Difference between revisions of "WPA supplicant"

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Install {{Pkg|wpa_supplicant}} from the [[official repositories]].
 
Install {{Pkg|wpa_supplicant}} from the [[official repositories]].
  
Optionally install also {{Pkg|wpa_supplicant_gui}}, which provides ''wpa_gui'', a graphical front-end for ''wpa_supplicant''.
+
Optionally also install {{Pkg|wpa_supplicant_gui}}, which provides ''wpa_gui'', a graphical front-end for ''wpa_supplicant''.
  
 
== Overview ==
 
== Overview ==

Revision as of 14:05, 12 December 2014

zh-CN:WPA Supplicant

wpa_supplicant is a cross-platform supplicant with support for WEP, WPA and WPA2 (IEEE 802.11i / RSN (Robust Secure Network)). It is suitable for desktops, laptops and embedded systems.

wpa_supplicant is the IEEE 802.1X/WPA component that is used in the client stations. It implements key negotiation with a WPA authenticator and it controls the roaming and IEEE 802.11 authentication/association of the wireless driver.

Installation

Install wpa_supplicant from the official repositories.

Optionally also install wpa_supplicant_gui, which provides wpa_gui, a graphical front-end for wpa_supplicant.

Overview

The first step to connect to an encrypted wireless network is having wpa_supplicant obtain authentication from a WPA authenticator. In order to do this, wpa_supplicant must be configured so that it will be able to submit the correct credentials to the authenticator.

Once the authentication is successful, it will be possible to connect to the network by normally obtaining an IP address by setting it manually with the iproute2 suite or using some networking program, like systemd-networkd or dhcpcd, to configure an interface to obtain an IP address automatically via DHCP. See also the wireless and wired network configuration articles for methods and examples.

Connecting with wpa_cli

This connection method allows scanning for the available networks, making use of wpa_cli, a command line tool which can be used to interactively configure wpa_supplicant at runtime. See wpa_cli(8) for details.

In order to use wpa_cli, a control interface must be specified for wpa_supplicant, and it must be given the rights to update the configuration. Do this by creating a minimal configuration file:

/etc/wpa_supplicant/example.conf
ctrl_interface=/run/wpa_supplicant
update_config=1

Now start wpa_supplicant with:

# wpa_supplicant -B -i interface -c /etc/wpa_supplicant/example.conf
Tip: To discover your wireless network interface name, issue the ip link command.

At this point run:

# wpa_cli

This will present an interactive prompt (>), which has tab completion and descriptions of completed commands.

Tip: The location of the socket can be set manually with the -p option. It is also possible to specify the interface to be configured with the -i option, otherwise the first found wireless interface managed by wpa_supplicant will be used.

Use the scan and scan_results commands to see the available networks:

> scan
OK
<3>CTRL-EVENT-SCAN-RESULTS
> scan_results
bssid / frequency / signal level / flags / ssid
00:00:00:00:00:00 2462 -49 [WPA2-PSK-CCMP][ESS] MYSSID
11:11:11:11:11:11 2437 -64 [WPA2-PSK-CCMP][ESS] ANOTHERSSID

To associate with MYSSID, add the network, set the credentials and enable it:

> add_network
0
> set_network 0 ssid "MYSSID"
> set_network 0 psk "passphrase"
> enable_network 0
<2>CTRL-EVENT-CONNECTED - Connection to 00:00:00:00:00:00 completed (reauth) [id=0 id_str=]
Note:
  • Each network is indexed numerically, so the first network will have index 0.
  • The PSK is computed from the quoted "passphrase" string, as also shown by the wpa_passphrase command. Nonetheless, you can enter the PSK directly by passing it to psk without quotes.

Finally save this network in the configuration file:

> save_config
OK

Once association is complete, all that is left to do is obtain an IP address as indicated in the #Overview, for example:

# dhcpcd interface

Connecting with wpa_passphrase

This connection method allows quickly connecting to a network whose SSID is already known, making use of wpa_passphrase, a command line tool which generates the minimal configuration needed by wpa_supplicant. For example:

$ wpa_passphrase MYSSID passphrase
network={
    ssid="MYSSID"
    #psk="passphrase"
    psk=59e0d07fa4c7741797a4e394f38a5c321e3bed51d54ad5fcbd3f84bc7415d73d
}

This means that wpa_supplicant can be associated with wpa_passphrase and simply started with:

# wpa_supplicant -B -i interface -c <(wpa_passphrase MYSSID passphrase)
Tip:
  • To discover your wireless network interface name, issue the ip link command.
  • Some unusually complex passphrases may require input from a file: wpa_passphrase MYSSID < passphrase.txt

Finally, you should obtain an IP address as indicated in the #Overview, for example:

# dhcpcd interface

Advanced usage

For networks of varying complexity, possibly employing extensive use of EAP, it will be useful to maintain a customised configuration file. For an overview of the configuration with examples, refer to wpa_supplicant.conf(5); for details on all the supported configuration parameters, refer to the example file /etc/wpa_supplicant/wpa_supplicant.conf.

Configuration

As is clear after reading #Connecting with wpa_passphrase, a basic configuration file can be generated with:

# wpa_passphrase MYSSID passphrase > /etc/wpa_supplicant/example.conf

This will only create a network section. A configuration file with some more common options may look like:

/etc/wpa_supplicant/example.conf
ctrl_interface=DIR=/run/wpa_supplicant GROUP=wheel
update_config=1
fast_reauth=1
ap_scan=1
network={
    ssid="MYSSID"
    #psk="passphrase"
    psk=59e0d07fa4c7741797a4e394f38a5c321e3bed51d54ad5fcbd3f84bc7415d73d
}

Further network blocks may be added manually, or using wpa_cli as illustrated in #Connecting with wpa_cli. In order to use wpa_cli, a control interface must be set with the ctrl_interface option. Setting GROUP=wheel allows users belonging to such group to execute wpa_cli. Also add update_config=1 so that changes made with wpa_cli to example.conf can be saved.

fast_reauth=1 and ap_scan=1 are the wpa_supplicant options active globally at the time of writing. Whether you need them, or other global options too for that matter, depends on the type of network to connect to. If you need other global options, simply copy them over to the file from /etc/wpa_supplicant/wpa_supplicant.conf.

Alternatively, wpa_cli set can be used to see options' status or set new ones. Multiple network blocks may be appended to this configuration: the supplicant will handle association to and roaming between all of them. The strongest signal defined with a network block usually is connected to by default, one may define priority= to influence behaviour.

An advantage to be mentioned in using a customized configuration file at /etc/wpa_supplicant/wpa_supplicant.conf is that it is used by default by dhcpcd. If you do so, you might want to make a backup of the original and delete the extensive network block examples in it. Otherwise, do not be surprised if your device suddenly connects to networks defined in them. In any case, changes to new versions of the configuration file should of course be merged.

Tip: To configure a network block to a hidden wireless SSID, which by definition will not turn up in a regular scan, the option scan_ssid=1 has to be defined in the network block.

Connection

Manual

First start wpa_supplicant command, whose most commonly used arguments are:

  • -B - Fork into background.
  • -c filename - Path to configuration file.
  • -i interface - Interface to listen on.
  • -D driver - Optionally specify the driver to be used. For a list of supported drivers see the output of wpa_supplicant -h.
    • nl80211 is the current standard, but not all wireless chip's modules support it.
    • wext is currently deprecated, but still widely supported.

See wpa_supplicant(8) for the full argument list. For example:

# wpa_supplicant -B -i interface -c /etc/wpa_supplicant/example.conf

followed by a method to obtain an ip address manually as indicated in the #Overview, for example:

# dhcpcd interface
Tip: dhcpcd has a hook that can lauch wpa_supplicant implicitly, see dhcpcd#10-wpa_supplicant.

At boot (systemd)

The wpa_supplicant package provides multiple systemd service files:

  • wpa_supplicant.service - uses D-Bus, recommended for NetworkManager users.
  • wpa_supplicant@.service - accepts the interface name as an argument and starts the wpa_supplicant daemon for this interface. It reads the configuration file in /etc/wpa_supplicant/wpa_supplicant-interface.conf.
  • wpa_supplicant-nl80211@.service - also interface specific, but explicitly forces the nl80211 driver (see below). The configuration file path is /etc/wpa_supplicant/wpa_supplicant-nl80211-interface.conf.
  • wpa_supplicant-wired@.service - also interface specific, uses the wired driver. The configuration file path is /etc/wpa_supplicant/wpa_supplicant-wired-interface.conf.

To enable wireless at boot, enable one of the services above on a particular wireless interface. For example:

# systemctl enable wpa_supplicant@interface

Now choose and enable a service to obtain an ip address for the particular interface as indicated in the #Overview, for example:

# systemctl enable dhcpcd@interface
Tip: dhcpcd has a hook that can lauch wpa_supplicant implicitly, see dhcpcd#10-wpa_supplicant.

wpa_cli action script

wpa_cli can run in daemon mode and execute a specified script based on events from wpa_supplicant. Two events are supported: CONNECTED and DISCONNECTED. Some environment variables are available to the script, see wpa_cli(8) for details.

The following example will use desktop notifications to notify the user about the events:

#!/bin/bash

case "$2" in
    CONNECTED)
        notify-send "WPA supplicant: connection established";
        ;;
    DISCONNECTED)
        notify-send "WPA supplicant: connection lost";
        ;;
esac

Remember to make the script executable, then use the -a flag to pass the script path to wpa_cli:

$ wpa_cli -a /path/to/script

See also