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OpenSolaris 2009.06 - man page for prex (opensolaris section 1)

prex(1) 				  User Commands 				  prex(1)

       prex - control tracing and manipulate probe points in a process or the kernel

       prex [-o trace_file_name] [-l libraries] [-s kbytes_size] cmd

       prex [-o trace_file_name] [-l libraries] [-s kbytes_size] -p pid

       prex -k [-s kbytes_size]

       The prex command is the part of the Solaris tracing architecture that controls probes in a
       process or the kernel. See tracing(3TNF) for an overview  of  this  tracing  architecture,
       including example source code using it.

       prex is the application used for external control of probes. It automatically preloads the
       libtnfprobe library. prex locates all the probes in a target executable or the kernel  and
       provides  an  interface for the user to manipulate them. It allows a probe to be turned on
       for tracing, debugging, or both. Tracing generates a TNF (Trace Normal  Form)  trace  file
       that  can be converted to ASCII by tnfdump(1) and used for performance analysis. Debugging
       generates a line to standard error whenever the probe is hit at run time.

       prex does not work on static executables. It only works on dynamic executables.

   Invoking prex
       There are three ways to invoke prex:

	   1.	  Use prex to start the target application cmd. In this case, the target applica-
		  tion	need  not be built with a dependency on libtnfprobe. See TNF_PROBE(3TNF).
		  prex sets the environment variable LD_PRELOAD to load libtnfprobe into the tar-
		  get  process.  See  ld(1). prex then uses the environment variable PATH to find
		  the target application.

	   2.	  Attach prex to a running application. In this case, the running target applica-
		  tion	should	have  libtnfprobe  already linked in. Alternatively, the user may
		  manually set LD_PRELOAD to include libtnfprobe.so.1 prior to invoking the  tar-

	   3.	  Use  prex  with the -k option to set prex to kernel mode. prex can then be used
		  to control probes in the Solaris kernel. In kernel  mode,  additional  commands
		  are  defined,  and some commands that are valid in other modes are invalid. See
		  Kernel Mode below.

   Control File Format and Command Language
       In a future release of prex, the command language may be moved to a syntax  that  is  sup-
       ported  by  an  existing scripting language like ksh(1). In the meantime, the interface to
       prex is uncommitted.

	   o	  Commands should be in ASCII.

	   o	  Each command is terminated with the NEWLINE character.

	   o	  A command can be continued onto the next line by ending the previous line  with
		  the backslash ("\") character.

	   o	  Tokens  in  a  command  must	be separated by whitespace (one or more spaces or

	   o	  The "#" character implies that the rest of the line is a comment.

   Basic prex Commands
		 Command			Result
       % prex a.out		     Attaches prex to your  pro-
				     gram and starts prex.
       prex> enable $all	     Enables all the probes.
       prex> quit resume	     Quits prex and resumes exe-
				     cution of program.

   Control File Search Path
       There are two different methods of communicating with prex:

	   o	  By specifications in a control file. During start-up, prex searches for a  file
		  named   .prexrc  in  the directories specified below. prex does not stop at the
		  first one it finds. This way a user can override any defaults that are set  up.
		  The search order is:


	   o	  By typing commands at the prex prompt.

       The  command language for both methods is the same and is specified in USAGE. The commands
       that return output will not make sense in a control file. The output will go  to  standard

       When  using  prex on a target process, the target will be in one of two states, running or
       stopped. This can be detected by the presence or absence  of  the  prex>  prompt.  If  the
       prompt  is absent, it means that the target process is running. Typing Control-C will stop
       the target pr ocess and return the user to the prompt. There is no guarantee that Control-
       C  will return to a prex prompt immediately. For example, if the target process is stopped
       on a job control stop (SIGSTOP), then Control-C in prex will wait  until  the  target  has
       been continued (SIGCONT). See Signals to Target Program below for more information on sig-
       nals and the target process.

       The following options are supported:

       -k		     kernel mode: prex is used to control probes in the  Solaris  kernel.
			     In  kernel  mode, additional commands are defined, and some commands
			     valid in other modes are invalid. See Kernel Mode	below.

       -l libraries	     The libraries mentioned are linked  in  to  the  target  application
			     using  LD_PRELOAD	(see  ld(1)).  This  option  cannot  be used when
			     attaching to a running process. The argument to the -l option should
			     be a space-separated string enclosed in double quotes. Each token in
			     the string is a library name. It follows the LD_PRELOAD rules on how
			     libraries should be specified and where they will be found.

       -o trace_file_name    File  to be used for the trace output. trace_file_name is assumed to
			     be relative to the current working directory of prex (that  is,  the
			     directory that the user was in when prex was started).

			     If  prex  attaches  to  a	process  that is already tracing, the new
			     trace_file_name  (if   provided)	will   not   be   used.   If   no
			     trace_file_name  is  specified,  the  default  is /$TMPDIR/trace-pid
			     where pid is the process id of the target program. If TMPDIR is  not
			     set, /tmp is used.

       -s kbytes_size	     Maximum size of the output trace file in Kbytes. The default size of
			     the trace kbytes_size is 4096 (2^10) bytes or 4  Mbytes  for  normal
			     usage,  and  384 or 384 kbytes in kernel mode. The minimum size that
			     can be specified is 128 Kbytes. The trace file can be thought of  as
			     a	least  recently  used  circular  buffer.  Once	the file has been
			     filled, newer events will overwrite the older ones.

       This section describes the usage of the prex utility.

       Probes are specified by a list of space-separated selectors. Selectors are of the form:


       (See TNF_PROBE(3TNF)). The "attribute=" is optional. If it is not specified,  it  defaults
       to "keys=".

       The attribute or value (generically called "spec") can be any of the following:

       IDENT	     Any  sequence  of	letters,  digits,  _, \, ., % not beginning with a digit.
		     IDENT implies an exact match.

       QUOTED_STR    Usually used to escape reserved words (any  commands  in  the  command  lan-
		     guage).  QUOTED_STR  implies an exact match and has to be enclosed in single
		     quotes (' ').

       REGEXP	     An ed(1) regular expression pattern match. REGEXP	has  to  be  enclosed  in
		     slashes  (/  /), A / can be included in a REGEXP by escaping it with a back-
		     slash \.

       The following grammar explains the syntax.

	 selector_list ::=   |		      /* empty */
			     selector_list selector
	 selector ::=	     spec=spec |  /* whitespace around `=' opt */
	 spec ::=	     IDENT |
			     QUOTED_STR |

       The terminals in the above grammar are:

	 IDENT =       [a-zA-Z_\.%]{[a-zA-Z0-9_\.%]}+
	 QUOTED_STR =  '[^\n']*'   /* any string in single quotes */
	 REGEXP =      /[^\n/]*/   /* regexp's have to be in / / */

       This is a list of the remaining grammar that is needed to understand  the  syntax  of  the
       command language (defined in next subsection):

	 filename ::=	  QUOTED_STR	/* QUOTED_STR defined above */
	 spec_list ::=	  /* empty */ |
			  spec_list spec  /* spec defined above */
	 fcn_handle ::=   &IDENT	/* IDENT defined above */
	 set_name ::=	  $IDENT	/* IDENT defined above */

   Command Language
	   1.	  Set Creation and Set Listing

		    create $set_name selector_list
		    list     sets	   # list the defined sets

		  create  can be used to define a set which contains probes that match the selec-
		  tor_list. The set $all is pre-defined as /.*/ and it matches all the probes.

	   2.	  Function Listing

		    list     fcns	 # list the available fcn_handle

		  The user can list the different  functions  that  can  be  connected	to  probe
		  points. Currently, only the debug function called &debug is available.

	   3.	  Commands to Connect and Disconnect Probe Functions

		    connect &fcn_handle $set_name
		    connect &fcn_handle selector_list
		    clear $set_name
		    clear selector_list

		  The  connect command is used to connect probe functions (which must be prefixed
		  by `&') to probes. The probes are specified either as  a  single  set  (with	a
		  `$'),  or  by  explicitly listing the probe selectors in the command. The probe
		  function has to be one that is listed by the list fcns  command.  This  command
		  does not enable the probes.

		  The  clear command is used to disconnect all connected probe functions from the
		  specified probes.

	   4.	  Commands to Toggle the Tracing Mode

		    trace $set_name
		    trace selector_list
		    untrace $set_name
		    untrace selector_list

		  The trace and untrace commands are used to toggle the tracing action of a probe
		  point  (that is, whether a probe will emit a trace record or not if it is hit).
		  This command does not enable the probes specified. Probes have  tracing  on  by
		  default.  The  most  efficient  way to turn off tracing is by using the disable
		  command. untrace is useful if you want debug output but no tracing.  If so, set
		  the state of the probe to enabled, untraced, and the debug function connected.

	   5.	  Commands to Enable and Disable Probes

		    enable $set_name
		    enable selector_list
		    disable $set_name
		    disable selector_list

		  The  enable and disable commands are used to control whether the probes perform
		  the action that they have been set up for. To trace a probe, it has to be  both
		  enabled  and	traced (using the trace command). Probes are disabled by default.
		  The list history command is used to list the	probe  control	commands  issued:
		  connect,  clear,  trace,  untrace, enable, and  disable. These are the commands
		  that are executed whenever a new shared object is brought in to the target pro-
		  gram	by  dlopen(3C).  See  the subsection, dlopen'ed Libraries, below for more

		  The following table shows the actions that result from specific combinations of
		  tracing, enabling, and connecting:

		    Enabled or	 Tracing State	   Debug State	      Results
		    Disabled	   (On/Off)	(Connected/Cleared)    In
		    Enabled	     On 	    Connected	     Tracing and

		    Enabled	     On 	    Cleared	     Tracing only

		    Enabled	     Off	    Connected	     Debugging only

		    Enabled	     Off	    Cleared	     Nothing

		    Disabled	     On 	    Connected	     Nothing

		    Disabled	     On 	    Cleared	     Nothing

		    Disabled	     Off	    Connected	     Nothing

		    Disabled	     Off	    Cleared	     Nothing

	   6.	  List History

		    list history		  # lists probe control command history

		  The  list  history command displays a list of the probe control commands previ-
		  ously issued in the tracing session, for example, connect, clear,  trace,  dis-
		  able. Commands in the history list are executed wherever a new shared object is
		  brought into the target program by dlopen(3C).

	   7.	  Commands to List Probes, List Values, or List Trace File Name

		    list spec_list probes $set_name  # list probes $all
		    list spec_list probes selector_list   # list name probes file=test.c
		    list values spec_list  # list values keys given in spec_list
		    list tracefile  # list tracefile

		  The first two commands list the selected attributes and values of the specified
		  probes. They can be used to check the state of a probe. The third command lists
		  the various values associated with the selected attributes. The fourth  command
		  lists the current tracefile.

	   8.	  Help Command

		    help topic

		  To  get  a  list of the help topics that are available, invoke the help command
		  with no arguments. If a topic argument is specified, help is printed	for  that

	   9.	  Source a File

		    source filename

		  The source command can be used to source a file of prex commands. source can be
		  nested (that is, a file can source another file). filename is a quoted string.

	   10.	  Process Control

		    continue	       # resumes the target process
		    quit kill	       # quit prex, kill target
		    quit resume        # quit prex, continue target
		    quit suspend       # quit prex, leave target suspended
		    quit	       # quit prex (continue or kill target)

		  The default quit will continue the target  process  if  prex	attached  to  it.
		  Instead,  if	prex  had  started  the target program, quit will kill the target

   dlopen'ed Libraries
       Probes in shared objects that are brought  in  by  dlopen(3C)  are  automatically  set  up
       according  to  the  command  history  of  prex.	When  a  shared  object  is  removed by a
       dlclose(3C), prex again needs to refresh its understanding of the  probes  in  the  target
       program.  This  implies	that there is more work to do for dlopen(3C) and dlclose(3C) --so
       they will take slightly longer. If a user is not interested in this  feature  and  doesn't
       want  to interfere with dlopen(3C) and dlclose(3C), detach prex from the target to inhibit
       this feature.

   Signals to Target Program
       prex does not interfere with signals that are delivered directly to  the  target  program.
       However, prex receives all signals normally generated from the terminal, for example, Con-
       trol-C (SIGINT), and Control-Z (SIGSTOP), and does not forward them to the target program.
       To signal the target program, use the kill(1) command from a shell.

   Interactions with Other Applications
       Process managing applications like dbx, truss(1), and prex cannot operate on the same tar-
       get program simultaneously. prex will not be able to attach to a  target  which	is  being
       controlled  by  another	application. A user can trace and debug a program serially by the
       following method: first attach prex to target (or start target through prex), set  up  the
       probes  using  the  command language, and then type quit suspend. The user can then attach
       dbx to the suspended process and debug it. A user can also suspend the target  by  sending
       it a SIGSTOP signal, and then by typing quit resume to prex. In this case, the user should
       also send a SIGCONT signal after invoking dbx on the stopped process  (else  dbx  will  be

   Failure of Event Writing Operations
       There  are a few failure points that are possible when writing out events to a trace file,
       for example, system call failures. These failures result in a failure code  being  set  in
       the  target process. The target process continues normally, but no trace records are writ-
       ten. Whenever a user enters Control-C to prex to get to a prex prompt, prex will check the
       failure code in the target and inform the user if there was a tracing failure.

   Target Executing a Fork or exec
       If  the	target	program  does  a fork(2), any probes that the child encounters will cause
       events to be logged to the same trace file. Events are annotated with a process id, so  it
       will  be  possible  to  determine  which  process  a particular event came from. In multi-
       threaded programs, there is a race condition with a thread doing a fork	while  the  other
       threads	are  still  running.   For  the  trace file not to get corrupted, the user should
       either use fork1(2), or make sure that all  other  threads  are	quiescent  when  doing	a

       If  the	target	program  itself  (not  any children it may fork(2)) does an exec(2), prex
       detaches from the target and exits. The user can reconnect prex with prex -p pid.

       A vfork(2) is generally followed quickly by an  exec(2) in the child, and in the  interim,
       the  child borrows the parent's process while the parent waits for the exec(2). Any events
       logged by the child from the parent process will appear to have been logged by the parent.

   Kernel Mode
       Invoking prex with the -k flag causes prex to run in kernel mode.  In  kernel  mode,  prex
       controls  probes  in  the Solaris kernel. See tnf_kernel_probes(4) for a list of available
       probes in the Solaris kernel. A few prex commands are unavailable  in  kernel  mode;  many
       other commands are valid in kernel mode only.

       The  -l,  -o,  and -p command-line options are not valid in kernel mode (that is, they may
       not be combined with the -k flag).

       The rest of this section describes the differences in the prex command language when  run-
       ning prex in kernel mode.

	   1.	  prex will not stop the kernel

		  When	prex attaches to a running user program, it stops the user program. Obvi-
		  ously, it cannot do this when attaching to the kernel.  Instead, prex  provides
		  a  ``tracing master switch'': no probes will have any effect unless the tracing
		  master switch is on.	This allows the user  to  iteratively  select  probes  to
		  enable, then enable them all at once by turning on the master switch.

		  The command

		    ktrace [ on | off ]

		  is used to inspect and set the value of the master switch. Without an argument,
		  prex reports the current state of the master switch.

		  Since prex will not stop or kill the kernel, the

		    quit resume


		    quit kill

		  commands are not valid in kernel mode.

	   2.	  No functions may be attached to probes in the kernel

		  In particular, the debug function is unavailable in kernel mode.

	   3.	  Trace output is written to an in-core buffer

		  In kernel mode, a trace output file is not  generated  directly,  in	order  to
		  allow probes to be placed in time-critical code. Instead, trace output is writ-
		  ten to an in-core buffer, and copied out by a separate program, tnfxtract(1).

		  The in-core buffer is not automatically created.  The  following  prex  command
		  controls buffer allocation and deallocation:

		    buffer [  alloc [  size ] |  dealloc ]

		  Without an argument, the buffer command reports the size of the currently allo-
		  cated buffer, if any. With an argument of alloc [size], prex allocates a buffer
		  of  the  given  size.  size  is in bytes, with an optional suffix of 'k' or 'm'
		  specifying a multiplier of 1024 or 1048576, respectively. If no  size is speci-
		  fied,  the   size specified on the command line with the -s option is used as a
		  default. If the -s command line option was not used, the ``default default'' is
		  384 kilobytes.

		  With an argument of dealloc, prex deallocates the trace buffer in the kernel.

		  prex	will  reject attempts to turn the tracing master switch on when no buffer
		  is allocated, and to deallocate the buffer when the tracing  master  switch  is
		  on.  prex  will  refuse to allocate a buffer when one is already allocated; use
		  buffer dealloc first.

		  prex will not allocate a buffer larger than one-half of  a  machine's  physical

	   4.	  prex supports per-process probe enabling in the kernel

		  In  kernel  mode,  it is possible to select a set of processes for which probes
		  are enabled. No trace output will be	written  when  other  processes  traverse
		  these  probe	points. This is called "process filter mode". By default, process
		  filter mode is off, and all processes cause the  generation  of  trace  records
		  when they hit an enabled probe.

		  Some	kernel	events	such as interrupts cannot be associated with a particular
		  user process.  By convention, these events are considered to	be  generated  by
		  process id 0.

		  prex	provides commands to turn process filter mode on and off, to get the cur-
		  rent status of the process filter mode switch, to add and delete processes  (by
		  process id) from the process filter set, and to list the current process filter

		  The process filter set is maintained even when process filter mode is off,  but
		  has no effect unless process filter mode is on.

		  When a process in the process filter set exits, its process id is automatically
		  deleted from the process filter set.

		  The command:

		    pfilter [ on | off | add pidlist | delete pidlist ]

		  controls the process filter switch, and process filter set membership. With  no
		  arguments,  pfilter  prints the current process filter set and the state of the
		  process filter mode switch:

		  on or off  set the state of the process filter mode switch.

	   add pidlist	     add or delete processes from the process filter set.  pidlist  is	a
	   delete pidlist    comma-separated list of one or more process ids.

       See tracing(3TNF) for complete examples showing, among other things, the use of prex to do
       simple probe control.

       When either the process or kernel is started, all probes are disabled.

       Example 1 Set creation and set listing

	 create $out name=/out/     # $out = probes with "out" in
				    #	value of "name" attribute
	 create $foo /page/ name=biodone   # $foo = union of
		# probes with "page" in value of keys attribute
		# probes with "biodone" as value of "name" attribute
	 list sets		    # list the defined sets
	 list fcns		    # list the defined probe fcns

       Example 2 Commands to trace and connect probe functions

	 trace foobar='on'	    # exact match on foobar attribute
	 trace $all		    # trace all probes (predefined set $all)
	 connect &debug $foo	    # connect debug func to probes in $foo

       Example 3 Commands to enable and disable probes

	 enable  $all		    # enable all probes
	 enable /vm/ name=alloc     # enable the specified probes
	 disable $foo		    # disable probes in set $foo
	 list history		    # list probe control commands issued

       Example 4 Process control

	 continue		    # resumes the target process
	 ^C			    # stop target; give control to prex
	 quit resume		    # exit prex, leave process running
					 # and resume execution of program

       Example 5 Kernel mode

	 buffer alloc 2m	    # allocate a 2 Megabyte buffer
	 enable $all		    # enable all probes
	 trace $all		    # trace all probes
	 ktrace on		    # turn tracing on
	 ktrace off		    # turn tracing back off
	 pfilter on		    # turn process filter mode on
	 pfilter add 1379	    # add pid 1379 to process filter
	 ktrace on		    # turn tracing on
				    # (only pid 1379 will be traced)

       .prexrc	      local prex initialization file

       ~/.prexrc      user's prex initialization file

       /proc/nnnnn    process files

       See attributes(5) for descriptions of the following attributes:

       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       |Availability		     |SUNWtnfc			   |

       ed(1), kill(1), ksh(1),	ld(1),	tnfdump(1),  tnfxtract(1),  truss(1),  exec(2),  fork(2),
       fork1(2),  vfork(2),  TNF_DECLARE_RECORD(3TNF),	TNF_PROBE(3TNF), dlclose(3C), dlopen(3C),
       gethrtime(3C),	libtnfctl(3TNF),   tnf_process_disable(3TNF),	tracing(3TNF),	 tnf_ker-
       nel_probes(4), attributes(5)

       Currently,  the	only  probe  function that is available is the &debug function. When this
       function is executed, it prints out the arguments sent in to the  probe	as  well  as  the
       value associated with the sunw%debug attribute in the detail field (if any) to stderr.

       For example, for the following probe point:

	 TNF_PROBE_2(input_values, "testapp main",
			 "sunw%debug 'have read input values successfully'",
			 tnf_long, int_input, x,
			 tnf_string, string_input, input);

       If  x was 100 and input was the string "success", then the output of the debug probe func-
       tion would be:

	 probe input_values; sunw%debug "have read input values successfully";
	 int_input=100; string_input="success";

       Some non-SPARC hardware lacks a true high-resolution timer, causing gethrtime() to  return
       the  same  value multiple times in succession. This can lead to problems in how some tools
       interpret the trace file. This situation can be improved by interposing a version of geth-
       rtime(),  which	causes	these  successive  values  to  be artificially incremented by one

	     static mutex_t lock;
	     static hrtime_t (*real_gethrtime)(void) = NULL;
	     static hrtime_t last_time = 0;

	     hrtime_t this_time;

	     if (real_gethrtime == NULL) {
		 real_gethrtime =
		      (hrtime_t (*)(void)) dlsym(RTLD_NEXT, "gethrtime");
	     this_time = real_gethrtime();

	     if (this_time <= last_time)
		 this_time = ++last_time;
		 last_time = this_time;

	     return (this_time);

       Of course, this does not increase the resolution of the timer, so timestamps for  individ-
       ual events are still relatively inaccurate. But this technique maintains ordering, so that
       if event A causes event B, B never appears to happen before or at the same time as A.

       dbx is available with the Sun Workshop Products.

       prex should issue a notification when a process id has been automatically deleted from the
       filter set.

       There is a known bug in prex which can result in this message:

	 Tracing shut down in target program due to an internal
	 error - Please restart prex and target

       When prex runs as root, and the target process is not root, and the tracefile is placed in
       a directory where it cannot be removed and re-created (a directory with the sticky bit on,
       like /tmp),mm then the target process will not be able to open the tracefile when it needs
       to. This results in tracing being disabled.

       Changing any of the circumstances listed above should fix the problem.  Either  don't  run
       prex  as  root, or run the target process as root, or specify the tracefile in a directory
       other than /tmp.

SunOS 5.11				    1 Mar 2004					  prex(1)

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