Open vSwitch on Linux, FreeBSD and NetBSD

This document describes how to build and install Open vSwitch on a generic Linux, FreeBSD, or NetBSD host. For specifics around installation on a specific platform, refer to one of the other installation guides listed in Installing Open vSwitch.

Build Requirements

To compile the userspace programs in the Open vSwitch distribution, you will need the following software:

  • GNU make

  • A C compiler, such as:

    • GCC 4.x.
    • Clang. Clang 3.4 and later provide useful static semantic analysis and thread-safety checks. For Ubuntu, there are nightly built packages available on clang’s website.
    • MSVC 2013. Refer to Open vSwitch on Windows for additional Windows build instructions.

    While OVS may be compatible with other compilers, optimal support for atomic operations may be missing, making OVS very slow (see lib/ovs-atomic.h).

  • libssl, from OpenSSL, is optional but recommended if you plan to connect the Open vSwitch to an OpenFlow controller. libssl is required to establish confidentiality and authenticity in the connections from an Open vSwitch to an OpenFlow controller. If libssl is installed, then Open vSwitch will automatically build with support for it.

  • libcap-ng, written by Steve Grubb, is optional but recommended. It is required to run OVS daemons as a non-root user with dropped root privileges. If libcap-ng is installed, then Open vSwitch will automatically build with support for it.

  • Python 2.7. You must also have the Python six library.

On Linux, you may choose to compile the kernel module that comes with the Open vSwitch distribution or to use the kernel module built into the Linux kernel (version 3.3 or later). See the Open vSwitch FAQ question “What features are not available in the Open vSwitch kernel datapath that ships as part of the upstream Linux kernel?” for more information on this trade-off. You may also use the userspace-only implementation, at some cost in features and performance. Refer to Open vSwitch without Kernel Support for details.

To compile the kernel module on Linux, you must also install the following:

  • A supported Linux kernel version.

    For optional support of ingress policing, you must enable kernel configuration options NET_CLS_BASIC, NET_SCH_INGRESS, and NET_ACT_POLICE, either built-in or as modules. NET_CLS_POLICE is obsolete and not needed.)

    On kernels before 3.11, the ip_gre module, for GRE tunnels over IP (NET_IPGRE), must not be loaded or compiled in.

    To configure HTB or HFSC quality of service with Open vSwitch, you must enable the respective configuration options.

    To use Open vSwitch support for TAP devices, you must enable CONFIG_TUN.

  • To build a kernel module, you need the same version of GCC that was used to build that kernel.

  • A kernel build directory corresponding to the Linux kernel image the module is to run on. Under Debian and Ubuntu, for example, each linux-image package containing a kernel binary has a corresponding linux-headers package with the required build infrastructure.

If you are working from a Git tree or snapshot (instead of from a distribution tarball), or if you modify the Open vSwitch build system or the database schema, you will also need the following software:

  • Autoconf version 2.63 or later.
  • Automake version 1.10 or later.
  • libtool version 2.4 or later. (Older versions might work too.)

To run the unit tests, you also need:

  • Perl. Version 5.10.1 is known to work. Earlier versions should also work.

The datapath tests for userspace and Linux datapaths also rely upon:

  • pyftpdlib. Version 1.2.0 is known to work. Earlier versions should also work.
  • GNU wget. Version 1.16 is known to work. Earlier versions should also work.
  • netcat. Several common implementations are known to work.
  • curl. Version 7.47.0 is known to work. Earlier versions should also work.
  • tftpy. Version 0.6.2 is known to work. Earlier versions should also work.

The ovs-vswitchd.conf.db(5) manpage will include an E-R diagram, in formats other than plain text, only if you have the following:

  • dot from graphviz (
  • Perl. Version 5.10.1 is known to work. Earlier versions should also work.

If you are going to extensively modify Open vSwitch, consider installing the following to obtain better warnings:

  • “sparse” version 0.4.4 or later (
  • GNU make.
  • clang, version 3.4 or later
  • flake8 along with the hacking flake8 plugin (for Python code). The automatic flake8 check that runs against Python code has some warnings enabled that come from the “hacking” flake8 plugin. If it’s not installed, the warnings just won’t occur until it’s run on a system with “hacking” installed.

You may find the ovs-dev script found in utilities/ useful.

Installation Requirements

The machine you build Open vSwitch on may not be the one you run it on. To simply install and run Open vSwitch you require the following software:

  • libc compatible with the libc used for build.
  • libssl compatible with the libssl used for build, if OpenSSL was used for the build.
  • On Linux, the same kernel version configured as part of the build.
  • For optional support of ingress policing on Linux, the “tc” program from iproute2 (part of all major distributions and available at
  • Python 2.7. You must also have the Python six library.

On Linux you should ensure that /dev/urandom exists. To support TAP devices, you must also ensure that /dev/net/tun exists.


This step is not needed if you have downloaded a released tarball. If you pulled the sources directly from an Open vSwitch Git tree or got a Git tree snapshot, then run in the top source directory to build the “configure” script:

$ ./


Configure the package by running the configure script. You can usually invoke configure without any arguments. For example:

$ ./configure

By default all files are installed under /usr/local. Open vSwitch also expects to find its database in /usr/local/etc/openvswitch by default. If you want to install all files into, e.g., /usr and /var instead of /usr/local and /usr/local/var and expect to use /etc/openvswitch as the default database directory, add options as shown here:

$ ./configure --prefix=/usr --localstatedir=/var --sysconfdir=/etc


Open vSwitch installed with packages like .rpm (e.g. via yum install or rpm -ivh) and .deb (e.g. via apt-get install or dpkg -i) use the above configure options.

By default, static libraries are built and linked against. If you want to use shared libraries instead:

$ ./configure --enable-shared

To use a specific C compiler for compiling Open vSwitch user programs, also specify it on the configure command line, like so:

$ ./configure CC=gcc-4.2

To use ‘clang’ compiler:

$ ./configure CC=clang

To supply special flags to the C compiler, specify them as CFLAGS on the configure command line. If you want the default CFLAGS, which include -g to build debug symbols and -O2 to enable optimizations, you must include them yourself. For example, to build with the default CFLAGS plus -mssse3, you might run configure as follows:

$ ./configure CFLAGS="-g -O2 -mssse3"

For efficient hash computation special flags can be passed to leverage built-in intrinsics. For example on X86_64 with SSE4.2 instruction set support, CRC32 intrinsics can be used by passing -msse4.2:

$ ./configure CFLAGS="-g -O2 -msse4.2"`

If you are on a different processor and don’t know what flags to choose, it is recommended to use -march=native settings:

$ ./configure CFLAGS="-g -O2 -march=native"

With this, GCC will detect the processor and automatically set appropriate flags for it. This should not be used if you are compiling OVS outside the target machine.


CFLAGS are not applied when building the Linux kernel module. Custom CFLAGS for the kernel module are supplied using the EXTRA_CFLAGS variable when running make. For example:

$ make EXTRA_CFLAGS="-Wno-error=date-time"

To build the Linux kernel module, so that you can run the kernel-based switch, pass the location of the kernel build directory on --with-linux. For example, to build for a running instance of Linux:

$ ./configure --with-linux=/lib/modules/$(uname -r)/build


If --with-linux requests building for an unsupported version of Linux, then configure will fail with an error message. Refer to the Open vSwitch FAQ for advice in that case.

If you wish to build the kernel module for an architecture other than the architecture of the machine used for the build, you may specify the kernel architecture string using the KARCH variable when invoking the configure script. For example, to build for MIPS with Linux:

$ ./configure --with-linux=/path/to/linux KARCH=mips

If you plan to do much Open vSwitch development, you might want to add --enable-Werror, which adds the -Werror option to the compiler command line, turning warnings into errors. That makes it impossible to miss warnings generated by the build. For example:

$ ./configure --enable-Werror

To build with gcov code coverage support, add --enable-coverage:

$ ./configure --enable-coverage

The configure script accepts a number of other options and honors additional environment variables. For a full list, invoke configure with the --help option:

$ ./configure --help

You can also run configure from a separate build directory. This is helpful if you want to build Open vSwitch in more than one way from a single source directory, e.g. to try out both GCC and Clang builds, or to build kernel modules for more than one Linux version. For example:

$ mkdir _gcc && (cd _gcc && ./configure CC=gcc)
$ mkdir _clang && (cd _clang && ./configure CC=clang)

Under certains loads the ovsdb-server and other components perform better when using the jemalloc memory allocator, instead of the glibc memory allocator. If you wish to link with jemalloc add it to LIBS:

$ ./configure LIBS=-ljemalloc


  1. Run GNU make in the build directory, e.g.:

    $ make

    or if GNU make is installed as “gmake”:

    $ gmake

    If you used a separate build directory, run make or gmake from that directory, e.g.:

    $ make -C _gcc
    $ make -C _clang

    For improved warnings if you installed sparse (see “Prerequisites”), add C=1 to the command line.


    Some versions of Clang and ccache are not completely compatible. If you see unusual warnings when you use both together, consider disabling ccache.

  2. Consider running the testsuite. Refer to Testing for instructions.

  3. Run make install to install the executables and manpages into the running system, by default under /usr/local:

    $ make install
  1. If you built kernel modules, you may install them, e.g.:

    $ make modules_install

    It is possible that you already had a Open vSwitch kernel module installed on your machine that came from upstream Linux (in a different directory). To make sure that you load the Open vSwitch kernel module you built from this repository, you should create a depmod.d file that prefers your newly installed kernel modules over the kernel modules from upstream Linux. The following snippet of code achieves the same:

    $ config_file="/etc/depmod.d/openvswitch.conf"
    $ for module in datapath/linux/*.ko; do
      modname="$(basename ${module})"
      echo "override ${modname%.ko} * extra" >> "$config_file"
      echo "override ${modname%.ko} * weak-updates" >> "$config_file"
    $ depmod -a

    Finally, load the kernel modules that you need. e.g.:

    $ /sbin/modprobe openvswitch

    To verify that the modules have been loaded, run /sbin/lsmod and check that openvswitch is listed:

    $ /sbin/lsmod | grep openvswitch


    If the modprobe operation fails, look at the last few kernel log messages (e.g. with dmesg | tail). Generally, issues like this occur when Open vSwitch is built for a kernel different from the one into which you are trying to load it. Run modinfo on openvswitch.ko and on a module built for the running kernel, e.g.:

    $ /sbin/modinfo openvswitch.ko
    $ /sbin/modinfo /lib/modules/$(uname -r)/kernel/net/bridge/bridge.ko

    Compare the “vermagic” lines output by the two commands. If they differ, then Open vSwitch was built for the wrong kernel.

    If you decide to report a bug or ask a question related to module loading, include the output from the dmesg and modinfo commands mentioned above.


Before starting ovs-vswitchd itself, you need to start its configuration database, ovsdb-server. Each machine on which Open vSwitch is installed should run its own copy of ovsdb-server. Before ovsdb-server itself can be started, configure a database that it can use:

$ mkdir -p /usr/local/etc/openvswitch
$ ovsdb-tool create /usr/local/etc/openvswitch/conf.db \

Configure ovsdb-server to use database created above, to listen on a Unix domain socket, to connect to any managers specified in the database itself, and to use the SSL configuration in the database:

$ mkdir -p /usr/local/var/run/openvswitch
$ ovsdb-server --remote=punix:/usr/local/var/run/openvswitch/db.sock \
    --remote=db:Open_vSwitch,Open_vSwitch,manager_options \
    --private-key=db:Open_vSwitch,SSL,private_key \
    --certificate=db:Open_vSwitch,SSL,certificate \
    --bootstrap-ca-cert=db:Open_vSwitch,SSL,ca_cert \
    --pidfile --detach --log-file


If you built Open vSwitch without SSL support, then omit --private-key, --certificate, and --bootstrap-ca-cert.)

Initialize the database using ovs-vsctl. This is only necessary the first time after you create the database with ovsdb-tool, though running it at any time is harmless:

$ ovs-vsctl --no-wait init

Start the main Open vSwitch daemon, telling it to connect to the same Unix domain socket:

$ ovs-vswitchd --pidfile --detach --log-file


At this point you can use ovs-vsctl to set up bridges and other Open vSwitch features. For example, to create a bridge named br0 and add ports eth0 and vif1.0 to it:

$ ovs-vsctl add-br br0
$ ovs-vsctl add-port br0 eth0
$ ovs-vsctl add-port br0 vif1.0

Refer to ovs-vsctl(8) for more details. You may also wish to refer to Testing for information on more generic testing of OVS.


When you upgrade Open vSwitch from one version to another you should also upgrade the database schema:

  1. Stop the Open vSwitch daemons, e.g.:

    $ kill `cd /usr/local/var/run/openvswitch && cat`
  2. Install the new Open vSwitch release by using the same configure options as was used for installing the previous version. If you do not use the same configure options, you can end up with two different versions of Open vSwitch executables installed in different locations.

  3. Upgrade the database, in one of the following two ways:

    • If there is no important data in your database, then you may delete the database file and recreate it with ovsdb-tool, following the instructions under “Building and Installing Open vSwitch for Linux, FreeBSD or NetBSD”.

    • If you want to preserve the contents of your database, back it up first, then use ovsdb-tool convert to upgrade it, e.g.:

      $ ovsdb-tool convert /usr/local/etc/openvswitch/conf.db \
  4. Start the Open vSwitch daemons as described under Starting above.

Hot Upgrading

Upgrading Open vSwitch from one version to the next version with minimum disruption of traffic going through the system that is using that Open vSwitch needs some considerations:

  1. If the upgrade only involves upgrading the userspace utilities and daemons of Open vSwitch, make sure that the new userspace version is compatible with the previously loaded kernel module.
  2. An upgrade of userspace daemons means that they have to be restarted. Restarting the daemons means that the OpenFlow flows in the ovs-vswitchd daemon will be lost. One way to restore the flows is to let the controller re-populate it. Another way is to save the previous flows using a utility like ovs-ofctl and then re-add them after the restart. Restoring the old flows is accurate only if the new Open vSwitch interfaces retain the old ‘ofport’ values.
  3. When the new userspace daemons get restarted, they automatically flush the old flows setup in the kernel. This can be expensive if there are hundreds of new flows that are entering the kernel but userspace daemons are busy setting up new userspace flows from either the controller or an utility like ovs-ofctl. Open vSwitch database provides an option to solve this problem through the other_config:flow-restore-wait column of the Open_vSwitch table. Refer to the ovs-vswitchd.conf.db(5) manpage for details.
  4. If the upgrade also involves upgrading the kernel module, the old kernel module needs to be unloaded and the new kernel module should be loaded. This means that the kernel network devices belonging to Open vSwitch is recreated and the kernel flows are lost. The downtime of the traffic can be reduced if the userspace daemons are restarted immediately and the userspace flows are restored as soon as possible.

The ovs-ctl utility’s restart function only restarts the userspace daemons, makes sure that the ‘ofport’ values remain consistent across restarts, restores userspace flows using the ovs-ofctl utility and also uses the other_config:flow-restore-wait column to keep the traffic downtime to the minimum. The ovs-ctl utility’s force-reload-kmod function does all of the above, but also replaces the old kernel module with the new one. Open vSwitch startup scripts for Debian, XenServer and RHEL use ovs-ctl’s functions and it is recommended that these functions be used for other software platforms too.

Reporting Bugs

Report problems to