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

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

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

           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

       -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.

           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

               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 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'

           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 2021-08-27.  (At that time, the date of the most recent commit
       that was found in the repository was 2021-08-20.)  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 to

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