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diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node68.html b/sag-0.6.1-www/Invisible/sag-0.6/node68.html new file mode 100644 index 0000000..3bd79e3 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node68.html @@ -0,0 +1,224 @@ +<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN"> +<!--Converted with LaTeX2HTML 96.1-h (September 30, 1996) by Nikos Drakos (nikos@cbl.leeds.ac.uk), CBLU, University of Leeds --> +<HTML> +<HEAD> +<TITLE>The boot process in closer look</TITLE> +<META NAME="description" CONTENT="The boot process in closer look"> +<META NAME="keywords" CONTENT="sag"> +<META NAME="resource-type" CONTENT="document"> +<META NAME="distribution" CONTENT="global"> +<LINK REL=STYLESHEET HREF="sag.css"> +</HEAD> +<BODY LANG="EN" > + <A NAME="tex2html1170" HREF="node69.html"><IMG WIDTH=37 HEIGHT=24 ALIGN=BOTTOM ALT="next" SRC="./next_motif.gif"></A> <A NAME="tex2html1168" HREF="node66.html"><IMG WIDTH=26 HEIGHT=24 ALIGN=BOTTOM ALT="up" SRC="./up_motif.gif"></A> <A NAME="tex2html1162" HREF="node67.html"><IMG WIDTH=63 HEIGHT=24 ALIGN=BOTTOM ALT="previous" SRC="./previous_motif.gif"></A> <A NAME="tex2html1172" HREF="node1.html"><IMG WIDTH=65 HEIGHT=24 ALIGN=BOTTOM ALT="contents" SRC="./contents_motif.gif"></A> <A NAME="tex2html1173" HREF="node114.html"><IMG WIDTH=43 HEIGHT=24 ALIGN=BOTTOM ALT="index" SRC="./index_motif.gif"></A> <BR> +<B> Next:</B> <A NAME="tex2html1171" HREF="node69.html">More about shutdowns</A> +<B>Up:</B> <A NAME="tex2html1169" HREF="node66.html">Boots And Shutdowns</A> +<B> Previous:</B> <A NAME="tex2html1163" HREF="node67.html">An overview of boots </A> +<BR> <P> +<H1><A NAME="SECTION00720000000000000000">The boot process in closer look</A></H1> +<P> +<A NAME="secbootcloseup"> </A> +<P> + You can boot Linux either from a floppy or from the hard + disk. The installation section in the Installation and + Getting Started guide ([<A HREF="node113.html#getting-started">Wel</A>]) + tells you how to install Linux so you can boot it the way + you want to. +<P> + When a PC is booted, the BIOS will do various tests to + check that everything looks all right,<A NAME="tex2html30" HREF="footnode.html#2102"><IMG ALIGN=BOTTOM ALT="gif" SRC="./foot_motif.gif"></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 <b>boot sector</b>; for a hard disk, it is also + called the <b>master boot record</b>, since a hard disk can + contain several partitions, each with their own boot sectors. +<A NAME="1980"> </A> +<A NAME="1981"> </A> +<A NAME="1982"> </A> +<A NAME="1983"> </A> +<A NAME="2103"> </A> +<A NAME="2104"> </A> +<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. +<A NAME="1986"> </A> +<A NAME="2105"> </A> +<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.) +<A NAME="1988"> </A> +<A NAME="2106"> </A> +<A NAME="1990"> </A> +<A NAME="1991"> </A> +<A NAME="1992"> </A> +<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 <TT>alt</TT>, <TT>shift</TT>, or <TT>ctrl</TT> 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> + With LILO, it is also possible to give a <b>kernel command + line argument</b>, after the name of the kernel or operating + system. +<P> + <b>META: </b> The are other boot loaders than LILO. Information about + them will be added in some future version. loadlin. +<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> + After the Linux kernel has been read into the memory, by + whatever means, and is started for real, roughly the following + things happen: +<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. +<A NAME="1998"> </A> +<A NAME="1999"> </A> +<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 <tt>rdev</tt><A NAME="2125"> </A>. +<A NAME="2001"> </A> +<A NAME="2002"> </A> +<A NAME="2003"> </A> +<A NAME="2004"> </A> +<LI> +<P> + After this, the kernel checks what other hardware there is + (hard disks, floppies, network adapters...), 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: +<A NAME="2005"> </A> +<A NAME="2006"> </A> +<A NAME="2007"> </A> +<A NAME="2008"> </A> + <BLOCKQUOTE> <PRE>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</PRE></BLOCKQUOTE> + The exact texts are different on different systems, depending + on the hardware, the version of Linux being used, and how + it has been configured. +<LI> +<P> + Then the kernel will try to mount the root filesystem. The + place is configurable at + compilation time, or any time with <tt>rdev</tt><A NAME="2127"> </A> + 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). +<A NAME="2012"> </A> +<A NAME="2013"> </A> +<A NAME="2014"> </A> +<A NAME="2015"> </A> +<A NAME="2016"> </A> +<A NAME="2017"> </A> +<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. +<A NAME="2018"> </A> +<A NAME="2019"> </A> +<A NAME="2020"> </A> +<LI> +<P> + After this, the kernel starts the program <tt>init</tt><A NAME="2129"> </A> + (located in <tt>/sbin/init</tt><A NAME="2131"> </A>) in + the background (this will always become process number 1). + <tt>init</tt><A NAME="2133"> </A> does various startup chores. The exact things it does + depends on how it is configured; see + chapter <A HREF="node73.html#chinit">7</A> for more information (not yet written). It will at least + start some essential background daemons. +<A NAME="2025"> </A> +<LI> +<P> + <tt>init</tt><A NAME="2135"> </A> then switches to multi-user mode, and starts + a <tt>getty</tt><A NAME="2137"> </A> for virtual consoles and serial lines. + <tt>getty</tt><A NAME="2139"> </A> is the program which lets people log in + via virtual consoles and serial terminals. <tt>init</tt><A NAME="2141"> </A> + may also start some other programs, depending on how + it is configured. +<A NAME="2030"> </A> +<A NAME="2031"> </A> +<A NAME="2032"> </A> +<A NAME="2033"> </A> +<LI> +<P> + After this, the boot is complete, and the system is up and + running normally. +<P> + </UL><HR><A NAME="tex2html1170" HREF="node69.html"><IMG WIDTH=37 HEIGHT=24 ALIGN=BOTTOM ALT="next" SRC="./next_motif.gif"></A> <A NAME="tex2html1168" HREF="node66.html"><IMG WIDTH=26 HEIGHT=24 ALIGN=BOTTOM ALT="up" SRC="./up_motif.gif"></A> <A NAME="tex2html1162" HREF="node67.html"><IMG WIDTH=63 HEIGHT=24 ALIGN=BOTTOM ALT="previous" SRC="./previous_motif.gif"></A> <A NAME="tex2html1172" HREF="node1.html"><IMG WIDTH=65 HEIGHT=24 ALIGN=BOTTOM ALT="contents" SRC="./contents_motif.gif"></A> <A NAME="tex2html1173" HREF="node114.html"><IMG WIDTH=43 HEIGHT=24 ALIGN=BOTTOM ALT="index" SRC="./index_motif.gif"></A> <BR> +<B> Next:</B> <A NAME="tex2html1171" HREF="node69.html">More about shutdowns</A> +<B>Up:</B> <A NAME="tex2html1169" HREF="node66.html">Boots And Shutdowns</A> +<B> Previous:</B> <A NAME="tex2html1163" HREF="node67.html">An overview of boots </A> +<P><ADDRESS> +<I>Lars Wirzenius <BR> +Sat Nov 15 02:32:11 EET 1997</I> +</ADDRESS> +</BODY> +</HTML> |