---
name: "CTR4"
section: "9"
platform: "linux"
package: "freebsd-manpages"
version: "6.0-5"
release: "Debian 4.0 (Etch)"
platforms: ["linux", "freebsd"]
url: "https://new.carta.tech/CTR4"
---

# CTR4(9)

kernel tracing facility

## NAME

**CTR0**, **CTR1**, **CTR2**, **CTR3**, **CTR4**, **CTR5** – kernel tracing facility

## SYNOPSIS

**#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\[\]*;

*void*\

**CTR0**(*u\_int mask*, *char \*format*);

*void*\

**CTR1**(*u\_int mask*, *char \*format*, *arg1*);

*void*\

**CTR2**(*u\_int mask*, *char \*format*, *arg1*, *arg2*);

*void*\

**CTR3**(*u\_int mask*, *char \*format*, *arg1*, *arg2*, *arg3*);

*void*\

**CTR4**(*u\_int mask*, *char \*format*, *arg1*, *arg2*, *arg3*, *arg4*);

*void*\

**CTR5**(*u\_int mask*, *char \*format*, *arg1*, *arg2*, *arg3*, *arg4*, *arg5*);

## DESCRIPTION

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

Events are created and logged in the kernel via the CTR*x* 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)](/printf/9.md) 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*. Note that the different macros differ only in the number of arguments each one takes, as indicated by its name. Each event is logged with a timestamp in addition to the log message.

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.

## EXAMPLES

This example demonstrates the use of tracepoints at the KTR\_PROC logging level.

```
void
mi_switch()
{
	...
	/*
	 * Pick a new current process and record its start time.
	 */
	...
	CTR3(KTR_PROC, "mi_switch: old proc %p (pid %d, %s)", p, p->p_pid,
	    p->p_comm);
	...
	cpu_switch();
	...
	CTR3(KTR_PROC, "mi_switch: new proc %p (pid %d, %s)", p, p->p_pid,
	    p->p_comm);
	...
}
```

## SEE ALSO

[ktr(4)](/ktr/4.md), [ktrdump(8)](/ktrdump/8.md)

## HISTORY

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

## BUGS

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.