Chapter 13. Mobile Computing with Linux

Table of Contents

13.1. Laptops
13.2. Mobile Hardware
13.3. Cellular Phones and PDAs
13.4. For More Information


This chapter provides an overview of the various aspects of using Linux for mobile computing. The various fields of use are briefly introduced and the essential features of the employed hardware are described. Software solutions for special requirements and options for maximum performance are covered along with possibilities to minimize power consumption. An overview of the most important sources of information about the subject concludes the chapter.

Most people associate mobile computing with laptops, PDAs, and cellular phones and the data exchange between them. This chapter extends the focus to mobile hardware components, such as external hard disks, flash drives, or digital cameras, which can be connected to laptops or desktop systems.

13.1. Laptops

13.1.1. Special Properties of Laptop Hardware

The hardware of laptops differs from that of a normal desktop system. This is because criteria like exchangeability, occupied space, and power consumption are relevant properties. The manufacturers of mobile hardware have developed the PCMCIA standard (Personal Computer Memory Card International Association). This standard covers memory cards, network interface cards, ISDN and modem cards, and external hard disks. How the support for such hardware is implemented in Linux, what needs to be taken into account during configuration, what software is available for the control of PCMCIA, and how to troubleshoot any possible problems is described in 14. PCMCIA.

13.1.2. Power Conservation

The inclusion of energy-optimized system components when manufacturing laptops contributes to their suitability for use without access to the electrical power grid. Their contribution towards conservation of power is at least as important as that of the operating system. SUSE LINUX supports various methods that influence the power consuption of a laptop and have varying effects on the operating time under battery power. The following list is ordered in descending order of contribution towards power conservation:

  • Throttling the CPU speed

  • Switching off the display illumination during pauses

  • Manual adjustment of the display illumination

  • Disconnection of unused, hotplug enabled accessories (USB CD-ROM, external mouse, unused PCMCIA cards, etc.)

  • Spinning down the hard disk when idling

Detailed background information about power management in SUSE LINUX and about operating the YaST power management module is provided in 16. Power Management.

13.1.3. Integration in Changing Operating Environments

Your system needs to adapt to changing operating environments when used for mobile computing. A lot of services depend on the environment and the underlying clients must be reconfigured. SUSE LINUX takes over this job for you.

Figure 13.1. Integrating a Laptop in a Network

Integrating a Laptop in a Network

The services affected in the case of a laptop commuting back and forth between a small home network and an office network are:

Network Configuration

This includes IP address allocation, name resolution, Internet connectivity, and connectivity to other networks.


A current database of available printers and an available print server must be present, depending on the network.

E-Mail and Proxies

As with printing, the list of the corresponding servers must be current.

Configuring X

If your laptop is temporarily connected to a beamer or an external monitor, the different display configurations need to be kept available.

SUSE LINUX offers two ways of integrating a laptop into existing operating environments that can be combined.


SCPM (system configuration profile management) allows storage of arbitrary configuration states of a system into a kind of “snapshot” called a profile. Profiles can be created for different situations. They are useful when a system is operated in changing environments (home network, office network). It is always possible to switch between profiles. Information about SCPM can be found in 15. System Configuration Profile Management. The kicker applet Profile Chooser in KDE allows switching between profiles. The application requires the root password before switching.


The service location protocol (SLP) simplifies the connection of a laptop to an existing network. Without SLP, the administrator of a laptop usually requires detailed knowledge of the services available in a network. SLP broadcasts the availability of a certain type of service to all clients in a local network. Applications that support SLP can process the information dispatched by SLP and be configured automatically. SLP can even be used for the installation of a system and spare the effort of searching for a suitable installation source. Detailed information about SLP can be found in 22.6. “SLP Services in the Network”.

The emphasis of SCPM lies on enabling and maintaining reproducible system conditions. SLP makes configuration of a networked computer a lot easier by automating much of it.

13.1.4. Software Options

There are various special task areas in mobile use that are covered by dedicated software: system monitoring (especially the battery charge), data synchronization, and wireless communication with peripherals and the Internet. The following sections cover the most important applications that SUSE LINUX provides for each task. System Monitoring

Two KDE system monitoring tools are provided by SUSE LINUX. The pure status display of the rechargeable battery of the laptop is handled by the applet KPowersave in the kicker. Complex system monitoring is performed by KSysguard. When using GNOME, the described functions are provided by GNOME ACPI (as panel applet) and System Monitor.


KPowersave is an applet that displays the state of the rechargeable battery in the control panel. The icon adjusts to represent the type of power supply. When working on AC power, a small plug icon is displayed. When working on batteries, the icon changes to a battery. The corresponding menu opens the YaST module for power management after requesting the root password. This allows setting the behavior of the system under different types of power supply. Information about power management and about the corresponding YaST module can be found in 16. Power Management.


KSysguard is an independent application that gathers all measurable parameters of the system into one monitoring environment. KSysguard has monitors for ACPI (battery status), CPU load, network, partitioning, and memory usage. It can furthermore watch and display all system processes. The presentation and filtering of the collected data can be customized. It is possible to monitor different system parameters in various data pages or collect the data of various machines in parallel over the network. KSysguard can also run as a daemon on machines without a KDE environment. More information about this program is provided in its integrated help function or in the SUSE help pages.

Figure 13.2. Monitoring the Battery State with KSysguard

Monitoring the Battery State with KSysguard Synchronizing Data

When switching between working on a mobile machine disconnected from the network and working at a networked workstation in an office, it is necessary to keep the processed data synchronous across all instances. This could include e-mail folders, directories, and individual files that need to be present for work on the road as well as at the office. The solution in both cases is as follows:

Synchronization of E-Mail

Use an IMAP account for storing your e-mails in the office network. The e-mails are then accesssed from the workstation using any disconnected IMAP–enabled e-mail client, like Mozilla Thunderbird Mail, Evolution, or KMail as described in the User Guide. The e-mail client needs to be configured, so the same folder is always accessed for Sent messages. This ensures that all messages are available along with their status information after the synchronization process has completed. Use the SMTP service implemented in the mail client for sending messages instead of the system-wide MTA postfix or sendmail to receive reliable feedback about unsent mail.

Synchronizing Files and Directories

There are several utilities suitable for synchronizing data between a laptop and a workstation. For detailed information, refer to 24. File Synchronization. Wireless Communication

As well as connecting to a home or office network with a cable, a laptop can also wirelessly connect to other computers, peripherals, cellular phones, or PDAs. Linux supports three types of wireless communication:


With the largest range of these wireless technologies, WLAN is the only one suitable for the operation of large and sometimes even spatially disjointed networks. Single machines can connect with each other to form an independent wireless network or access the Internet. Devices called access points act as base stations for WLAN-enabled devices and play intermediate for access to the Internet. A mobile user can switch between various access points, depending on location and which access point is offering the best connection. Like in cellular telephony, a large network is available to WLAN users without binding them to a specific location for accessing it. Details about WLAN can be found in 17.1. “Wireless LAN”.


Bluetooth has the broadest application spectrum of all wireless technologies. It can be used for communication between computers (laptop) and PDAs or cellular phones, as can IrDA. It can also be used to connect various computers within visible range. Bluetooth is also used to connect wireless system components, like a keyboard or mouse. The range of this technology is, however, not sufficient to connect remote systems to a network. WLAN is the technology of choice for communicating through physical obstacles like walls. More information about bluetooth, its applications, and configuration can be found in 17.2. “Bluetooth”.


IrDA is the wireless technology with the shortest range. Both communication parties must be within viewing distance of each other. Obstacles like walls cannot be overcome. One possible application of IrDA is the transmission of a file from a laptop to a cellular phone. The short path from the laptop to the cellular phone is then covered using IrDA. The long range transport of the file to the recipient of the file is handled by the mobile network. Another application of IrDA is the wireless transmission of printing jobs in the office. More information about IrDA can be found in 17.3. “Infrared Data Transmission”.

13.1.5. Data Security

Ideally, you protect data on your laptop against unauthorized access in multiple ways. Possible security measures can be taken in the following areas:

Protection against Theft

Always physically secure your system against theft whenever possible. Various securing tools, like chains, are available in retail stores.

Securing Data on the System

Important data should not only be encrypted during transmission, but also on the hard disk. This ensures its safety in case of theft. The creation of an encrypted partition with SUSE LINUX is described in 27.3. “Encrypting Partitions and Files”.

Network Security

Any transfer of data should be secured, no matter how it takes place. General security issues regarding Linux and networks can be found in 27.4. “Security and Confidentiality”. Security measures related to wireless networking are provided in 17. Wireless Communication.