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 not.
==, >=, <=, >, <, &, |, && 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.
-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 process.
Used -P to trace the process' children too (if kernel supports
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 match.
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
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).
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 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.
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 firstname.lastname@example.org] If you have a bug report for
this manual page, send it to Steven Rostedt <email@example.com>.
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