+ Point 6: Linux Administration
[6/12/2009 06:02:00 PM | ]

A Linux computer can be configured to manage end-users and their passwords and various other tasks, such as network-related tasks, user-related tasks, and file system-related tasks. In addition, you can use Pluggable Authentication Module (PAM) to authenticate end-users on a range of services, such as telnet, File Transfer Protocol (FTP), and HyperText Transfer Protocol (HTTP).

This ReferencePoint discusses administering Linux using Linuxconf, installing new packages, and configuring server operations, such as starting and stopping services. It also explains how to apply patches to the kernel.

Linuxconf

Linuxconf is an administrative utility shipped with most distributions of Linux. It can be invoked from the shell or a graphical user interface (GUI), such as K Desktop Environment (KDE) or GNU-Network Object Model Environment (GNOME).


Note

You need to log on as the root user to perform administrative tasks.

Linuxconf allows you to configure, control, and view the status of various services and devices in Linux, as shown in Figure 2-4-1:

This figure shows the Linuxconf window that allows you to perform administrative tasks in Linux.
Figure 2-4-1: The Linuxconf Window

Use Linuxconf to perform tasks related to networking, user management, file systems, associated peripherals, and booting as well as miscellaneous tasks.

Network Related Tasks

Linuxconf lets you change network parameters, such as host name, Domain Naming Service (DNS), routing, Internetwork Packet Exchange (IPX), and Point-to-Point Protocol (PPP). To change the network parameters, click the Networking button in the Linuxconf window. The Network configurator window of Linuxconf appears, as shown in Figure 2-4-2:

This figure shows the Network configurator window of Linuxconf that allows you to customize network related parameters for Linux.
Figure 2-4-2: The Network configurator Window

Host Name and IP Network Devices

To modify the host name related settings for the server, click the Host name and IP network devices button in the Network configurator window. The Host name and IP devices window appears, as shown in Figure 2-4-3:

This figure shows the Host name and IP devices window. It lets you specify the host name, the domain name, and Ethernet adaptors for the computer.
Figure 2-4-3: The Host name and IP devices Window

This window also lets you specify the Ethernet adaptor to be used. You can configure up to 4 adaptors for use with your computer. It also lets you specify how the host should be assigned an IP address. The host can be assigned an IP address either by specifying it in the window or by configuring the server to assign the address automatically.

Name Server Specification

To change DNS related settings, click the Name server specification (DNS) button. The Resolver configuration window appears, as shown in Figure 2-4-4. This window lets you specify DNS related settings, such as the default domain, IP of name servers, and search domains:

This figure shows the Resolver configuration window in which you can specify various DNS related settings.
Figure 2-4-4: The Resolver configuration Window

The DNS related settings enable you to specify how the computer will look up addresses of other machines.

The default domain is the name of the domain that this machine belongs to. The IP of name server 1 option allows you to specify the name server for the network that will resolve all host names to IP addresses. IP of name server 2 is an optional specification, which allows you to specify other DNS server that can be used in case the primary name server is shutdown or has crashed. The search domain options are optional and must always be left empty, except in rare cases.

Routing and Gateways

To change routing and gateway related settings, click the Routing and gateways button. The Routes to other networks window appears, as shown in Figure 2-4-5. This window lets you specify settings related to routing:

This figure shows the Routes to other networks window that lets you specify routes to other networks, hosts, and alternate local nets.
Figure 2-4-5: The Routes to other networks Window

Note

Routing enables specifying the path to be followed by the network traffic to reach the destination hosts or networks. The Routes to other network windows also enables specifying routing parameters for the network.

IPX Interface Setup

IPX needs to be set up if the network uses the IPX/Netware protocol. The IPX interface configuration window allows you to specify the IPX adaptor and its configuration. It also allows you to specify the internal net number and the internal node number required for Netware.

To modify the IPX interface related settings, click the IPX interface setup button. The IPX interface configuration window appears, as shown in Figure 2-4-6, which lets you specify IPX related configuration settings:

This figure shows the IPX interface configuration window that lets you specify IPX configuration related settings.
Figure 2-4-6: The IPX interface configuration Window

PPP/SLIP/PLIP Configurations

The PPP, SLIP, and PLIP interfaces help a computer establish connection with another computer through a modem or other communication devices. For example, a connection based on PPP interface using the /dev/ttys0 port allows the computer to establish a connection to an Internet service provider (ISP) using the modem. SLIP and PLIP are rarely used.

The PPP/Slip/Plip configurations window allows you to add connections to another computer via a modem or any other communication device. These devices can operate on PPP, SLIP, or PLIP interfaces. These interfaces help the computer establish a connection to another computer.

To modify the PPP/SLIP/PLIP related configurations, click the PPP/Slip/Plip button. The PPP/Slip/Plip configurations window appears, as shown in Figure 2-4-7:

This figure shows the PPP/Slip/Plip configurations window that lets you add a connection shortcut for a computer.
Figure 2-4-7: The PPP/Slip/Plip configurations Window

User Related Tasks

Use Linuxconf to perform user-related tasks, such as add, delete, and modify users. You can also use it to set policies for passwords, user accounts, and shells.

To perform user-related tasks, click the Users button in the Linuxconf window. The User account configurator window of Linuxconf appears, as shown in Figure 2-4-8:

This figure shows the User account configurator window. It lets you perform tasks related to user management.
Figure 2-4-8: The User account configurator Window

Adding Users

To add users or view user information, click the User accounts button. The User accounts window appears, as shown in Figure 2-4-9:

This figure shows the User accounts window. It enables adding new users and modifying options for them.
Figure 2-4-9: The User accounts Window

To add a user to the computer, click the Add button in the User accounts window. The User account creation window appears, as shown in Figure 2-4-10:

This figure shows the User account creation window.
Figure 2-4-10: The User account creation Window

When adding new user accounts, specify:

  • Login name, which is used by the user to log on to the computer.

  • Full name of the user.

  • Group to which the user belongs.

  • Home directory of the user, where all files and personalization settings will be stored. The home directory is the default directory that is open when the user logs on to the computer.

  • Command interpreter for the shell the user will use. It can be any shell installed on the computer, such as bash, sh, ksh, and rsh.

  • User ID of the user assigned for specific tasks, such as quota management.

When adding users, also specify optional parameters for the account, such as account expiration, password expiration, and must keep days that make sure the user logs on regularly.

You can also set privileges for the account, such as: may use linuxconf, may activate config changes, and may shutdown. These options are required when assigning specific privileges to certain accounts. For example, John Smith, a Web server administrator, may require privileges for Apache administration to add, modify, and delete content on the Web site.

Figure 2-4-11 shows the Privileges Tab of the User account creation window:

This figure shows the Privileges Tab of the User account creation window.
Figure 2-4-11: The Privileges Tab of the User account creation Window

Viewing and Modifying User Information

User information of the account, such as Login name, Full name, and group, can be modified. To view or modify the information of an account, click the account name. Figure 2-4-12 shows the User information window for the user, news:

This figure shows the User information window.
Figure 2-4-12: The User information Window

Adding Groups

Users can be classified in groups, which enables you to collectively assign permissions to members of a group. To add groups, click the Group definitions button. The User groups window appears, as shown in Figure 2-4-13:

This figure shows the User groups window.
Figure 2-4-13: The User groups Window

Click the Add button to add a group. The Group specification window appears, as shown in Figure 2-4-14:

This figure shows the Group specification window.
Figure 2-4-14: The Group specification Window

When adding new groups, specify:

  • Group name for the new group. No two groups can have the same name.

  • Group ID for the new group. No two groups can have the same ID.

  • Alternate members for the group, such as root, bob, or Cathy.

You can also specify the directory for each group.

Viewing and Modifying Group Information

To view the information pertaining to a group, click the group name. You can modify the Group name, the Group ID, and alternate members for that group. Figure 2-4-15 shows the Group specification window for the user, news:

This figure shows the Group specification window for the user news. It allows you to view and modify Group name, Group ID, and Alternate members for the group.
Figure 2-4-15: The Group Specification Window for the User news

Changing Root Password

To change the root password for the system, click Change root password button. The Changing password window appears, as shown in Figure 2-4-16:

This figure shows the Changing password window.
Figure 2-4-16: The Changing password Window

Caution

Be sure not to lose the root password because you can't make any changes without it.

Special Accounts

Linux supports special accounts that are used for specific services, such as PPP, Post Office Protocol (POP), and Unix-to-Unix Copy (UUCP).

To add, view, delete, or modify special accounts, click the Special accounts tab in the User account configurator window. Figure 2-4-17 shows the Special accounts tab of the User account configurator window:

This figure shows the Special accounts tab of the User configurator window. It lets you add, view, delete, and modify special accounts such as PPP, SLIP, and UUCP accounts.
Figure 2-4-17: The Special accounts Tab of the User account configurator Window

Note

The method to add, modify, view, or delete special user accounts is the same as that for normal accounts.

Policies

Linuxconf lets you specify policies for user accounts and passwords, such as minimum length for passwords, access permissions, and minimum number of non-alphabetic characters in passwords. Figure 2-4-18 shows the Policies tab of the User account configurator window:

This figure shows the Policies tab of the User account configurator window, which lets you set policies for user accounts, passwords, and access permissions.
Figure 2-4-18: The Policies Tab of the User Account configurator Window

The policies tab lets you set:

  • Password & account policies: For user accounts and passwords.

  • Available user shells: For users, shows the list of shells that are installed on the system and the default shell that must be used when a user logs on.

  • Available PPP shells: For special accounts. It shows the list of PPP scripts installed on the system and the default shell that must be used for a PPP account.

  • Available SLIP shells: For special accounts. It shows the list of SLIP scripts installed on the system and the default shell that must be used for a SLIP account.

  • Message of the day: Is shown every time a user logs on. It is a welcome message set by the root user.


File System Related Tasks

Linuxconf lets you perform file system related tasks. It can be used to configure settings, such as drives in the computer that can be accessed from the workstation and drives in the Network File System (NFS). To perform file system related tasks, click the File systems button in the Linuxconf window. The File system configurator window appears, as shown in Figure 2-4-19:

This figure shows the Filesystem configurator window, which lets you perform file system related tasks such as configuring access for local and network drives.
Figure 2-4-19: The Filesystem configurator Window

Accessing Local Drives

Linuxconf lets you specify which drives in the system can be accessed from the workstation. Drives are located in the /dev folder of Linux. To access a drive in Linux, you need to first mount it.

To add, view, or delete a local drive, click the Access local drive button. The Local volume window appears, as shown in Figure 2-4-20:

This figure shows the Local volume window. It lets you add, view, or delete local drives that can be accessed from the workstation.
Figure 2-4-20: The Local volume Window

To add a new local drive definition, click the Add button in the Local volume window. The Volume specification window appears, as shown in Figure 2-4-21:

This figure shows the Volume specification window. It lets you add a local drive to the workstation.
Figure 2-4-21: The Volume specification Window

When you add new volumes, specify the:

  • Partition that needs to be mounted. All partitions and non-removable storage devices are listed in the /dev directory.

  • Type of the file system for the volume. A volume can be of any of the types supported by Linux, such as ext2, minix, and vfat.

  • Mount point for the volume. A volume can be mounted anywhere in the Linux file system, but it is generally mounted in the /mnt directory.

To view, modify, or delete volumes, click the volume entry in the Local volume window. This shows the Volume specification window. Click the Options tab and set options for the volume, such as Read only, User mountable, and Not mount at boot time, as shown in Figure 2-4-22:

This figure shows the Options tab of the Volume specification window.
Figure 2-4-22: The Options Tab of the Volume specification Window

Accessing NFS Drives

Linuxconf allows you to specify which NFS drives can be accessed from the workstation. NFS drives are located on the network. To access a NFS drive, click the Access nfs volume button. The NFS volume window appears, as shown in Figure 2-4-23:

This figure shows the NFS volume window.
Figure 2-4-23: The NFS volume Window

To add a new NFS volume definition, click the Add button in the NFS volume window. The Volume specification window appears, as shown in Figure 2-4-24:

This figure shows the Volume specification window. It lets you add NFS volumes to the system that can be accessed from the workstation.
Figure 2-4-24: The Volume specification Window

When you add NFS volumes, specify the:

  • Server in which the NFS volume exists.

  • Volume in the server that needs to be mounted.

  • Mount point where the volume needs to be mounted on the system.

Set options for the NFS volume, such as, Soft mount, Background mount, and Nolock mount, as shown in Figure 2-4-25:

This figure shows the NFS options Tab of Volume specification window.
Figure 2-4-25: The NFS options Tab of the Volume specification Window

Configuring Swap Drives

Swap drives are used by Linux as virtual memory. Linuxconf enables configuring swap drives and files. To add, view, or delete swap files and drives, click the Configure swap files and partitions button. The Swap space window appears, as shown in Figure 2-4-26:

This figure shows the Swap space window of Linuxconf, which lets you add, delete, and modify swap drives.
Figure 2-4-26: The Swap space Window

To add a swap drive, click the Add button in the Swap space window. This shows the Volume specification window, as shown in Figure 2-4-27:

This figure shows the Volume specification window.
Figure 2-4-27: The Volume Specification Window with a New Swap Drive

When adding swap drives to the system, specify the partition in which the swap partition needs to be created.


Miscellaneous Tasks

Linuxconf lets you perform miscellaneous tasks for Linux, such as setting the default run level, configuring the kernel and system logs. To do so, click the Miscellaneous button in the Linuxconf window. The Miscellaneous services window appears, as shown in Figure 2-4-28:

This figure shows the Miscellaneous services window.
Figure 2-4-28: The Miscellaneous services Window

Setting Default Runlevel

The run level in Linux specifies the default mode in which the system should boot. Set the run level for the system for maintenance, text console, or a graphical workstation. Setting the run level enables Linux allocate the resources more effectively. To select a run level for the system, click the Default runlevel button. The Init default runlevel window appears, as shown in Figure 2-4-29:

This figure shows the Init default runlevel window for the system, which lets you specify into which level the system must boot.
Figure 2-4-29: The Init default runlevel Window

The default runlevels available in Linux are:

  • Run level 1 Single user/Maintenance: Is used when only a single user is using the system or if the system is down for maintenance.

  • Run level 2: Is left empty and can be customized to suit the requirements of a system.

  • Run level 3 Text Console: Provides only a shell console. It is used in situations such as development or acting as a server only, where GUI is not required.

  • Run level 4: Is left empty and can be customized to suit the requirements of a system.

  • Run level 5 Graphical workstation: Is used when all services and graphics of the system are used. This is the normal run level for the system.

Configuring the Kernel

Using Linuxconf, set options for the kernel, such as maximum file handles, shared memory size, and maximum processes. To set kernel options, click the Kernel Configuration button. The Kernel Configuration window appears, as shown in Figure 2-4-30:

This figure shows the Kernel Configuration Window, which lets you set options for the kernel that alter system performance.
Figure 2-4-30: The Kernel Configuration Window

The File System tab enables specifying the maximum number of file handles that the kernel can handle. This number specifies to the kernel how many I/O operations it can perform at a point of time. This option is higher for systems being used for services such as Web servers.

The General tab, as shown in Figure 2-4-31, lets you set generic options for the kernel:

This figure shows the General tab of the Kernel Configuration window.
Figure 2-4-31: The General Tab of the Kernel Configuration Window

The options are:

  • Ctrl-alt-del: Specifies whether or not to enable rebooting by hitting the Ctrl-alt-del key combinations.

  • Shared memory size: Specifies the size of the shared memory that can be used.

  • Maximum processes: Specifies the maximum number of processes that can be executed.


Caution

An invalid configuration can lead to a system crash. Make sure you do not change these settings unless you are absolutely sure of what you are doing.

Configuring System Logs

Linuxconf lets you specify the location of the log files for various services. You can also specify options to synchronize the file after every message. To configure system logs, click the System logs button. The Syslog files window appears, as shown in Figure 2-4-32:

This figure shows the Syslog files Window, which lets you configure system logs.
Figure 2-4-32: The Syslog files Window

When you add a new log file, specify:

  • Syslog file or destination: Indicates where the file contents will be stored. If it is the syslog file, entries will be appended. If it is a new destination, a new file is created and the content is stored.

  • Selections: Indicates what will be stored in the log file.


Boot Related Tasks

Linuxconf allows you to perform boot related tasks, such as whether or not the system should boot with graphics enabled.

To set the boot mode, click the Boot button in the Linuxconf window. This shows the Boot configuration window. Click the Default boot mode button. The Boot mode configuration window appears, as shown in Figure 2-4-33:

This figure shows the Boot mode configuration window.
Figure 2-4-33: The Boot mode configuration Window

The boot mode options are:

  • Boot time menu enabled: Enables Linux to show a list while booting that displays the various operating systems, and boot modes for Linux.

  • Default operation mode: Specifies the default boot mode. The available modes are Graphic & Network, and Text mode & Network.

  • Delay to activate: Specifies the duration for which the boot menu should be shown before the system boots from the default mode.

  • Prompt timeout: Specifies the duration for which the prompt should be shown before the GUI boots.


Installing and Uninstalling Packages

Packages in Linux are shipped in the .rpm format. These are installable files that decompress and install the specified software in the system automatically.

Packages can be installed and uninstalled using the rpm command run in the shell. You can also install and uninstall software in GUI mode using the software manager package provided with the specific Linux distribution.

Installing Packages Using Shell

The rpm command provides a variety of options that can be used to perform package related tasks. To install a package on the system, execute the command:

rpm –Uvh

This command installs the specified package on the system. The –U parameter specifies rpm to install the package. The –v parameter shows the lists of files in the package in verbose mode. The –h parameter shows the hash marks as the package installs.

For example, executing the command:

rpm –Uvh qmail-1.03.rpm

installs the qmail program on the system, and shows list of files and hash marks while installing.


Note

If you want to use automatic install, the package should be in .rpm format.

Installing Packages Using Software Manager

To install packages using the Software Manager provided with Mandrake Linux:

  1. Open Mandrake Control Center.

  2. Select System from the left pane.

  3. Click the Software Manager icon. The Software Manager window appears, as shown in Figure 2-4-34:

    This figure shows the Software Manager window. It lets you install new packages and uninstall existing ones.
    Figure 2-4-34: The Software Manager Window

  1. Click the Installable tab. It shows the list of packages that can be installed. You can add new sources of packages by clicking the Define sources button.

  2. Select the package that needs to be installed. It will be shown in the Selected sub-window. Click the Install/Remove button. Software Manger installs the selected package.

Uninstalling Packages Using Shell

Uninstalling removes a package and all dependent files from the system. Use the rpm command to uninstall packages from the system. To uninstall a package from the system, execute the command:

rpm –e

This command uninstalls the package from the system. For example, executing the command:

rpm –e postgresql

removes the postgresql package from the system.

Uninstalling Packages Using Software Manager

Use the Software Manager provided with Mandrake Linux to uninstall packages from the system. To uninstall packages using Software Manager:

  1. Open the Software Manager in the Control Center.

  2. Click the Installed tab. It shows the list of software that is currently installed.

  3. Select the package to uninstall. It will be shown in the Select sub-window. Click the Install/Remove button. Software Manager uninstalls the selected package.

Starting and Stopping Services

Various services such as FTP, HTTP, and telnet run in Linux. The Mandrake control center allows you to start, stop, and restart services at any point.

Starting Services

Services can be started using the Mandrake Control Center. To start a service:

  1. Open Mandrake Control Center.

  2. Select System from the left pane.

  3. Click the Services icon. The Mandrake Control Center: Services and daemons window appears, as shown in Figure 2-4-35:

    This figure shows the Services and daemons sub-menu.
    Figure 2-4-35: The Mandrake Control Center: Services and daemons Window

    To start a service:

    • Select a service and click the Start button. The services and daemons sub-window shows the list of services installed on the system along with their current status. The service starts successfully if no errors are encountered. You can also set a service to start at boot-time by selecting the On boot radio button.

    • Specify the command: start at the shell prompt. For example, 

      /etc/rc.d/init.d/sendmail start

Stopping Services

Services can be stopped using Mandrake control center. To stop a service:

  1. Open the Mandrake Control Center.

  2. Select System from the left pane.

  3. Click the Services icon. This shows Services and daemons sub-window.

  4. Select a service and click the Stop button. The service stops and unloads from memory.

To stop services from the shell, use the command stop. For example, 

/etc/rc.d/init.d/sendmail stop

Linux Kernel Patches

The kernel is the core software that runs an operating system. It is accountable for flexibility, security, and generic features of the operating system. The Linux kernel, by default, has been designed to be secure. It can be customized to suit particular needs of a system.

For more information on Linux Kernel, see the Understanding Linux Kernel ReferencePoint.

Downloading the Kernel Patch

There are several patches available for Linux kernels. Kernels are classified as experimental and stable versions. Stable kernels have an even number in the second place in their version numbers. For example, 2.4.2 is a stable kernel because it is denoted by 4 in the second place. Experimental kernels have an odd number in the second place in their version numbers. For example, 2.3.2 is an experimental kernel because it is denoted by 3 in the second place.

The latest stable version of kernel at this point is Linux kernel version 2.4.19. Download the patch-2.4.19.gz file. You can download it at http://www.kernel.org.

Unpacking and Configuring the Kernel Patch

The kernel patch is in the gunzip format. It needs to be unpacked before it can be installed.

To unpack the downloaded patch:

  1. Copy the downloaded file into the /usr/src directory using the command:

    cp patch-2.4.19.gz /usr/src

  1. Unpack the kernel using the command:

    tar xzpf patch-2.4.19.gz

These commands copy the downloaded file into the /usr/src directory and extract the contents of the archive there.

To configure the new kernel patch, execute the make command using the command:

make config

This command allows you to specify which portions of the kernel are to be enabled or disabled. Typing yes or no for individual options of the kernel does this.

You could also use a menu-based text interface or an X-windows based GUI interface for making the configuration. To use a menu-based text interface, execute the command:

make menuconfig

This command allows you to specify kernel configuration options in a menu- based text interface.

To use an X-windows based GUI interface, execute the command:

make xconfig

This command lets you specify kernel configuration options in an X-windows based GUI interface.

For more information on configuring the kernel, see the Configuring and Compiling the Linux Kernel ReferencePoint.

Compiling and Installing the Kernel Patch

Compile the kernel after configuring it. The new kernel may have dependencies, which need to be installed to ensure proper functioning. The old kernel files present in the system need to be removed before the new kernel can be installed. Therefore, a compiled binary image of the new kernel needs to be generated to enable the system to boot the new kernel. If you enable any modules while configuring the patch, they need to be compiled and installed. To compile and install the kernel:

  1. Generate the list of dependencies using the command:

    make dep

  1. Clean the old kernel files in the system using the command:

    make clean

    This command removes the compiled files of the old kernel present in the system.

  1. Create the binary kernel image using the command:

    make bzImage

    This command creates the compiled binary image of the new kernel. This binary kernel image is used while booting.

  1. Compile and install modules using:

    make modules_install

    This command compiles the modules and installs them on the system.

Configuring LILO

Linux Loader (LILO ) is a boot loader that loads Linux and other operating systems present on the system. You need to configure LILO to boot the newly patched kernel that has been installed. To configure LILO:

  1. Copy the compiled binary kernel image to a file called vmlinuz-new in the root directory using the command:

    cp bzImage /vmlinuz-new

    This command copies the compiled binary image of the new kernel to the root directory.

  1. Insert the lines into the /etc/lilo.conf file.

    image=/vmlinuz-new
    label=linux-new
    root=/dev/hda3
    vga=normal
    read-only

    These lines in the lilo.conf file specify options for LILO. The image=/vmlinuz-new option allows LILO to boot the new kernel. The label=linux-new is shown when the system boots and the LILO menu is shown. This is necessary if there is more than one kernel that can be booted. The root option specifies where the Linux file system is located. The vga=normal option specifies to LILO to boot in normal graphics mode. The read-only parameter specifies that the kernel is read-only.

  1. Update the LILO boot-map by executing:

    /sbin/lilo

    LILO creates a boot-map for the new kernel when it is executed at the shell prompt. LILO boots the new kernel when the system is rebooted.