KTRACE(2)

KTRACE(2) | System Calls Manual | KTRACE(2)

# NAME

`ktrace`, `fktrace` —
process tracing

# LIBRARY

Standard C Library (libc, -lc)

# SYNOPSIS

`#include <sys/param.h>`
`#include <sys/ktrace.h>`

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

int
`fktrace`(int fd, int ops, int trpoints, pid_t pid);

# DESCRIPTION

The `ktrace`() function 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 gives the pathname of the file to be used for tracing. The file must exist and be 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. If using `fktrace`() then instead of passing a filename as tracefile, a file descriptor is passed as fd and behaviour is otherwise the same.

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_EMUL | Trace emulation changes.
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 */
    	short	ktr_version;		/* trace record version */
    	pid_t	ktr_pid;		/* process id */
    	char	ktr_comm[MAXCOMLEN+1];	/* command name */
    	struct	timespec ktr_time;	/* timestamp */
    	lwpid_t	ktr_lid;
    };

The `ktr_len` field specifies the length of the data that follows this header. The `ktr_type` and `ktr_version` fields (whose ordering in the structure depends on byte order) specify the format of this data. The `ktr_pid`, `ktr_lid`, and `ktr_comm` fields specify the process and command generating the record. The `ktr_time` field gives the time (with nanosecond resolution) that the record was generated.

The generic header is followed by `ktr_len` bytes of a `ktr_type` record of version `ktr_version`. The type specific records are defined in the ⟨sys/ktrace.h⟩ include file.

# RETURN VALUES

On successful completion a value of 0 is returned. Otherwise, a value of -1 is returned and errno is set to show the error.

# ERRORS

`ktrace`() will fail if:

[`EACCES`]
  Search permission is denied for a component of the path prefix.
[`EINVAL`]
  The pathname contains a character with the high-order bit set.
[`EIO`]
  An I/O error occurred while reading from or writing to the file system.
[`ELOOP`]
  Too many symbolic links were encountered in translating the pathname.
[`ENAMETOOLONG`]
  A component of a pathname exceeded {`NAME_MAX`} characters, or an entire path name exceeded {`PATH_MAX`} characters.
[`ENOENT`]
  The named tracefile does not exist.
[`ENOTDIR`]
  A component of the path prefix is not a directory.

# SEE ALSO

kdump(1), ktrace(1)

# HISTORY

A `ktrace` function call first appeared in 4.4BSD.

March 19, 2016 | NetBSD 10.0