Kernel Utilities (Mac OS X for Unix Geeks)

8.2.1. 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. For details on building the kernel or obtaining source code from CVS, see Chapter 7.

8.2.2. Kernel Module Utilities

The following list describes utilities for manipulating kernel modules. For more information, see the kernel extension tutorials available at http://www.opensource.apple.com/projects/documentation/howto. These utilities must be run by root or by someone with superuser privileges.

kextload: Loads an extension bundle.
kextunload: Unloads an extension bundle.
kextstat: Displays the status of currently loaded kernel extensions. Table 8-5 describes this utility's output.

Table 8-5. Information displayed by kextstat


Index
Refs
Address
Size
Wired
Name (Version)
<Linked Against>

Figure 8-5 shows sample output.

Figure 8-5. Partial output of kextstat

8.2.3. 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. You can set a variable with sysctl -w name=value. You must have superuser privileges to set a variable.

Table 8-6 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 8-6. sysctl's kernel state variables

Name	Type	Writable	Description
hw.busfrequency	int	no	Bus frequency in hertz. Divide by one million to get a megahertz figure.
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 to get a megahertz figure.
hw.epoch	int	no	Variable that indicates whether your hardware is in the New World or the Old World. Old World Macintoshes (pre-G3) will 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.machine	string	no	Machine class (Power Macintosh on most systems).
hw.model	string	no	Machine model.
hw.ncpu	int	no	Number of CPUs.
hw.pagesize	int	no	Software page size in bytes.
hw.physmem	int	no	Physical memory in bytes.
hw.usermem	int	no	Non-kernel memory.
hw.vectorunit	int	no	Variable that indicates whether you are running on an AltiVec-enabled CPU.
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.dummy	n/a	n/a	Unused.
kern.hostid	int	yes	Host identifier.
kern.hostname	string	yes	Hostname.
kern.job_control	int	no	Variable that indicates whether job control is available.
kern.maxfiles	int	yes	Maximum number of open files.
kern.maxproc	int	yes	Maximum number of simultaneous processes.
kern.maxvnodes	int	yes	Maximum number of vnodes.
kern.ngroups	int	no	Maximum number of supplemental groups.
kern.netboot	int	no	Variable that indicates whether the system booted via NetBoot.
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.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.symfile	string	no	The kernel symbol file.
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.sysv.shmall	int	yes	The maximum size of a shared memory segment.
kern.version	string	no	The kernel version string.
net.inet.*	various	n/a	IPv4 settings.
net.key.*	various	n/a	IPSec key management settings.
net.inet6.*	various	n/a	IPv6 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.

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.