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in your file system. Protecting different parts of the file system If you have many users on a system, and the users become suddenly very piggy and consume all of the file system space, the entire system can fail. For example, there may be no place for temporary files to be copied (so the programs writing to temporary files may fail), and incoming mail may fail to be written to mail boxes. With multiple mounted partitions, if one partition runs out, the others can continue to work fine. Backups There are some fast ways of backing up data from your computer that involve copying the entire image of a disk or partition. If you want to restore that partition later, you can simply copy it back (bit-by-bit) to a hard disk. With smaller partitions, this approach can be done fairly efficiently. Protecting from disk failure If one disk (or part of one disk) fails, by having multiple partitions mounted on your file system, you may be able to continue working and just fix the one disk that fails. When a disk partition is mounted on the file system, all directories and subdirectories below that mount point are then stored on that partition. So, for example, if you were to mount one partition on / and one on /usr, everything below the /usr mount point would be stored on the second partition while everything else would be stored on the first partition. If you then mounted another partition on /usr/local, everything below that mount point would be on the third partition, while everything else below /usr would be on the second partition. Tip Here s something to look out for, particularly if you are mounting file systems from other computers. What if a remote file system is unmounted from your computer, then you go to save a file in that mount point directory? What happens is that you will write the file to that directory and it will be stored on your local hard disk. When the remote file system is remounted, however, the file you saved will seem to disappear. To get the file back, you will have to unmount the remote file system (causing the file to reappear), move the file to another location, remount the file system, and copy the file back there. Mount points that are often mentioned as being candidates for separate partitions include: /, /home, /usr, and /var. The root file system (/) is the catchall for directories that aren t in other mount points. The /home file systems is where all the user accounts are typically stored. Applications and documentation are stored in /usr. Below the /var mount point is where log files, temporary files, server files (Web, FTP, and so on), and lock files are stored (i.e., items that need disk space for your computer s applications to keep running). Cross-Reference See Chapter 2 for further information on partitioning techniques. The fact that multiple partitions are mounted on your file system is basically invisible to people using your Red Hat Linux system. The only times they will care will be if a partition runs out of space or if they need to save or use information from a particular device (such as a floppy disk or file system on another computer). Of course, any user can check this by simply typing the mount command. For a personal Red Hat Linux system, I don t see much need for different partitions. Many people just mount their entire file system on root (/). Then, they just have to make sure that the entire file system doesn t run out of room. Mounting file systems Most of your hard disks are mounted automatically for you. When you installed Red Hat Linux, you were asked to create partitions and indicate the mount points for those partitions. When you boot Red Hat Linux, all Linux partitions should be mounted. For that reason, this section focuses mostly on how to mount other types of devices so that they become part of your Red Hat Linux file system.
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A part of the Linux file system, Swap space for Linux, or Other file system types (perhaps containing other bootable operating systems.) For our purposes, I want to focus on partitions that are used for the Linux file system. To see what partitions are currently set up on your hard disk, you can use the fdisk command as follows: # fdisk -l Figure 10-5 shows how the fdisk command displays partition information in a Terminal window. Figure 10-5: View disk partitions with the fdisk command. This output shows the disk partitioning for a computer running both Red Hat Linux and Microsoft Windows. You can see that the Linux partition on /dev/hda3 has most of the space available for data. There is a Windows partition (/dev/hda1) and a Linux swap partition (/dev/hda5). There is also a small /boot partition (49MB) on /dev/hda2. In this case, the root partition for Linux has 31.881GB of disk space and resides on /dev/hda3. Next, to see what partitions are actually being used for your Linux system, you can use the mount command (with no options). The mount command can show you which of the available disk partitions are actually mounted and where they are mounted. # mount /dev/hda3 on / type ext3 (rw) none on /proc type proc (rw) /dev/hda2 on /boot type ext3 (rw) none on /dev/pts type devpts (rw,gid=5,mode=0620) Note Notice that /proc and /dev/pts are shown as file systems because they represent different file system types (proc and devpts, respectively). The word “none,” however, indicates that they are not associated with a separate partition. The only mounted partitions in this case are /dev/hda2 and /dev/hda3, which provide space for the /boot directory (which contains data for booting Linux) and rest of the Linux file system beginning from the root (/), respectively. If you were to have multiple partitions mounted on your file system, they would be shown here as well. After the word “type,” you can see the type of file system contained on the device. (See the description of different file system types later in this chapter.) Particularly on larger Linux systems, you may have multiple partitions for several reasons: Multiple hard disks You may have several hard disks available to your users. In that case you would have to mount each disk (and possibly several partitions from each disk) in different locations
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Loading modules You can load any module that has been compiled and installed (to the /lib/modules directory) into your running kernel using the insmod command. The most common reasons for loading a module are that you want to use a feature temporarily (such as loading a module to support a special file system on a floppy you want to access) or to identify module that will be used by a particular piece of hardware that could not be autodetected. Here is an example of the insmod command being used to load the parport module. The parport module is used to provide the core functions for sharing a parallel port with multiple devices. # insmod parport Using /lib/modules/2.4.6-3.1/kernel/drivers/parport/parport.o After parport is loaded you could load the parport_pc module to define the PC-style ports that are available through the interface. The parport_pc module lets you optionally define the addresses and IRQ numbers associated with each device sharing the parallel port. Here is an example: # insmod parport_pc io=0×3bc irq=auto In the previous example, a device is identified as having an address of 0×3bc. The IRQ for the device is auto-detected. The insmod command loads modules temporarily. At the next system reboot, the modules you enter disappear. To permanently add the module to your system, add the insmod command line to one of the start-up scripts that are run a boot time. Removing modules You can remove a module from a running kernel using the rmmod command. For example, to remove the module parport_pc from the current kernel, type the following: # rmmod parport_pc If the module is not currently busy, the parport_pc module is removed from the running kernel. Working with File Systems File systems in Red Hat Linux are organized in a hierarchy, beginning from root (/) and continuing downward in a structure of directories and subdirectories. As an administrator of a Red Hat Linux system, it is your duty to make sure that all the disk drives that represent your file system are available to the users of the computer. It is also your job to make sure that there is enough disk space in the right places in the file system for users to store the information they need. File systems are organized differently in Linux than they are in MS Windows operating systems. Instead of drive letters (e.g., A:, B:, C:) for each local disk, network file system, CD-ROM, or other type of storage medium, everything fits neatly into the directory structure. It is up to an administrator to create a mount point in the file system and then connect the disk to that point in the file system. Cross Reference Information on how the Linux file system is organized is provided in Chapter 3. The organization of your file system begins when you install Linux. Part of the installation process is to divide your hard disk (or disks) into partitions. Those partitions can then be assigned to:
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Documentation The /usr/src/linux-2.4/Documentation directory contains lots of plain-text files describing different aspects of the kernel and related drivers. Of particular interest is the modules.txt file (which describes how to work with modules) and the Configure.help file (which contains all the help files hardware drivers). kernel-doc The kernel-doc software package (available on CD-2 of the Red Hat Linux distribution) contains a large set of documents describing the kernel and drivers. These documents are stored in the /usr/share/doc/kernel-doc* directory. After modules have been built, they are installed in the /lib/modules/2.4* directory. The name of the directory is based on the current release number of the kernel. Modules that are in that directory can then be loaded and unloaded as they are needed. Note In previous releases, Red Hat Linux stored modules in the /lib/modules directory, rather than the /lib/moduels/2.4* directory. This structure allows you to store modules on your system that relate to different kernel versions you may be running. Listing loaded modules To see which modules are currently loaded into the running kernel on your computer, you can use the lsmod command. Here is an example: # lsmod Module Size Used by sr_mod 15120 0 (autoclean) es1371 26784 0 (autoclean) ac97_codec 8704 0 (autoclean) [es1371] gameport 1920 0 (autoclean) [es1371] soundcore 4112 4 (autoclean) [es1371] binfmt_misc 6272 1 nuscsitcp 17200 0 (unused) autofs 10816 1 (autoclean) tulip 46400 1 ipchains 36960 0 (unused) ide-scsi 8192 0 scsi_mod 93568 3 [sr_mod nuscsitcp ide-scsi] hid 18160 0 (unused) input 3456 0 [hid] usb-uhci 21440 0 (unused) usbcore 50432 1 [hid usb-uhci] ext3 50656 2 jbd 39376 2 [ext3] This output shows a variety of modules that have been loaded on a Linux system. The modules loaded on this system include several to support the Ensoniq 1371 sound card that is installed (es1371, ac97_codec, gameport, and soundcore). There are also modules to support the IDE CD-ROM drive that runs in SCSI emulation on this system (scsi_mod, sr_mod, nuscsitcp, and ide-scsi). To find information about any of the loaded modules, you can use the modinfo command. For example, you could type the following: # modinfo -d es1371 “ES1371 AudioPCI97 Driver” Not all modules have descriptions available. In this case, however, the es1371 module is described as an ES1371 AudioPCI87 Driver. You can also use the -a option to see the author of the module or -n to see the object file representing the module. The author information often has the e-mail address of the driver’s creator, so you can contact the author if you have problems or questions about it.
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The following is a list of actions kudzu takes when a device is removed: Network Removes the alias for the Ethernet interface (eth0, eth1, etc.). SCSI Removes the alias for the SCSI host adapter (scsi_hostadapter). Mouse Removes the link to /dev/mouse. Modem Removes the link to /dev/modem. CD-ROM Removes the link to /dev/cdrom. Scanner Removes the link to /dev/scanner. The only known problems with kudzu have to do with probing serial devices and video cards on a running Red Hat Linux system. If serial devices or older video cards are in use while kudzu is probing them, activity on those devices can be disturbed. Configuring Modules In a perfect world, by the time you have installed and booted Red Hat Linux, all of your hardware should be detected and available for access. While Red Hat Linux is rapidly moving closer to that world, there are times when you need to take special steps to get your computer hardware working. Red Hat Linux comes with tools for configuring the drivers that stand between the programs you run (such as CD players and Web browsers) and the hardware they use (CD-ROM drives and network cards). The intention is to have the drivers your system needs most often built into the kernel; these are called resident drivers. Other drivers that are added dynamically as needed are referred to as loadable modules. Cross-Reference Chapter 2 contain descriptions of how to rebuild your kernel, including how to place drivers into your system as either resident kernel drivers or to have them available as loadable modules. This section describes how to display, add, and remove loadable modules in Linux. Note Besides providing hardware interfaces, modules can also provide interfaces for file systems, network services, binary formats, and other operating system features. Finding available modules If you have installed the Linux kernel source code (kernel-source package), source code files for available drivers are stored in subdirectories of the /usr/src/linux-2.4/drivers directory. There are several ways of finding information about these drivers: make xconfig With /usr/src/linux-2.4 as your current directory, type make xconfig from a Terminal window on the desktop. Select the category of module you are interested in and click Help next to the driver that interests you. The help information that appears tells you the module name and a description of the driver.
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Reconfiguring Hardware with kudzu When you add or remove hardware from your computer and reboot Red Hat Linux, a window appears during the reboot process advising that hardware has either been added or removed and asking if you want to reconfigure it. The program that detects and reconfigures your hardware is called kudzu. The kudzu program is a hardware autodetection and configuration tool that runs automatically at boot time. If you like, you can also start kudzu while Red Hat Linux is running. In either case, here is what kudzu does: 1. It checks the hardware connected to your computer. 2. It compares the hardware it finds to the database of hardware information stored in the /etc/sysconfig/hwconf file. 3. It prompts you to change your system configuration, based on new or removed hardware that was detected. The following is a list of hardware that kudzu can detect (according to the kudzu README file), followed by a description of what kudzu does to configure the device. Other devices may be detected as well (such as USB devices). Network devices Adds an Ethernet interface alias (eth0, eth1, etc.) if necessary and either migrates the old device configuration or creates a new one. SCSI Adds an alias for scsi_hostadapter. Video card Runs the Xconfigurator command to configure the video card. Sound card Runs the sndconfig command to configure and test the sound card. Mouse Links the new mouse device to /dev/mouse and runs the mouseconfig command to configure and test the mouse. Modem Links the new modem device to /dev/modem. CD-ROM Links the CD-ROM device to /dev/cdrom. Scanner Links the new scanner device to /dev/scanner. Keyboard Runs the kbdconfig command to reconfigure the keyboard. Also, if you are using a serial console, it makes sure /etc/inittab and /etc/securetty are configured to be used by a serial console.
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Figure 10-3: Set up TCP/IP network connections with the Network configurator. Cross-Reference While the Network configurator (netconf) window works well in most cases, I recommend that you refer to Chapter 15 before you configure your networking interfaces. That chapter contains more in-depth descriptions on setting up a network and recommends using some different tools for configuration. User Account configurator (userconf) Manage your computer s user accounts. It lets you add regular user and group definitions, then assign passwords to users. You can also add special user accounts, such as those that let you automatically log in and start a PPP, SLIP, UUCP, or POP connection. Figure 10-4 shows the User Account configurator window. Figure 10-4: Add regular and special user accounts in the User Account configurator.
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commands, file permissions, modules, system profiles, and linuxconf add-ons are configured and used in linuxconf. Date & time Change the date, time, and time zone from this task. When you have made changes to any configurations that require programs to be restarted, you can click Act/Changes. Then click the Activate the Changes button that appears. If errors are reported, click Yes to view those messages. Then you can view the log that was created from the changes. Linuxconf subsection commands Instead of using linuxconf, you can use commands to go directly to particular configuration sections. Here those commands: Filesystem configurator (fsconf) Configures the file systems that your computer can access. This can include local drives and NFS volumes (mounted from remote computers). It also allows you to configure swap files and partitions, set quota defaults, and check the permissions of certain files. Figure 10-2 shows the Filesystem configurator window. Figure 10-2: Mount local and remote file systems using Filesystem configurator. Network configurator (netconf) Configures your TCP/IP network. It lets you add everything you need to create connections to modems and Ethernet LANs. You can set up the Domain Name System (DNS), routing and gateways, and serial communications (PPP, SLIP, or PLIP). Figure 10-3 shows the Network configurator window.
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Another network service you can configure includes configuring an IPX interface. IPX is a networking interface protocol popular with NetWare servers. If you make any changes to your network configuration, you can activate those changes by clicking the Act/Changes button. You can either preview what needs to be done to activate the changes or click Activate the changes for the changes to be implemented and the network to be restarted. Under Server tasks, you can share your file systems with other computers on the network (using NFS) and set up IP aliases for virtual hosts. Other linuxconf configuration tasks Besides networking tasks, you can select from several other basic system tasks in linuxconf. Under User Accounts, you can add normal user accounts, special user accounts, and policies regarding user accounts. Under File systems, you can add definitions of mountable local drives or NFS file systems (from remote systems) that can later be added to or removed from your system (using mount and unmount tasks described in the Control section). Finally, you can add parameters that have an impact on how your Linux system boots. Linuxconf control tasks The Control section of linuxconf lets you work with Linux features that change the ongoing operation of your Red Hat Linux system. Here are some of the tasks you can do from this section: Activate configuration For changes that you make to take effect, some services have to be stopped and restarted. This task checks what needs to be restarted, based on the changes you have made, then restarts those services when you say you are ready. Shutdown/Reboot Use this task to either shut down and halt your computer or reboot it. Control service activity You can enable or disable a variety of network services by selecting this task. Mount/Unmount file systems Any local or NFS file systems you configured to be mountable (in the Configuration section) can be mounted or unmounted using these tasks. Configure superuser scheduled tasks You can add commands that are run at a set schedule (using the cron facility) as the root user by adding entries under this task. Archive configurations With this task, you can archive the configuration files you have set up so that you can recall these saved configuration files later. This can be used to get you back to a sane state if your configuration files get wrecked. Switch system profile You can recall a past archive of configuration files (and save the current configuration files) using this task. Linuxconf management Select tasks from this section to change the way configuration files,
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Ctrl+X If the current field contains a pop-up selection list (indicated by a down arrow), this key opens the list. F3 Escapes from any dialog. Ctrl+A Goes to the beginning of the line. Ctrl+B Goes up one page. Ctrl+D Deletes the current character. Ctrl+E Goes to the end of the line. Ctrl+F Goes down one page. Ctrl+K Deletes text to the end of the line. Linuxconf configuration tasks Under the configuration section in linuxconf are tasks for setting up your network, creating user accounts, working with file systems, initializing system services, and choosing boot modes. Networking tasks are divided into those that apply to your computer as a client and those that apply to it as a server. Linuxconf networking tasks Client networking tasks let you view and configure information associated with your computer s host name, the network interfaces that are attached to your computer, and the routes you can use to get to other hosts and networks. Click the plus sign (+) next to Client tasks and select Host name and IP network devices. From the window that appears, here are some of the items you can change: Hostname Your hostname is how other computers on the network identify yours. It can contain the full hostname.domainname form. Adaptor The network interfaces (i.e., Ethernet cards, PPP dial-up connections, etc.) that give you access to the network can be viewed by clicking the Adaptor tabs on this form. The information you would need to enter in this form is described in detail in Chapter 15, Setting Up a Local Area Network. Your system resolves Internet host names into IP addresses by identifying DNS servers that can do name to address resolution. Click the Name Server Specification (DNS) task to add your default domain and one or more name servers. You can also indicate which domains to search for addresses. Under Routing and Gateways, you can define how your networking requests are routed across gateway machines (those that are connected to your subnetwork and another subnetwork) to reach beyond your local network. You can also specify routes to other local area networks.
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