KTRACE(2)

NAME
ktrace - process tracing

LIBRARY
libc

SYNOPSIS
#include <sys/param.h>
#include <sys/time.h>
#include <sys/ktrace.h>
int
ktrace(const char *tracefile, int ops, int trpoints, int pid);

DESCRIPTION
The ktrace() function enables or disables tracing of one or more processes. Users may only trace their own processes. By default only the super-user can trace setuid or setgid programs. This restriction can be removed by setting the sysctl kern.ktrace_suid to a non-zero value.

The tracefile 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 parameter specifies the requested ktrace operation. The defined operations are:

KTROP_SET
    Enable trace points specified in trpoints.
KTROP_CLEAR
    Disable trace points specified in trpoints.
KTROP_CLEARFILE
    Stop all tracing.
KTRFLAG_DESCEND
    The tracing change should apply to the specified process and all its current children.

The trpoints parameter 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 generate much output).
KTRFAC_PSIG
    Trace posted signals.
KTRFAC_CSW
    Trace context switch points.
KTRFAC_SYSCTL
    Trace sysctls.
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 */
    	caddr_t	ktr_buf;
    };

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_buf is an internal kernel pointer and is not useful.

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.

RETURN VALUES

ERRORS
The ktrace() 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.

[ENOSYS]
    The kernel was not compiled with ktrace support.

SEE ALSO
kdump(1), ktrace(1), utrace(2), sysctl(8)

HISTORY
A ktrace() function call first appeared in 4.4BSD.