Difference between pages "GUID Booting Guide" and "FLOP:Ports-2015"

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== Introduction ==
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{{FLOP
 
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|Created on=2015/02/23
GPT, which stands for GUID Partition Table, is a disk partitioning scheme that was introduced by Intel for Itanium architecture systems, as part of EFI, the Extensible Firmware Interface. While you are probably not using an Itanium architecture computer, and you are likely using a BIOS-based rather than an EFI-based system, you still may want to use GPT partitioning. Why? Because the standard MBR-based partitioning scheme only supports system disks that are less than 2TiB in size. On modern systems, especially systems with hardware RAID logical volumes, it is very easy to go beyond the 2TiB limit. GUID partition tables support disks that are larger than 2TiB in size.
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|Summary=Collection of ideas and changes for the ports-2015 tree. The goal is to perform many scheduled changes with a single user configuration change.
 
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|Author=Mgorny,
=== GPT Technology Overview ===
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|Reference Bug=FL-1877
 
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This section contains a technical overview of GPT technology.
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GUID partition tables support up to 512 partitions. GPT data structures are stored in the first sectors of the drive with a secondary copy stored at the end of the drive. This allows the partitioning scheme of your disk to be recovered in situations where the primary partition table has been corrupted.
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For compatibility with legacy partitioning tools, GPT partitioning tools typically rewrite the MBR partition table (generally located in the first sector of the disk) in a way those tools will interpret it like ''"This disk has only one partition (of an unknown type) covering the whole disk".''
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It is possible to convert an existing MBR-partitioned disk to GPT format using the <tt>gdisk</tt> command. Please carefully read the <tt>gdisk</tt> man page before using this capability, as it is potentially dangerous, particularly if you are performing it on your boot disk.
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{{ fancyimportant|Funtoo Linux fully supports GPT on x86-32bit and x86-64-bit systems. GPT is supported on SPARC systems, but currently only for non-boot disks.
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== Procedure ==
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Users of ports-2012 tree will be informed that the current repository is deprecated, and provided with complete migration instructions. The instructions will cover both necessary and optional changes that can be done conveniently along with the necessary switch.
  
=== Booting GPT ===
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== Changes ==
 
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=== History cut-off ===
If you decide to use a GPT-based partitioning scheme for your system disk, either out of necessity due to a 2TiB+ disk, or because you want to try GPT out, then the question arises -- how do you get the darn thing to boot? This is where the new <tt>GRUB</tt> boot loader comes in. The new <tt>GRUB</tt> (version 1.9x, found at <tt>sys-boot/grub</tt>) is a redesign of the original <tt>GRUB</tt> (version 0.9x, now called <tt>sys-boot/grub-legacy</tt> in Funtoo) boot-loader that includes very mature support for booting from GPT-based disks.
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As an implication of starting a new tree, all history is cut-off. While users were cloning the repository with --depth=1, old clones have accumulated a large history of changes. This history will be discarded with the new clone. This will significatly decrease the size of portage tree and the size of portage tree compressed tarball, if someone prefer to use it. Eventually, portage tree will grow up again.
 
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Now, let's take a look at how to get GPT-based booting working under Funtoo Linux.
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== Getting Started ==
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The first thing you'll need to do is to use a LiveCD. I recommend [http://www.sysresccd.org/Main_Page System Rescue CD] for this task as it is Gentoo-based and includes all the proper tools. Go ahead and boot the LiveCD, and then get to the point where you are ready to partition your system disk.
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At this point, you have two choices as to what partitioning tool to use. You can use either <tt>gdisk</tt> or <tt>parted</tt>. <tt>gdisk</tt> is a very nice <tt>fdisk</tt>-like partitioning tool that supports GPT partitioning. It is rather new software but seems to work quite well. The other tool you can use, GNU <tt>parted</tt>, has been around for a while and is more mature, but is harder to use.
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We'll take a look at how to create partitions using <tt>gdisk</tt>. Alternatively, <code>cgdisk</code>, curses-based gdisk for users familiar with cfdisk or <code>sgdisk</code>, command-line tool can be used for creating and managing GPT partitions.
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== Partitioning Using Gdisk ==
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OK, the first step is using <tt>gdisk</tt> is to start it up, specifying the disk you want to modify:
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<pre># gdisk /dev/sda</pre>
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You should find <tt>gdisk</tt> very familiar to <tt>fdisk</tt>. Here is the partition table we want to end up with:
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<pre>Command (? for help): p
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Disk /dev/sda: 312581808 sectors, 149.1 GiB
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Disk identifier (GUID): 17
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Partition table holds up to 128 entries
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First usable sector is 34, last usable sector is 312581774
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Total free space is 0 sectors (0 bytes)
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Number  Start (sector)    End (sector)  Size      Code  Name
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  1              34          204833  100.0 MiB  0700  Linux/Windows data
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  2          204834          270369  512.0 kiB  EF02  BIOS boot partition
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  3          270370        1318945  512.0 MiB  8200  Linux swap
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  4        1318946      312581774  148.4 GiB  0700  Linux/Windows data
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Command (? for help): </pre>
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Above, you'll see that we have a 100 MiB boot partition, a 512 kiB &quot;BIOS boot partition&quot;, 512 MiB of swap, and the remaining disk used by a 148.4 GiB root partition.
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The one new thing here is the &quot;BIOS boot partition.&quot; What is it? In GRUB-speak, this BIOS boot partition is basically the location of the meat of GRUB's boot loading code - the quivalent of the <tt>stage1_5</tt> and <tt>stage2</tt> files in legacy GRUB. Since GPT-based partition tables have less &quot;bonus&quot; space than their MBR equivalents, and explicit partition of code <tt>EF02</tt> is required to hold the guts of the boot loader.
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In all other respects, the partition table is similar to that of an MBR-based disk. We have a boot and root partition with code <tt>0700</tt>, and a Linux swap partition with code <tt>8200</tt>. One this partition table has been written to disk and appropriate <tt>mkfs</tt> and <tt>mkswap</tt> commands are issued, <tt>/dev/sda1</tt> will be used to hold <tt>/boot</tt>, <tt>/dev/sda2</tt> will be used by the new GRUB directly, <tt>/dev/sda3</tt> will house our swap and <tt>/dev/sda4</tt> will hold our root filesystem.
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Go ahead and create filesystems on these partitions, and then mount the root and boot filesystems to <tt>/mnt/gentoo</tt> and <tt>/mnt/gentoo/boot</tt> respectively. Now go ahead and unpack a stage3 tarball to <tt>/mnt/gentoo</tt> and chroot in as you normally do.
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== Configuring The Kernel ==
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Your kernel will need a couple of extra GPT-related options enabled in order for it to make sense of your GPT partitions and find your filesystems. These options can be found under <tt>Enable the block layer ---&gt; Partition Types</tt>:
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<pre>[*] Advanced Partition Selection (PARTITION_ADVANCED)
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[*] EFI GUID Partition Support (EFI_PARTITION)</pre>
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If you are using a non-Funtoo distribution then you may need to append a proper <tt>rootfstype=</tt> option to your kernel boot options to allow Linux to properly mount the root filesystem when <tt>Advanced Partition Selection</tt> is enabled. [[Boot-Update]] does this for you automatically.
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Now just go ahead and compile and install your kernel, and copy it to <tt>/boot/bzImage</tt>.
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== Booting The System ==
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To get the system booted, you will want to first edit <tt>/etc/fstab</tt> inside the chroot so that it reflects the partitions and filesystems you just created. Then, emerge <tt>boot-update</tt> version 1.4_beta2 or later:
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<pre># emerge boot-update</pre>
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=== Portage upgrade / repos.conf switch ===
[[Boot-Update]] is a front-end for the GRUB 1.9x boot loader and provides a necessary simplified configuration interface. <tt>boot-update</tt> is used to generate boot loader configuration files. But before we get to <tt>boot-update</tt>, we first need to install GRUB to your hard disk. This is done as follows:
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Reference: {{Bug|FL-1761}}, [[Repository Configuration]]
  
<pre># grub-install /dev/sda</pre>
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As a part of upstream Portage changes, the upgrade is accompanied with some configuration file changes. Aside them, repository configuration is moved to repos.conf and the repository name becomes significant. Merging this with ports-2015 switch allows users to update the configuration in new format already.
<tt>grub-install</tt> will detect and use <tt>/dev/sda2</tt> and use it to store its boot loader logic.
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Now it's time to create an <tt>/etc/boot.conf</tt> file. For more information on all available options, consult the [[Boot-Update]] guide -- I'll show you a sample configuration for the sample GPT partition scheme above:
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=== Repository rename ===
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Reference: {{Bug|FL-1801}}
  
<pre>boot {
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Right now, the main repository inherits the name 'gentoo'. This is a bit confusing, considering that it is a modified Funtoo variant of the package tree. Changing the name to 'funtoo' would improve consistency and carry some bit of 'branding' into packages. Merging this into ports-2015 switch allows users to consciously update all repository references if necessary, and combines the change with necessity of specifying repository name in repos.conf.
        generate grub
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        default bzImage
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}
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&quot;Funtoo Linux&quot; {
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== Other possible changes ==
        kernel bzImage
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=== Filesystem structure reorganization ===
}</pre>
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Since users will be required to clone the new repository, it may be desired to suggest some best practices for filesystem layout. This specifically includes separating ebuilds from distfiles & packages, and using a multi-repository layout. Historically, portage tree inspired by FreeBSD ports, located in <code>/usr/portage>. This FHS layout is different in BSD and in Linux and we will probably move it elsewhere, see below for a suggestion and possible pros and cons.
Once <tt>/etc/boot.conf</tt> has been created, then type:
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<pre># boot-update</pre>
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Example layout suggested by mgorny:
This will auto-generate a <tt>/boot/grub/grub.cfg</tt> file for you, and you will now be able to reboot into Funtoo Linux using a GPT partitioning scheme.
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# all repositories in ''/var/db/repos/${repo_name}'' (i.e. Funtoo repository in ''/var/db/repos/funtoo'', and possible overlays as other directories in ''/var/db/repos''),
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# distfiles in ''/var/cache/portage/distfiles'',
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# binary packages in ''/var/cache/portage/packages''.
  
For more information on all the options available for <tt>/etc/boot.conf</tt>, please consult the [[Boot-Update]] guide.
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Users can be recommended to use a separate filesystem that can handle small files efficiently for ''/var/db/repos'', e.g. btrfs, reiserfs or possibly squashfs.
  
[[Category:Articles]]
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{{FLOPFooter}}

Revision as of 13:50, February 23, 2015

Created on
2015/02/23
Original Author(s)
{{#set:Author={{ #show: User:Mgorny | ?Full name }}}}{{ #show: User:Mgorny | ?Full name }}
Status
Reference Bug
FL-1877

Funtoo Linux Optimization Proposal: Ports-2015

Collection of ideas and changes for the ports-2015 tree. The goal is to perform many scheduled changes with a single user configuration change.

Procedure

Users of ports-2012 tree will be informed that the current repository is deprecated, and provided with complete migration instructions. The instructions will cover both necessary and optional changes that can be done conveniently along with the necessary switch.

Changes

History cut-off

As an implication of starting a new tree, all history is cut-off. While users were cloning the repository with --depth=1, old clones have accumulated a large history of changes. This history will be discarded with the new clone. This will significatly decrease the size of portage tree and the size of portage tree compressed tarball, if someone prefer to use it. Eventually, portage tree will grow up again.

Portage upgrade / repos.conf switch

Reference: FL-1761, Repository Configuration

As a part of upstream Portage changes, the upgrade is accompanied with some configuration file changes. Aside them, repository configuration is moved to repos.conf and the repository name becomes significant. Merging this with ports-2015 switch allows users to update the configuration in new format already.

Repository rename

Reference: FL-1801

Right now, the main repository inherits the name 'gentoo'. This is a bit confusing, considering that it is a modified Funtoo variant of the package tree. Changing the name to 'funtoo' would improve consistency and carry some bit of 'branding' into packages. Merging this into ports-2015 switch allows users to consciously update all repository references if necessary, and combines the change with necessity of specifying repository name in repos.conf.

Other possible changes

Filesystem structure reorganization

Since users will be required to clone the new repository, it may be desired to suggest some best practices for filesystem layout. This specifically includes separating ebuilds from distfiles & packages, and using a multi-repository layout. Historically, portage tree inspired by FreeBSD ports, located in /usr/portage>. This FHS layout is different in BSD and in Linux and we will probably move it elsewhere, see below for a suggestion and possible pros and cons.

Example layout suggested by mgorny:

  1. all repositories in /var/db/repos/${repo_name} (i.e. Funtoo repository in /var/db/repos/funtoo, and possible overlays as other directories in /var/db/repos),
  2. distfiles in /var/cache/portage/distfiles,
  3. binary packages in /var/cache/portage/packages.

Users can be recommended to use a separate filesystem that can handle small files efficiently for /var/db/repos, e.g. btrfs, reiserfs or possibly squashfs.


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