ONLamp.com    
 Published on ONLamp.com (http://www.onlamp.com/)
 See this if you're having trouble printing code examples


Essential System Administration, 3rd Edition

Top Five Open Source Packages for System Administrators

by Æleen Frisch, author of Essential System Administration, 3rd Edition
11/07/2002

This is the third installment of a five-part series in which I introduce my current list of the most useful and widely applicable open source administrative tools. In general, these tools can make your job easier, no matter what Unix operating system your computers run.

#3: GRUB

Administrators who take care of Linux systems are undoubtedly familiar with the LILO boot loader. LILO (or Linux Loader) was a great tool in its time, and it enabled you to boot not only the Linux operating system, but also any other operating system that might be running on the same Intel-based PC hardware (including all of the various versions of Windows).

There is a newer, more general and flexible boot loader coming into wide usage. It is named GRUB: the GRand Unified Bootloader. It was originally written by Erich Boleyn and is now part of the GNU project. Current development is overseen and led by Gordon Matzigkeit and Okuji Yoshinori. The project's home page is http://www.gnu.org/software/grub.

The GRUB developers are very enthusiastic about their program (and rightly so), as indicated by this quote from Gordon Matzigkeit:

Some people like to acknowledge both the operating system and kernel when they talk about their computers, so they might say they use "GNU/Linux" or "GNU/Hurd." Other people seem to think that the kernel is the most important part of the system, so they like to call their GNU operating systems "Linux systems." I, personally, believe that [both are] a grave injustice, because the boot loader is the most important software of all.

[Accordingly,] I used to refer to the above systems as either "LILO" or "GRUB" systems. Unfortunately, nobody ever understood what I was talking about; now I just use the word "GNU" as a pseudonym for GRUB. So, if you ever hear people talking about their alleged "GNU" systems, remember that they are actually paying homage to the best boot loader around: GRUB!

In This Series

Number Five: Amanda
The countdown begins with Amanda, an enterprise backup utility.

Number Four: LDAP
The countdown continues with LDAP, a protocol that supports a directory service.

Number Two: Nagios
The countdown continues with Nagios, a feature-rich network monitoring package.

If Gordon has his way, someday all "Linux" systems, "FreeBSD" systems, and so on, will be GRUB systems. In fact, the most recent versions of Red Hat Linux and SuSE Linux install GRUB by default or offer it as an option.

How GRUB Is Better

I prefer GRUB to other boot loaders for the following reasons:

Related Reading

Essential System Administration
Tools and Techniques for Linux and Unix Administration
By Æleen Frisch

GRUB Components

GRUB includes the following main components:

How GRUB Names Disks

Before we consider the process of configuring GRUB, we need to note how disks are referred to within this package. GRUB defines its own disk notation so that disk partitions and slices can be indicated, regardless of the operating system that they happen to hold. The following example shows the general disk syntax:

(hdn,p)

where n is the disk number (starting at 0), and p is the partition number (again, starting at 0). For example, the second partition on the third hard disk would be designated as:

(hd2,1)

For operating systems that further subdivide the hard-disk partition, this syntax adds a third field consisting of the (sub)partition letter within the slice (physical partition). For example, the a partition in the first slice on the first hard disk under FreeBSD would be designated as:

(hd0,0,a)

Some GRUB Recipes

We're now ready to look at the GRUB configuration file (grub.conf). Here are some sample lines from its first, general section:

# general section
splashimage (hd0,0)/grub/splash.xpm.gz   Pretty picture behind the menu. 
default 0                    Default boot entry (numbering starts at 0).
timeout 30                               Menu timeout period in seconds.
password -md5 xxxxxxx             Use grub-md5-crypt to encode password.

These lines specify the image displayed behind the boot menu, the menu timeout period and default entry to boot, and the boot password.

The remainder of the file specifies the items on the boot menu. Here are two examples that boot the Linux operating system on the first partition on the first hard disk (selecting different kernels):

title Linux
   root (hd0,0)
   kernel /vmlinuz ro root=/dev/hda2
   initrd /initrd.img

title Test-Linux
   root (hd0,0) 
   kernel /vmlinuz-test ro root=/dev/hda3
   initrd /initrd.img-test

The title lines indicate the menu item text. The root lines specify the partition where the boot loader is located. All directory references are assumed to be relative to the root of this partition. Thus, the location of the vmlinuz files specified in the kernel lines is in the root directory of this partition.

The kernel lines specify the path to the Linux kernel in each case, along with any parameters to be passed to it. In this case, a separate /boot partition is being used, so the root parameter is passed to the kernel; the latter indicates the location of the system root directory (such as /). Thus, we can tell that the kernel images reside at /boot/vmlinuz* from the point of view of the booted Linux system. The initrd lines similarly specify the path to the initrd.img file (if used).

Booting FreeBSD is also very simple:

title FreeBSD
   # use the 1st BSD subpartition in disk 1 partition 3
   root (hd0,2,a) 
   kernel /boot/loader

Related Reading

Essential System Administration Pocket Reference
Commands and File Formats
By Æleen Frisch

This stanza again specifies the boot partition and locates the FreeBSD final-stage boot loader. This is the recommended practice (rather than directly invoking the FreeBSD kernel).

This stanza defines a bootable Windows partition:

title Win2K
   root (hd0,2) 
   makeactive 
   chainloader +1

The boot partition is specified in the usual way. The makeactive command activates the partition, and the chainloader command hands off the boot process to local boot loader (for example, NTLDR).

In general, GRUB can boot operating systems on any disk. However, in some cases, it is easier to boot non-Unix operating systems on the second hard disk if you logically "swap" the first two drives. GRUB uses entries like these to do so:

map (hd0) (hd1)
map (hd1) (hd0)

GRUB also has the nice feature of remembering what operating system was last booted and making it the default for the next time. To enable this capability, set the default entry to saved (in the general section), and add a savedefault directive to the end of each stanza:

title Linux
   ...
   savedefault

Installing GRUB

Once you've created the configuration file, installing GRUB is very easy. It is done with the grub-install utility that is included with the package. This tool has the following general syntax:

# grub-install [--root-directory=/dir] disk

where disk is the boot partition, specified in either GRUB's format or the local format (for example, (hd0) or /dev/hda, etc.).

The --root-directory option specifies the directory location of a separate boot partition (for example, /boot under Linux).

For more information about GRUB, consult the following:

If you liked this article and would like to receive the free ESA3 newsletter, you can sign up here.

Æleen Frisch has been a system administrator for over 20 years, tending a plethora of VMS, Unix, Macintosh, and Windows systems. If you liked this article and would like to receive the free ESA3 newsletter, you can sign up at http://www.aeleen.com/esa3_news.htm.


O'Reilly & Associates recently released (August 2002) Essential System Administration, 3rd Edition.


Return to ONLamp.com.

Copyright © 2009 O'Reilly Media, Inc.