To be able to use Bluetooth, you need a Bluetooth adapter (either a built-in adapter or an external device), drivers, and a Bluetooth protocol stack. The Linux kernel already contains the basic drivers for using Bluetooth. The Bluez system is used as protocol stack. To make sure the applications work with Bluetooth, the base packages bluez-libs and bluez-utils must be installed. These packages provide a number of needed services and utilities. Additionally, some adapters (Broadcom, AVM BlueFritz!) require the bluez-firmware package to be installed. The bluez-cups package enables printing over Bluetooth connections.

A Bluetooth system consists of four interlocked layers that provide the desired functionality:

When inserting a Bluetooth adapter, the respective driver is loaded by the hotplug system. After the driver is loaded, the system checks the configuration files to see if Bluetooth should be started. If this is the case, it determines the services to start. Based on this information, the respective daemons are started. Bluetooth adapters are probed upon installation. If one or more are found, Bluetooth is enabled. Otherwise the Bluetooth system is deactivated. Any Bluetooth device added later must be enabled manually.

In Bluetooth, services are defined by means of profiles, such as the file transfer profile, the basic printing profile, and the personal area network profile. To enable a device to use the services of another device, both must understand the same profile—a piece of information that is often missing on the device package and in the manual. Unfortunately, some manufacturers do not comply strictly with the definitions of the individual profiles. Despite this, communication between the devices usually works smoothly.

In the following text, local devices are those physically connected to the computer. All other devices that can only be accessed over wireless connections are referred to as remote devices.

Use the YaST Bluetooth module, shown in Figure 17.2, “YaST Bluetooth Configuration”, to configure Bluetooth support on your system. As soon as hotplug detects a Bluetooth adapter on your system (for example, during booting or when you plug in an adapter), Bluetooth is automatically started with the settings configured in this module.

Figure 17.2. YaST Bluetooth Configuration

In the first step of the configuration, determine whether Bluetooth services should be started on your system. If you have enabled the Bluetooth services, two things can be configured. First, the ‘Device Name’. This is the name other devices display when your computer has been discovered. There are two placeholders available—%h stands for the hostname of the system (useful, for example, if it is assigned dynamically by DHCP) and %d inserts the interface number (only useful if you have more than one Bluetooth adapter in your computer). For example, if you enter Laptop %h in the field and DHCP assigns the name unit123 to your computer, other remote devices would know your computer as Laptop unit123.

The ‘Security manager’ parameter is related to the behavior of the local system when a remote device tries to connect. The difference is in the handling of the PIN number. Either allow any device to connect without a PIN or determine how the correct PIN is chosen if one is needed. You can enter a PIN (stored in a configuration file) in the appropriate input field. If a device tries to connect, it first uses this PIN. If it fails, it falls back to using no PIN. For maximum security, it is best to choose the third option, “Always ask user for PIN”. This option allows you to use different PINs for different (remote) devices.

Click ‘Advanced Daemon Configuration’ to enter the dialog for selecting and configuring the available services (called profiles in Bluetooth). All available services are displayed in a list and can be enabled or disabled by clicking ‘Activate’ or ‘Deactivate’. Click ‘Edit’ to open a dialog in which to specify additional arguments for the selected service (daemon). Do not change anything unless you are familiar with the service. After completing the configuration of the daemons, exit this dialog by clicking ‘OK’.

Back in the main dialog, click ‘Security Options’ to enter the security dialog and specify encryption, authentication, and scan settings. Then exit the security dialog to return to the main dialog. After you close the main dialog with ‘Finish’, your Bluetooth system is ready for use.

From the main dialog, you can reach the ‘Device and Service Classes’ dialog, too. Bluetooth devices are grouped into various device classes. In this dialog, choose the correct one for your computer, such as “Desktop” or “Laptop.” The device class is not very important, unlike the service class, also set here. Sometimes remote Bluetooth devices, like cell phones, only allow certain functions if they can detect the correct service class set on your system. This is often the case for cell phones that expect a class called “Object Transfer” before they allow the transfer of files from or to the computer. You can choose multiple classes. It is not useful to select all classes “just in case.” The default selection should be appropriate in most cases.

To use Bluetooth to set up a network, activate ‘PAND’ in the ‘Advanced Daemon Configuration’ dialog and set the mode of the daemon with ‘Edit’. For a functional Bluetooth network connection, one pand must operate in the ‘Listen’ mode and the peer in the ‘Search’ mode. By default, the ‘Listen’ mode is preset. Adapt the behavior of your local pand. Additionally, configure the bnepX interface (X stands for the device number in the system) in the YaST ‘Network Card’ module.

The configuration files for the individual components of the Bluez system are located in the directory /etc/bluetooth. The only exception is the file /etc/sysconfig/bluetooth for starting the components, which is modified by the YaST module.

The configuration files described below can only be modified by the user root. Currently, there is no graphical user interface to change all settings. The most important ones can be set using the YaST Bluetooth module, described in Section 17.2.2.1, “Configuring Bluetooth with YaST”. All other settings are only of interest for experienced users with special cases. Usually, the default settings should be adequate.

A PIN number provides basic protection against unwanted connections. Mobile phones usually query the PIN when establishing the first contact (or when setting up a device contact on the phone). For two devices to be able to communicate, both must identify themselves with the same PIN. On the computer, the PIN is located in the file /etc/bluetooth/pin.

	Security of Bluetooth Connections
Despite the PINs, the transmission between two devices may not be fully secure. By default, the authentication and encryption of Bluetooth connections is deactivated. Activating authentication and encryption may result in communication problems with some Bluetooth devices.

Various settings, such as the device names and the security mode, can be changed in the configuration file /etc/bluetooth/hcid.conf. Usually, the default settings should be adequate. The file contains comments describing the options for the various settings.

Two sections in the included file are designated as options and device. The first contains general information that hcid uses for starting. The latter contains settings for the individual local Bluetooth devices.

One of the most important settings of the options section is security auto;. If set to auto, hcid tries to use the local PIN for incoming connections. If it fails, it switches to none and establishes the connection anyway. For increased security, this default setting should be set to user to make sure that the user is requested to enter a PIN every time a connection is established.

Set the name under which the computer is displayed on the other side in the device section. The device class, such as Desktop, Laptop, or Server, is defined in this section. Authentication and encryption are also enabled or disabled here.

hcitool can be used to determine whether local and remote devices are detected. The command hcitool dev lists the local devices. The output generates a line in the form interface_name device_address for every detected local device.

Search for remote devices with the command hcitool inq. Three values are returned for every detected device: the device address, the clock offset, and the device class. The device address is important, because other commands use it for identifying the target device. The clock offset mainly serves a technical purpose. The class specifies the device type and the service type as a hexadecimal value.

The command hcitool name device-address can be used to determine the device name of a remote device. In the case of a remote computer, the class and the device name correspond to the information in its /etc/bluetooth/hcid.conf. Local device addresses generate an error output.

The command /usr/sbin/hciconfig delivers further information about the local device. If hciconfig is executed without any arguments, the output shows device information, such as the device name (hciX), the physical device address (a 12-digit number in the form 00:12:34:56:78), and information about the amount of transmitted data.

hciconfig hci0 name displays the name that is returned by your computer when it receives requests from remote devices. As well as querying the settings of the local device, hciconfig can be used for modifying these settings. For example, hciconfig hci0 name TEST sets the name to TEST.

The program sdptool can be used to check which services are made available by a specific device. The command sdptool browse device_address returns all services of a device. Use the command sdptool search service_code to search for a specific service. This command scans all accessible devices for the requested service. If one of the devices offers the service, the program prints the full service name returned by the device together with a brief description. View a list of all possible service codes by entering sdptool without any parameters.

In the first example, a network connection is established between the hosts H1 and H2. These two hosts have the Bluetooth device addresses baddr1 and baddr2 (determined on both hosts with the command hcitool dev as described above). The hosts should be identified with the IP addresses 192.168.1.3 (H1) and 192.168.1.4 (H2).

The Bluetooth connection is established with the help of pand (personal area networking). The following commands must be executed by the user root. The description focuses on the Bluetooth-specific actions and does not provide a detailed explanation of the network command ip.

Enter the command pand -s to start pand on the host H1. Subsequently, a connection can be established on the host H2 with the command pand -c baddr1. If you enter ip link show on one of the hosts to list the available network interfaces, the output should contain an entry like the following:

 bnep0: <BROADCAST,MULTICAST> mtu 1500 qdisc noop qlen 1000 
 link/ether 00:12:34:56:89:90 brd ff:ff:ff:ff:ff:ff

Instead of 00:12:34:56:89:90, the output should contain the local device address baddr1 or baddr2. Now this interface must be assigned an IP address and activated. On H1, this can be done with the following two commands:

ip addr add 192.168.1.3/24 dev bnep0
ip link set bnep0 up

On H2:

ip addr add 192.168.1.4/24 dev bnep0
ip link set bnep0 up

Now H1 can be accessed from H2 under the IP 192.168.1.3. Use the command ssh 192.168.1.4 to access H2 from H1, assuming H2 runs an sshd, which is activated by default in SUSE LINUX. The command ssh 192.168.1.4 can also be run as a normal user.

The second example shows how to transfer a photograph created with a mobile phone with a built-in digital camera to a computer (without incurring additional costs for the transmission of a multimedia message). Although the menu structure may differ on various mobile phones, the procedure is usually quite similar. Refer to the manual of your phone, if necessary. This example describes the transfer of a photograph from a Sony Ericsson mobile phone to a laptop. The service Obex-Push must be available on the computer and the computer must grant the mobile phone access. In the first step, the service is made available on the laptop. This is done by means of the opd daemon from the package bluez-utils. Start the daemon with the following command:

opd --mode OBEX --channel 10 --daemonize --path /tmp --sdp 

Two important parameters are used: --sdp registers the service with sdpd and --path /tmp instructs the program where to save the received data—in this case to /tmp. You can also specify any other directory to which you have write access.

Now the mobile phone must get to know the computer. To do this, open the ‘Connect’ menu on the phone and select ‘Bluetooth’. If necessary, click ‘Turn On’ before selecting ‘My devices’. Select ‘New device’ and let your phone search for the laptop. If a device is detected, its name appears in the display. Select the device associated with the laptop. If you encounter a PIN query, enter the PIN specified in /etc/bluetooth/pin. Now your phone recognizes the laptop and is able to exchange data with the laptop. Exit the current menu and go to the image menu. Select the image to transfer and press ‘More’. In the next menu, press ‘Send’ to select a transmission mode. Select ‘Via Bluetooth’. The laptop should be listed as a target device. Select the laptop to start the transmission. The image is then saved to the directory specified with the opd command. Audio tracks can be transferred to the laptop in the same way.