ktrace(1) [opendarwin man page]

KTRACE(1)						    BSD General Commands Manual 						 KTRACE(1)

NAME

     ktrace -- enable kernel process tracing

SYNOPSIS

     ktrace [-aCcdi] [-f trfile] [-g pgrp | -p pid] [-t trstr]
     ktrace [-adi] [-f trfile] [-t trstr] command

DESCRIPTION

     The ktrace command enables kernel trace logging for the specified processes.  Kernel trace data is logged to the file ktrace.out.	The kernel
     operations that are traced include system calls, namei translations, signal processing, and I/O.

     Once tracing is enabled on a process, trace data will be logged until either the process exits or the trace point is cleared.  A traced
     process can generate enormous amounts of log data quickly; It is strongly suggested that users memorize how to disable tracing before
     attempting to trace a process.  The following command is sufficient to disable tracing on all user owned processes, and, if executed by root,
     all processes:

	   $ ktrace -C

     The trace file is not human readable; use kdump(1) to decode it.

     The options are as follows:

     -a      Append to the trace file instead of recreating it.

     -C      Disable tracing on all user owned processes, and, if executed by root, all processes in the system.

     -c      Clear the trace points associated with the specified file or processes.

     -d      Descendants; perform the operation for all current children of the designated processes.

     -f file
	     Log trace records to file instead of ktrace.out.

     -g pgid
	     Enable (disable) tracing on all processes in the process group (only one -g flag is permitted).

     -i      Inherit; pass the trace flags to all future children of the designated processes.

     -p pid  Enable (disable) tracing on the indicated process id (only one -p flag is permitted).

     -t trstr
	     The string argument represents the kernel trace points, one per letter.  The following table equates the letters with the trace-
	     points:

	     c	   trace system calls
	     n	   trace namei translations
	     i	   trace I/O
	     s	   trace signal processing
	     u	   userland traces
	     w	   context switches

     command
	     Execute command with the specified trace flags.

     The -p, -g, and command options are mutually exclusive.

EXAMPLES

     # trace all kernel operations of process id 34
	   $ ktrace -p 34

     # trace all kernel operations of processes in process group 15 and # pass the trace flags to all current and future children
	   $ ktrace -idg 15

     # disable all tracing of process 65
	   $ ktrace -cp 65

     # disable tracing signals on process 70 and all current children
	   $ ktrace -t s -cdp 70

     # enable tracing of I/O on process 67
	   $ ktrace -ti -p 67

     # run the command "w", tracing only system calls
	   $ ktrace -tc w

     # disable all tracing to the file "tracedata"
	   $ ktrace -c -f tracedata

     # disable tracing of all processes owned by the user
	   $ ktrace -C

SEE ALSO

     kdump(1)

BUGS

     Only works if file is a regular file.

HISTORY

     The ktrace command appeared in 4.4BSD.

BSD
								   June 6, 1993 							       BSD

KTRACE(2)						      BSD 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/uio.h>
     #include <sys/ktrace.h>

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

DESCRIPTION

     The ktrace() system call 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 argument 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 argument 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 argument 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_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 */
	     intptr_t	     ktr_tid;	     /* was ktr_buffer */
     };

     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_tid field holds a threadid.

     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.

SYSCTL TUNABLES

     The following sysctl(8) tunables influence the behaviour of ktrace():

     kern.ktrace.geniosize
	     bounds the amount of data a traced I/O request will log to the trace file.

     kern.ktrace.request_pool
	     bounds the number of trace events being logged at a time.

     Sysctl tunables that control process debuggability (as determined by p_candebug(9)) also affect the operation of ktrace().

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() system call 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.

     A thread may be unable to log one or more tracing events due to a temporary shortage of resources.  This condition is remembered by the ker-
     nel, and the next tracing request that succeeds will have the flag KTR_DROP set in its ktr_type field.

SEE ALSO

     kdump(1), ktrace(1), utrace(2), sysctl(8), p_candebug(9)

HISTORY

     The ktrace() system call first appeared in 4.4BSD.

BSD
								   July 13, 2008							       BSD