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Some error checking is done. In many cases, linuxconf will prevent you from entering invalid values in the fields. Options are offered. If, for example, you are adding a network interface, you can click a pull-down menu to select from the interfaces that Linux knows about (such as PPP or Ethernet). Administrative activities are divided into three major categories in linuxconf: Config, Control, and Status. Config activities let you set up your network interfaces (for both client and server features), work with user accounts, configure file systems, and manage how Linux boots. Control activities let you work with features that have already been configured, including starting and stopping services, mounting/unmounting file systems, and controlling the files and systems used by linuxconf. Status activities let you view system logs. Starting linuxconf You can start linuxconf from the System menu (Programs System LinuxConf) or from a Terminal window (linuxconf &). Figure 10-1 shows the LinuxConf window. Figure 10-1: linuxconf centralizes Linux administration in one graphical window. Tip linuxconf can also be operated from Netscape or another Web browser. To allow that, you must simply allow the local or remote computer to access the service. To use the service from a remote computer, the remote computer requests port number 98 from your computer. For example, if the linuxconf server is named comp1, you can start linuxconf by typing the Web address: http://comp1:98/ from the remote host. Before you can use the service, you need to enter the root password. You need to activate the linuxconf service to allow a user from a remote computer to use linuxconf. From the linuxconf Config tab, select Networking, Misc, and Linuxconf network access. Then click Enable network access and type the names of the hosts and/or networks you want to allow to access the service. Next, you need to edit the /etc/xinetd.d/linuxconf-web file and change disable = yes to disable = no. Then type /etc/init.d/xinetd restart to make the linuxconf Web service available. To choose a task to perform in linuxconf, click the task in the left column. A form representing the task appears on the right. Select the options you want and fill in the necessary information. Accept the changes by clicking Accept or OK. Click Cancel when you are done. You can also use the following function keys and control keys with linuxconf:
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swaps Shows the swap partitions that are currently mounted on your system, along with their sizes and the amount of space being used. net/dev Displays the contents of the net/dev file to see your active network interfaces. sys/* Looks at the contents of these directories for information related to debugging (debug), devices (dev), file systems (fs), the kernel (kernel), networks (net), and processes (proc). The net directory contains some of the most useful information. Go to /proc/sys/net/ipv4 and list the contents of these files to see when certain features are turned on or off. For example, ip_forward will tell you if IP forwarding is turned on for your computer (0 for off or 1 for on). Graphical Administrative Interfaces To try to simplify Linux administration, several graphical administrative utilities are now available. These interfaces attempt to organize the information you need to get a whole job done in one place. The interface handles putting the information you enter into the correct configuration files and setting up the correct commands to run. Graphical interfaces are a step in the right direction toward making Linux useable by the general population. The problem is, however, that these don t yet allow you to do everything you need to do, so you will often find yourself having to edit a configuration file by hand after you have entered the information into that file using a graphical application. You will find that you need to do this less for simple tasks (such as adding a user account) than you will for more complex tasks (such as configuring servers). Another downside of graphical administrative interfaces in Linux is that they tend to cause versions of Linux to diverge. For example, the configuration files created when you set up a dial-out Internet connection using PPP with the Network configurator in Red Hat Linux are different from the files you would create setting up PPP on a different version of Linux. This can make it a bit difficult to get information on your particular situation. The following sections describe the major graphical interfaces used to do administration for Red Hat Linux. Using linuxconf The most complete graphical utility for working with Red Hat Linux is linuxconf. It contains features for configuring networking (client and server tasks), creating user accounts, and working with the file system. Note Red Hat is phasing out support for linuxconf. In fact, unless you do an “everything” install of Red Hat Linux, it’s likely that linuxconf isn’t even installed on your system. If linuxconf is not found, you can install it from the second Red Hat Linux installation CD (CD-2). As Red Hat creates GUI interfaces to replace linuxconf features (particularly in the area of network configuration), you should consider using those tools instead of linuxconf. As a GUI, linuxconf isn t fancy. Don t expect to see lots of icons or to be able to drag and drop items on the display. It does, however, offer some advantages over just editing configuration files directly: Configuration and control tools for many different features are all contained in one place. Just click an activity in the left column and a form for configuring the item appears in the right column. You don t have to search blindly in /etc for the right files to edit.
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Cross-Reference Chapter 11 contains information on how to set up and manage users in Linux. The kernel The heart of the Linux system is called the kernel. The kernel provides the interface between you (and the programs you run) and the hardware (hard disks, RAM, network cards, etc.). Using the /proc file system, you can find out a lot of information about your kernel, by simply displaying the contents of /proc files. For each process currently running in Linux, there is a directory in /proc consisting of the process number for the running process. (Type ps aux | more to see the running processes and their associated PID numbers.) The /proc directory contains other files that are connected to certain features (such as networking, SCSI devices, and other components). To display the contents of /proc files, you can use the cat command. For example, change to the /proc directory (cd /proc), then type the following command: # cat version The output of this command contains the Linux version number and other information (such as the compiler version and the system install date). There are other files under the /proc directory structure that you can also list to find out interesting information about your running Linux system. Here are a few files that you can “cat” to get information: cpuinfo Tells you the type of CPU in your computer, the speed (CPU MHz), the CPU family, and other information related to your computer s processor. devices Displays the character and block devices currently being used on your computer, along with their major device numbers. ioports Shows the I/O port addresses for the devices on your computer. meminfo Contains information about memory usage and swap space usage. You can see the total amounts of memory and the how much is currently being used. modules Shows a list of modules that are currently installed in the system. mounts Displays the file systems that are currently mounted in the system. partitions Contains the names of your hard disk partitions, the number of blocks in each partition, and each partition s major and minor device number. pci Lists the PCI devices installed in your computer. You can see the bus device numbers, names, and other information. For cards that are installed (such Ethernet or modem cards), you can see their IRQs, addresses, and other information.
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Current date and time Processor type The following is an example of the uname -a command (the -a prints all the information at once): $ uname -a Linux mycomputer 2.4.6-3.1 #1 Sat Oct 27 19:09:11 EDT 2001 i686 unknown The system s hostname is used to identify your computer (in particular, it is used by remote systems to contact you over a network). The Linux release number (2.4.6-3.1) identifies the release of the Linux kernel that you have installed. Check this number to make sure you have the latest kernel. You can change your computer name using the hostname command as follows: # hostname yourcomputer The hostname is read automatically by different programs that need to indicate what computer is being used. For example, your shell command line prompt probably automatically displays the hostname. You can also print other information that relates to how your computer is named from the perspective of the network. For example, dnsdomainname lists your domain name (used for the Internet). If your computer uses NIS services, you can print your NIS domain name with the domainname command. Disk partitions and sizes Before Red Hat Linux can be installed, areas of the hard disk are divided up to hold Linux data, swap space, and any other operating systems you may want on your computer. These divisions are called partitions. You can view and change your disk partitions, using the fdisk command (described later in this chapter). If you have multiple partitions, you need to watch the percentage of space used on each mounted partition. If, for example, space runs out on a separate /var file system, programs that need to spool data (such as mail and printing utilities), write to log files in /var/log, or use temporary file space in /var/tmp may fail. Even if plenty of space is available in the root partition or another partition, if the assigned partition runs out of space, it won t draw from other partitions. More information on monitoring and managing file systems is included later in this chapter. Users User login accounts are listed in the /etc/passwd file. You can list the contents of this file to see what users have accounts on your Linux system as follows: # less /etc/passwd Administrative logins (up to UID 100 in the third colon-separated field) should make up most of the first few entries in this file. Regular user accounts (with UIDs above 100) are usually added in after the administrative accounts. As an administrator of a multiuser Red Hat Linux system, you need to make sure that user accounts are kept up to date. To keep your Red Hat Linux system secure, you need to remove users when they leave your organization (or at least deactivate their passwords if their home directories still contain information that your organization needs).
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Current date and time Processor type The following is an example of the uname -a command (the -a prints all the information at once): $ uname -a Linux mycomputer 2.4.6-3.1 #1 Sat Oct 27 19:09:11 EDT 2001 i686 unknown The system s hostname is used to identify your computer (in particular, it is used by remote systems to contact you over a network). The Linux release number (2.4.6-3.1) identifies the release of the Linux kernel that you have installed. Check this number to make sure you have the latest kernel. You can change your computer name using the hostname command as follows: # hostname yourcomputer The hostname is read automatically by different programs that need to indicate what computer is being used. For example, your shell command line prompt probably automatically displays the hostname. You can also print other information that relates to how your computer is named from the perspective of the network. For example, dnsdomainname lists your domain name (used for the Internet). If your computer uses NIS services, you can print your NIS domain name with the domainname command. Disk partitions and sizes Before Red Hat Linux can be installed, areas of the hard disk are divided up to hold Linux data, swap space, and any other operating systems you may want on your computer. These divisions are called partitions. You can view and change your disk partitions, using the fdisk command (described later in this chapter). If you have multiple partitions, you need to watch the percentage of space used on each mounted partition. If, for example, space runs out on a separate /var file system, programs that need to spool data (such as mail and printing utilities), write to log files in /var/log, or use temporary file space in /var/tmp may fail. Even if plenty of space is available in the root partition or another partition, if the assigned partition runs out of space, it won t draw from other partitions. More information on monitoring and managing file systems is included later in this chapter. Users User login accounts are listed in the /etc/passwd file. You can list the contents of this file to see what users have accounts on your Linux system as follows: # less /etc/passwd Administrative logins (up to UID 100 in the third colon-separated field) should make up most of the first few entries in this file. Regular user accounts (with UIDs above 100) are usually added in after the administrative accounts. As an administrator of a multiuser Red Hat Linux system, you need to make sure that user accounts are kept up to date. To keep your Red Hat Linux system secure, you need to remove users when they leave your organization (or at least deactivate their passwords if their home directories still contain information that your organization needs).
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Tip Because most Red Hat Linux administrative features are expected to be administered by the root user, e-mail for other administrative accounts is routed to the root user. If you want other administrative users to receive their own e-mail, delete the aliases for those users from the /etc/aliases file. Here are the administrative logins that are configured automatically for Linux systems. By tradition, these logins are assigned UID numbers under 100. These logins have no passwords by default, so you can t use any administrative login separately until you assign it a password. To make an administrative login useful, you may need to change permissions of some executables, spool files, and log files so that they are owned by the administrative login: lp This user can control some printing features. Having a separate lp administrator allows someone other than the super user to do such things as move or remove lp logs and print spool files. The home directory for lp is /var/spool/lpd. mail This user can work with administrative e-mail features. The mail group has group permissions to use mail files in /var/spool/mail (which is also the mail user s home directory). uucp This user owns various uucp commands (once used as the primary method for dial-up serial communications). It is the owner of log files in /var/log/uucp, spool files in /var/spool, administrative commands (such as uuchk, uucico, uuconv, and uuxqt) in /usr/sbin, and user commands (uucp, cu, uuname, uustat, and uux) in /usr/bin. The home directory for uucp is /var/spool/uucp. bin This user owns many commands in /bin in traditional UNIX systems. This is not the case in Red Hat Linux, because root tends to own most executable files. The home directory of bin is /bin. news This user could be used to do administration of Internet news services, depending on how you set permission for /var/spool/news and other news-related resources. The home directory for news is /var/spool/news. Getting to Know Your System Knowing how your Red Hat Linux system is set up will help you with your task of administering that system. This is especially true if you did not set up the system yourself. This section covers a few commands you can run to understand how a Linux system is configured. Hostname and Linux version The uname command can print some basic information about your Linux system. This information can include: Operating system name (i.e., Linux) System s host name Linux release number
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The main utilities for logging error and debugging messages for Linux are the syslogd and klogd daemons. General system logging is done by syslogd. Logging that is specific to kernel activity is done by klogd. Logging is done according to information in the /etc/syslog.conf file. Messages are typically directed to log files that are usually in the /var/log directory. Here are some common log files from that directory and the messages they contain: boot.log Contains messages related to system services starting and stopping when Linux boots up and shuts down, respectively. cron Contains messages output by the cron command (which is used to run tasks at set times). Here you can see when tasks start and any error conditions that may have occurred. dmesg Contains boot-up messages that can be useful in debugging hardware failures. (You can run the dmesg command to see these messages.) maillog Activities of the sendmail daemon (which forwards e-mail to other computers) are logged in this file. messages Messages associated with many daemon processes are directed to the messages file. secure Contains messages that may indicate security breeches. Connections from remote hosts are logged, as are attempts to log in to your system. xferlog Shows which files have been transferred to and from your FTP server. Besides these files, messages are also directed to several directories located in the /var/log directory. These directories include: httpd Messages from the Apache Web server are logged to files in this directory. news Messages related to the Internet News service (INN). samba Messages from the Samba service, for sharing files and printers with Windows systems. uucp Messages from the UNIX-to-UNIX copy (uucp) facility are stored here. Using other administrative logins You don t hear much about other administrative logins (besides root) being used with Red Hat Linux. It was a fairly common practice in UNIX systems to have several different administrative logins that allowed administrative tasks to be split among several users. For example, a person sitting near a printer could have lp permissions to move print jobs to another printer if they knew a printer wasn t working. These logins are available with Linux, however, so you may want to look into using them.
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/etc/httpd Contains a variety of files used to configure the behavior of your Apache Web server (specifically, the httpd daemon process). /etc/init.d Contains the permanent copies of run-level scripts. These scripts are linked to files in the /etc/rc?.d directories to have each service associated with a script started or stopped for the particular run level. The ? is replaced by the run level number (0 through 6). /etc/pcmcia Contains configuration files that allow you to have a variety of PCMCIA cards configured for your computer. (PCMCIA slots are those openings on your laptop that allow you to have credit-card-sized cards attached to your computer. You can attach such devices as modems and external CD-ROMs.) /etc/ppp Contains several configuration files used to set up Point-to-Point protocol (so that you can have your computer dial out to the Internet). /etc/rc?.d There is a separate rc?.d directory for each valid system state: rc0.d (shutdown state), rc1.d (single-user state), rc2.d (multiuser state), rc3.d (multiuser plus networking state), rc4.d (user-defined state), rc5.d (multiuser, networking, plus GUI login state), and rc6.d (reboot state). /etc/security Contains files that set a variety of default security conditions for your computer. /etc/skel Any files contained in this directory are automatically copied to a user s home directory when that user is added to the system. By default, most of these files are dot (.) files, such as .kde (a directory for setting KDE desktop defaults) and .bashrc (for setting default values used with the bash shell). /etc/sysconfig Contains important system configuration files that are created and maintained by several Red Hat applications (including netcfg and linuxconf). /etc/uucp Contains configuration files used with Taylor UUCP (a nonstandard version of the uucp facility that is used to create modem, direct line, and other serial connections with other computers). /etc/xinetd.d Contains a set of files, each of which defines a network service that the xinetd daemon listens for on a particular port. When the xinetd daemon process receives a request for a service, it uses the information in these files to determine which daemon processes to start to handle the request. Administrative log files One of the things that Linux does well is keep track of itself. This is a good thing, when you consider how much can go wrong with a complex operating system. Sometimes you are trying to get a new facility to work and it fails without giving you the foggiest reason why. Other times you want to monitor your system to see if people are trying to access your computer illegally. In any of those cases, you can use log files to help track down the problem.
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rpmfind Contains configuration information used by the rpmfind command to search for RPM software packages on the Internet. services Defines TCP/IP services and their port assignments. shadow Contains encrypted passwords for users that are defined in the passwd file. (This is viewed as a more secure way to store passwords than the original encrypted password in the passwd file. The passwd file needs to be publicly readable, whereas the shadow file can be unreadable by all but the root user.) shells Lists the shell command line interpreters (bash, sh, csh, etc.) that are available on the system, as well as their locations. sudoers Sets commands that can be run by users, who may not otherwise have permission to run the command, using the sudo command. In particular, this file is used to provide selected users with root permission. syslog.conf Defines what logging messages are gathered by the syslogd daemon and what files they are stored in. (Typically, log messages are stored in files contained in the /var/log directory.) termcap Lists definitions for character terminals, so that character-based applications know what features are supported by a given terminal. Graphical terminals and applications have made this file obsolete to most people. (Termcap was the BSD UNIX way of storing terminal information; UNIX System V used definitions in /usr/share/terminfo files.) /etc/X11 Contains subdirectories that each contain system-wide configuration files used by X and different X window managers available with Red Hat Linux. The XF86Config file (which makes your computer and monitor usable with X) and configuration directories containing files used with xdm and xinit to start X are contained here. Directories relating to window managers contain files that include the default values that a user will get if that user starts one of these window managers on your system. Window managers that may have system-wide configuration files in these directories include: WindowMaker, fvwm2, GNOME (gdm), and Twm (twm). Note Some of the files and directories in /etc/X11 are linked to locations in the /usr/X11R6 directory structure. /etc/cron* Directories in this set contain files that define how the crond utility runs applications on a daily (cron.daily), hourly (cron.hourly), monthly (cron.monthly), or weekly (cron.weekly) schedule. /etc/default Contains files that set default values for various utilities. For example, the file for the useradd command defines the default group number, home directory, password expiration date, shell, and skeleton directory (/etc/skel) that are used when creating a new user account.
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inittab Contains information that defines what programs start and stop when Red Hat Linux boots, shuts down, or goes into different states in between. issue Contains the lines that are displayed when a terminal is ready to let you log in to Red Hat Linux from a local terminal, or the console in text mode. issue.net Contains login lines that are displayed to users that try to log in to the Linux system from a computer on the network using the telnet service. lilo.conf Sets various parameters used by the Linux boot loader (lilo) to boot your Linux system. In particular, it lists information about the bootable partitions on your computer. (If you are using grub, which has replaced lilo as the default boot manager, the lilo.conf file is not used.) mail.rc Sets system-wide parameters associated with using mail. man.config Used by the man command to determine the default path to the location of man pages. modules.conf Contains aliases and options related to loadable kernel modules used by your computer. mtab Contains a list of file systems that are currently mounted. passwd Stores account information for all valid users for the system. Also includes other information, such as the home directory and default shell. printcap Contains definitions for the printers configured for your computer. profile Sets system-wide environment and start-up programs for all users. This file is read when the user logs in. protocols Sets protocol numbers and names for a variety of Internet services. redhat-release Contains a string identifying the current Red Hat release number. resolv.conf Identifies the locations of DNS name server computers that are used by TCP/IP to translate Internet host.domain names into IP addresses. rpc Defines remote procedure call names and numbers.
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