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KTRACE(2)                DragonFly System Calls Manual               KTRACE(2)


NAME

     ktrace - process tracing


LIBRARY

     Standard C Library (libc, -lc)


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

     The ktrace() function returns the value 0 if successful; otherwise the
     value -1 is returned and the global variable errno is set to indicate the
     error.


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.

DragonFly 6.5-DEVELOPMENT        April 4, 2023       DragonFly 6.5-DEVELOPMENT

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