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Fio was originally written to save me the hassle of writing special test case programs when I wanted to test a specific workload, either for performance reasons or to find/reproduce a bug. The process of writing such a test app can be tiresome, especially if you have to do it often. Hence I needed a tool that would be able to simulate a given I/O workload without resorting to writing a tailored test case again and again.

A test work load is difficult to define, though. There can be any number of processes or threads involved, and they can each be using their own way of generating I/O. You could have someone dirtying large amounts of memory in a memory mapped file, or maybe several threads issuing reads using asynchronous I/O. fio needed to be flexible enough to simulate both of these cases, and many more.

Fio spawns a number of threads or processes doing a particular type of I/O action as specified by the user. fio takes a number of global parameters, each inherited by the thread unless otherwise parameters given to them overriding that setting is given. The typical use of fio is to write a job file matching the I/O load one wants to simulate.


Fio resides in a git repo, the canonical place is:

Snapshots are frequently generated and :file:`fio-git-*.tar.gz` include the git meta data as well. Other tarballs are archives of official fio releases. Snapshots can download from:

There are also two official mirrors. Both of these are automatically synced with the main repository, when changes are pushed. If the main repo is down for some reason, either one of these is safe to use as a backup:

Mailing list

The fio project mailing list is meant for anything related to fio including general discussion, bug reporting, questions, and development. For bug reporting, see REPORTING-BUGS.

An automated mail detailing recent commits is automatically sent to the list at most daily. The list address is, subscribe by sending an email to with

subscribe fio

in the body of the email. Archives can be found here:

or here:

and archives for the old list can be found here:


Fio was written by Jens Axboe <> to enable flexible testing of the Linux I/O subsystem and schedulers. He got tired of writing specific test applications to simulate a given workload, and found that the existing I/O benchmark/test tools out there weren't flexible enough to do what he wanted.

Jens Axboe <> 20060905


Fio is maintained by Jens Axboe < and Vincent Fu <> - however, for reporting bugs please use the fio reflector or the GitHub page rather than email any of them directly. By using the public resources, others will be able to learn from the responses too. Chances are also good that other members will be able to help with your inquiry as well.

Binary packages

Starting with Debian "Squeeze", fio packages are part of the official Debian repository. .
Starting with Ubuntu 10.04 LTS (aka "Lucid Lynx"), fio packages are part of the Ubuntu "universe" repository. .
Red Hat, Fedora, CentOS & Co:
Starting with Fedora 9/Extra Packages for Enterprise Linux 4, fio packages are part of the Fedora/EPEL repositories. .
Mandriva has integrated fio into their package repository, so installing on that distro should be as easy as typing urpmi fio.
Arch Linux:
An Arch Linux package is provided under the Community sub-repository:
Packages for Solaris are available from OpenCSW. Install their pkgutil tool ( and then install fio via pkgutil -i fio.
Beginning with fio 3.31 Windows installers for tagged releases are available on GitHub at The latest installers for Windows can also be obtained as GitHub Actions artifacts by selecting a build from These require logging in to a GitHub account.
Packages for BSDs may be available from their binary package repositories. Look for a package "fio" using their binary package managers.


Just type:

$ ./configure
$ make
$ make install

Note that GNU make is required. On BSDs it's available from devel/gmake within ports directory; on Solaris it's in the SUNWgmake package. On platforms where GNU make isn't the default, type gmake instead of make.

Configure will print the enabled options. Note that on Linux based platforms, the libaio development packages must be installed to use the libaio engine. Depending on the distro, it is usually called libaio-devel or libaio-dev.

For gfio, gtk 2.18 (or newer), associated glib threads, and cairo are required to be installed. gfio isn't built automatically and can be enabled with a --enable-gfio option to configure.

To build fio with a cross-compiler:

$ make clean
$ make CROSS_COMPILE=/path/to/toolchain/prefix

Configure will attempt to determine the target platform automatically.

It's possible to build fio for ESX as well, use the --esx switch to configure.


The minimum versions of Windows for building/running fio are Windows 7/Windows Server 2008 R2. On Windows, Cygwin ( is required in order to build fio. To create an MSI installer package install WiX from and run :file:`dobuild.cmd` from the :file:`os/windows` directory.

How to compile fio on 64-bit Windows:

  1. Install Cygwin ( Install make and all packages starting with mingw64-x86_64. Ensure mingw64-x86_64-zlib are installed if you wish to enable fio's log compression functionality.
  2. Open the Cygwin Terminal.
  3. Go to the fio directory (source files).
  4. Run make clean && make -j.

To build fio for 32-bit Windows, ensure the -i686 versions of the previously mentioned -x86_64 packages are installed and run ./configure --build-32bit-win before make.

It's recommended that once built or installed, fio be run in a Command Prompt or other 'native' console such as console2, since there are known to be display and signal issues when running it under a Cygwin shell (see mintty/mintty#56 and for details).


Fio uses Sphinx to generate documentation from the reStructuredText files. To build HTML formatted documentation run make -C doc html and direct your browser to :file:`./doc/output/html/index.html`. To build manual page run make -C doc man and then man doc/output/man/fio.1. To see what other output formats are supported run make -C doc help.


Fio works on (at least) Linux, Solaris, AIX, HP-UX, OSX, NetBSD, OpenBSD, Windows, FreeBSD, and DragonFly. Some features and/or options may only be available on some of the platforms, typically because those features only apply to that platform (like the solarisaio engine, or the splice engine on Linux).

Some features are not available on FreeBSD/Solaris even if they could be implemented, I'd be happy to take patches for that. An example of that is disk utility statistics and (I think) huge page support, support for that does exist in FreeBSD/Solaris.

Fio uses pthread mutexes for signaling and locking and some platforms do not support process shared pthread mutexes. As a result, on such platforms only threads are supported. This could be fixed with sysv ipc locking or other locking alternatives.

Other *BSD platforms are untested, but fio should work there almost out of the box. Since I don't do test runs or even compiles on those platforms, your mileage may vary. Sending me patches for other platforms is greatly appreciated. There's a lot of value in having the same test/benchmark tool available on all platforms.

Note that POSIX aio is not enabled by default on AIX. Messages like these:

Symbol resolution failed for /usr/lib/libc.a(posix_aio.o) because:
    Symbol _posix_kaio_rdwr (number 2) is not exported from dependent module /unix.

indicate one needs to enable POSIX aio. Run the following commands as root:

# lsdev -C -l posix_aio0
    posix_aio0 Defined  Posix Asynchronous I/O
# cfgmgr -l posix_aio0
# lsdev -C -l posix_aio0
    posix_aio0 Available  Posix Asynchronous I/O

POSIX aio should work now. To make the change permanent:

# chdev -l posix_aio0 -P -a autoconfig='available'
    posix_aio0 changed

Running fio

Running fio is normally the easiest part - you just give it the job file (or job files) as parameters:

$ fio [options] [jobfile] ...

and it will start doing what the jobfile tells it to do. You can give more than one job file on the command line, fio will serialize the running of those files. Internally that is the same as using the :option:`stonewall` parameter described in the parameter section.

If the job file contains only one job, you may as well just give the parameters on the command line. The command line parameters are identical to the job parameters, with a few extra that control global parameters. For example, for the job file parameter :option:`iodepth=2 <iodepth>`, the mirror command line option would be :option:`--iodepth 2 <iodepth>` or :option:`--iodepth=2 <iodepth>`. You can also use the command line for giving more than one job entry. For each :option:`--name <name>` option that fio sees, it will start a new job with that name. Command line entries following a :option:`--name <name>` entry will apply to that job, until there are no more entries or a new :option:`--name <name>` entry is seen. This is similar to the job file options, where each option applies to the current job until a new [] job entry is seen.

fio does not need to run as root, except if the files or devices specified in the job section requires that. Some other options may also be restricted, such as memory locking, I/O scheduler switching, and decreasing the nice value.

If jobfile is specified as -, the job file will be read from standard input.