TweetFollow Us on Twitter

Process Control

Volume Number: 18 (2002)
Issue Number: 10
Column Tag: Section 7

Process Control

ps, top, kill, ...

by Rich Morin

A recent foray into Internet Radio conflicted in some manner with the OSX screen saver on my desktop machine. As a result, I was unable to get the screen saver to go away. I tried all of the usual tricks: hitting mouse buttons, moving the mouse, advancing to keyboard keys (e.g., shift, return) and finally "magic key combinations" (e.g., command-option-escape). No luck.

On Mac OS 9, my next steps would have been to try a "three-finger salute" (i.e., command-control-power), followed by pushing the reset button and if need be, pulling the plug. This being a BSD-based machine, however, I had a better solution at hand.

I went to another machine on the local net, logged into my desktop machine, and killed a couple of sorely-confused processes. I then logged out and returned to my desk, flushed with victory and the knowledge that I had a useful Section 7 topic in hand.

Advance Preparation

My "remote login" trick wouldn't have worked without a bit of advance preparation. OSX, for very good reasons, turns off most "remote services", by default. I don't recommend turning services on, willy-nilly, but ftp and ssh are so handy that I wouldn't want to live without them. And, because my desktop machine is hidden behind a firewall, I consider the risk to be pretty minimal (your mileage may vary).

In any case, here's how to allow remote ftp and ssh on an OSX 10.2 machine: In the System Preferences application, select the Sharing dialog. Under the "Services" tab, turn on the checkboxes labelled "FTP Access" and "Rmote Login".

You will also need a way to "find" your machine from the other one. This can be achieved in any number of ways, including DNS (Domain Name System), /etc/hosts files, etc. Your network administrator will (or should :-) know how to make this happen on your local network. As a last resort, you can use your machine's IP (Internet Protocol) address as a name.

Logging In

Because ftp and ssh aren't OSX-specific tools, you can log in remotely from almost any operating system. This being an OSX-related column, however, I'll assume that you're running OSX. If you're not, you'll have to deal with the vagaries of installing and starting up the needed clients on the machine you're on. On OSX, just start up a Terminal window and type:

% ssh <me>@<mydesk>
<me>@<mydesk>s password:

The first time you do this from a given machine, you'll be asked whether you trust the SSH keys on your desktop machine. Say yes (:-). After entering your password, you'll get a prompt from your desktop machine:

<me>@<mydesk> [~] 1: 

There are all sorts of things you can do at this point, but try not to get too excited and do something you'll regret. Think "delicate surgery", rather than "hack and slash". Thus, the first thing we want to do is find out a bit about the programs that are running over on the desktop machine. To do this, we'll use the top command, which displays system usage statistics and then lists the top processes, in terms of CPU utilization:

<me>@<mydesk> [~] 2: top
Processes:  65 total, 3 running, 62 sleeping... 190 threads   17:39:16
Load Avg:   2.15, 1.46, 1.35
CPU usage:  62.3% user, 37.7% sys, 0.0% idle
SharedLibs: num =  116, resident = 23.2M code, ...
MemRegions: num = 4936, resident =  159M + 13.0M private, ...
VM:         4.22G + 45.8M  5363(0) pageins, 0(0) pageouts   
   PID COMMAND            %CPU      TIME         ...
   758 top                7.9%      0:38.79   ...
   703 tcsh               0.0%      0:00.34   ...
   702 sshd               0.0%      0:00.78   ...
   701 ssh                0.0%      0:00.86   ...
   692 CCacheServ         0.0%      0:06.09   ...
   610 Finder             0.0%      0:18.75   ... 
   ...

Unlike most BSD commands, top doesn't just run and go away. Instead, it refreshes its display about once a second, letting you see if things are changing. When you're done viewing the display, type "q" (or Conrtol-C) and the program will terminate. Alternatively, just start up another Terminal window, leaving top running in the first one...

The system usage statistics are a bit arcane; look at top's man page if you want the details. For now, just note that the number of processes should normally be under 100 and that the load average (time-averaged system load) should be under five. If you see higher values on your machine, you may have a runaway application.

Because top's process list is sorted by CPU utilization, active programs tend to "bubble up". So, look near the top of the list for suspects. In some cases, killing off a sijngle process won't be enough; to restore my desktop to proper functionality, I had to kill the screen saver, the Internet Radio application, and the Finder!

I issued a separate kill com mand for each process I wanted to terminate, specifying the PID (process ID). This let me see and evaluate the effect of each action:

^C<me>@<mydesk> [~] 3: kill -9 610

Be sure to get the PID right; you don't want to kill off an innocent application, by mistake! By the way, kill can do more than just terminate processes. It can send any desired "signal" to one or more specified processes. So, for example, it can be used to tell processes to check their configuration files, etc.

If you can't figure out which command you need to kill, you may need to get a different view of the information. The ps command lists "process status" information, in a variety of formats. For our present purposes, "ps awx" is a reasonable idiom:

<me>@<mydesk> [~] 4: ps awx
  PID  TT  STAT      TIME COMMAND
    1  ??  SLs    0:00.03 /sbin/init     
    2  ??  SL     0:02.35 /sbin/mach_init        
   41  ??  Ss     0:02.24 kextd
  ...

To list the commands in a different order, just pipe together some commands:

<me>@<mydesk> [~] 5: ps awx | sort +3 -rn | more
   62  ??  Ss    56:09.79 .../WindowServer
  ...
  PID  TT  STAT      TIME COMMAND
  994 std  R+     0:00.00 more
  993 std  R+     0:00.01 sort +3 -rn
  ...
  610  ??  S      0:18.80 .../MacOS/Finder -psn_0_3538945
  ...

Transliterated, the pipeline above says to run the output of ps through a line-oriented sort (sorting by the fourth column, in reverse numeric order), then pipe the result through more (a text viewing command). If you know what command you're looking for, of course, you can use grep:

<me>@<mydesk> [~] 6: ps awx | grep Finder
 1006 std  R+     0:00.00 grep Finder
  610  ??  S      0:18.80 .../Finder -psn_0_3538945

With the advent of OSX 10.2, I feel more comfortable in recommending FreeBSD-related books to OSX users and programmers. There are still some differences, to be sure, but any book that covers FreeBSD 4.X commands will be a good match for the OSX 10.2 command set.

Although processes are the workhorses of any BSD system, there are few books that spend much time on them. Quite a few man pages relate to processes, however, and the DOSSIER (www.ptf.com/dossier) volume "Processes: FreeBSD" brings them together in a single volume.


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

Latest Forum Discussions

See All

Top Mobile Game Discounts
Every day, we pick out a curated list of the best mobile discounts on the App Store and post them here. This list won't be comprehensive, but it every game on it is recommended. Feel free to check out the coverage we did on them in the links... | Read more »
Price of Glory unleashes its 1.4 Alpha u...
As much as we all probably dislike Maths as a subject, we do have to hand it to geometry for giving us the good old Hexgrid, home of some of the best strategy games. One such example, Price of Glory, has dropped its 1.4 Alpha update, stocked full... | Read more »
The SLC 2025 kicks off this month to cro...
Ever since the Solo Leveling: Arise Championship 2025 was announced, I have been looking forward to it. The promotional clip they released a month or two back showed crowds going absolutely nuts for the previous competitions, so imagine the... | Read more »
Dive into some early Magicpunk fun as Cr...
Excellent news for fans of steampunk and magic; the Precursor Test for Magicpunk MMORPG Crystal of Atlan opens today. This rather fancy way of saying beta test will remain open until March 5th and is available for PC - boo - and Android devices -... | Read more »
Prepare to get your mind melted as Evang...
If you are a fan of sci-fi shooters and incredibly weird, mind-bending anime series, then you are in for a treat, as Goddess of Victory: Nikke is gearing up for its second collaboration with Evangelion. We were also treated to an upcoming... | Read more »
Square Enix gives with one hand and slap...
We have something of a mixed bag coming over from Square Enix HQ today. Two of their mobile games are revelling in life with new events keeping them alive, whilst another has been thrown onto the ever-growing discard pile Square is building. I... | Read more »
Let the world burn as you have some fest...
It is time to leave the world burning once again as you take a much-needed break from that whole “hero” lark and enjoy some celebrations in Genshin Impact. Version 5.4, Moonlight Amidst Dreams, will see you in Inazuma to attend the Mikawa Flower... | Read more »
Full Moon Over the Abyssal Sea lands on...
Aether Gazer has announced its latest major update, and it is one of the loveliest event names I have ever heard. Full Moon Over the Abyssal Sea is an amazing name, and it comes loaded with two side stories, a new S-grade Modifier, and some fancy... | Read more »
Open your own eatery for all the forest...
Very important question; when you read the title Zoo Restaurant, do you also immediately think of running a restaurant in which you cook Zoo animals as the course? I will just assume yes. Anyway, come June 23rd we will all be able to start up our... | Read more »
Crystal of Atlan opens registration for...
Nuverse was prominently featured in the last month for all the wrong reasons with the USA TikTok debacle, but now it is putting all that behind it and preparing for the Crystal of Atlan beta test. Taking place between February 18th and March 5th,... | Read more »

Price Scanner via MacPrices.net

AT&T is offering a 65% discount on the ne...
AT&T is offering the new iPhone 16e for up to 65% off their monthly finance fee with 36-months of service. No trade-in is required. Discount is applied via monthly bill credits over the 36 month... Read more
Use this code to get a free iPhone 13 at Visi...
For a limited time, use code SWEETDEAL to get a free 128GB iPhone 13 Visible, Verizon’s low-cost wireless cell service, Visible. Deal is valid when you purchase the Visible+ annual plan. Free... Read more
M4 Mac minis on sale for $50-$80 off MSRP at...
B&H Photo has M4 Mac minis in stock and on sale right now for $50 to $80 off Apple’s MSRP, each including free 1-2 day shipping to most US addresses: – M4 Mac mini (16GB/256GB): $549, $50 off... Read more
Buy an iPhone 16 at Boost Mobile and get one...
Boost Mobile, an MVNO using AT&T and T-Mobile’s networks, is offering one year of free Unlimited service with the purchase of any iPhone 16. Purchase the iPhone at standard MSRP, and then choose... Read more
Get an iPhone 15 for only $299 at Boost Mobil...
Boost Mobile, an MVNO using AT&T and T-Mobile’s networks, is offering the 128GB iPhone 15 for $299.99 including service with their Unlimited Premium plan (50GB of premium data, $60/month), or $20... Read more
Unreal Mobile is offering $100 off any new iP...
Unreal Mobile, an MVNO using AT&T and T-Mobile’s networks, is offering a $100 discount on any new iPhone with service. This includes new iPhone 16 models as well as iPhone 15, 14, 13, and SE... Read more
Apple drops prices on clearance iPhone 14 mod...
With today’s introduction of the new iPhone 16e, Apple has discontinued the iPhone 14, 14 Pro, and SE. In response, Apple has dropped prices on unlocked, Certified Refurbished, iPhone 14 models to a... Read more
B&H has 16-inch M4 Max MacBook Pros on sa...
B&H Photo is offering a $360-$410 discount on new 16-inch MacBook Pros with M4 Max CPUs right now. B&H offers free 1-2 day shipping to most US addresses: – 16″ M4 Max MacBook Pro (36GB/1TB/... Read more
Amazon is offering a $100 discount on the M4...
Amazon has the M4 Pro Mac mini discounted $100 off MSRP right now. Shipping is free. Their price is the lowest currently available for this popular mini: – Mac mini M4 Pro (24GB/512GB): $1299, $100... Read more
B&H continues to offer $150-$220 discount...
B&H Photo has 14-inch M4 MacBook Pros on sale for $150-$220 off MSRP. B&H offers free 1-2 day shipping to most US addresses: – 14″ M4 MacBook Pro (16GB/512GB): $1449, $150 off MSRP – 14″ M4... Read more

Jobs Board

All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.