summaryrefslogtreecommitdiffstats
path: root/docs/gnulinux/grub_cbfs.html
diff options
context:
space:
mode:
authorFrancis Rowe <info@gluglug.org.uk>2014-11-05 20:52:36 (EST)
committer Francis Rowe <info@gluglug.org.uk>2014-11-05 20:52:36 (EST)
commit8b2219bfa2da36e7809588ef723a10483a6e137f (patch)
tree8c4d74b9efbdabc1a2604b8cbd508c006c225241 /docs/gnulinux/grub_cbfs.html
parent7429bdcdbb4fc51c61897115112468642afeecfc (diff)
downloadlibreboot-8b2219bfa2da36e7809588ef723a10483a6e137f.zip
libreboot-8b2219bfa2da36e7809588ef723a10483a6e137f.tar.gz
libreboot-8b2219bfa2da36e7809588ef723a10483a6e137f.tar.bz2
Documentation: *major* cleanup.
Cleanup was long overdue. Old structure was messy and inefficient.
Diffstat (limited to 'docs/gnulinux/grub_cbfs.html')
-rw-r--r--docs/gnulinux/grub_cbfs.html400
1 files changed, 400 insertions, 0 deletions
diff --git a/docs/gnulinux/grub_cbfs.html b/docs/gnulinux/grub_cbfs.html
new file mode 100644
index 0000000..c9a0f45
--- /dev/null
+++ b/docs/gnulinux/grub_cbfs.html
@@ -0,0 +1,400 @@
+<!DOCTYPE html>
+<html>
+<head>
+ <meta charset="utf-8">
+ <meta name="viewport" content="width=device-width, initial-scale=1">
+
+ <style type="text/css">
+ @import url('../css/main.css');
+ </style>
+
+ <title>Libreboot documentation: GRUB menu</title>
+</head>
+
+<body>
+ <header>
+ <h1 id="pagetop">How to change your default GRUB menu</h1>
+ <aside>Or <a href="index.html">back to main index</a></aside>
+ </header>
+
+ <p>
+ Libreboot uses the GRUB <a href="http://www.coreboot.org/Payloads#GRUB_2">payload</a>
+ by default, which means that the GRUB configuration file
+ (where your GRUB menu comes from) is stored directly alongside libreboot
+ and it's GRUB payload executable, inside
+ the flash chip. In context, this means that installing distributions and managing them
+ is handled slightly differently compared to traditional BIOS systems.
+ </p>
+
+ <p>
+ A libreboot (or coreboot) ROM image is not simply &quot;flat&quot;; there is an actual
+ filesystem inside called CBFS (coreboot filesystem). A utility called 'cbfstool'
+ allows you to change the contents of the ROM image. In this case, libreboot is configured
+ such that the 'grub.cfg' and 'grubtest.cfg' files exists directly inside CBFS instead of
+ inside the GRUB payload's 'memdisk' (which is itself stored in CBFS).
+ </p>
+
+ <p>
+ Here is an excellent writeup about CBFS (coreboot filesystem):
+ <a href="http://lennartb.home.xs4all.nl/coreboot/col5.html">http://lennartb.home.xs4all.nl/coreboot/col5.html</a>.
+ </p>
+
+<hr/>
+
+ <h2>Table of Contents</h2>
+
+ <ul>
+ <li><a href="#getting_started">Getting started</a></li>
+ <li><a href="#build_cbfstool">Build 'cbfstool' from source</a></li>
+ <li><a href="#which_rom">Which ROM image should I use?</a></li>
+ <li><a href="#extract_grubtest">Extract grubtest from the ROM image</a>
+ <li>
+ <a href="#example_modifications">Example modifications for <i>grubtest.cfg</i></a>
+ <ul>
+ <li><a href="#example_modifications_trisquel">Trisquel GNU/Linux-libre</a></li>
+ <li><a href="#example_modifications_parabola">Parabola GNU/Linux-libre</a></li>
+ </ul>
+ </li>
+ <li><a href="#reinsert_modified_grubtest">Re-insert the modified grubtest.cfg into the ROM image</a></li>
+ <li><a href="#test_it">Test it!</a>
+ <li><a href="#final_steps">Final steps</a></li>
+ <li><a href="#troubleshooting">Troubleshooting</a></li>
+ </ul>
+
+<hr/>
+
+ <h2 id="getting_started">Getting started</h2>
+
+ <p>
+ Download the latest release from
+ <a href="http://libreboot.org/">http://libreboot.org/</a>
+ <br/><b>If you downloaded from git, refer to
+ <a href="../git/index.html#build_meta">../git/index.html#build_meta</a> before continuing.</b>
+ </p>
+
+ <p>
+ <a href="../git/index.html#build_dependencies">Install the build dependencies</a>.
+ </p>
+
+ <p>
+ <a href="#pagetop">Back to top of page.</a>
+ </p>
+
+<hr/>
+
+ <h2 id="build_cbfstool">Build 'cbfstool' from source</h2>
+
+ <p>
+ If you are working with libreboot_src, then you can run <b><i>make</i></b> command in
+ libreboot_src/coreboot/util/cbfstool to build the <b><i>cbfstool</i></b> and <b><i>rmodtool</i></b>
+ executable.
+ </p>
+ <p>
+ Alternatively if you are working with libreboot_bin, then you can run <b><i>./builddeps-cbfstool</i></b>
+ command inside libreboot_bin/; a <b><i>cbfstool</i></b> and <b><i>rmodtool</i></b>
+ executable will appear under libreboot_bin/
+ </p>
+
+ <p>
+ <a href="#pagetop">Back to top of page.</a>
+ </p>
+
+<hr/>
+
+ <h2 id="which_rom">Which ROM image should I use?</h2>
+
+ <p>
+ You can work directly with one of the ROM's already included in the libreboot ROM archives. For the purpose of
+ this tutorial it is assumed that your ROM is named <i>libreboot.rom</i> so please make sure to adapt.
+ </p>
+
+ <p>
+ If you want to re-use the ROM that you currently have flashed (and running) then see
+ <a href="../git/index.html#build_flashrom">../git/index.html#build_flashrom</a>
+ and then run:<br/>
+ <b>$ sudo ./flashrom -p internal -r libreboot.rom</b><br/>
+ Notice that this is using <b>&quot;-r&quot;</b> (read) instead of <b>&quot;-w&quot;</b> (write).
+ This will create a dump (copy) of your current firmware and name it <b>libreboot.rom</b>.
+ You need to take ownership of the file. For example:<br/>
+ <b>$ sudo chown yourusername:yourusername libreboot.rom</b><br/>
+ <b># chown yourusername:yourusername libreboot.rom</b>
+ </p>
+
+ <p>
+ If you currently have flashed a ROM image from an older version, it is recommended to update first:
+ basically, modify one of the latest ROM's and then flash it.
+ </p>
+
+ <p>
+ <a href="#pagetop">Back to top of page.</a>
+ </p>
+
+<hr/>
+
+ <h2 id="extract_grubtest">Extract grubtest.cfg from the ROM image</h2>
+
+ <p>
+ Display contents of ROM:<br/>
+ <b>$ ./cbfstool libreboot.rom print</b>
+ </p>
+
+ <p>
+ The libreboot.rom file contains your <i>grub.cfg</i> and <i>grubtest.cfg</i> files.
+ You should extract, modify and re-insert the copy first. grub.cfg will load first,
+ but it has a menu entry for switching to the copy (grubtest.cfg).
+ This reduces your chance of making a mistake that could make your machine unbootable (or very hard to boot).
+ </p>
+
+ <p>
+ Extract grubtest.cfg from the ROM image:<br/>
+ <b>$ ./cbfstool libreboot.rom extract -n grubtest.cfg -f grubtest.cfg</b>
+ </p>
+
+ <p>
+ Now you have a grubtest.cfg in cbfstool directory. Edit it however you wish.
+ </p>
+
+ <p>
+ <a href="#pagetop">Back to top of page.</a>
+ </p>
+
+<hr/>
+
+ <div class="important">
+
+ <h2 id="example_modifications">Example modifications for <i>grubtest.cfg</i></h2>
+
+ <p>
+ These are some common examples of ways in which the grubtest.cfg file can be modified.
+ </p>
+
+ <h3 id="example_modifications_trisquel">Trisquel GNU/Linux-libre</h3>
+
+ <p>
+ As an example, on my test system in /boot/grub/grub.cfg (on the HDD/SSD) I see for the main menu entry:
+ </p>
+ <ul>
+ <li><b>linux /boot/vmlinuz-3.15.1-gnu.nonpae root=UUID=3a008e14-4871-497b-95e5-fb180f277951 ro crashkernel=384M-2G:64M,2G-:128M quiet splash $vt_handoff</b></li>
+ <li><b>initrd /boot/initrd.img-3.15.1-gnu.nonpae</b></li>
+ </ul>
+
+ <p>
+ <b>ro</b>, <b>quiet</b>, <b>splash</b>, <b>crashkernel=384M-2G:64M,2G-:128M</b> and
+ <b>$vt_handoff</b> can be safely ignored.
+ </p>
+
+ <p>
+ I use this to get my partition layout:<br/>
+ $ <b>lsblk</b>
+ </p>
+
+ <p>
+ In my case, I have no /boot partition, instead /boot is on the same partition as / on sda1.
+ Yours might be different. In GRUB terms, sda means ahci0. 1 means msdos1, or gpt1, depending
+ on whether I am using MBR or GPT partitioning. Thus, /dev/sda1 is GRUB is (ahci0,msdos1) or
+ (ahci0,gpt1). In my case, I use MBR partitioning so it's (ahci0,msdos1).
+ 'msdos' is GRUB's name simply because this partitioning type is traditionally used by MS-DOS.
+ It doesn't mean you have a proprietary OS.
+ </p>
+
+ <p>
+ Trisquel doesn't keep the filenames of kernels consistent, instead it keeps old kernels and
+ new kernel updates are provided with the version in the filename. This can make GRUB payload
+ a bit tricky. Fortunately, there are symlinks /vmlinuz and /initrd.img
+ so if your /boot and / are on the same partition, you can set GRUB to boot from that.
+ These are also updated automatically when installing kernel updates from your distributions
+ apt-get repositories.
+ <b>
+ Note: when using <a href="http://jxself.org/linux-libre">jxself kernel releases</a>,
+ these are not updated at all and you have to update them manually.
+ </b>
+ </p>
+
+ <p>
+ For the GRUB payload's grubtest.cfg (in the 'Load Operating System' menu entry), we therefore have (in this example):<br/>
+ <b>set root='ahci0,msdos1'</b><br/>
+ <b>linux /vmlinuz root=UUID=3a008e14-4871-497b-95e5-fb180f277951</b><br/>
+ <b>initrd /initrd.img</b>
+ </p>
+
+ <p>
+ Optionally, you can convert the UUID to it's real device name, for example /dev/sda1 in this case.
+ sdX naming isn't very reliable, though, which is why UUID is used for most distributions.
+ </p>
+
+ <p>
+ Alternatively, if your /boot is on a separate partition then you cannot rely on the /vmlinuz and /initrd.img symlinks.
+ Instead, go into /boot and create your own symlinks (update them manually when you install a new kernel update).<br/>
+ $ <b>sudo -s</b><br/>
+ # <b>cd /boot/</b><br/>
+ # <b>rm -rf vmlinuz initrd.img</b><br/>
+ # <b>ln -s <u>kernel</u> ksym</b><br/>
+ # <b>ln -s <u>initrd</u> isym</b><br/>
+ # <b>exit</b>
+ </p>
+
+ <p>
+ Replace the underlined <b>kernel</b> and <b>initrd</b> filenames above with the actual filenames, of course.
+ </p>
+
+ <p>
+ Then your grubtest.cfg menu entry (for payload) becomes like that, for example if / was on sda2 and /boot was on sda1:<br/>
+ <b>set root='ahci0,msdos1'</b><br/>
+ <b>linux /ksym root=/dev/sda2</b><br/>
+ <b>initrd /isym</b>
+ </p>
+
+ <p>
+ There are lots of possible variations so please try to adapt.
+ </p>
+
+ <h3 id="example_modifications_parabola">Parabola GNU/Linux-libre</h3>
+
+ <p>
+ You can basically adapt the above. Note however that Parabola does not keep old kernels still installed, and the file names
+ are always consistent, so you don't need to boot from symlinks, you can just use the real thing directly.
+ </p>
+
+ </div>
+
+ <p>
+ <a href="#pagetop">Back to top of page.</a>
+ </p>
+
+<hr/>
+
+ <h2 id="reinsert_modified_grubtest">Re-insert the modified grubtest.cfg into the ROM image</h2>
+
+ <p>
+ Delete the grubtest.cfg that remained inside the ROM:<br/>
+ <b>$ ./cbfstool libreboot.rom remove -n grubtest.cfg</b>
+ </p>
+
+ <p>
+ Display ROM contents and now you see grubtest.cfg no longer exists there:<br/>
+ <b>$ ./cbfstool libreboot.rom print</b>
+ </p>
+
+ <p>
+ Add the modified version that you just made:<br/>
+ <b>$ ./cbfstool libreboot.rom add -n grubtest.cfg -f grubtest.cfg -t raw</b>
+ </p>
+
+ <p>
+ Now display ROM contents again and see that it exists again:<br/>
+ <b>$ ./cbfstool libreboot.rom print</b>
+ </p>
+
+ <p>
+ <a href="#pagetop">Back to top of page.</a>
+ </p>
+
+<hr/>
+
+ <h2 id="test_it">Test it!</h2>
+
+ <p>
+ <b>
+ Now you have a modified ROM. Refer back to <a href="../install/index.html#flashrom">../install/index.html#flashrom</a> for information
+ on how to flash it. Once you have done that, shut down and then boot up with your new test configuration.
+ </b>
+ </p>
+
+ <p>
+ Choose (in GRUB) the menu entry that switches to grubtest.cfg. If it works, then your config is safe and you can continue below.
+ </p>
+
+ <p>
+ <b>
+ If it does not work like you want it to, if you are unsure or sceptical in any way,
+ then re-do the steps above until you get it right! Do *not* proceed past this point
+ unless you are 100% sure that your new configuration is safe (or desirable) to use.
+ </b>
+ </p>
+
+ <p>
+ <a href="#pagetop">Back to top of page.</a>
+ </p>
+
+<hr/>
+
+ <h2 id="final_steps">Final steps</h2>
+
+ <p>
+ Create a copy of grubtest.cfg, called grub.cfg, which is the same except for one difference:
+ change the menuentry 'Switch to grub.cfg' to 'Switch to grubtest.cfg' and inside it,
+ change all instances of grub.cfg to grubtest.cfg. This is so that the main config still
+ links (in the menu) to grubtest.cfg, so that you don't have to manually switch to it, in
+ case you ever want to follow this guide again in the future (modifying the already modified config)<br/>
+ $ <b>sed -e 's:(cbfsdisk)/grub.cfg:(cbfsdisk)/grubtest.cfg:g' -e 's:Switch to grub.cfg:Switch to grubtest.cfg:g' &lt; grubtest.cfg &gt; grub.cfg</b><br/>
+ </p>
+
+ <p>
+ Delete the grub.cfg that remained inside the ROM:<br/>
+ <b>$ ./cbfstool libreboot.rom remove -n grub.cfg</b>
+ </p>
+
+ <p>
+ Display ROM contents and now you see grub.cfg no longer exists there:<br/>
+ <b>$ ./cbfstool libreboot.rom print</b>
+ </p>
+
+ <p>
+ Add the modified version that you just made:<br/>
+ <b>$ ./cbfstool libreboot.rom add -n grub.cfg -f grub.cfg -t raw</b>
+ </p>
+
+ <p>
+ Now display ROM contents again and see that it exists again:<br/>
+ <b>$ ./cbfstool libreboot.rom print</b>
+ </p>
+
+ <p>
+ <b>
+ Now you have a modified ROM. Refer back to <a href="../install/index.html#flashrom">../install/index.html#flashrom</a> for information
+ on how to flash it. Once you have done that, shut down and then boot up with your new configuration.
+ </b>
+ </p>
+
+ <p>
+ <a href="#pagetop">Back to top of page.</a>
+ </p>
+
+<hr/>
+
+ <h2 id="troubleshooting">Troubleshooting</h2>
+
+ <p>
+ A user reported that segmentation faults occur with cbfstool
+ when using this procedure depending on the size of the grub.cfg being re-insterted.
+ In his case, a minimum size of 857 bytes was required. This could (at the time of
+ this release) be a bug in cbfstool that should be investigated with the coreboot
+ community. If cbfstool segfaults, then keep this in mind. 'strace' (or gdb? clang?)
+ could be used for debugging. This was in libreboot 5th release (based on coreboot
+ from late 2013), and I'm not sure if the issue perists in the current releases.
+ I have not been able to reproduce it. strace (from that user) is here:
+ <a href="cbfstool_libreboot5_strace">cbfstool_libreboot5_strace</a>.
+ The issue has been reported by a few users, so it does not happen all the time:
+ this bug (if it still exists) could (should) be reproduced.
+ </p>
+
+ <p>
+ <a href="#pagetop">Back to top of page.</a>
+ </p>
+
+<hr/>
+
+ <p>
+ Copyright &copy; 2014 Francis Rowe &lt;info@gluglug.org.uk&gt;<br/>
+ This document is released under the Creative Commons Attribution-ShareAlike 4.0 International Public License and all future versions.
+ A copy of the license can be found at <a href="../license.txt">../license.txt</a>.
+ </p>
+
+ <p>
+ This document is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See <a href="../license.txt">../license.txt</a> for more information.
+ </p>
+
+</body>
+</html>