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Chapter 3. System ConfigurationOne of the main strengths of Red Hat Linux is that the operating system can be configured to do just about anything. In the past, this meant editing sometimes cryptic configuration files by hand, then restarting system services and crossing your fingers in the hope that your changes were correctly made. Additionally, the variety of configuration options can be bewildering to new users, who may not know where to look for a particular configuration file. Red Hat Linux provides two system configuration utilities: linuxconf and the control panel. The control panel provides a launcher for various Red Hat system configuration tools, including linuxconf. Instructions on how to use the control panel and the tools it includes can be found in the section called System Configuration with the Control Panel. The linuxconf configuration tool can ease some of the burdens of system configuration. Linuxconf is both:
While linuxconf can do nearly everything the control panel tools can, there are two areas in which the control panel still holds the upper hand:
Let's take a look at linuxconf. System Configuration with linuxconfLinuxconf allows you to configure and control various aspects of your system, and is capable of handling a wide range of programs and tasks. Complete documentation of linuxconf could be a separate book in its own right and is certainly more than we can cover in this chapter. Instead, we'll focus on common tasks such as adding new users and getting connected to a network. More information on linuxconf, including its most recent release can be found at the linuxconf website: http://www.solucorp.qc.ca/linuxconf/ The linuxconf website includes fairly extensive information, including a description, rationale, history, list of contacts, and a lot of other information in addition to the software. The website is maintained by linuxconf's creator and developer, Jacques Gelinas, so it includes the latest news about linuxconf. This chapter will go into detail on just a few of linuxconf's capabilities. If you just need a quick reference to show you where to go in linuxconf for the tasks covered by this chapter, see the section called Finding Your Way Through linuxconf. If you need more help with linuxconf, please try these sources:
Running linuxconfYou'll need to be root to run linuxconf, so if you're in your user account, su to become root. Now, type linuxconf at the shell prompt to begin the program. Linuxconf User InterfacesLinuxconf has four user interfaces:
Linuxconf will start in either character-cell or X mode, depending on your DISPLAY environment variable. The first time you run linuxconf, an introductory message will be shown; although it is only displayed once, accessing help from the main screen will give you the same basic information. Linuxconf includes some context-specific help. For information on any specific aspect of linuxconf, select Help from the screen you'd like help with. Note that not all help screens are complete at this time; as help screens are updated, they will be included in subsequent versions of linuxconf. gnome-linuxconf Interfacegnome-linuxconf makes it easy to navigate the hierarchical structure of linuxconf.
When you use the tree menu view, finding the appropriate panel should be simple and fast. Collapse and expand sections by clicking on the + or - next to the menu item. Selected entries will appear as tabs in the right-hand panel and will remain there until closed. If you end up with more tabs open than you like, just select Cancel on the bottom of each tab to close it without making any changes, or Accept to implement them. Enabling Web-Based linuxconf AccessFor security reasons, Web-based access to linuxconf is disabled by default. Before attempting to access linuxconf with a Web browser, you'll need to enable access. Here's how to do it:
Web-based access should be enabled. To test it out, go to a system that you added to the access control list. Then, launch your Web browser, and enter the following URL:
(Replace <host> with your system's hostname, of course. Also, remove the "disable=yes" line from the /etc/xinetd.d/linuxconf file and then run the command /sbin/service xinetd reload from a shell prompt.) You should see the main linuxconf page. Note that you will need to enter your system's root password to gain access beyond the first page. You can also enable network-wide access to linuxconf by following the same steps, by entering a network name instead of a hostname. Adding a User AccountAdding a user is one of the most basic tasks you will encounter in administering your system. To add a user:
The User account creation screen includes the Base info, Params and Privileges sections. Only the Login name is required, but you should be aware of the other fields, which you may or may not want to fill in. Base info for User AccountsThe Login name is the name of the account and is usually all lowercase letters. First or last names, initials or some combination thereof are fairly common login names. For a user named John T. Smith, smith, john, jts, or jsmith would be common user names. Of course spike or something else works just fine, too. You can also use numbers, so jts2 would be fine if you had a second person with the same initials. There is no default for this field. The Full name is the name of the user or the account. For an individual, it would be their name, John T. Smith for example. If the account represents a position rather than a person, the full name might be the title. So an account called webmaster might have a full name of Red Hat Webmaster or just Webmaster. There is no default for this field. Since Red Hat Linux uses the User Private Group scheme, each user will be assigned to a default group consisting only of the user. For more information on User Private Groups, see the section called User Private Groups in Chapter 2. In the Supplementary groups field, you can specify additional groups. Group names should be separated by spaces. The default for this field is blank, meaning no supplementary groups are specified. The Home directory specifies the home or login directory for the account. The default is /home/login, where login is replaced by the login name. A home directory is your starting point in the directory structure when you log in, or if in X, for each Xterm window opened. This is also where account specific preference files are stored. The Command interpreter is the default shell for the account. The bash shell is the default shell for Red Hat Linux. The User ID (UID) is the number associated with each user account. This is automatically generated by the system when the account is created, so just leave this field blank. The system uses the UID to identify an account. Params for User AccountsThe Params are used for password and account management. By default, all of the settings are Ignored, so they are unused. Must keep # days sets a minimum number of days for a user's password. The Must change after # days field can be set to make a user's password expire after a certain number of days. If you want to warn them that the password is going to expire (a good idea), the Warn # days before expiration field should be used. If you'd like to have their account set to expire after a certain number of days, use the Account expire after # days field. You could alternatively set a hard Expiration date. Privileges for User AccountsIn the Privileges section, you can grant access and/or control over various aspects of system configuration. As a default, regular users are denied all privileges on this screen. You may instead choose to grant or to silently grant them specific privileges. The difference between Granted and Granted/silent is that if the privilege is granted, linuxconf will ask for the user's password before allowing them the privilege. If the privilege is granted silently, linuxconf will not prompt for their password. Generally, careful system administrators won't grant users any system configuration privileges unless it is absolutely necessary. If you do grant privileges, be careful when granting them silently. If a user with silently granted privileges logs in to his/her machine and walks away, their privileges are wide open for the next person who sits down at their desk. Silently granted privileges are less risky if used on machines in a physically restricted area. May use linuxconf: the user is allowed to access all of linuxconf's capabilities, and they can set up or change linuxconf parameters. Note that use of linuxconf is separate from the privilege of activating configuration changes. System administrators might want to grant the use of linuxconf, but deny the activation privilege, so that the sysadmin has a final "yes/no" on whether to activate any configuration changes. May activate config changes: After you change a parameter in linuxconf, at some point you'll have to indicate to linuxconf that the changes you made should be applied. Depending upon the flavor of linuxconf that you're using, you might do this by clicking on an Activate the changes button in GUI linuxconf, or clicking on an Accept button in Web-based linuxconf, or selecting an Accept button in text-mode linuxconf, etc. You can grant the privilege of activating changes to a user. In that case, the user will be able to activate any changed system configuration parameters in linuxconf. May shutdown: A user can be granted the right to shutdown the system. Note that Red Hat Linux is set in /etc/inittab to cleanly shutdown following the Ctrl-Alt-Del keystroke combination. You can also grant the user the privileges to switch network modes, to view system logs, and even give someone superuser equivalence. Once you have entered the login name and any other desired information select the Accept button at the bottom of the screen. If you decide against creating a new user, select Cancel instead. When you click on Accept linuxconf will prompt you to enter the password, as in Figure 3-6. You'll have to re-type the password, to prevent unusable passwords caused by typos. Passwords must be at least six characters in length, but you can increase the required length and set other parameters for users' passwords at the Users Accounts => Policies => Password & Account Policies screen. Good passwords contain a combination of letters, numbers, and special characters. It should use both upper case and lower case letters. Don't use your username, your anniversary, your social security number, your dog's name, your middle name or the word root. Don't use any variation of a word associated with your account or with yourself. Don't use a word that can be found in a dictionary; dictionary words are easy to crack. A simple technique for creating a password is to use the first letters from each word of a phrase that is familiar to you (a line from a favorite song might be appropriate). Make a few letters uppercase, and insert a few numbers and/or special characters in place of letters and you'll have a decent password. Press the Accept button again when finished. The system will let you know if it thinks the password is easy to crack; if you get a warning message, don't use the password. Modifying a User Account
To implement the changes select Accept. If you decide against making any changes select Cancel. This guarantees that no changes are made. Changing a User's Password
Linuxconf will prompt you to enter the new password. There is also a field called Confirmation where you will need to type the password again. This is to prevent you from mistyping the password. See the section called Adding a User Account for guidance on choosing a password. If you decide against changing the password, select Cancel. Once you have entered the new password select Accept. Changing the Root PasswordBecause of the security implications of root access, linuxconf requires you to verify that you currently have access to the root account.
You'll first need to enter the current root password to verify access to the root account. Once you have entered root's current password, it will prompt you for a new password. In the Confirmation field, type the password again. This is to prevent you from mistyping the password. See the section called Adding a User Account if you need guidance on choosing a password. Be sure to choose a good password! If you decide against changing the root password, just select Cancel. Once you have entered the new password select Accept. Disabling a User AccountDisabling a user's account is preferable to deleting a user's account, unless you need the storage space or you're certain that his/her data will not be needed in the future. If a user's account is disabled, they will not be allowed to log in.
The account is disabled and can be enabled later using a similar method. Enabling a User AccountBy default, all newly created user accounts are enabled. If you need to enable an account, you can use linuxconf to do it. Open Config => Users accounts => Normal => User accounts. Select an account. Select the The account is enabled checkbox. Deleting a User Account
To delete an account:
Linuxconf will then prompt you with a list of options. The default option is to archive the account's data. The archive option has the following effects:
Selecting Delete the account's data on the Deleting account <accountname> screen (see Figure 3-7) will:
Selecting Leave the account's data in place on the Deleting account <accountname> screen (see Figure 3-7) will:
GroupsAll users belong to one or more groups. Just as each file has a specific owner, each file belongs to a particular group as well. The group might be specific to the owner of the file, or may be a group shared by all users. The ability to read, write or execute a file can be assigned to a group; this is separate from the owner's rights. For example, the owner of a file will be able to write to a document, while other group members may only be able to read it. Creating a GroupTo create a new group:
You may see a filter screen, depending upon the settings in Control => Filters. Either provide a filter, or select Accept to bypass the filter. Select Add at the bottom of the User groups screen. Enter a group name. You may also wish to specify members of the group and can do so in the Alternate members field. The list of users should be space delimited, meaning that each username must have a space between it and the next one. Leave the Group name field blank, so that the system will assign a Group ID (GID) to your new group. When you're finished, select Accept and the group will be created. Deleting a GroupTo delete a group:
The group's files will still remain and their respective owners will still have sole control over them. The group name will be replaced with the deleted group's ID. The files may be assigned to a new group by using the chgrp command. More information on chgrp can be found by typing the command info chgrp or man chgrp at the shell prompt. If a new group is created and the deleted group's ID is specified then the new group will have access to the deleted group's files. Don't worry, linuxconf doesn't recycle old group numbers any more than it does old user IDs, so it won't happen by accident. Modifying Group MembershipThere are two ways to modify the list of users that belong to a group. You can either update each user account itself, or you can update the group definitions. In general, the fastest way is to update each of the group definitions. If you're planning on changing more information for each user than just the group information, then updating each user account may prove easier. We'll start by detailing the group definitions method.
This will automatically update each user account with the group showing up in the Supplementary groups field if added or absent if removed. Adding and removing groups can also be done by modifying each individual user account.
This will automatically update the group definitions. Repeat the process for each user. FilesystemsA filesystem is composed of files and directories, all starting from a single root directory. The root directory may contain any number of files and other directories, with each directory in turn following suit. The average filesystem often looks like an inverted tree with the directories as branches and the files as leaves. Filesystems reside on mass storage devices such as diskette drives, hard drives, and CD-ROMs. For example, a diskette drive on DOS and Windows machines is typically referenced by A:\. This describes both the device (A:), and the root directory on that device (\). The primary hard drive on the same systems is typically referred to as the "C" drive because the device specification for the first hard drive is C:. To specify the root directory on the C drive, you would use C:\. Under this arrangement, there are two filesystems — the one on A:, and the one on C:. In order to specify any file on a DOS/Windows filesystem, you must either explicitly specify the device on which the file resides, or it must be on the system's default drive (which is where DOS' C prompt comes from — that's the default drive in a system with a single hard drive). Under Linux, it is possible to link the filesystems on several mass storage devices together into a single, larger, filesystem. This is done by placing one device's filesystem "under" a directory on another device's filesystem. So while the root directory of a diskette drive on a DOS machine may be referred to as A:\, the same drive on a Linux system may be accessible as /mnt/floppy. The process of merging filesystems in this way is known as mounting. When a device is mounted, it is then accessible to the system's users. The directory "under" which a mounted device's filesystem becomes accessible is known as the mount point. In the previous paragraph's example, /mnt/floppy was the diskette drive's mount point. Note that there are no restrictions (other than common conventions) as to the naming of mount points. We could have just as easily mounted the floppy to /long/path/to/the/floppy/drive. One thing to keep in mind is that all of a device's files and directories are relative to its mount point. Consider the following example:
So, if the above describes the individual filesystems, and you mount the CD-ROM at /foo, the new operating system directory structure would be:
To mount a filesystem make sure to be logged in as root, or become root using the su command. For the latter, type su at the shell prompt and then enter the root password. Once you are root, type mount followed by the device and then the mount point. For example, to mount the first diskette drive on /mnt/floppy, you would type the command mount /dev/fd0 /mnt/floppy. At installation, Red Hat Linux will create /etc/fstab. This file contains information on devices and associated mount points. The advantage to this file is that it allows you to shorten your mount commands and it controls which filesystems are automatically mounted when the system is booted. Using the information in /etc/fstab, you can type mount and then either the mount point or the device. The mount command will look for the rest of the information in /etc/fstab. It's possible to modify this file by hand, or by using linuxconf. Reviewing Your Current FilesystemWe'll start by looking at your current directory structure.
The fields, as shown in Figure 3-10, are:
Filesystems from other machines on a network may also be available. These can range from single small directories to entire volumes. No information on Size or Partition type is available for these partitions, either. Additional information on NFS filesystems (should you have any available) will be contained under: Config => File systems => Access nfs volume The screen is similar to the Local Volume screen (see Figure 3-10, with some notable differences in the information provided for each entry:
Adding NFS MountsNFS (Network File System) is a way for computers to share sections of their local filesystem across a network. These sections may be as small as a single directory, or include thousands of files in a vast hierarchy of directories. For example, many companies will have a single mail server with individuals' mail files served as an NFS mount to each users' local systems. To add an NFS mount:
The three fields on the Base tab are what you'll need to concern yourself with next (see Figure 3-11).
This is all you need to get the mount created. Linuxconf will update your /etc/fstab file accordingly. If you are aware of additional requirements, please read the help file on the Volume specification screen and see the mount man page for more information. Once you have entered the information, select Accept. Getting Connected with Linuxconf (Network Configuration)The first thing to determine when getting hooked up is whether you're connecting to a local area network, such as a group of computers in an office, or a wide area network, such as the Internet. Before continuing, it's important to know what hardware you have and how you intend to connect. If you're going to dial into another computer, then make sure your modem is installed and that the cables are arranged properly. If you're using a network card, make sure it is installed properly and that the cables are correctly connected. Regardless of what network configuration you specify, if every phone line or cable is not in place, you'll never get connected. Network ConnectionsSetting up a network connection over Ethernet requires an entirely different type of setup. Network connections to Token Ring or ARCnet networks follow a similar procedure, but will not be discussed here.
The first item on this screen is a check box to indicate whether this adaptor is enabled or not. It should be checked if this is the one you intend to use. Below that is a choice of Config modes. Manual means that you will be providing all the information and entering it yourself. Dhcp and Bootp mean that your machine will be getting its network configuration information from a remote DHCP or BOOTP server. If you're not sure what option to choose, talk to your network administrator. Required fields for DHCP or BOOTP:
For DHCP and bootp configurations you only need to specify the Net device and the Kernel module. For the Net device, you will choose from a list where the eth prefix represents Ethernet cards, arc specifies an ARCnet card and tr specifies Token Ring cards. A complete list of network cards and their respective modules can be found in Appendix A. For the most up-to-date list, please see our website at:
The netmask information may be set by default, although depending on what kind of network you are setting up, or becoming a part of, you may need to specify this. If you are connecting to an ISP, ask them for the information. Most likely it will be 255.255.255.0. Required fields for manual configuration:
Information on net devices and kernel modules is described above. The appropriate primary name + domain and IP address will depend on whether you are adding the computer to an existing network or creating a new network. For connecting to an existing network, contact your network administrator for the information. Getting a network connected to the Internet is beyond the scope of this book, and we recommend the following starting point: TCP/IP Network Administration, 2nd Edition, by Craig Hunt (O'Reilly and Associates). If you're setting up a private network that won't ever be connected to the Internet, then you can choose any primary name + domain name you would like and have several choices for IP addresses (See Table 3-1). Table 3-1. Addresses and Examples
The three sets of numbers above correspond to class a, b, and c networks respectively. The classes are used to describe the number of IP addresses available as well as the range of numbers. The numbers above have been set aside for private networks.
Name Server SpecificationA name server and default domain are also needed to establish a network connection. The name server is used to translate host names such as private.network.com to their corresponding IP address such as 192.168.7.3. The default domain tells the computer where to look if a fully qualified hostname isn't specified. Fully qualified means that the full address is given, so foo.redhat.com is the fully qualified hostname, while the hostname is simply foo. If you specified your default domain as redhat.com, then you could use just the hostname to connect successfully. For example ftp foo would be sufficient if your search domain is redhat.com, while ftp foo.redhat.com would be required if it wasn't. To specify the nameserver, open Config => Networking => Client tasks => Name server specification (DNS). Nameservers are ranked according to the order in which they are accessed, so it's not unusual to see nameservers referred to as primary, secondary, tertiary and so on down the list if more than one is specified. Each of these must be an IP address and not a name, since the computer has no way to resolve the name until it connects to a nameserver. In addition to a default domain, you can also specify search domains. Search domains work differently; they progress from one to six in a similar manner to the nameserver. However, they all take precedence over the default domain! Keep this in mind when specifying search domains. Search domains are not commonly used. The one item not yet covered is the check box for DNS usage. If you are running a small private network with no Internet connection, then using /etc/hosts files and keeping them all synchronized will work. As you add more and more machines, the complexity increases until it is easier to have a single machine run a DNS than to continue to sync /etc/hosts files. Another reason for not using DNS is if your network is going to use NIS instead. Note that NIS can be used in conjunction with DNS. So to sum it all up, unless you know why using /etc/hosts or NIS would be best for your situation, DNS is probably going to be your best choice. You can add, modify, or delete entries from the /etc/hosts file using linuxconf. Open Config => Networking => Misc => Information about other hosts. To modify or delete an entry select it. To delete the entry, select Del at the bottom of the host/network definition screen. To modify it, change the information as necessary. To add a new entry, select Add at the bottom of the /etc/hosts screen. This will also open the host/network definition screen. Required Fields:
Optional Fields:
Once finished, select Accept. Finding Your Way Through linuxconfThis table provides a quick reference for this chapter. Unfortunately, it doesn't provide a complete quick reference for linuxconf, which has many more capabilities than this documentation provides. Table 3-2. Linuxconf Quick Reference
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