17.3. System Configuration

17.2. Kernel Utilities

Mac OS X includes various utilities that interact with the kernel. With these utilities, you can debug a running kernel, load and unload kernel modules or extensions, or set kernel variables.

17.2.1. ddb

The ddb utility can debug a running kernel. It is not included with the current version of Mac OS X. If you want to use ddb, you can find its source code in the xnu (Darwin kernel) source code (http://www.opensource.apple.com/darwinsource/).

17.2.2. ktrace

Use ktrace to perform kernel tracing (tracing system calls and other operations) on a process. To launch a program and generate a kernel trace (ktrace.out, which is not human-readable), use ktrace command, as in ktrace emacs. Kernel tracing ends when you exit the process or disable tracing with ktrace -cp pid. You can get human readable output from a ktrace file with kdump -f ktrace.out.

17.2.3. Kernel Module Utilities

The following list describes utilities for manipulating kernel modules. For more information, see the kernel extension tutorials available at http://www.opendarwin.org/en/articles/:

kextload

Loads an extension bundle. Requires superuser privileges.

kextunload

Unloads an extension bundle. Requires superuser privileges.

kextstat

Displays the status of currently loaded kernel extensions. Table 17-5 describes this utility's output. Figure 17-6 shows sample output.

Figure 17-6. Partial output of kextstat

Table 17-5. Information displayed by kextstat

Item number	Column	Description
1	Index	Index number of the loaded extension. Extensions are loaded in sequence; gaps in this sequence signify extensions that have been unloaded.
2	Refs	Number of references to this extension from other extensions.
3	Address	Kernel space address of the extension.
4	Size	Amount of kernel memory (in bytes) used by the extension.
5	Wired	Amount of wired kernel memory (in bytes) used by the extension.
6	Name (Version)	Name and version of the extension.
7	<Linked Against>	Index of kernel extensions to which this extension refers.

17.2.4. sysctl

sysctl is a standard BSD facility for configuring kernel state variables . Use sysctl name to display a variable name, as in sysctl kern.ostype. Use sysctl -a to display all variables. If you have superuser privileges, you can set a variable with sysctl -w name=value.

Table 17-6 lists the sysctl variables on Mac OS X. See the sysctl(3) manpage for a description of the sysctl system call and more detailed information on the kernel state variables.

Table 17-6. sysctl's kernel state variables

Name	Type	Writable	Description
hw.activecpu	int	no	The number of CPUs currently active (may be affected by power management settings).
hw.availcpu	int	no	Number of available CPUs.
hw.busfrequency	int	no	Bus frequency in hertz. Divide by one million for a megahertz figure.
hw.busfrequency_max	int	no	Maximum bus frequency in hertz.
hw.busfrequency_min	int	no	Minimum bus frequency in hertz.
hw.byteorder	int	no	Variable that returns 4321, showing the ordering of four bytes on the PowerPC platform.
hw.cachelinesize	int	no	The cache line size in bytes.
hw.cpufrequency	int	no	CPU frequency in hertz. Divide by one million for a megahertz figure.
hw.cpufrequency_max	int	no	Maximum CPU frequency in hertz.
hw.cpufrequency_min	int	no	Minimum CPU frequency in hertz.
hw.cpusubtype	int	no	The mach-o subtype of the CPU (see /System/Library/Frameworks/Kernel.framework/Versions/A/Headers/mach/machine.h).
hw.cputype	int	no	The mach-o type of the CPU.
hw.epoch	int	no	Variable that indicates whether your hardware is "New World" or "Old World." Old World Macintoshes (pre-G3) have a value of 0.
hw.l1dcachesize	int	no	Level 1 data cache size in bytes.
hw.l1icachesize	int	no	Level 1 instruction cache size in bytes.
hw.l2cachesize	int	no	Level 2 cache size in bytes.
hw.l2settings	int	no	Level 2 cache settings.
hw.l3cachesize	int	no	Level 3 cache size in bytes.
hw.l3settings	int	no	Level 3 cache settings.
hw.logicalcpu	int	no	Number of logical CPUs.
hw.logicalcpu_max	int	no	Maximum number of available logical CPUs.
hw.machine	string	no	Machine class (Power Macintosh on most systems).
hw.memsize	int	no	Memory size.
hw.model	string	no	Machine model.
hw.ncpu	int	no	Number of CPUs.
hw.optional.altivec	int	no	Indicates whether AltiVec is enabled.
hw.optional.datastreams	int	no	Indicates whether PowerPC data stream instructions are supported by the CPU.
hw.optional.dcba	int	no	Indicates whether the PowerPC DCBA instruction is supported by the CPU.
hw.optional.floatingpoint	int	no	Indicates whether floating-point operations are supported by the CPU.
hw.optional.graphicsops	int	no	Indicates whether graphics operations are supported by the CPU.
hw.optional.stfiwx	int	no	Indicates whether the PowerPC STFIWX instruction is supported by the CPU.
hw.pagesize	int	no	Software page size in bytes.
hw.physicalcpu	int	no	Number of physical CPUs.
hw.physicalcpu_max	int	no	Maximum available physical CPUs.
hw.physmem	int	no	Physical memory in bytes.
hw.tbfrequency	int	no	The base frequency used by Mac OS X for its timing services.
hw.usermem	int	no	Non-kernel memory.
hw.vectorunit	int	no	Variable that indicates whether you are running on an AltiVec-enabled CPU.
kern.aiomax	int	no	Maximum AIO requests.
kern.aioprocmax	int	no	Maximum AIO requests per process.
kern.aiothreads	int	no	Maximum number of AIO worker threads.
kern.argmax	int	no	Maximum number of arguments supported by exec( ).
kern.boottime	struct timeval	no	The time when the system was booted.
kern.clockrate	struct clockinfo	no	System clock timings.
kern.coredump	int	yes	Determines whether core dumps are enabled.
kern.corefile	string	yes	Location of core dump files (%P is replaced with process id).
kern.delayterm	int	unknown	Unknown or undocumented.
kern.dummy	n/a	n/a	Unused.
kern.hibernatefile	string	yes	Unknown or undocumented.
kern.hibernatemode	int	yes	Unknown or undocumented.
kern.hostid	int	yes	Host identifier.
kern.hostname	string	yes	Hostname.
kern.ipc.*	various	n/a	Various IPC settings.
kern.job_control	int	no	Variable that indicates whether job control is available.
kern.low_pri_delay	int	yes	Set/reset throttle delay in milliseconds.
kern.low_pri_window	int	yes	Set/reset throttle window in milliseconds.
kern.maxfiles	int	yes	Maximum number of open files.
kern.maxfilesperproc	int	yes	Maximum number of open files per process.
kern.maxproc	int	yes	Maximum number of simultaneous processes.
kern.maxprocperuid	int	yes	Maximum number of simultaneous processes per user.
kern.maxvnodes	int	yes	Maximum number of vnodes.
kern.netboot	int	no	Variable that indicates whether the system booted via NetBoot.
kern.ngroups	int	no	Maximum number of supplemental groups.
kern.nisdomainname	string	yes	NIS domain name.
kern.osrelease	string	no	Operating system release version.
kern.osrevision	int	no	Operating system revision.
kern.ostype	string	no	Operating system name.
kern.posix.sem.max	int	yes	Maximum number of POSIX semaphores.
kern.posix1version	int	no	The version of POSIX 1003.1 with which the system attempts to comply.
kern.saved_ids	int	no	This is set to 1 if saved set-group and set-user IDs are available.
kern.securelevel	int	increment only	The system security level.
kern.shreg_private	int	no	Indicates whether shared memory regions can be privatized.
kern.sugid_coredump	int	yes	Determines whether SUID and SGID files are allowed to dump core.
kern.sugid_scripts	int	yes	Determines whether to permit SUID and SGID scripts.
kern.symfile	string	no	The kernel symbol file.
kern.sysv.*	various	n/a	System V semaphore settings. See /System/Library/Frameworks/Kernel.framework/Versions/A/Headers/sys/sysctl.h.
kern.sysv.shmall	int	yes	The maximum size of a shared memory segment.
kern.sysv.shmmax	int	yes	The maximum number of shared memory pages.
kern.sysv.shmmin	int	yes	The maximum number of shared memory segments per process.
kern.sysv.shmmni	int	yes	The maximum number of shared memory segments.
kern.sysv.shmseg	int	yes	The minimum size of a shared memory segment.
kern.usrstack	int	no	Address of USRSTACK.
kern.version	string	no	The kernel version string.
net.appletalk.routermix			Unknown or undocumented.
net.inet.*	various	n/a	IPv4 settings.
net.inet6.*	various	n/a	IPv6 settings.
net.key.*	various	n/a	IPSec key management settings.
net.link.ether.inet.*	various	n/a	Ethernet settings.
net.local.*	various	n/a	Various network settings.
user.bc_base_max	int	no	Maximum ibase/obase available in the bc calculator.
user.bc_dim_max	int	no	Maximum array size available in the bc calculator.
user.bc_scale_max	int	no	Maximum scale value available in the bc calculator.
user.bc_string_max	int	no	Maximum string length available in the bc calculator.
user.coll_weights_max	int	no	Maximum number of weights that can be used with LC_COLLATE in the locale definition file.
user.cs_path	string	no	Value for PATH that can find all the standard utilities.
user.expr_nest_max	int	no	Maximum number of expressions you can nest within parentheses using expr.
user.line_max	int	no	Maximum length in bytes of an input line used with a text-processing utility.
user.posix2_c_bind	int	no	Variable that returns 1 if the C development environment supports the POSIX C Language Bindings Option; otherwise, the result will be 0.
user.posix2_c_dev	int	no	Variable that returns 1 if the C development environment supports the POSIX C Language Development Utilities Option; otherwise, the result will be 0.
user.posix2_char_term	int	no	Variable that returns 1 if the systems supports at least one terminal type specified in POSIX 1003.2; otherwise, the result will be 0.
user.posix2_fort_dev	int	no	Variable that returns 1 if the system supports the POSIX FORTRAN Development Utilities Option; otherwise, the result will be 0.
user.posix2_fort_run	int	no	Variable that returns 1 if the system supports the POSIX FORTRAN Runtime Utilities Option; otherwise, the result will be 0.
user.posix2_localedef	int	no	Variable that returns 1 if the system allows you to create locale; otherwise, the result will be 0.
user.posix2_sw_dev	int	no	Variable that returns 1 if the system supports the POSIX Software Development Utilities Option; otherwise, the result will be 0.
user.posix2_upe	int	no	Variable that returns 1 if the system supports the POSIX User Portable Utilities Option; otherwise, the result will be 0.
user.posix2_version	int	no	Variable that returns the POSIX 1003.2 version with which the system attempts to comply.
user.re_dup_max	int	no	Maximum repeated occurrences of a regular expression when using interval notation.
user.stream_max	int	no	Maximum number of streams a process may have open.
user.tzname_max	int	no	Maximum number of types supported for a time zone name.
vfs.*	various	n/a	Various VFS settings.
vm.loadavg	string	no	Current load average.
vm.swapusage	string	no	Current swap file usage.