KTR(9) FreeBSD Kernel Developer's Manual KTR(9)


CTR0, CTR1, CTR2, CTR3, CTR4, CTR5kernel tracing facility


#include < sys/param.h>
#include < sys/ktr.h>

extern int ktr_cpumask;
extern int ktr_entries;
extern int ktr_extend;
extern int ktr_mask;
extern int ktr_verbose;
extern struct ktr_entry ktr_buf[];

CTR0( u_int mask, char *format);

CTR1( u_int mask, char *format, arg1);

CTR2( u_int mask, char *format, arg1, arg2);

CTR3( u_int mask, char *format, arg1, arg2, arg3);

CTR4( u_int mask, char *format, arg1, arg2, arg3, arg4);

CTR5( u_int mask, char *format, arg1, arg2, arg3, arg4, arg5);

CTR6( u_int mask, char *format, arg1, arg2, arg3, arg4, arg5, arg6);


KTR provides a circular buffer of events that can be logged in a printf(9) style fashion. These events can then be dumped with ddb(4), gdb(1) or ktrdump(8).

Events are created and logged in the kernel via the CTRx macros. The first parameter is a mask of event types ( KTR_*) defined in < sys/ktr.h>. The event will be logged only if any of the event types specified in mask are enabled in the global event mask stored in ktr_mask. The format argument is a printf(9) style format string used to build the text of the event log message. Following the format string are zero to five arguments referenced by format. Each event is logged with a file name and source line number of the originating CTR call, and a timestamp in addition to the log message.

The event is stored in the circular buffer with supplied arguments as is, and formatting is done at the dump time. Do not use pointers to the objects with limited lifetime, for instance, strings, because the pointer may become invalid when buffer is printed.

Note that the different macros differ only in the number of arguments each one takes, as indicated by its name.

The ktr_entries variable contains the number of entries in the ktr_buf array. These variables are mostly useful for post-mortem crash dump tools to locate the base of the circular trace buffer and its length.

The ktr_mask variable contains the run time mask of events to log.

The CPU event mask is stored in the ktr_cpumask variable.

The ktr_verbose variable stores the verbose flag that controls whether events are logged to the console in addition to the event buffer.


This example demonstrates the use of tracepoints at the KTR_PROC logging level.

  * Pick a new current process and record its start time. 
 CTR3(KTR_PROC, "mi_switch: old proc %p (pid %d)", p, p->p_pid); 
 CTR3(KTR_PROC, "mi_switch: new proc %p (pid %d)", p, p->p_pid); 


ktr(4), ktrdump(8)


The KTR kernel tracing facility first appeared in BSD/OS 3.0 and was imported into FreeBSD 5.0.


Currently there is one global buffer shared among all CPUs. It might be profitable at some point in time to use per-CPU buffers instead so that if one CPU halts or starts spinning, then the log messages it emitted just prior to halting or spinning will not be drowned out by events from the other CPUs.

The arguments given in CTRx() macros are stored as u_long, so do not pass arguments larger than size of an u_long type. For example passing 64bit arguments on 32bit architectures will give incorrect results.

November 30, 2008 FreeBSD