NAME
ktrace —
process tracing
SYNOPSIS
#include
<sys/types.h>
#include <sys/param.h>
#include <sys/uio.h>
#include <sys/ktrace.h>
int
ktrace(const
char *tracefile, 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 superuser can trace setuid or
setgid programs. ktrace() is only available on
kernels compiled with the KTRACE option.
tracefile gives the pathname of the file to
be used for tracing. The file must exist, be writable by the calling
process, and not be a symbolic link. 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_EMUL- Trace emulation changes.
KTRFAC_CSW- Trace context switch points.
KTRFAC_STRUCT- Trace various structs
KTRFAC_USER- Trace user data coming from utrace(2) calls.
KTRFAC_INHERIT- Inherit tracing to future children.
The pid parameter refers to a process ID. If it is negative, it refers to a process group ID.
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 {
uint ktr_type; /* trace record type */
pid_t ktr_pid; /* process id */
pid_t ktr_tid; /* thread id */
struct timespec ktr_time; /* timestamp */
char ktr_comm[MAXCOMLEN+1]; /* command name */
size_t ktr_len; /* length of buf */
};
The ktr_len field specifies the length of the ktr_type data that follows this header. The ktr_pid, ktr_tid, and ktr_comm fields specify the process, thread, 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. 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:
- [
ENOTDIR] - A component of the path prefix is not a directory.
- [
EINVAL] - No trace points were selected.
- [
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 or the path refers to a symbolic link.
- [
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.
- [
ESRCH] - No process can be found corresponding to that specified by pid.
SEE ALSO
HISTORY
A ktrace() function call first appeared in
4.4BSD.