---
name: "ktrace"
section: "2freebsd"
platform: "linux"
package: "freebsd-manpages"
version: "12.2-2"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/ktrace/2freebsd"
---

# ktrace(2freebsd)

process tracing

## NAME

**ktrace** – process tracing

## LIBRARY

Standard C Library (libc, -lc)

## SYNOPSIS

**#include \<sys/param.h\>**

**#include \<sys/time.h\>**

**#include \<sys/uio.h\>**

**#include \<sys/ktrace.h\>**

*int*\

**ktrace**(*const char \*tracefile*, *int ops*, *int trpoints*, *int pid*);

## DESCRIPTION

The **ktrace**() system call enables or disables tracing of one or more processes. Users may only trace their own processes. Only the super-user can trace setuid or setgid programs.

The *tracefile* argument gives the pathname of the file to be used for tracing. The file must exist and be a regular file writable by the calling process. All trace records are always appended to the file, so the file must be truncated to zero length to discard previous trace data. If tracing points are being disabled (see KTROP\_CLEAR below), *tracefile* may be NULL.

The *ops* argument specifies the requested ktrace operation. The defined operations are:

| | |
| --- | --- |
| KTROP\_SET | Enable trace points specified in |
| KTROP\_CLEAR | Disable trace points specified in |
| KTROP\_CLEARFILE | Stop all tracing. |
| KTRFLAG\_DESCEND | The tracing change should apply to the |

The *trpoints* argument specifies the trace points of interest. The defined trace points are:

| | |
| --- | --- |
| KTRFAC\_SYSCALL | Trace system calls. |
| KTRFAC\_SYSRET | Trace return values from system calls. |
| KTRFAC\_NAMEI | Trace name lookup operations. |
| KTRFAC\_GENIO | Trace all I/O (note that this option can |
| KTRFAC\_PSIG | Trace posted signals. |
| KTRFAC\_CSW | Trace context switch points. |
| KTRFAC\_USER | Trace application-specific events. |
| KTRFAC\_STRUCT | Trace certain data structures. |
| KTRFAC\_SYSCTL | Trace sysctls. |
| KTRFAC\_PROCCTOR | Trace process construction. |
| KTRFAC\_PROCDTOR | Trace process destruction. |
| KTRFAC\_CAPFAIL | Trace capability failures. |
| KTRFAC\_FAULT | Trace page faults. |
| KTRFAC\_FAULTEND | Trace the end of page faults. |
| KTRFAC\_INHERIT | Inherit tracing to future children. |

Each tracing event outputs a record composed of a generic header followed by a trace point specific structure. The generic header is:

```
struct ktr_header {
	int		ktr_len;		/* length of buf */
	short		ktr_type;		/* trace record type */
	pid_t		ktr_pid;		/* process id */
	char		ktr_comm[MAXCOMLEN+1];	/* command name */
	struct timeval	ktr_time;		/* timestamp */
	intptr_t	ktr_tid;		/* was ktr_buffer */
};
```

The *ktr\_len* field specifies the length of the *ktr\_type* data that follows this header. The *ktr\_pid* and *ktr\_comm* fields specify the process and command generating the record. The *ktr\_time* field gives the time (with microsecond resolution) that the record was generated. The *ktr\_tid* field holds a thread id.

The generic header is followed by *ktr\_len* bytes of a *ktr\_type* record. The type specific records are defined in the ⟨sys/ktrace.h⟩ include file.

## SYSCTL TUNABLES

The following [sysctl(8)](/sysctl/8.md) tunables influence the behaviour of **ktrace**():

- *kern.ktrace.geniosize*

  bounds the amount of data a traced I/O request will log to the trace file.

- *kern.ktrace.request\_pool*

  bounds the number of trace events being logged at a time.

Sysctl tunables that control process debuggability (as determined by [p\_candebug(9)](/p_candebug/9.md)) also affect the operation of **ktrace**().

## RETURN VALUES

The **ktrace()** function returns the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate the error.

## ERRORS

The **ktrace**() system call will fail if:

- \[ENOTDIR\]

  A component of the path prefix is not a directory.

- \[ENAMETOOLONG\]

  A component of a pathname exceeded 255 characters, or an entire path name exceeded 1023 characters.

- \[ENOENT\]

  The named tracefile does not exist.

- \[EACCES\]

  Search permission is denied for a component of the path prefix.

- \[ELOOP\]

  Too many symbolic links were encountered in translating the pathname.

- \[EIO\]

  An I/O error occurred while reading from or writing to the file system.

- \[EINTEGRITY\]

  Corrupted data was detected while reading from the file system.

- \[ENOSYS\]

  The kernel was not compiled with **ktrace** support.

A thread may be unable to log one or more tracing events due to a temporary shortage of resources. This condition is remembered by the kernel, and the next tracing request that succeeds will have the flag KTR\_DROP set in its *ktr\_type* field.

## SEE ALSO

[kdump(1)](/kdump/1.md), [ktrace(1)](/ktrace/1.md), [utrace(2)](/utrace/2.md), [sysctl(8)](/sysctl/8.md), [p\_candebug(9)](/p_candebug/9.md)

## HISTORY

The **ktrace**() system call first appeared in 4.4BSD.