KEXT_LOGGING(8) BSD System Manager's Manual KEXT_LOGGING(8)NAME
kext logging — verbose/logging flags for kernel extensions (kexts) in the
kernel and command-line utilities
DESCRIPTION
The kext management facilities of Mac OS X allow for logging of kext
activity at all system levels, from the kernel to the user-space kext
daemon and most command-line kext tools. The -verbose (-v) flag of the
tools provides a simple system of levels that apply a set of lower level
binary logging flags appropriate to each tool, for maximally useful ver‐
bose output. The binary log specification is used for kernel logging and
is also available for use with the -verbose option when you need precise
control over logging.
ENABLING LOGGING
For command-line tools the -verbose (-v) and -quiet (-q) flags control
verbose output. The -verbose flag accepts a decimal level from 0-6 or a
hexadecimal log specification, both described below. The -verbose flag
temporarily sets the log spec within the kernel, and captures any log
messages from the kernel to print along with the tool's own log messages.
If you wish to alter the logging behavior of kextd(8), you will need to
edit its launchd.plist(5) file in
/System/Library/LaunchdDaemons/com.apple.kextd.plist.
To enable kernel kext logging (in /var/log/kernel.log) on a long-term
basis, use the kextlog boot arg or sysctl(8) parameter. You can set it
as root using nvram(8) like so:
nvram boot-args="kextlog=0xlogspec other_boot_args"
where logspec is a hexadecimal log specification, as described below
under “BINARY LOG SPECIFICATION”.
Caution: Enabling logging at a high level via boot arg can greatly slow
down system startup time.
To change the kextlog setting at any time use sysctl(8):
sysctl -w debug.kextlog=0xlogspec
VERBOSE LEVELS
As mentioned, for the command-line kext tools you use the -verbose (-v)
flag, which takes an optional argument that is either a decimal level
from 0-6, or a hexadecimal log specification (described under “BINARY LOG
SPECIFICATION”). The details of each level vary by tool, but in general
they are:
0 Errors only (that is, suppress warnings). Tools with a
-verbose flag also support a -quiet flag to suppress all
output.
1 (or none) Basic information about program operation.
2 Basic information about program progress, including files
created.
3 Information about individual kexts, link/load operation, and
processing of I/O Kit personalities.
4 Detailed information about kext operations, including C++
class construction/destruction, and for archives, about com‐
pression and architectures processed.
5 Debug-level information about internal operations.
6 Identical to level 5 but with bit 0x8 turned on (see the
hecadecimal log specification for details).
BINARY LOG SPECIFICATION
The binary log specification is a 32-bit value comprising a log level
with a bitmask divided into several regions from the least-significant
nibble (corresponding to digits from right to left in a hexadecimal rep‐
resentation). This table describes the regions and bits used; unlisted
regions and bits are reserved for future use:
Nibble 0 The log level, from 0-7. Each level includes all levels
below it. This is generally two higher than the decimal
level specified with -verbose.
Log level 0 - Silent.
Log level 1 - Errors.
Log level 2 - Warnings.
Log level 3 - Basic outcome/result.
Log level 4 - Operation progress.
Log level 5 - Steps in a given operation.
Log level 6 - Detailed logging.
Log level 7 - Debug level logging.
In addition, bit 0x8 of this nibble controls whether kext-
specific log messages are always printed. kextcache(8) and
kextunload(8) turn this bit on with their -verbose flag.
See “PER-KEXT LOGGING” for more information.
Nibbles 1-2 Activity flags relevant to general tool use, as in develop‐
ment scenarios. The -verbose flag always includes these. 8
bits total.
Nibble 1, Bit 0 (0x10) - General activity.
Nibble 1, Bit 1 (0x20) - Load activity.
Nibble 1, Bit 2 (0x40) - IPC and load settings.
Nibble 1, Bit 3 (0x80) - Archive processing.
Nibble 2 - Reserved.
Nibbles 3-7 Activity flags for internal operations, for debugging the
kext management system itself. These are available only
when using a hexadecimal log specification; the -verbose
flag never includes these. 20 bits total.
Nibble 3, Bit 0 (0x1000) - Kext validation.
Nibble 3, Bit 1 (0x2000) - Kext authentication.
Nibble 3, Bit 2 (0x4000) - Kext dependency resolution.
Nibble 4, Bit 0 (0x10000) - Directory scan (booter data scan
in the kernel).
Nibble 4, Bit 1 (0x20000) - File I/O.
Nibble 4, Bit 2 (0x40000) - Kext bookkeeping.
Nibble 5, Bit 0 (0x100000) - Link activity.
Nibble 5, Bit 1 (0x200000) - C++ patching activity.
Nibbles 6-7 - Reserved.
PER-KEXT LOGGING
Many log messages apply to the kext being processed. The kernel and most
of the command-line kext tools do not log these messages by default. You
can enable these messages for an individual kext by specifying an
OSBundleEnableKextLogging property in its Info.plist file with a boolean
value of true. For convenience, kextutil(8) automatically sets this
property for the kexts it is loading.
You can activate all per-kext log messages using level 6 with the
-verbose flag or by turning on bit 0x8 in a hexadecimal log specifica‐
tion. For convenience, kextcache(8) and kextunload(8) do this for all
verbose levels of their -verbose flag.
MAPPING VERBOSE LEVELS TO LOG SPECIFICATIONS
Here is a list of the exact hecadecimal log specifications applied by
each of the -verbose levels:
0 equivalent to 0x0 for all tools.
(default level)
equivalent to 0xff2, 0xff9 for kextcache(8) and
kextunload(8), 0xff3 for kextd(8) and for kextcache(8)
spawned by kextd(8).
1 (or none) equivalent to 0xff3, or 0xffa for kextcache(8) and
kextunload(8).
2 equivalent to 0xff4, or 0xffb for kextcache(8) and
kextunload(8).
3 equivalent to 0xff5, or 0xffc for kextcache(8) and
kextunload(8).
4 equivalent to 0xff6, or 0xffd for kextcache(8) and
kextunload(8).
5 equivalent to 0xff7, or 0xffe for kextcache(8) and
kextunload(8).
6 equivalent to 0xfff for all tools.
FILES
/var/log/kernel.log The kernel log file, where kernel kext activity is
logged.
/var/log/system.log The system log file, where kextd(8) activity is
logged.
/System/Library/LaunchdDaemons/com.apple.kextd.plist
Edit this launchd.plist(5) file to specify verbose
logging for kextd(8).
SEE ALSOsyslog(1), kextcache(8), kextd(8), kextlibs(8), kextload(8),
kextunload(8), kextutil(8)Darwin March 6, 2009 Darwin
