, British Columbia based software developer Wondershare has posted an interesting infographic tracking the development of Microsoft’s flagship Windows operating system over the years,... Read more
27-inch 3.5GHz 5K iMac on sale for $81 off MS...
Adorama has the 27″ 3.5GHz 5K iMac on sale for $2218, $81 off MSRP, including a free copy of Apple’s 3-Year AppleCare Protection Plan. Shipping is free, and Adorama charges sales tax in NY & NJ... Read more
Back-to-School with Tablet and Smartphone Acc...
Belkin helps you prepare for the coming school year with a wide variety of the latest mobile and tablet accessories to outfit both grade school and college students. The line-up includes charging... Read more
11-inch MacBook Airs on sale for $100 off MSR...
Best Buy has 11-inch MacBook Airs on sale for $100 off MSRP. Choose free shipping or free local store pickup (if available). Sale prices for online orders only, in-store prices may vary: - 11″ 1.6GHz... Read more
iPad Air 2 on sale for up to $100 off MSRP
Best Buy has iPad Air 2s on sale for up to $100 off MSRP on their online store for a limited time. Choose free shipping or free local store pickup (if available). Sale prices available for online... Read more
Sale! 13-inch MacBook Pros on sale for $100 o...
B&H Photo has 13″ MacBook Pros on sale for $100 off MSRP. Shipping is free, and B&H charges NY sales tax only: - 13″ 2.5GHz/500GB MacBook Pro: $999.99 save $100 - 13″ 2.7GHz/128GB Retina... Read more
Sale! Save $100 on 13-inch MacBook Airs this...
B&H Photo has the 13″ 1.6GHz/128GB MacBook Air on sale for $899.99 including free shipping plus NY tax only. Their price is $100 off MSRP, and it’s the lowest price available for this model.... Read more

Jobs Board

*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
Infrastructure Engineer - *Apple* /Mac - Hil...
Infrastructure Engineer - Apple /Mac Job Code: 1608 # of openings: 1 Description Our fortune 500 client is looking to hire an experienced Infrastructure Engineer to join Read more
Executive Administrative Assistant, *Apple*...
…supporting presentation development for senior leadership. * User experience with Apple hardware and software is preferred. Additional Requirements The following list Read more
*Apple* Bus Company is now hirin - Apple Bus...
Apple Bus Company is now hiring school bus drivers in the Pettis County area. Class B CDL preferred. Free training provided. No nights or weekends required. Flexible Read more
*Apple* Certified Mac Technician - Updated 6...
…and friendly, hands-on technical support to customers troubleshooting and repairing Apple /Mac products with courtesy, speed and skill. Use your problem-solving skills Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.