TRACE-CMD-SET(1)
================

NAME
----
trace-cmd-set - set a configuration parameter of the Ftrace Linux internal tracer

SYNOPSIS
--------
*trace-cmd set* ['OPTIONS'] ['command']

DESCRIPTION
-----------
The trace-cmd(1) set command will set a configuration parameter of the Ftrace
Linux kernel tracer. The specified *command* will be run after the ftrace state
is set. The configured ftrace state can be restored to default
using the trace-cmd-reset(1) command.

OPTIONS
-------
*-p* 'tracer'::
    Specify a tracer. Tracers usually do more than just trace an event.
    Common tracers are: *function*, *function_graph*, *preemptirqsoff*,
    *irqsoff*, *preemptoff* and *wakeup*. A tracer must be supported by the
    running kernel. To see a list of available tracers, see trace-cmd-list(1).

*-e* 'event'::
    Specify an event to trace. Various static trace points have been added to
    the Linux kernel. They are grouped by subsystem where you can enable all
    events of a given subsystem or specify specific events to be enabled. The
    'event' is of the format "subsystem:event-name". You can also just specify
    the subsystem without the ':event-name' or the event-name without the
    "subsystem:". Using "-e sched_switch" will enable the "sched_switch" event
    where as, "-e sched" will enable all events under the "sched" subsystem.

    The 'event' can also contain glob expressions. That is, "*stat*" will
    select all events (or subsystems) that have the characters "stat" in their
    names.

    The keyword 'all' can be used to enable all events.

*-T*::
    Enable a stacktrace on each event. For example:

          <idle>-0     [003] 58549.289091: sched_switch:         kworker/0:1:0 [120] R ==> trace-cmd:2603 [120]
          <idle>-0     [003] 58549.289092: kernel_stack:         <stack trace>
=> schedule (ffffffff814b260e)
=> cpu_idle (ffffffff8100a38c)
=> start_secondary (ffffffff814ab828)

*--func-stack*::
    Enable a stack trace on all functions. Note this is only applicable
    for the "function" plugin tracer, and will only take effect if the
    -l option is used and succeeds in limiting functions. If the function
    tracer is not filtered, and the stack trace is enabled, you can live
    lock the machine.

*-f* 'filter'::
    Specify a filter for the previous event. This must come after a *-e*. This
    will filter what events get recorded based on the content of the event.
    Filtering is passed to the kernel directly so what filtering is allowed
    may depend on what version of the kernel you have. Basically, it will
    let you use C notation to check if an event should be processed or not.

[source,bison]
----
    ==, >=, <=, >, <, &, |, && and ||
----

    The above are usually safe to use to compare fields.

*-R* 'trigger'::
    Specify a trigger for the previous event. This must come after a *-e*.
    This will add a given trigger to the given event. To only enable the trigger
    and not the event itself, then place the event after the *-v* option.

    See Documentation/trace/events.txt in the Linux kernel source for more
    information on triggers.

*-v*::
    This will negate options specified after it on the command line. It affects:
[verse]
--
     *-e*: Causes all specified events to not be traced. This is useful for
           selecting a subsystem to be traced but to leave out various events.
           For example: "-e sched -v -e "\*stat\*"" will enable all events in
           the sched subsystem except those that have "stat" in their names.
     *-B*: Deletes the specified ftrace instance. There must be no
           configuration options related to this instance in the command line.
           For example: "-v -B bar -B foo" will delete instance bar and create
           a new instance foo.
    Note: the *-v* option was taken from the way grep(1) inverts the following
    matches.
--
*-P* 'pid'::
    This will filter only the specified process IDs. Using *-P* will let you
    trace only events that are caused by the process.

*-c*::
     Used *-P* to trace the process' children too (if kernel supports it).

*--user*::
     Execute the specified *command* as given user.

*-C* 'clock'::
     Set the trace clock to "clock".

     Use trace-cmd(1) list -C to see what clocks are available.

*-l* 'function-name'::
    This will limit the 'function' and 'function_graph' tracers to only trace
    the given function name. More than one *-l* may be specified on the
    command line to trace more than one function. The limited use of glob
    expressions are also allowed. These are 'match\*' to only filter functions
    that start with 'match'. '\*match' to only filter functions that end with
    'match'. '\*match\*' to only filter on functions that contain 'match'.

*-g* 'function-name'::
    This option is for the function_graph plugin. It will graph the given
    function. That is, it will only trace the function and all functions that
    it calls. You can have more than one *-g* on the command line.

*-n* 'function-name'::
    This has the opposite effect of *-l*. The function given with the *-n*
    option will not be traced. This takes precedence, that is, if you include
    the same function for both *-n* and *-l*, it will not be traced.

*-d*::
    Some tracer plugins enable the function tracer by default. Like the
    latency tracers. This option prevents the function tracer from being
    enabled at start up.

*-D*::
    The option *-d* will try to use the function-trace option to disable the
    function tracer (if available), otherwise it defaults to the proc file:
    /proc/sys/kernel/ftrace_enabled, but will not touch it if the function-trace
    option is available.  The *-D* option will disable both the ftrace_enabled
    proc file as well as the function-trace option if it exists.

    Note, this disable function tracing for all users, which includes users
    outside of ftrace tracers (stack_tracer, perf, etc).

*-O* 'option'::
    Ftrace has various options that can be enabled or disabled. This allows
    you to set them. Appending the text 'no' to an option disables it.
    For example: "-O nograph-time" will disable the "graph-time" Ftrace
    option.

*-b* 'size'::
    This sets the ring buffer size to 'size' kilobytes. Because the Ftrace
    ring buffer is per CPU, this size is the size of each per CPU ring buffer
    inside the kernel. Using "-b 10000" on a machine with 4 CPUs will make
    Ftrace have a total buffer size of 40 Megs.

*-B* 'buffer-name'::
    If the kernel supports multiple buffers, this will add a buffer with
    the given name. If the buffer name already exists, that buffer is just
    reset.

    After a buffer name is stated, all events added after that will be
    associated with that buffer. If no buffer is specified, or an event
    is specified before a buffer name, it will be associated with the
    main (toplevel) buffer.

     trace-cmd set -e sched -B block -e block -B time -e timer sleep 1

    The above is will enable all sched events in the main buffer. It will
    then create a 'block' buffer instance and enable all block events within
    that buffer. A 'time' buffer instance is created and all timer events
    will be enabled for that event.

*-m* 'size'::
    The max size in kilobytes that a per cpu buffer should be. Note, due
    to rounding to page size, the number may not be totally correct.
    Also, this is performed by switching between two buffers that are half
    the given size thus the output may not be of the given size even if
    much more was written.

    Use this to prevent running out of diskspace for long runs.

*-M* 'cpumask'::
    Set the cpumask for to trace. It only affects the last buffer instance
    given. If supplied before any buffer instance, then it affects the
    main buffer. The value supplied must be a hex number.

     trace-cmd set -p function -M c -B events13 -e all -M 5

    If the -M is left out, then the mask stays the same. To enable all
    CPUs, pass in a value of '-1'.

*-i*::
    By default, if an event is listed that trace-cmd does not find, it
    will exit with an error. This option will just ignore events that are
    listed on the command line but are not found on the system.

*-q* | *--quiet*::
    Suppresses normal output, except for errors.

*--max-graph-depth* 'depth'::
    Set the maximum depth the function_graph tracer will trace into a function.
    A value of one will only show where userspace enters the kernel but not any
    functions called in the kernel. The default is zero, which means no limit.

*--cmdlines-size* 'size'::
    Set the number of entries the kernel tracing file "saved_cmdlines" can
    contain. This file is a circular buffer which stores the mapping between
    cmdlines and PIDs. If full, it leads to unresolved cmdlines ("<...>") within
    the trace. The kernel default value is 128.

*--module* 'module'::
    Filter a module's name in function tracing. It is equivalent to adding
    ':mod:module' after all other functions being filtered. If no other function
    filter is listed, then all modules functions will be filtered in the filter.

    '--module snd'  is equivalent to  '-l :mod:snd'

    '--module snd -l "*jack*"' is equivalent to '-l "*jack*:mod:snd"'

    '--module snd -n "*"' is equivalent to '-n :mod:snd'

*--stderr*::
    Have output go to stderr instead of stdout, but the output of the command
    executed will not be changed. This is useful if you want to monitor the
    output of the command being executed, but not see the output from trace-cmd.

*--fork*::
    If a command is listed, then trace-cmd will wait for that command to finish,
    unless the *--fork* option is specified. Then it will fork the command and
    return immediately.

*--verbose*[='level']::
     Set the log level. Supported log levels are "none", "critical", "error", "warning",
     "info", "debug", "all" or their identifiers "0", "1", "2", "3", "4", "5", "6". Setting the log
     level to specific value enables all logs from that and all previous levels.
     The level will default to "info" if one is not specified.

     Example: enable all critical, error and warning logs

      trace-cmd set --verbose=warning

EXAMPLES
--------

Enable all events for tracing:

[source,shell]
----
 # trace-cmd set -e all
----

Set the function tracer:

[source,shell]
----
 # trace-cmd set -p function
----


SEE ALSO
--------
trace-cmd(1), trace-cmd-report(1), trace-cmd-start(1), trace-cmd-stop(1),
trace-cmd-extract(1), trace-cmd-reset(1), trace-cmd-split(1),
trace-cmd-list(1), trace-cmd-listen(1), trace-cmd-profile(1)

AUTHOR
------
Written by Tzvetomir Stoyanov (VMware) <tz.stoyanov@gmail.com>

RESOURCES
---------
https://git.kernel.org/pub/scm/utils/trace-cmd/trace-cmd.git/

COPYING
-------
Copyright \(C) 2010 Red Hat, Inc. Free use of this software is granted under
the terms of the GNU Public License (GPL).
