140 Part II . The SUSE System Figure 5-2: Konqueror displaying the choice of man pages for crontab Figure 5-3: Konqueror displaying man 1 crontab
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Chapter 5 . Documentation 139 previous section, you can use the man-k command to list all relevant man pages for a given topic, as in the following example of the output from the man -kcrontab command: crontab (1) - maintain crontab files for individual users (V3) crontab (5) - tables for driving cron Working with Man Pages Graphically If you are working graphically, you may prefer to use Konqueror as your viewer for man pages. If you type the location man:/ into Konqueror s location bar, Konqueror displays a top-level index of manual pages on the system, showing clearly the hierarchy (see Figure 5-1). Figure 5-1: Konqueror displaying the top-level man pages index If you use Konqueror as your man page viewer, you can browse all the pages in a particular section simply by clicking the link, or you can find a page or pages by typing, for example, man:/crontab in the location bar (see Figure 5-2). Of course, you can also print man pages like the one shown in Figure 5-3 from Konqueror if you want (although they won t actually look as good as if you printed them from the command line, as described earlier in this chapter).
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138 Part II . The SUSE System Administration). Man pages are stored under a single directory hierarchy, the directory /usr/share/man on Linux systems. (Older Linux and other Unix-like systems often store these under the directory /usr/man.) Each section has its own subdirectory for example, man1, man2, man3, and so on. Table 5-1 lists the man pages sections and their corresponding types of information. Table 5-1 Man Pages Sections Section Number Type of Man Pages 2 System calls 3 Subroutines and library functions 4 Devices, special files, device drivers, and associated file formats 5 File formats 6 Games 7 Miscellaneous 8 System administration commands 9 Kernel N New 1 User commands In certain cases, man pages may have the same name but different content in different sections. Thus, for example, you will see the man page for the crontab program with the following: user@bible:~> man 1 crontab However, you will see the man page describing the structure of a crontab file with the following: user@bible:~> man 5 crontab When searching for man pages on a particular command-line program, you may therefore want to consider the type of information that you are looking for and provide a specific man page section to zero in on the information. As mentioned in the
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Chapter 5 . Documentation 137 useful. The man pages are normally stored in directories under /usr/share/man and are normally stored as gzipped files to save space on your system. Man pages are written in a simple markup language known as nroff that is interpreted by the man command to produce nicely formatted output for the screen. You can print a text version of a man page by using a command such as the following: user@bible:~> man cp | lpr You can also create a more nicely formatted printed output by using the man command s -t option, which processes the man page using a formatter (groff GNU roff) and generates output in the PostScript printer format, as follows: user@bible:~> man -t cp | lpr If you want to save the nicely formatted output as a PostScript file so that you can print or display it later, you can redirect the output of the man-t command into a file, as in the following example: user@bible:~> man -t cp > manpage.ps To find out more about the use of the man command, you can, of course, look at its man page: user@bible:~> man man To search for a man page, you can use the man command with the -k (keyword) option: user@bible:~> man -k copy This will list one-sentence summaries of man pages that are relevant to the word copy. It does this by searching a database of man page summaries known as the whatis database. You can use this summary to determine which man page you may want to view in full. Another command that does essentially the same thing is the apropos command, which searches the same database of available man pages used by the man-k command, looking for a specified phrase. An equivalent example of using apropos is the following: user@bible:~> apropos copy Working with Man Page Sections On Linux systems, man pages are divided into ten general sections according to the type of information that they provide. The ones that you are most likely to use frequently are sections 1 (User Commands), 5 (File Formats), and 8 (System
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136 Part II . The SUSE System With the release of SUSE 10.0, the printed documentation has been slimmed down, so that the boxed copy includes only the book entitled SUSE Linux 10.0 Start-up. The other documentation has been combined into a single package called suselinuxmanual_en. This package installs all the SUSE-specific documentation (the book SUSE Linux Reference and SUSE Linux 10.0 Start-up) in HTML format to the directory /usr/share/doc/manual/. The main book consists of 49 chapters. The PDF versions of both books are in the directory docu/ in the root directory of the installation media. The SUSE manuals have their strengths and weaknesses. They are very well produced and clearly printed; and the look and feel of both the printed and the HTML versions is elegant and easy to read. The main manual SUSE Linux Reference should be regarded (as its name implies) as a reference book. Its coverage of the system as a whole is remarkably good, and certain chapters provide good information that is hard to find elsewhere. The installation chapter covers most common problems and includes short sections on setting up Logical Volume Management (LVM) and software RAID (Redundant Array of Inexpensive Disks). The network section includes subsections on Samba, Lightweight Directory Access Protocol (LDAP), and Network Information System (NIS), and a good introduction to setting up the Domain Name System (DNS). All of this information is somewhat pared down, as a whole book could be written on any one of the topics, but the advantage is that there is a good description of setting up these services specifically on SUSE Linux, using the YaST modules. The Start-up book is a 275-page introduction to installing and using SUSE Linux, aimed mainly at the new desktop user. There are a good general description of YaST and introductions to the main features of both the KDE and Gnome desktops. The chapter entitled Getting to Know Linux Software gives a useful comparison between the desktop applications available on Linux and the commonly used Windows equivalents. The SUSE Linux Enterprise Server 9 printed manual is similar to the Administration Guide that was issued with the SUSE 9.x versions. Man Pages Man pages (man is short for manual) are the original form of online Unix documentation. Traditionally, command-line programs have associated man pages that are installed as part of the package that the program belongs to. To access a man page (for example the man page of the cp command), type man cp: user@bible:~> man cp The man command displays a somewhat terse but usually complete and accurate summary of the options and usage of the command. A large number of commands have man pages, which provide a quick and easy way of checking on command syntax and usage. Many man pages include command examples, which can be quite
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Documentation One of the misconceptions that are still fairly widespread about Linux is that it is not well documented. This goes with the preconceptions that people have about the nature of open source software: they think that while proprietary systems come with copious glossy manuals, with Linux you have to be a programmer who can read the source code to understand the system. The truth is much more refreshing and interesting. In our experience it is usually much easier to find relevant and specific information about Linux and open source software than about proprietary products. The spirit of open source means that there are a variety of sources of good information about the software from official documentation provided by commercial vendors to mailing lists, newsgroup postings, and other ephemeral information. Finding Help on Your SUSE System Although this chapter surveys a whole spectrum of information sources about SUSE Linux and associated utilities, we will start with documentation that you can find on your system or in your purchased package of SUSE Linux, including the official SUSE documentation. The SUSE Manuals Your copy of SUSE Linux or SUSE Linux Enterprise Server comes with official printed documentation. Versions of SUSE up to 9.3 contained two printed books: SUSE Linux Administration Guide and SUSE Linux User Guide. These were also included on the installation disks in electronic form in both HTML and PDF formats with the package names suse-linux-adminguide_en, suse-linux-adminguide_ en-pdf, suse-linux-userguide_en, and suse-linux-userguide_en-pdf. When installed, these documents can be found under the directory /usr/share/doc/manual/. 5 CHAPTER …. In This Chapter Using the SUSE manuals Using man and info pages Using the SUSE Help Center Package documentation Reviewing Linux Documentation Project resources Finding help online ….
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134 Part II . The SUSE System You will find that you can now log in to the system as root without a password. As soon as you are logged on, set the password immediately and try to remember it. The Rescue System is something every administrator and user should have in his or her arsenal as it can help you fix pretty much any lethal problem you have on a Linux system, regardless of whether it is SUSE-based or not. This chapter has provided a great deal of information about the Linux boot process and the way in which you can start various services by associating them with Linux runlevels. You learned how to customize the boot process for both Linux-only and dual-boot Windows/Linux systems. The last section explained various ways to correct boot process configuration problems. All in all, this chapter should have you well on your way to becoming a Linux system administrator (or the administrator of your own home Linux system). The only thing remaining is experience, which you will accumulate as you perform more and more of your daily activities on your SUSE Linux system. …
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Chapter 4 . Booting the System 133 As an example of using the SUSE Rescue System, we will take the case of a forgotten root password and reset this with the Rescue System. Caution Some of you might see a large security problem with what we are about to do. If malicious users have physical access to a server, they are quite able to reset the root password of the machine using this method. This is why the physical security of a machine is as important as the security of the machine from an operational standpoint. To reset the root password from the SUSE Rescue System, follow these steps: 1. When the Rescue System has loaded, you will be prompted to select the keyboard map that you are using (which defines the type of keyboard that you are using). After the kernel executes, loads the initial ramdisk, and starts various system processes, you will then be asked to log in. Just enter root as the username, and you will be dropped into the Linux system from the initial ramdisk. 2. At this point, you need to identify the partition that contains /etc. This will usually be your / (root) partition. Mount the partition under /mnt. The following example uses /dev/hda3as the root partition: mount /dev/hda3 /mnt 3. When mounted, you need to edit the file /mnt/etc/shadow to reset the root password. You can edit this file using any text editor, although vi is the only screen-oriented text editor that is provided in the SUSE Rescue System. Remember that you mounted your system s root partition under /mnt; which is why the location of the /etc/shadow file has changed. The shadow file is a system file that contains encrypted passwords of the users on the system. The file can be read and written to only by the root superuser. 4. When loaded, you need to find the entry for the root user. Find the encrypted password, which is the second field (fields in the file are separated by a colon). When found, delete the password so that there are just two colons next to each other (::), and save the file. 5. After the file has been edited, change the directory to / (root) and unmount the filesystem by issuing the following: umount /mnt 6. When unmounted, you can reboot the system by typing reboot and pressing the Enter key, or just pressing the reboot key on the machine. Remember to remove your optical media as the system reboots, or you may accidentally boot from it. Note
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132 Part II . The SUSE System The SUSE Rescue System We have talked about fixing system problems by changing the boot runlevel of the system temporarily, but what if you encounter a dire problem such as forgetting the root password! This requires another approach because you will need the root password at some point. Figure 4-4: Logging in to init 1 SUSE realizes the need to be able to repair a Linux system, which generally requires Linux tools and access to the ailing Linux system using those tools, and so has included a Rescue System on the first CD or DVD in your SUSE installation set. To load the Rescue System, use the optical media, and select Rescue System from the initial boot menu. The kernel from the CD will load, and an initial ramdisk containing a fuller Linux system will be loaded. This Rescue System has built-in support for the types of Linux filesystems discussed in this book, as well as to IDE hard drives. If you are using a SCSI disk, this ramdisk also includes the main modules for loading a SCSI disk.
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Chapter 4 . Booting the System 131 In both cases, the 1 tells init to load up the system in runlevel 1. This, as you may remember, is the runlevel that signifies single-user mode with no network. This is the lowest usable runlevel that is needed only if there is a problem with the system. Figure 4-3: Adding the runlevel to the GRUB boot loader If, on the other hand, you know your runlevel configuration is sound, but you want to manually stop a certain service starting up, you can add PROMPT_FOR_CONFIRM= yes in /etc/systconfig/boot. As shown in Figure 4-4, you will be asked for the root password to log in to the sys tem (this is why you should never forget you root password). Once logged in you can then turn off processes as we talked about with the chkconfig script or fix any other problems that the system has. Once fixed, you can then reboot the system normally. Because specifying a runlevel to GRUB and LILO is a temporary change, you are able to let the system start up normally without having to interrupt the nor mal operation of LILO or GRUB.
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