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diff --git a/sag-0.6.1-www/sag-0.6.1.html/x1602.html b/sag-0.6.1-www/sag-0.6.1.html/x1602.html new file mode 100644 index 0000000..5ca2228 --- /dev/null +++ b/sag-0.6.1-www/sag-0.6.1.html/x1602.html @@ -0,0 +1,398 @@ +<!DOCTYPE HTML PUBLIC "-//Norman Walsh//DTD DocBook HTML 1.0//EN"> +<HTML +><HEAD +><TITLE +>The boot process in closer look</TITLE +><META +NAME="GENERATOR" +CONTENT="Modular DocBook HTML Stylesheet"><LINK +REL="HOME" +TITLE="The Linux System Administrators' Guide" +HREF="book1.html"><LINK +REL="UP" +TITLE="Boots And Shutdowns" +HREF="c1582.html"><LINK +REL="PREVIOUS" +TITLE="Boots And Shutdowns" +HREF="c1582.html"><LINK +REL="NEXT" +TITLE="More about shutdowns" +HREF="x1650.html"></HEAD +><BODY +BGCOLOR="#FFFFFF" +TEXT="#000000" +><DIV +CLASS="NAVHEADER" +><TABLE +WIDTH="100%" +BORDER="0" +CELLPADDING="0" +CELLSPACING="0" +><TR +><TH +COLSPAN="3" +ALIGN="center" +>The Linux System Administrators' Guide</TH +></TR +><TR +><TD +WIDTH="10%" +ALIGN="left" +VALIGN="bottom" +><A +HREF="c1582.html" +>Prev</A +></TD +><TD +WIDTH="80%" +ALIGN="center" +VALIGN="bottom" +>Chapter 6. Boots And Shutdowns</TD +><TD +WIDTH="10%" +ALIGN="right" +VALIGN="bottom" +><A +HREF="x1650.html" +>Next</A +></TD +></TR +></TABLE +><HR +ALIGN="LEFT" +WIDTH="100%"></DIV +><DIV +CLASS="SECT1" +><H1 +CLASS="SECT1" +><A +NAME="AEN1602" +>The boot process in closer look</A +></H1 +><P +>You can boot Linux either from a floppy or from the hard + disk. The installation section in the Installation and + Getting Started guide (XXX citation) + tells you how to install Linux so you can boot it the way + you want to.</P +><P +>When a PC is booted, the BIOS will do various tests to + check that everything looks all right, + + <A +NAME="AEN1606" +HREF="#FTN.AEN1606" +>[1]</A +> + + and will then start the actual booting. It will choose a disk + drive (typically the first floppy drive, if there is a floppy + inserted, otherwise the first hard disk, if one is installed + in the computer; the order might be configurable, however) + and will then read its very first sector. This is called the + <I +CLASS="GLOSSTERM" +>boot sector</I +>; for a hard disk, it is also + called the <I +CLASS="GLOSSTERM" +>master boot record</I +>, since a + hard disk can contain several partitions, each with their own + boot sectors.</P +><P +>The boot sector contains a small program (small enough to + fit into one sector) whose responsibility is to read the actual + operating system from the disk and start it. When booting Linux + from a floppy disk, the boot sector contains code that just reads + the first few hundred blocks (depending on the actual kernel + size, of course) to a predetermined place in memory. On a Linux + boot floppy, there is no filesystem, the kernel is just stored + in consecutive sectors, since this simplifies the boot process. + It is possible, however, to boot from a floppy with a filesystem, + by using LILO, the LInux LOader.</P +><P +>When booting from the hard disk, the code in the master + boot record will examine the partition table (also in the master + boot record), identify the active partition (the partition that is + marked to be bootable), read the boot sector from that partition, + and then start the code in that boot sector. The code in the + partition's boot sector does what a floppy disk's boot sector + does: it will read in the kernel from the partition and start it. + The details vary, however, since it is generally not useful to + have a separate partition for just the kernel image, so the + code in the partition's boot sector can't just read the disk + in sequential order, it has to find the sectors wherever the + filesystem has put them. There are several ways around this + problem, but the most common way is to use LILO. (The details + about how to do this are irrelevant for this discussion, however; + see the LILO documentation for more information; it is most + thorough.)</P +><P +>When booting with LILO, it will normally go right ahead + and read in and boot the default kernel. It is also possible + to configure LILO to be able to boot one of several kernels, + or even other operating systems than Linux, and it is possible + for the user to choose which kernel or operating system is to + be booted at boot time. LILO can be configured so that if one + holds down the <B +CLASS="KEYCAP" +>alt</B +>, <B +CLASS="KEYCAP" +>shift</B +>, or + <B +CLASS="KEYCAP" +>ctrl</B +> key at boot time (when LILO is loaded), + LILO will ask what is to be booted and not boot the default + right away. Alternatively, LILO can be configured so that it + will always ask, with an optional timeout that will cause the + default kernel to be booted.</P +><P +>With LILO, it is also possible to give a <I +CLASS="GLOSSTERM" +>kernel + command line argument</I +>, after the name of the kernel + or operating system.</P +><P +>Booting from floppy and from hard disk have both their + advantages, but generally booting from the hard disk is nicer, + since it avoids the hassle of playing around with floppies. + It is also faster. However, it can be more troublesome to install + the system to boot from the hard disk, so many people will first + boot from floppy, then, when the system is otherwise installed + and working well, will install LILO and start booting from the + hard disk.</P +><P +>After the Linux kernel has been read into the memory, by + whatever means, and is started for real, roughly the following + things happen: + + <P +></P +><UL +><LI +><P +> The Linux kernel is installed compressed, so it will first + uncompress itself. The beginning of the kernel image + contains a small program that does this. + </P +></LI +><LI +><P +> If you have a super-VGA card that Linux + recognizes and that has some special text modes (such as 100 + columns by 40 rows), Linux asks you which mode + you want to use. During the kernel compilation, it is + possible to preset a video mode, so that this is never asked. + This can also be done with LILO or <B +CLASS="COMMAND" +>rdev</B +>. + </P +></LI +><LI +><P +> After this, the kernel checks what other hardware there is + (hard disks, floppies, network adapters, etc), and configures + some of its device drivers appropriately; while it does this, + it outputs messages about its findings. For example, when I + boot, I it looks like this: + +<PRE +CLASS="SCREEN" +><TT +CLASS="COMPUTEROUTPUT" +>LILO boot: +Loading linux. +Console: colour EGA+ 80x25, 8 virtual consoles +Serial driver version 3.94 with no serial options enabled +tty00 at 0x03f8 (irq = 4) is a 16450 +tty01 at 0x02f8 (irq = 3) is a 16450 +lp_init: lp1 exists (0), using polling driver +Memory: 7332k/8192k available (300k kernel code, 384k reserved, 176k data) +Floppy drive(s): fd0 is 1.44M, fd1 is 1.2M +Loopback device init +Warning WD8013 board not found at i/o = 280. +Math coprocessor using irq13 error reporting. +Partition check: + hda: hda1 hda2 hda3 +VFS: Mounted root (ext filesystem). +Linux version 0.99.pl9-1 (root@haven) 05/01/93 14:12:20</TT +></PRE +> + + The exact texts are different on different systems, depending + on the hardware, the version of Linux being used, and how + it has been configured. + </P +></LI +><LI +><P +> Then the kernel will try to mount the root + filesystem. The place is configurable at compilation time, or + any time with <B +CLASS="COMMAND" +>rdev</B +> or LILO. The filesystem + type is detected automatically. If the mounting of the root + filesystem fails, for example because you didn't remember to + include the corresponding filesystem driver in the kernel, the + kernel panics and halts the system (there isn't much it can do, + anyway). </P +><P +>The root filesystem is usually mounted read-only (this can + be set in the same way as the place). This makes it possible + to check the filesystem while it is mounted; it is not a good + idea to check a filesystem that is mounted read-write. + </P +></LI +><LI +><P +> After this, the kernel starts + the program <B +CLASS="COMMAND" +>init</B +> (located in + <TT +CLASS="FILENAME" +>/sbin/init</TT +>) in the background (this will + always become process number 1). <B +CLASS="COMMAND" +>init</B +> does + various startup chores. The exact things it does depends on how + it is configured; see <A +HREF="c1705.html" +>Chapter 7</A +> for more information + (not yet written). It will at least start some essential + background daemons. </P +></LI +><LI +><P +> <B +CLASS="COMMAND" +>init</B +> then switches to + multi-user mode, and starts a <B +CLASS="COMMAND" +>getty</B +> for virtual + consoles and serial lines. <B +CLASS="COMMAND" +>getty</B +> is the + program which lets people log in via virtual consoles and serial + terminals. <B +CLASS="COMMAND" +>init</B +> may also start some other + programs, depending on how it is configured. </P +></LI +><LI +><P +> After this, the boot is complete, and the system + is up and running normally. </P +></LI +></UL +> + </P +></DIV +><H3 +>Notes</H3 +><TABLE +BORDER="0" +CLASS="FOOTNOTES" +WIDTH="100%" +><TR +><TD +ALIGN="LEFT" +VALIGN="TOP" +WIDTH="5%" +><A +NAME="FTN.AEN1606" +HREF="x1602.html#AEN1606" +>[1]</A +></TD +><TD +ALIGN="LEFT" +VALIGN="TOP" +WIDTH="95%" +><P +>This is called + the <I +CLASS="GLOSSTERM" +>power on self test</I +>, or + <I +CLASS="GLOSSTERM" +>POST</I +> for short.</P +></TD +></TR +></TABLE +><DIV +CLASS="NAVFOOTER" +><HR +ALIGN="LEFT" +WIDTH="100%"><TABLE +WIDTH="100%" +BORDER="0" +CELLPADDING="0" +CELLSPACING="0" +><TR +><TD +WIDTH="33%" +ALIGN="left" +VALIGN="top" +><A +HREF="c1582.html" +>Prev</A +></TD +><TD +WIDTH="34%" +ALIGN="center" +VALIGN="top" +><A +HREF="book1.html" +>Home</A +></TD +><TD +WIDTH="33%" +ALIGN="right" +VALIGN="top" +><A +HREF="x1650.html" +>Next</A +></TD +></TR +><TR +><TD +WIDTH="33%" +ALIGN="left" +VALIGN="top" +>Boots And Shutdowns</TD +><TD +WIDTH="34%" +ALIGN="center" +VALIGN="top" +><A +HREF="c1582.html" +>Up</A +></TD +><TD +WIDTH="33%" +ALIGN="right" +VALIGN="top" +>More about shutdowns</TD +></TR +></TABLE +></DIV +></BODY +></HTML +>
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