Section 3.2. Process Management
Each command you invoke or program that you run from a Terminal window becomes a child of that terminal's shell. The Terminal window can juggle many child processes at once, but only one at a time is brought to the foreground, writing its output (through the Unix standard output file handle) to the Terminal, and accepting keyboard input (via Unix standard input) from the user . Any other processes are either placed in the backgroundrunning but not displaying any interface or accepting inputor suspended ( paused ) in the process of execution.
You can control the application in the foreground by sending it Unix signals via the keystrokes listed in Table 3-1. Programs usually respond to them as listed, though individual programs may interpret them differently. (The Emacs text editor, for example, ties a text-searching function to the Control-S keystroke.)
Table 3-1. Foreground process control keystrokes
| Keystroke | Description |
|---|---|
| Control-C | Sends an interrupt signal, which usually causes the program to exit. |
| Control-D | Sends an end-of-file signal. If a program is accepting multiple lines of input from you, this signals that you're finished providing it. |
| Control-Z | Suspends the process in the foreground, and returns you to the command line. |
| Control-S | Suspends the process in the foreground, but keeps it in the foreground. |
| Control-Q | Resumes a suspended process, and brings it to the foreground. |
|
is a legacy Mac keyboard shortcut for interrupting programs; it's often used to quickly invoke the Cancel button in dialog windows. Table 3-2 lists some Terminal commands that are useful for viewing and controlling backgrounded processes . You can find complete references for them in Chapter 2. See the next section to find out a process's process ID number (PID), which many of these commands require. (You can also use the more convenient %N syntax described by that section when working with processes that are children of the current Terminal window's shell.)
Table 3-2. Process control commands
| Command | Description |
|---|---|
| ps | Lists Terminal-based processes belonging to you. |
| jobs | Lists processes that are children of this terminal's shell process. |
| fg pid | Foregrounds (and resumes, if suspended) the process with that pid . |
| bg pid | Backgrounds (and resumes, if suspended) the process with that pid . |
| kill - signal pid | Sends a signal (the terminate signal, by default) to the process with that pid . |
| killall - signal process- name | Sends a signal (the terminate signal, by default) to all processes with that name. |
3.2.1. Seeing processes
Typing ps by itself displays a simple list of all the shells you are running, as well as all their child processes:
andy@honey[~/mosxnut3]$ ps PID TT STAT TIME COMMAND 1692 p1 S 0:00.35 -bash 3273 p2 S 0:00.02 -bash 3284 p2 S+ 0:00.75 ssh chimpy 3311 p3 S 0:00.02 -bash 3313 p3 S+ 0:00.05 vim outline.pod 3883 p4 S 0:00.02 -bash 3886 p4 S+ 0:00.10 make perl 3950 p4 S+ 0:00.01 cc -c -DPERL_CORE -fno-common -DPERL_DARWIN -no- 3958 p4 S+ 0:00.01 powerpc-apple-darwin8-gcc-4.0.0 -c -DPERL_CORE - 3959 p4 R+ 0:00.07 /usr/libexec/gcc/powerpc-apple-darwin8/4.0.0/cc1 - 3960 p4 S+ 0:00.00 as -arch ppc -o op.o 3961 p4 S+ 0:00.00 /usr/libexec/gcc/darwin/ppc/as -arch ppc -o op.o
Here you can see that the user andy owns four instances of the bash shell. Within these shells, a vi session is active, ssh has connected to a server called "chimpy", and make is building an instance of Perl. make itself is calling elements of the GCC compiler suite, such as cc and as .
The numbers in the first column of the table show the PID number of each process. These are what you can feed to the commands listed in Table 3-2 in order to foreground, background, or send signals to them.
Alternatively, you can use shell-relative PIDs with these commands. Invoking jobs lists only those the processes running as children to the current shell:
andy@honey[~/mosxnut3]$ jobs [1] running sudo bin/safe_mysqld [2] + vi README andy@honey[~/mosxnut3]$
The bracketed numbers leading each row of this output table can be used instead of PIDs when issuing process-control commands. The number can be prefaced with a percentage sign (%) to show that you're using a relative PID. So, to foreground that vi process, type fg %2 . In this particular instance, you can also type fg for the same effect; the plus-sign symbol next to the number says it's a child process, and hence the default target for commands like fg and bg .
|
To see a list of all the processes you're running on this machine, use ps x :
andy@honey[~/mosxnut3]$ ps x PID TT STAT TIME COMMAND 97 ?? Ss 0:13.66 /System/Library/Frameworks/ApplicationServices 98 ?? Ss 0:03.03 /System/Library/CoreServices/loginwindow.app/ 212 ?? Ss 0:00.52 /System/Library/CoreServices/pbs 218 ?? S 0:38.93 /System/Library/CoreServices/Dock.app/Contents/ 220 ?? S 0:13.46 /System/Library/CoreServices/SystemUIServer.app/ 222 ?? S 0:17.76 /System/Library/CoreServices/Finder.app/Contents/ 225 ?? S 0:00.30 /Applications/iTunes.app/Contents/Resources/ 227 ?? S 0:01.10 /Applications/iCal.app/Contents/Resources/ 322 ?? S 0:00.69 /System/Library/Services/AppleSpell.service/ 358 ?? S 0:00.47 /System/Library/CoreServices/RemoteManagement/ 359 ?? S 0:00.04 /System/Library/CoreServices/RemoteManagement/ 388 ?? S 0:34.33 /Applications/Quicksilver.app/Contents/MacOS/ 1463 ?? S 0:02.15 /System/Library/CoreServices/Dock.app/Contents/ 1469 ?? S 0:01.26 /System/Library/CoreServices/Dock.app/Contents/ 1684 ?? S 0:32.87 /Applications/iChat.app/Contents/MacOS/iChat -psn_ 1686 ?? S 4:06.34 /Applications/Firefox.app/Contents/MacOS/firefox- 1687 ?? S 1:30.28 /Applications/Utilities/Terminal.app/Contents/ 1688 ?? Ss 0:02.53 /System/Library/Frameworks/InstantMessage.framewor 1691 ?? S 0:03.85 /Applications/iCal.app/Contents/MacOS/iCal -psn_0_ 1693 ?? S 2:42.60 /Applications/X-Chat Aqua.app/Contents/MacOS/ 3180 ?? S 4:53.76 /Applications/Microsoft Office 2004/Microsoft Word 3182 ?? S 0:04.51 /Applications/Microsoft Office 2004/Office/ 3261 ?? S 0:00.90 /Applications/Stickies.app/Contents/MacOS/Stickies 3278 ?? S 3:09.86 /Applications/iTunes.app/Contents/MacOS/iTunes 3299 ?? SNs 0:02.06 /System/Library/Frameworks/CoreServices.framework/ 3304 ?? S 0:14.04 /System/Library/CoreServices/Dock.app/Contents/ 1692 p1 S 0:00.35 -bash 3273 p2 S 0:00.02 -bash 3284 p2 S+ 0:00.76 ssh blitz 3311 p3 S 0:00.02 -bash 3313 p3 S+ 0:00.05 vim outline.pod 3883 p4 S 0:00.03 -bash 4405 p4 S+ 0:00.09 make perl 4443 p4 S+ 0:00.00 /bin/sh -c 'sh cflags "optimize='-pg'" toke.o' 4444 p4 S+ 0:00.00 /bin/sh -c 'sh cflags "optimize='-pg'" toke.o' 4445 p4 R+ 0:00.03 sh cflags optimize='-pg' toke.o
This lists both the Terminal-controlled programs and the Aqua applications that are running, as well as the frameworks, system services, and plug-ins used by those applications. They are, after all, just Unix programs, all with their own PIDs.
Running ps with the aux options lists every single process running on the machine, regardless of context or user. This would, at a typical moment in any Mac OS X machine's life, be enough to fill a couple of pages of this book. You can pipe this output through the grep command to automatically filter the results: ps ax grep bash shows a table describing all the bash processes every user is currently running, for example.
For a friendlier interface to browsing active processes, see the Activity Monitor ( /Applications/Utilities ).
3.2.1.1. Sending signals with kill and killall
As its name suggests, kill 's most common function involves terminating programs, through its default usage: kill pid . Actually, kill sends a Unix signal of some kind to the program, and the default happens to be the terminate ( TERM ) signal. You can send different signals through the kill - signal pid syntax, where signal is a signal name or number.
The even more violent-sounding killall is often more convenient than kill is. This really just lets you refer to processes by their name, saving you from having to look up their PIDs first. For example, killall tail sends the TERM signal to all tail processes running under one name.
killall -HUP process is a traditional Unix idiom for having a continually running process (such as a network daemon) reload its configuration information. However, if a Startup Script is available for this service, you should favor running that instead, even if they both ultimately have a similar effect; see the section "StartupItems" in Chapter 11.
3.2.2. Mac OS X's Console Mode
While not quite an alternative to using the Terminal, Mac OS X offers a console login mode that lets you boot into Darwin's command-line interface instead of Aqua.
To enter console mode, you first need to configure Mac OS X's login window so it only displays the name and passwords fields. To do this, launch System Preferences, and go to Accounts 
Login Options. In the Login Options pane, turn off automatic login, and set the "Display login window as option to "Name and password." Next, at the login window, identify yourself as >console and click Log In (or press Return) without providing a password; the login window gets replaced by a standard Unix login prompt. Just type in your username and password as directed, and you're in.
Once you log out (through the logout command or by exit ing your shell program), the Mac OS X's standard login window appears once more. You need to pull the >console trick again in order to reenter console mode; otherwise , subsequent logins will launch the Finder, as usual.
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