Updated: 07 November 2015
wpa_supplicant [ -BddfhKLqqsTtuvW ] [ -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:
Supported WPA/IEEE 802.11i features:
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).
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.
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
If the specific driver wrapper is not known beforehand, it is possible to specify multiple comma separated driver wrappers on the command line. wpa_supplicant will use the first driver wrapper that is able to initialize the interface.
wpa_supplicant -Dnl80211,wext -c/etc/wpa_supplicant.conf -iwlan0
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 nl80211 -N \ -c wpa2.conf -i ath0 -D wext
Current hardware/software requirements:
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:
First, make a configuration file, e.g. /etc/wpa_supplicant.conf, that describes the networks you are interested in. See (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 fi
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 fi
wpa_supplicant is copyright (c) 2003-2014, Jouni Malinen <firstname.lastname@example.org> and contributors. All Rights Reserved.
This program is licensed under the BSD license (the one with advertisement clause removed).
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