Section: (8)
Updated: 15 February 2009
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wpa_supplicant - Wi-Fi Protected Access client and IEEE 802.1X supplicant  


wpa_supplicant [ -BddfhKLqqtuvW ] [ -iifname ] [ -cconfig file ] [ -Ddriver ] [ -PPID_file ] [ -foutput file ]



Wireless networks do not require physical access to the network equipment in the same way as wired networks. This makes it easier for unauthorized users to passively monitor a network and capture all transmitted frames. In addition, unauthorized use of the network is much easier. In many cases, this can happen even without user's explicit knowledge since the wireless LAN adapter may have been configured to automatically join any available network.

Link-layer encryption can be used to provide a layer of security for wireless networks. The original wireless LAN standard, IEEE 802.11, included a simple encryption mechanism, WEP. However, that proved to be flawed in many areas and network protected with WEP cannot be consider secure. IEEE 802.1X authentication and frequently changed dynamic WEP keys can be used to improve the network security, but even that has inherited security issues due to the use of WEP for encryption. Wi-Fi Protected Access and IEEE 802.11i amendment to the wireless LAN standard introduce a much improvement mechanism for securing wireless networks. IEEE 802.11i enabled networks that are using CCMP (encryption mechanism based on strong cryptographic algorithm AES) can finally be called secure used for applications which require efficient protection against unauthorized access.

wpa_supplicant is an implementation of the WPA Supplicant component, i.e., the part that runs in the client stations. It implements WPA key negotiation with a WPA Authenticator and EAP authentication with Authentication Server. In addition, it controls the roaming and IEEE 802.11 authentication/association of the wireless LAN driver.

wpa_supplicant is designed to be a "daemon" program that runs in the background and acts as the backend component controlling the wireless connection. wpa_supplicant supports separate frontend programs and an example text-based frontend, wpa_cli, is included with wpa_supplicant.

Before wpa_supplicant can do its work, the network interface must be available. That means that the physical device must be present and enabled, and the driver for the device must be loaded. The daemon will exit immediately if the device is not already available.

After wpa_supplicant has configured the network device, higher level configuration such as DHCP may proceed. There are a variety of ways to integrate wpa_supplicant into a machine's networking scripts, a few of which are described in sections below.

The following steps are used when associating with an AP using WPA:

wpa_supplicant requests the kernel driver to scan neighboring BSSes
wpa_supplicant selects a BSS based on its configuration
wpa_supplicant requests the kernel driver to associate with the chosen BSS
If WPA-EAP: integrated IEEE 802.1X Supplicant completes EAP authentication with the authentication server (proxied by the Authenticator in the AP)
If WPA-EAP: master key is received from the IEEE 802.1X Supplicant
If WPA-PSK: wpa_supplicant uses PSK as the master session key
wpa_supplicant completes WPA 4-Way Handshake and Group Key Handshake with the Authenticator (AP)
wpa_supplicant configures encryption keys for unicast and broadcast
normal data packets can be transmitted and received


Supported WPA/IEEE 802.11i features:

WPA-PSK ("WPA-Personal")
WPA with EAP (e.g., with RADIUS authentication server) ("WPA-Enterprise") Following authentication methods are supported with an integrate IEEE 802.1X Supplicant:
EAP-PEAP/MSCHAPv2 (both PEAPv0 and PEAPv1)
EAP-PEAP/TLS (both PEAPv0 and PEAPv1)
EAP-PEAP/GTC (both PEAPv0 and PEAPv1)
EAP-PEAP/OTP (both PEAPv0 and PEAPv1)
EAP-PEAP/MD5-Challenge (both PEAPv0 and PEAPv1)
LEAP (note: requires special support from the driver for IEEE 802.11 authentication)
(following methods are supported, but since they do not generate keying material, they cannot be used with WPA or IEEE 802.1X WEP keying)
key management for CCMP, TKIP, WEP104, WEP40
RSN/WPA2 (IEEE 802.11i)
PMKSA caching


A summary of available driver backends is below. Support for each of the driver backends is chosen at wpa_supplicant compile time. For a list of supported driver backends that may be used with the -D option on your system, refer to the help output of wpa_supplicant (wpa_supplicant -h).

(default) Host AP driver (Intersil Prism2/2.5/3). (this can also be used with Linuxant DriverLoader).
Agere Systems Inc. driver (Hermes-I/Hermes-II).
MADWIFI 802.11 support (Atheros, etc.).
Linux wireless extensions (generic).
Linux ndiswrapper.
Broadcom wl.o driver.
Intel ipw2100/2200 driver.
wpa_supplicant wired Ethernet driver
wpa_supplicant Broadcom switch driver
BSD 802.11 support (Atheros, etc.).
Windows NDIS driver.


Most command line options have global scope. Some are given per interface, and are only valid if at least one -i option is specified, otherwise they're ignored. Option groups for different interfaces must be separated by -N option.

-b br_ifname
Optional bridge interface name. (Per interface)
Run daemon in the background.
-c filename
Path to configuration file. (Per interface)
-C ctrl_interface
Path to ctrl_interface socket (Per interface. Only used if -c is not).
-i ifname
Interface to listen on. Multiple instances of this option can be present, one per interface, separated by -N option (see below).
Increase debugging verbosity (-dd even more).
-D driver
Driver to use. (Per interface, see the available options below.)
-f output file
Log output to specified file instead of stdout.
-g global ctrl_interface
Path to global ctrl_interface socket. If specified, interface definitions may be omitted.
Include keys (passwords, etc.) in debug output.
Include timestamp in debug messages.
Help. Show a usage message.
Show license (GPL and BSD).
Driver parameters. (Per interface)
-P PID_file
Path to PID file.
Decrease debugging verbosity (-qq even less).
Enabled DBus control interface. If enabled, interface definitions may be omitted.
Show version.
Wait for a control interface monitor before starting.
Start describing new interface.


In most common cases, wpa_supplicant is started with:

wpa_supplicant -B -c/etc/wpa_supplicant.conf -iwlan0

This makes the process fork into background.

The easiest way to debug problems, and to get debug log for bug reports, is to start wpa_supplicant on foreground with debugging enabled:

wpa_supplicant -c/etc/wpa_supplicant.conf -iwlan0 -d

wpa_supplicant can control multiple interfaces (radios) either by running one process for each interface separately or by running just one process and list of options at command line. Each interface is separated with -N argument. As an example, following command would start wpa_supplicant for two interfaces:

wpa_supplicant \
        -c wpa1.conf -i wlan0 -D hostap -N \
        -c wpa2.conf -i ath0 -D madwifi


Current hardware/software requirements:

Linux kernel 2.4.x or 2.6.x with Linux Wireless Extensions v15 or newer
Microsoft Windows with WinPcap (at least WinXP, may work with other versions)


Host AP driver for Prism2/2.5/3 (development snapshot/v0.2.x)
(http://hostap.epitest.fi/) Driver needs to be set in Managed mode (iwconfig wlan0 mode managed). Please note that station firmware version needs to be 1.7.0 or newer to work in WPA mode.
Linuxant DriverLoader
(http://www.linuxant.com/driverloader/) with Windows NDIS driver for your wlan card supporting WPA.
Agere Systems Inc. Linux Driver
(http://www.agere.com/support/drivers/) Please note that the driver interface file (driver_hermes.c) and hardware specific include files are not included in the wpa_supplicant distribution. You will need to copy these from the source package of the Agere driver.
madwifi driver for cards based on Atheros chip set (ar521x)
(http://sourceforge.net/projects/madwifi/) Please note that you will need to modify the wpa_supplicant .config file to use the correct path for the madwifi driver root directory (CFLAGS += -I../madwifi/wpa line in example defconfig).
ATMEL AT76C5XXx driver for USB and PCMCIA cards
Linux ndiswrapper
(http://ndiswrapper.sourceforge.net/) with Windows NDIS driver.
Broadcom wl.o driver
This is a generic Linux driver for Broadcom IEEE 802.11a/g cards. However, it is proprietary driver that is not publicly available except for couple of exceptions, mainly Broadcom-based APs/wireless routers that use Linux. The driver binary can be downloaded, e.g., from Linksys support site (http://www.linksys.com/support/gpl.asp) for Linksys WRT54G. The GPL tarball includes cross-compiler and the needed header file, wlioctl.h, for compiling wpa_supplicant. This driver support in wpa_supplicant is expected to work also with other devices based on Broadcom driver (assuming the driver includes client mode support).
Intel ipw2100 driver
Intel ipw2200 driver
Linux wireless extensions
In theory, any driver that supports Linux wireless extensions can be used with IEEE 802.1X (i.e., not WPA) when using ap_scan=0 option in configuration file.
Wired Ethernet drivers
Use ap_scan=0.
BSD net80211 layer (e.g., Atheros driver)
At the moment, this is for FreeBSD 6-CURRENT branch.
Windows NDIS
The current Windows port requires WinPcap (http://winpcap.polito.it/). See README-Windows.txt for more information.

wpa_supplicant was designed to be portable for different drivers and operating systems. Hopefully, support for more wlan cards and OSes will be added in the future. See developer.txt for more information about the design of wpa_supplicant and porting to other drivers. One main goal is to add full WPA/WPA2 support to Linux wireless extensions to allow new drivers to be supported without having to implement new driver-specific interface code in wpa_supplicant.  


The wpa_supplicant system consists of the following components:

the configuration file describing all networks that the user wants the computer to connect to.
the program that directly interacts with the network interface.
the client program that provides a high-level interface to the functionality of the daemon.
a utility needed to construct wpa_supplicant.conf files that include encrypted passwords.


First, make a configuration file, e.g. /etc/wpa_supplicant.conf, that describes the networks you are interested in. See wpa_supplicant.conf(5) for details.

Once the configuration is ready, you can test whether the configuration works by running wpa_supplicant with following command to start it on foreground with debugging enabled:

wpa_supplicant -iwlan0 -c/etc/wpa_supplicant.conf -d

Assuming everything goes fine, you can start using following command to start wpa_supplicant on background without debugging:

wpa_supplicant -iwlan0 -c/etc/wpa_supplicant.conf -B

Please note that if you included more than one driver interface in the build time configuration (.config), you may need to specify which interface to use by including -D<driver name> option on the command line.  


For example, following small changes to pcmcia-cs scripts can be used to enable WPA support:

Add MODE="Managed" and WPA="y" to the network scheme in /etc/pcmcia/wireless.opts.

Add the following block to the end of start action handler in /etc/pcmcia/wireless:

if [ "$WPA" = "y" -a -x /usr/local/bin/wpa_supplicant ]; then
    /usr/local/bin/wpa_supplicant -B -c/etc/wpa_supplicant.conf -i$DEVICE

Add the following block to the end of stop action handler (may need to be separated from other actions) in /etc/pcmcia/wireless:

if [ "$WPA" = "y" -a -x /usr/local/bin/wpa_supplicant ]; then
    killall wpa_supplicant

This will make cardmgr start wpa_supplicant when the card is plugged in.  


wpa_background(8) wpa_supplicant.conf(5) wpa_cli(8) wpa_passphrase(8)  


wpa_supplicant is copyright (c) 2003-2007, Jouni Malinen <j@w1.fi> and contributors. All Rights Reserved.

This program is dual-licensed under both the GPL version 2 and BSD license. Either license may be used at your option.