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KTRACE(2)                 OpenBSD Programmer's Manual                KTRACE(2)

     ktrace - process tracing

     #include <sys/types.h>
     #include <sys/param.h>
     #include <sys/uio.h>
     #include <sys/ktrace.h>

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

     The ktrace() function enables or disables tracing of one or more process-
     es.  Users may only trace their own processes.  Only the superuser can
     trace setuid or setgid programs.

     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 symbol-
     ic 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 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.

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

     ktrace() will fail if:

     [ENOTDIR]       A component of the path prefix is not a directory.

     [EINVAL]        The pathname contains a character with the high-order bit

     [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.

     kdump(1), ktrace(1)

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

OpenBSD 3.0                      June 4, 1993                                2