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209 lines
9.5 KiB
XML
209 lines
9.5 KiB
XML
<?xml version="1.0" encoding="ISO-8859-1"?>
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<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
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<!ENTITY % general-entities SYSTEM "../general.ent">
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%general-entities;
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]>
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<sect1 id="ch-bootable-grub" role="wrap">
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<?dbhtml filename="grub.html"?>
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<sect1info condition="script">
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<productname>grub</productname>
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<productnumber>&grub-version;</productnumber>
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<address>&grub-url;</address>
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</sect1info>
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<title>Using GRUB to Set Up the Boot Process</title>
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<note>
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<para>
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If your system has UEFI support and you wish to boot LFS with UEFI,
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you should skip this page, and configure GRUB with UEFI support
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using the instructions provided in
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<ulink url="&blfs-book;postlfs/grub-setup.html">the BLFS page</ulink>.
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</para>
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</note>
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<sect2>
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<title>Introduction</title>
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<warning><para>Configuring GRUB incorrectly can render your system
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inoperable without an alternate boot device such as a CD-ROM or bootable
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USB drive. This section is not required to boot your LFS system. You may
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just want to modify your current boot loader, e.g. Grub-Legacy, GRUB2, or
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LILO.</para></warning>
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<para> Ensure that an emergency boot disk is ready to <quote>rescue</quote>
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the computer if the computer becomes unusable (un-bootable). If you do not
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already have a boot device, you can create one. In order for the procedure
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below to work, you need to jump ahead to BLFS and install
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<userinput>xorriso</userinput> from the <ulink
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url="&blfs-book;multimedia/libisoburn.html">
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libisoburn</ulink> package.</para>
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<screen role="nodump"><userinput>cd /tmp
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grub-mkrescue --output=grub-img.iso
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xorriso -as cdrecord -v dev=/dev/cdrw blank=as_needed grub-img.iso</userinput></screen>
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</sect2>
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<sect2>
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<title>GRUB Naming Conventions</title>
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<para>GRUB uses its own naming structure for drives and partitions in
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the form of <emphasis>(hdn,m)</emphasis>, where <emphasis>n</emphasis>
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is the hard drive number and <emphasis>m</emphasis> is the partition
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number. The hard drive numbers start from zero, but the partition numbers
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start from one for normal partitions (from five for extended partitions).
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Note that this is different from earlier versions where
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both numbers started from zero. For example, partition <filename
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class="partition">sda1</filename> is <emphasis>(hd0,1)</emphasis> to
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GRUB and <filename class="partition">sdb3</filename> is
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<emphasis>(hd1,3)</emphasis>. In contrast to Linux, GRUB does not
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consider CD-ROM drives to be hard drives. For example, if using a CD
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on <filename class="partition">hdb</filename> and a second hard drive
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on <filename class="partition">hdc</filename>, that second hard drive
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would still be <emphasis>(hd1)</emphasis>.</para>
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</sect2>
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<sect2>
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<title>Setting Up the Configuration</title>
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<para>GRUB works by writing data to the first physical track of the
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hard disk. This area is not part of any file system. The programs
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there access GRUB modules in the boot partition. The default location
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is /boot/grub/.</para>
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<para>The location of the boot partition is a choice of the user that
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affects the configuration. One recommendation is to have a separate small
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(suggested size is 200 MB) partition just for boot information. That way
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each build, whether LFS or some commercial distro, can access the same boot
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files and access can be made from any booted system. If you choose to do
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this, you will need to mount the separate partition, move all files in the
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current <filename class="directory">/boot</filename> directory (e.g. the
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Linux kernel you just built in the previous section) to the new partition.
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You will then need to unmount the partition and remount it as <filename
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class="directory">/boot</filename>. If you do this, be sure to update
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<filename>/etc/fstab</filename>.</para>
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<para>Leaving <filename class="directory">/boot</filename> on
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the current LFS partition will also work, but configuration
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for multiple systems is more difficult.</para>
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<para>Using the above information, determine the appropriate
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designator for the root partition (or boot partition, if a separate
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one is used). For the following example, it is assumed that the root
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(or separate boot) partition is <filename
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class="partition">sda2</filename>.</para>
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<para>Install the GRUB files into <filename
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class="directory">/boot/grub</filename> and set up the boot track:</para>
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<warning>
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<para>The following command will overwrite the current boot loader. Do not
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run the command if this is not desired, for example, if using a third party
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boot manager to manage the Master Boot Record (MBR).</para>
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</warning>
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<screen role="nodump"><userinput>grub-install /dev/sda</userinput></screen>
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<note>
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<para>If the system has been booted using UEFI,
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<command>grub-install</command> will try to install files for the
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<emphasis>x86_64-efi</emphasis> target, but those files
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have not been installed in <xref linkend="chapter-building-system"/>.
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If this is the case, add <option>--target i386-pc</option> to the
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command above.</para>
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</note>
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<!-- This does not seem to be true any more
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<note><para><application>grub-install</application> is a script and calls another
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program, grub-probe, that may fail with a message "cannot stat `/dev/root'".
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If so, create a temporary symbolic link from your root partition to /dev/root:</para>
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<screen role="nodump"><userinput>ln -sv /dev/sda2 /dev/root</userinput></screen>
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<para>The symbolic link will only be present until the system is rebooted.
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The link is only needed for the installation procedure.
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</para></note>
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-->
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</sect2>
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<sect2 id="grub-cfg">
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<title>Creating the GRUB Configuration File</title>
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<para>Generate <filename>/boot/grub/grub.cfg</filename>:</para>
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<screen><userinput>cat > /boot/grub/grub.cfg << "EOF"
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<literal># Begin /boot/grub/grub.cfg
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set default=0
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set timeout=5
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insmod ext2
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set root=(hd0,2)
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menuentry "GNU/Linux, Linux &linux-version;-lfs-&version;" {
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linux /boot/vmlinuz-&linux-version;-lfs-&version; root=/dev/sda2 ro
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}</literal>
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EOF</userinput></screen>
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<note><para>From <application>GRUB</application>'s perspective, the
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kernel files are relative to the partition used. If you
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used a separate /boot partition, remove /boot from the above
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<emphasis>linux</emphasis> line. You will also need to change the
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<emphasis>set root</emphasis> line to point to the boot partition.
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</para></note>
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<note>
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<para>The GRUB designator for a partition may change if you added or
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removed some disks (including removable disks like USB thumb devices).
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The change may cause boot failure because
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<filename>grub.cfg</filename> refers to some <quote>old</quote>
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designators. If you wish to avoid such a problem, you may use
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the UUID of a partition and the UUID of a filesystem instead of a GRUB designator to
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specify a device.
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Run <command>lsblk -o UUID,PARTUUID,PATH,MOUNTPOINT</command> to show
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the UUIDs of your filesystems (in the <literal>UUID</literal> column) and
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partitions (in the <literal>PARTUUID</literal> column). Then replace
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<literal>set root=(hdx,y)</literal> with
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<literal>search --set=root --fs-uuid <replaceable><UUID of the filesystem
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where the kernel is installed></replaceable></literal>, and replace
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<literal>root=/dev/sda2</literal> with
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<literal>root=PARTUUID=<replaceable><UUID of the partition where LFS
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is built></replaceable></literal>.</para>
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<para>Note that the UUID of a partition is completely different from the
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UUID of the filesystem in this partition. Some online resources may
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instruct you to use
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<literal>root=UUID=<replaceable><filesystem UUID></replaceable></literal>
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instead of
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<literal>root=PARTUUID=<replaceable><partition UUID></replaceable></literal>,
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but doing so will require an initramfs, which is beyond the scope of
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LFS.</para>
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<para>The name of the device node for a partition in
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<filename class='directory'>/dev</filename> may also change (this is less
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likely than a GRUB designator change). You can also replace
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paths to device nodes like <literal>/dev/sda1</literal> with
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<literal>PARTUUID=<replaceable><partition UUID></replaceable></literal>,
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in <filename>/etc/fstab</filename>, to avoid a potential boot failure
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in case the device node name has changed.</para>
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</note>
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<para>GRUB is an extremely powerful program and it provides a tremendous
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number of options for booting from a wide variety of devices, operating
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systems, and partition types. There are also many options for customization
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such as graphical splash screens, playing sounds, mouse input, etc. The
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details of these options are beyond the scope of this introduction.</para>
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<caution><para>There is a command, <application>grub-mkconfig</application>, that
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can write a configuration file automatically. It uses a set of scripts in
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/etc/grub.d/ and will destroy any customizations that you make. These scripts
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are designed primarily for non-source distributions and are not recommended for
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LFS. If you install a commercial Linux distribution, there is a good chance
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that this program will be run. Be sure to back up your grub.cfg file.</para></caution>
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</sect2>
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</sect1>
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