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 file.

       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 mask.)

       - 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 respectively.

       - 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

       - 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

              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 data

       -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

              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), btt(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
       2020-11-01.  (At that time, the date of the most recent commit that
       was found in the repository was 2020-05-20.)  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

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)