trace-cmd-set(1) — Linux manual page


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

NAME         top

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

SYNOPSIS         top

       trace-cmd set [OPTIONS] [command]

DESCRIPTION         top

       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         top

       -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

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

           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)

           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.

               ==, >=, <=, >, <, &, |, && 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.

           This will negate options specified after it on the command line.
           It affects:

                -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

       -P pid
           This will filter only the specified process IDs. Using -P will
           let you trace only events that are caused by the process.

           Used -P to trace the process' children too (if kernel supports

           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

           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.

           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'.

           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

       -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'

           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.

           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.

EXAMPLES         top

       Enable all events for tracing:

            # trace-cmd set -e all

       Set the function tracer:

            # trace-cmd set -p function

SEE ALSO         top

       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),

AUTHOR         top

       Written by Tzvetomir Stoyanov (VMware) <[1]>

RESOURCES         top


COPYING         top

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

NOTES         top


COLOPHON         top

       This page is part of the trace-cmd (a front-end for Ftrace) project.
       Information about the project can be found at [unknown -- if you
       know, please contact] If you have a bug report for
       this manual page, send it to Steven Rostedt <>.
       This page was obtained from the project's upstream Git repository
       on 2020-08-13.  (At that time, the date of the most recent commit
       that was found in the repository was 2020-07-22.)  If you discover
       any rendering problems in this HTML version of the page, or you
       believe there is a better or more up-to-date source for the page, or
       you have corrections or improvements to the information in this
       COLOPHON (which is not part of the original manual page), send a mail

                                 06/09/2020                 TRACE-CMD-SET(1)