source: postlfs/config/bootdisk.xml@ 036393e1

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Last change on this file since 036393e1 was 036393e1, checked in by Larry Lawrence <larry@…>, 20 years ago

more corner sweeping

git-svn-id: svn://svn.linuxfromscratch.org/BLFS/trunk/BOOK@838 af4574ff-66df-0310-9fd7-8a98e5e911e0

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1<sect1 id="postlfs-config-bootdisk">
2<?dbhtml filename="bootdisk.html" dir="postlfs"?>
3<title>Creating a custom bootdisk</title>
4
5<para>How to create a decent bootdisk</para>
6<para>The intent here is to create a "rescue bootdisk" that will load
7enough 'linux' to enable you to do rescue operations. With what is presented here
8you will be able to do file manipulation, mounting and unmounting, and other tasks.
9This however is not the limit. The minimal disk is described here, and you can
10add anything you can fit on the floppy.</para>
11<para>
12Boot disk/Rescue Disk
13</para>
14<para>
15First we will create a loopback file to build our rescue disk image on, next
16we'll make a file system on the image file, then we'll use 'mount' to mount
17the file as a regular disk, allowing us to read and write files from the loopback file.
18The following commands will build us a 4 MB image.
19</para>
20<screen><userinput>dd if=/dev/zero of=/tmp/rfloppy bs=1k count=4096 &amp;&amp;
21mke2fs -m 0 -N 2000 /tmp/rfloppy &amp;&amp;
22mount -o loop /tmp/rfloppy /mnt/loop1 &amp;&amp;
23rmdir /mnt/loop1/lost+found/</userinput></screen>
24
25
26<para>
27Now that we have a file mounted and usable, let's prepare it to be
28filled with useful material. Since this is only a rescue floppy we'll
29only need to set up the minimum directories.</para>
30<para><screen><userinput>mkdir /mnt/loop1/{dev,proc,etc,sbin,bin,lib,mnt,usr,var}</userinput></screen></para>
31<para>Next, we will set up the device files. I use devfs on my system, so
32the following command works well, as I only have the devices I use
33anyway. If you used MAKEDEV to create your devices, you'll want to
34trim the <filename>/mnt/loop1/dev</filename> directory to reclaim the inode space wasted
35by all of the devices in the <filename>dev</filename> directory you don't use.</para>
36<para><screen><userinput>cp -dpR /dev/* /mnt/loop1/dev</userinput></screen></para>
37<para>Now to tend to the <filename>/etc</filename> directory. To start, all we will do is use
38the passwd and group file that worked for our static chroot environment
39when we built LFS. We'll also copy the startup scripts over and a few other files
40that serve well as starting points.</para>
41<para><screen><userinput>cp -ax /etc/rc* /mnt/loop1/etc
42cp -ax /etc/fstab /mnt/loop1/etc
43echo "root:x:0:0:root:/root:/bin/bash" &gt; /mnt/loop1/etc/passwd
44cat &gt; /mnt/loop1/etc/group &lt;&lt; "EOF"
45root:x:0:
46bin:x:1:
47sys:x:2:
48kmem:x:3:
49tty:x:4:
50tape:x:5:
51daemon:x:6:
52floppy:x:7:
53disk:x:8:
54lp:x:9:
55dialout:x:10:
56audio:x:11:
57EOF</userinput></screen>
58</para>
59<para>
60
61To prevent automatic mounting of hard drive partitions,
62make sure to add the noauto option in their fstab entry. Also, add the
63following entries to the <filename>/mnt/loop1/etc/fstab</filename> to assist with mounting our
64floppy and the ram image</para>
65<para><screen>/dev/ram0 / ext2 defaults
66/dev/fd0 / ext2 defaults</screen></para>
67
68<para>Next, we will install <ulink
69url="http://www.busybox.net/downloads/busybox-0.60.4.tar.bz2">busybox</ulink>
70onto the image. Busybox incorporates many of the unix functions into a single small executable file.</para>
71<screen><userinput>make &amp;&amp;
72make PREFIX=/mnt/loop1 install &amp;&amp;
73cp -ax /var/utmp /mnt/loop1/var &amp;&amp;
74mkdir /mnt/loop1/var/log</userinput></screen>
75<para>
76Also, keeping in mind your space limitations, copy any other binaries and libraries you
77need to the image. Use the <userinput>ldd</userinput> command to
78see which libraries you will need to copy over for any executables.
79</para>
80<para>
81Now, since I use devfs to create devices on the fly and free up precious
82inodes on the floppy, we'll also install devfsd to facilitate the
83devices that busybox expects to find.</para>
84
85<screen><userinput>mv GNUmakefile Makefile &amp;&amp;
86make &amp;&amp;
87make PREFIX=/mnt/loop1 install &amp;&amp;
88cp /lib/libc.so.6 /lib/ld-linux.so.2 /lib/libdl.so.2 /tmp &amp;/&amp;
89strip --strip-deb /tmp/ld-linux.so.2 /tmp/libc.so.6 /tmp/libdl.so.2 &amp;&amp;
90mv /tmp/ld-linux.so.2 /tmp/libc.so.6 /tmp/libdl.so.2 /mnt/loop1/lib/</userinput></screen>
91<para>
92We will also need to set up an rc script to handle the devfsd startup.
93Put this in <filename>/mnt/loop1/etc/init.d/rcS</filename>.</para>
94<screen>#!/bin/sh
95mount -t devfs devfs /dev
96/sbin/devfsd /dev</screen>
97
98<para>
99Next create your compressed root filesystem. We use -9 with gzip to
100make the smallest possible compressed image.</para>
101<screen><userinput>umount /mnt/loop1 &amp;&amp; dd if=/tmp/rfloppy bs=1k | gzip -v9 > rootfs.gz</userinput></screen>
102<screen><userinput>ls -l rootfs.gz</userinput> to make sure it will fit on the diskette.</screen>
103<para>
104Make a custom kernel that is optimized for size. Include only those features
105you will need to rescue your system. no sense in building in support for things
106like xfree86 dri, etc, as most rescues are performed from the command prompt.
107</para>
108<screen><userinput>dd if=rescueimg of=/dev/floppy/0 bs=1k</userinput>
109 429+1 records in
110 429+1 records out
111<userinput>rdev /dev/floppy/0 /dev/floppy/0</userinput>
112<userinput>rdev -R /dev/floppy/0 0</userinput>
113</screen>
114
115<para>In this example the rescueimage(KERNEL) was 429+1 blocks in size.
116We will remember this for the next command. We now write the root file
117system right after the kernel on the floppy by doing 16384+429+1=
11816814.</para>
119<screen><userinput>rdev -r /dev/floppy/0 16814</userinput></screen>
120
121
122<screen><userinput>dd if=rootfs.gz of=/dev/floppy/0 bs=1k seek=430</userinput></screen>
123<para>In this command we use seek to find the end of the kernel (429+1) and write the root file system to the floppy.
124</para>
125</sect1>
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