KTRDUMP(8) BSD System Manager's Manual KTRDUMP(8)NAME
ktrdump -- print kernel ktr trace buffer
SYNOPSIS
ktrdump [-cfqrtH] [-i ktrfile] [-M core] [-N system] [-o outfile]
DESCRIPTION
The ktrdump utility is used to dump the contents of the kernel ktr trace buffer.
The following options are available:
-c Print the CPU number that each entry was logged from.
-f Print the file and line number that each entry was logged from.
-q Quiet mode; do not print the column header.
-r Print relative timestamps rather than absolute timestamps.
-t Print the timestamp for each entry.
-H Print the thread ID for each entry.
-i ktrfile File containing saved ktr trace events; for more information see the ktr(4) manual page.
-N system The kernel image to resolve symbols from. The default is the value returned via getbootfile(3).
-M core The core file or memory image to read from. The default is /dev/mem.
-o outfile The file to write the output to. The default is standard output.
SEE ALSO ktr(4), ktr(9)HISTORY
The ktrdump utility first appeared in FreeBSD 5.0.
AUTHORS
The ktrdump utility was implemented by Jake Burkholder <jake@FreeBSD.org>.
This manual page was written by Chad David <davidc@FreeBSD.org>.
BSD February 6, 2015 BSD
Check Out this Related Man Page
KTR(4) BSD Kernel Interfaces Manual KTR(4)NAME
ktr -- kernel tracing facility
SYNOPSIS
options KTR
options ALQ
options KTR_ALQ
options KTR_COMPILE=(KTR_LOCK|KTR_INTR|KTR_PROC)
options KTR_CPUMASK=0x3
options KTR_ENTRIES=8192
options KTR_MASK=(KTR_INTR|KTR_PROC)
options KTR_VERBOSE
DESCRIPTION
The ktr facility allows kernel events to be logged while the kernel executes so that they can be examined later when debugging. The only
mandatory option to enable ktr is ``options KTR''.
The KTR_ENTRIES option sets the size of the buffer of events. It must be a power of two. The size of the buffer in the currently running
kernel can be found via the read-only sysctl debug.ktr.entries. By default the buffer contains 1024 entries.
Event Masking
Event levels can be enabled or disabled to trim excessive and overly verbose logging. First, a mask of events is specified at compile time
via the KTR_COMPILE option to limit which events are actually compiled into the kernel. The default value for this option is for all events
to be enabled.
Secondly, the actual events logged while the kernel runs can be further masked via the run time event mask. The KTR_MASK option sets the
default value of the run time event mask. The runtime event mask can also be set by the loader(8) via the debug.ktr.mask environment vari-
able. It can also be examined and set after booting via the debug.ktr.mask sysctl. By default the run time mask is set to log only KTR_GEN
events. The definitions of the event mask bits can be found in <sys/ktr.h>.
Furthermore, there is a CPU event mask whose default value can be changed via the KTR_CPUMASK option. A CPU must have the bit corresponding
to its logical id set in this bitmask for events that occur on it to be logged. This mask can be set by the loader(8) via the
debug.ktr.cpumask environment variable. It can also be examined and set after booting via the debug.ktr.cpumask sysctl. By default events
on all CPUs are enabled.
Verbose Mode
By default, events are only logged to the internal buffer for examination later, but if the verbose flag is set then they are dumped to the
kernel console as well. This flag can also be set from the loader via the debug.ktr.verbose environment variable, or it can be examined and
set after booting via the debug.ktr.verbose sysctl. If the flag is set to zero, which is the default, then verbose output is disabled. If
the flag is set to one, then the contents of the log message and the CPU number are printed to the kernel console. If the flag is greater
than one, then the filename and line number of the event are output to the console in addition to the log message and the CPU number. The
KTR_VERBOSE option sets the flag to one.
Examining the Events
The KTR buffer can be examined from within ddb(4) via the show ktr [/v] command. This command displays the contents of the trace buffer one
page at a time. At the ``--more--'' prompt, the Enter key displays one more entry and prompts again. The spacebar displays another page of
entries. Any other key quits. By default the timestamp, filename, and line number are not displayed with each log entry. If the /v modi-
fier is specified, then they are displayed in addition to the normal output. Note that the events are displayed in reverse chronological
order. That is, the most recent events are displayed first.
Logging ktr to Disk
The KTR_ALQ option can be used to log ktr entries to disk for post analysis using the ktrdump(8) utility. This option depends on the ALQ
option. Due to the potentially high volume of trace messages the trace mask should be selected carefully. This feature is configured
through a group of sysctls.
debug.ktr.alq_file displays or sets the file that ktr will log to. By default its value is /tmp/ktr.out. If the file name is changed
while ktr is enabled it will not take effect until the next invocation.
debug.ktr.alq_enable enables logging of ktr entries to disk if it is set to one. Setting this to 0 will terminate logging.
debug.ktr.alq_max is the maximum number of entries that will be recorded to disk, or 0 for infinite. This is helpful for limiting the
number of particularly high frequency entries that are recorded.
debug.ktr.alq_depth determines the number of entries in the write buffer. This is the buffer that holds entries before they are written to
disk and defaults to the value of the KTR_ENTRIES option.
debug.ktr.alq_failed records the number of times we failed to write an entry due to overflowing the write buffer. This may happen if the
frequency of the logged ktr messages outpaces the depth of the queue.
debug.ktr.alq_cnt records the number of entries that have currently been written to disk.
SEE ALSO ktrdump(8), alq(9), ktr(9)HISTORY
The KTR kernel tracing facility first appeared in BSD/OS 3.0 and was imported into FreeBSD 5.0.
BSD January 25, 2005 BSD