KTRACE(2) BSD Programmer's Manual KTRACE(2)NAMEktrace - process tracing
SYNOPSIS
#include <sys/types.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 process-
es.
The tracefile gives the pathname of the file to be used for tracing. The
file must be a regular file, must exist and must be writable by the call-
ing 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 speci-
fied process and all its current children.
The trpoints parameter specifies the trace points of interest. The de-
fined 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 gen-
erate much output).
KTRFAC_PSIG Trace posted signals.
KTRFAC_CSW Trace context switch points.
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.
Users may only trace their own processes. Only the superuser may trace
set-UID or set-GID programs. Only one user at a time may trace a pro-
cess; additional ktrace() requests for the same process may change the
tracing parameters for the process but they will not (for example) add
another tracing 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.
ERRORSKtrace() will fail if:
[EACCES] The named tracefile exists and is not a regular file.
[EACCES] Search permission is denied for a component of the path
prefix.
[EINVAL] No tracepoints were specified.
[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 255 characters, or an
entire path name exceeded 1023 characters.
[ENOENT] The named tracefile does not exist.
[ENOTDIR] A component of the path prefix is not a directory.
[EPERM] None of the specified processes could be traced (or un-
traced) because the requesting process did not have root
privileges and each of the specified processes had a dif-
ferent real UID from the caller, was set-UID or set-GID,
or was already being traced by a superuser process.
[ESRCH] The requested process or process group does not exist.
SEE ALSOktrace(1), kdump(1)HISTORY
A ktrace function call first appeared in 4.4BSD.
4th Berkeley Distribution May 7, 1998 2