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.
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).
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  58549.289091: sched_switch: kworker/0:1:0  R ==> trace-cmd:2603 
<idle>-0  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.
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.
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
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
Execute the specified command as given user.
Set the trace clock to "clock".
Use trace-cmd(1) list -C to see what clocks are available.
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
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.
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).
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.
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.
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.
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.
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.
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.
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.
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.
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 email@example.com] If you have a
bug report for this manual page, send it to Steven Rostedt
<firstname.lastname@example.org>. This page was obtained from the project's
upstream Git repository
on 2021-06-20. (At that time, the date of the most recent commit
that was found in the repository was 2021-06-09.) If you
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