blktrace(8) — Linux manual page


BLKTRACE(8)                                                  BLKTRACE(8)

NAME         top

       blktrace - generate traces of the i/o traffic on block devices

SYNOPSIS         top

       blktrace -d dev [ -r debugfs_path ] [ -o output ] [ -w time ] [
       -a action ] [ -A action_mask ] [ -v ]

DESCRIPTION         top

       blktrace is a block layer IO tracing mechanism which provides
       detailed information about request queue operations up to user
       space. There are three major components: a kernel component, a
       utility to record the i/o trace information for the kernel to
       user space, and utilities to analyse and view the trace
       information.  This man page describes blktrace, which records the
       i/o event trace information for a specific block device to a

       The blktrace utility extracts event traces from the kernel (via
       the relaying through the debug file system). Some background
       details concerning the run-time behaviour of blktrace will help
       to understand some of the more arcane command line options:

       - blktrace receives data from the kernel in buffers passed up
         through the debug file system (relay). Each device being traced
         has a file created in the mounted directory for the debugfs,
         which defaults to /sys/kernel/debug -- this can be overridden
         with the -r command line argument.

       - blktrace defaults to collecting all events that can be traced.
         To limit the events being captured, you can specify one or more
         filter masks via the -a option.

         Alternatively, one may specify the entire mask utilising a
         hexadecimal value that is version-specific. (Requires
         understanding of the internal representation of the filter

       - As noted above, the events are passed up via a series of
         buffers stored into debugfs files. The size and number of
         buffers can be specified via the -b and -n arguments

       - blktrace stores the extracted data into files stored in the
         local directory. The format of the file names is (by default)
         device.blktrace.cpu, where device is the base device name (e.g,
         if we are tracing /dev/sda, the base device name would be sda);
         and cpu identifies a CPU for the event stream.

         The device portion of the event file name can be changed via
         the -o option.

       - blktrace may also be run concurrently with blkparse to produce
         live output -- to do this specify -o - for blktrace.

       - The default behaviour for blktrace is to run forever until
         explicitly killed by the user (via a control-C, or sending
         SIGINT signal to the process via invocation the kill (1)
         utility). Also you can specify a run-time duration for blktrace
         via the -w option -- then blktrace will run for the specified
         number of seconds, and then halt.

OPTIONS         top

       -A hex-mask
              Set filter mask to hex-mask (see below for masks)

       -a mask
              Add mask to current filter (see below for masks)

       -b size
              Specifies buffer size for event extraction (scaled by
              1024). The default buffer size is 512KiB.

       -d dev
              Adds dev as a device to trace

       -I file
              Adds the devices found in file as devices to trace

       -n num-sub
              Specifies number of buffers to use. blktrace defaults to 4
              sub buffers.

              Run in network listen mode (blktrace server)

       -h hostname
              Run in network client mode, connecting to the given host

       -p number
              Network port to use (default 8462)

              Make the network client NOT use sendfile() to transfer

       -o basename
              Specifies base name for input files. Default is
              device.blktrace.cpu.  Specifying -o - runs in live mode
              with blkparse (writing data to standard out).

       -D dir
              Prepend file to output file name(s)

              This only works when supplying a single device, or when
              piping the output via "-o -" with multiple devices.

       -r rel-path
              Specifies debugfs mount point

              Outputs version

              Outputs version

       -w seconds
              Sets run time to the number of seconds specified

FILTER MASKS         top

       The following masks may be passed with the -a command line
       option, multiple filters may be combined via multiple -a command
       line options.

              barrier: barrier attribute
              complete: completed by driver
              discard: discard / trim traces
              fs: requests
              issue: issued to driver
              pc: packet command events
              queue: queue operations
              read: read traces
              requeue: requeue operations
              sync: synchronous attribute
              write: write traces
              notify: trace messages
              drv_data: additional driver specific trace

REQUEST TYPES         top

       blktrace distinguishes between two types of block layer requests,
       file system and SCSI commands. The former are dubbed fs requests,
       the latter pc requests. File system requests are normal
       read/write operations, i.e.  any type of read or write from a
       specific disk location at a given size. These requests typically
       originate from a user process, but they may also be initiated by
       the vm flushing dirty data to disk or the file system syncing a
       super or journal block to disk. pc requests are SCSI commands.
       blktrace sends the command data block as a payload so that
       blkparse can decode it.

EXAMPLES         top

       To trace the i/o on the device /dev/sda and parse the output to
       human readable form, use the following command:

           % blktrace -d /dev/sda -o - | blkparse -i -

       This same behaviour can be achieve with the convenience script
       btrace.  The command

           % btrace /dev/sda

       has exactly the same effect as the previous command. See btrace
       (8) for more information.

       To trace the i/o on a device and save the output for later
       processing with blkparse, use blktrace like this:

           % blktrace /dev/sda /dev/sdb

       This will trace i/o on the devices /dev/sda and /dev/sdb and save
       the recorded information in the files sda and sdb in the current
       directory, for the two different devices, respectively.  This
       trace information can later be parsed by the blkparse utility:

           % blkparse sda sdb

       which will output the previously recorded tracing information in
       human readable form to stdout.  See blkparse (1) for more

AUTHORS         top

       blktrace was written by Jens Axboe, Alan D. Brunelle and Nathan
       Scott.  This man page was created from the blktrace documentation
       by Bas Zoetekouw.

REPORTING BUGS         top

       Report bugs to <>

COPYRIGHT         top

       Copyright © 2006 Jens Axboe, Alan D. Brunelle and Nathan Scott.
       This is free software.  You may redistribute copies of it under
       the terms of the GNU General Public License
       <>.  There is NO WARRANTY, to
       the extent permitted by law.
       This manual page was created for Debian by Bas Zoetekouw.  It was
       derived from the documentation provided by the authors and it may
       be used, distributed and modified under the terms of the GNU
       General Public License, version 2.
       On Debian systems, the text of the GNU General Public License can
       be found in /usr/share/common-licenses/GPL-2.

SEE ALSO         top

       btrace(8), blkparse(1), verify_blkparse(1), blkrawverify(1),

COLOPHON         top

       This page is part of the blktrace (Linux block layer I/O tracer)
       project.  Information about the project can be found at [unknown
       -- if you know, please contact] It is not
       known how to report bugs for this man page; if you know, please
       send a mail to  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 2021-06-28.)  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

blktrace git-20070306202522  March  6, 2007                  BLKTRACE(8)

Pages that refer to this page: blkparse(1)blkrawverify(1)bno_plot(1)btt(1)iowatcher(1)verify_blkparse(1)blkiomon(8)btrace(8)btrecord(8)btreplay(8)