<HTML ><HEAD ><TITLE >Configure the boot loader</TITLE ><META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.7"><LINK REL="HOME" TITLE="Remote Serial Console HOWTO" HREF="index.html"><LINK REL="PREVIOUS" TITLE="Optionally configure the BIOS" HREF="bios.html"><LINK REL="NEXT" TITLE="Configure the LILO boot loader" HREF="configure-boot-loader-lilo.html"></HEAD ><BODY CLASS="CHAPTER" BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#0000FF" VLINK="#840084" ALINK="#0000FF" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="3" ALIGN="center" >Remote Serial Console HOWTO</TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="bottom" ><A HREF="bios.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="80%" ALIGN="center" VALIGN="bottom" ></TD ><TD WIDTH="10%" ALIGN="right" VALIGN="bottom" ><A HREF="configure-boot-loader-lilo.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="CHAPTER" ><H1 ><A NAME="CONFIGURE-BOOT-LOADER" ></A >Chapter 4. Configure the boot loader</H1 ><DIV CLASS="TOC" ><DL ><DT ><B >Table of Contents</B ></DT ><DT >4.1. <A HREF="configure-boot-loader-lilo.html" >Configure the <SPAN CLASS="APPLICATION" >LILO</SPAN > boot loader</A ></DT ><DT >4.2. <A HREF="configure-boot-loader-grub.html" >Configure the <SPAN CLASS="APPLICATION" >GRUB</SPAN > boot loader</A ></DT ><DT >4.3. <A HREF="configure-boot-loader-syslinux.html" >Configure the <SPAN CLASS="APPLICATION" >SYSLINUX</SPAN > boot loader</A ></DT ></DL ></DIV ><P >When a PC boots the CPU it runs code from Read-Only Memory. This code is the Basic Input/Output System, or <SPAN CLASS="ACRONYM" >BIOS</SPAN >. The <SPAN CLASS="ACRONYM" >BIOS</SPAN > then loads a boot loader from the Master Boot Record of the first hard disk.<A NAME="AEN810" HREF="#FTN.AEN810" ><SPAN CLASS="footnote" >[1]</SPAN ></A > In turn, the boot loader reads the operating system into memory and then runs it.<A NAME="AEN822" HREF="#FTN.AEN822" ><SPAN CLASS="footnote" >[2]</SPAN ></A ></P ><P >Neither the <SPAN CLASS="ACRONYM" >BIOS</SPAN > nor the boot loader are strictly necessary. For example, there are <A HREF="http://www.acl.lanl.gov/linuxbios/" TARGET="_top" >versions of Linux</A > that run directly from the flash memory which usually contains the <SPAN CLASS="ACRONYM" >BIOS</SPAN >. Linux was originally designed to run without an interactive boot loader, by placing the kernel at particular sectors of the disk.</P ><P >The benefits of using a boot loader are:</P ><P ></P ><UL ><LI ><P >Multiple operating systems can be booted. See the <A HREF="http://www.tldp.org/HOWTO/Linux+Windows-HOWTO/" TARGET="_top" ><I CLASS="CITETITLE" ><SPAN CLASS="SYSTEMITEM" >Linux</SPAN > + <SPAN CLASS="SYSTEMITEM" >Windows</SPAN > HOWTO</I ></A > for more information.</P ></LI ><LI ><P >Parameters can be passed to the kernel interactively. This is useful for solving hardware problems; for example, some interrupt lines can be disabled, direct memory access to some drives can be disabled, and so on. See the <A HREF="http://www.tldp.org/HOWTO/BootPrompt-HOWTO.html" TARGET="_top" ><I CLASS="CITETITLE" ><SPAN CLASS="SYSTEMITEM" >Linux</SPAN > BootPrompt-HOWTO</I ></A > for a list of kernel parameters.</P ></LI ><LI ><P >Differing kernels can be interactively loaded. This is useful when deploying a new kernel, as it provides simple fallback to a proven kernel.</P ></LI ></UL ><P >For these reasons systems administrators want to be able to interactively control the boot loader from the serial console.</P ><P ><SPAN CLASS="APPLICATION" >LILO</SPAN >, <SPAN CLASS="APPLICATION" >GRUB</SPAN > and <SPAN CLASS="APPLICATION" >SYSLINUX</SPAN > are popular boot loaders for <SPAN CLASS="PRODUCTNAME" ><SPAN CLASS="ACRONYM" >IBM</SPAN > <SPAN CLASS="ACRONYM" >PC</SPAN >s</SPAN >. Find which of these boot loaders your <SPAN CLASS="SYSTEMITEM" >Linux</SPAN > installation uses and then follow the instructions for your boot loader in the following section.</P ></DIV ><H3 CLASS="FOOTNOTES" >Notes</H3 ><TABLE BORDER="0" CLASS="FOOTNOTES" WIDTH="100%" ><TR ><TD ALIGN="LEFT" VALIGN="TOP" WIDTH="5%" ><A NAME="FTN.AEN810" HREF="configure-boot-loader.html#AEN810" ><SPAN CLASS="footnote" >[1]</SPAN ></A ></TD ><TD ALIGN="LEFT" VALIGN="TOP" WIDTH="95%" ><P >As usual with <SPAN CLASS="PRODUCTNAME" ><SPAN CLASS="ACRONYM" >IBM PC/AT</SPAN ></SPAN > hardware <SPAN CLASS="QUOTE" >"loads a boot loader from the <SPAN CLASS="ACRONYM" >MBR</SPAN > of the first hard disk"</SPAN > is a simplification. <SPAN CLASS="ACRONYM" >BIOS</SPAN > settings permitting, the <SPAN CLASS="ACRONYM" >MBR</SPAN > can be loaded from the first two detected hard disks of any controller card containing a <SPAN CLASS="ACRONYM" >BIOS</SPAN > extension. Thus the <SPAN CLASS="ACRONYM" >MBR</SPAN > can be loaded from one of the first two detected <SPAN CLASS="ACRONYM" >IDE</SPAN > disks and one of the first two detected <SPAN CLASS="ACRONYM" >SCSI</SPAN > disks.</P ></TD ></TR ><TR ><TD ALIGN="LEFT" VALIGN="TOP" WIDTH="5%" ><A NAME="FTN.AEN822" HREF="configure-boot-loader.html#AEN822" ><SPAN CLASS="footnote" >[2]</SPAN ></A ></TD ><TD ALIGN="LEFT" VALIGN="TOP" WIDTH="95%" ><P >Another simplification. A 512 byte <SPAN CLASS="ACRONYM" >MBR</SPAN > is too small to contain a program big enough to load a complex operating system. Thus most boot loaders have two stages, the first stage is located in the <SPAN CLASS="ACRONYM" >MBR</SPAN > and is only able to load the second stage of the boot loader from somewhere on a disk (such as the boot sector of the first partition). The second stage of the boot loader presents the user interface and loads the operating system.</P ></TD ></TR ></TABLE ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE SUMMARY="Footer navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="bios.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="index.html" ACCESSKEY="H" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="configure-boot-loader-lilo.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >Optionally configure the <SPAN CLASS="ACRONYM" >BIOS</SPAN ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" > </TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >Configure the <SPAN CLASS="APPLICATION" >LILO</SPAN > boot loader</TD ></TR ></TABLE ></DIV ></BODY ></HTML >