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14 <h1>The rEFInd Boot Manager:<br />Methods of Booting Linux</h1>
15
16 <p class="subhead">by Roderick W. Smith, <a
17 href="mailto:rodsmith@rodsbooks.com">rodsmith@rodsbooks.com</a></p>
18
19 <p>Originally written: 3/19/2012; last Web page update:
20 11/8/2015, referencing rEFInd 0.10.0</p>
21
22
23 <p>This Web page is provided free of charge and with no annoying outside ads; however, I did take time to prepare it, and Web hosting does cost money. If you find this Web page useful, please consider making a small donation to help keep this site up and running. Thanks!</p>
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120
121 <hr />
122
123 <p>This page is part of the documentation for the rEFInd boot manager. If a Web search has brought you here, you may want to start at the <a href="index.html">main page.</a></p>
124
125 <hr />
126
127 <div style="float:right; width:55%">
128
129 <p>Windows and Mac OS X both provide relatively simple EFI boot loader programs. Launch them, and if they're launched from the correct locations and have the correct files in place, they'll boot their respective OSes. This makes rEFInd's job easy; it just locates the boot loader program files and runs them.</p>
130
131 </div>
132
133 <div class="navbar">
134
135 <h4 class="tight">Contents</h4>
136
137 <ul>
138
139 <li class="tight"><a href="#traditional">Using a Traditional Linux Boot Loader</li>
140
141 <li class="tight"><a href="#quickstart">Using the EFI Stub Loader: Three Configuration Options</a>
142
143 <ul>
144
145 <li class="tight"><a href="#easiest">For Those With Foresight or Luck: The Easiest Method</a></li>
146
147 <li class="tight"><a href="#testing">Preparing a Test Configuration</a></li>
148
149 <li class="tight"><a href="#reconfigure">If You Need to Reconfigure Your Partitions....</a></li>
150
151 </ul></li>
152
153 <li class="tight"><a href="#efistub">EFI Stub Loader Support Technical Details</a></li>
154
155 </ul>
156
157 </div>
158
159 <p>Under Linux, by contrast, things can get complicated. As detailed on my <a href="http://www.rodsbooks.com/efi-bootloaders/index.html">Managing EFI Boot Loaders for Linux</a> page, several different EFI boot loaders for Linux exist, and all of them require configuration. If you're lucky, your distribution will have set up a Linux boot loader in a sensible way, in which case rEFInd should detect it and it will work as easily as a Windows or Mac OS X boot loader. If you're not lucky, though, you may need to configure it further. rEFInd offers options to help out with this task. Naturally, rEFInd supports <a href="#traditional">traditional Linux boot loaders.</a> It works even better with the Linux EFI stub loader, so I provide <a href="#quickstart">instructions on starting with it.</a> For those interested in manual configuration, I also provide <a href="#efistub">detailed instructions</a> on how the EFI stub support works and how to configure it.</p>
160
161 <a name="traditional">
162 <h2>Using a Traditional Linux Boot Loader</h2>
163 </a>
164
165 <p>I consider <a href="http://www.rodsbooks.com/efi-bootloaders/elilo.html">ELILO</a>, <a href="http://www.rodsbooks.com/efi-bootloaders/grub_legacy.html">GRUB Legacy</a>, <a href="http://www.rodsbooks.com/efi-bootloaders/grub2.html">GRUB 2</a>, and <a href="http://www.rodsbooks.com/efi-bootloaders/syslinux.html">SYSLINUX</a> to be traditional Linux boot loaders. These programs all exist independent of the Linux kernel, but they can load a kernel and hand off control to it. All four programs have their own configuration files that reside in the same directory as the boot loader itself (or optionally elsewhere, in the case of GRUB 2).</p>
166
167 <p>Ordinarily, rEFInd will detect these traditional boot loaders and provide main menu entries for them. If the boot loader exists in a directory with a name that matches a Linux distribution's icon filename, you'll automatically get a distribution-specific icon to refer to the boot loader.</p>
168
169 <p>If you prefer, you can disable automatic scanning and create an entry in <tt>refind.conf</tt> for your distribution, as described on the <a href="configfile.html">Configuring the Boot Manager</a> page. This method is harder to set up but can be preferable if you want to customize your options.</p>
170
171 <a name="quickstart">
172 <h2>Using the EFI Stub Loader: Three Configuration Options</h2>
173 </a>
174
175 <p>The EFI stub loader is basic and reliable, but it requires some setup to use it on some computers. It also requires that you run a kernel with the same bit width as your EFI. In most cases, this means running a 64-bit kernel, since 32-bit EFI-based computers are so rare. I describe three methods of using the EFI stub loader: an <a href="#easiest">easiest method</a> for those with compatible partition and filesystem layouts, a <a href="#testing">quick test configuration</a> for those without such a layout, and <a href="#reconfigure">a long-term setup</a> for those without the ideal setup.</p>
176
177 <a name="easiest">
178 <h3>For Those With Foresight or Luck: The Easiest Method</h3>
179 </a>
180
181 <p>This method requires that your <tt>/boot</tt> directory, whether it's on a separate partition or is a regular directory in your root (<tt>/</tt>) filesystem, be readable by the EFI. At the moment, all EFI implementations can read FAT and Macs can read HFS+. By using <a href="drivers.html">drivers,</a> you can make any EFI read HFS+, ISO-9660, ReiserFS, ext2fs, ext3fs, ext4fs, Btrfs, or other filesystems. Thus, if you use any of these filesystems on a regular partition (not an LVM or RAID configuration) that holds your kernels in <tt>/boot</tt>, you qualify for this easy method. The default partition layouts used by Ubuntu, Fedora, and many other distributions qualify, because they use one of these filesystems (usually ext4fs) in a normal partition or on a separate <tt>/boot</tt> partition. You must also have a 3.3.0 or later Linux kernel with EFI stub support, of course.</p>
182
183 <p>If you installed rEFInd 0.6.0 or later with its <tt>refind-install</tt> (formerly <tt>install.sh</tt>) script from your regular Linux installation, chances are everything's set up; you should be able to reboot and see your Linux kernels as boot options. If you installed manually, from OS X, or from an emergency system, though, you may need to do a couple of things manually:
184
185 <ul>
186
187 <li>Copy the relevant driver file for your filesystem and architecture to
188 the <tt>drivers</tt> or <tt>drivers_<tt class="variable">arch</tt></tt>
189 subdirectory of the rEFInd installation directory on the EFI System
190 Partition (ESP). You may need to create this subdirectory, too.</li>
191
192 <li>Create a <tt>refind_linux.conf</tt> file in your <tt>/boot</tt>
193 directory. The <tt>mkrlconf</tt> script that comes with rEFInd
194 should do this job, or you can do it manually as described <a
195 href="#efistub">later.</a> Starting with version 0.6.12, rEFInd can
196 create minimal boot options from <tt>/etc/fstab</tt>, if <tt>/boot</tt>
197 is <i>not</i> a separate partition, so a <tt>refind_linux.conf</tt>
198 file may not be strictly necessary. Version 0.9.0 also adds the ability
199 to identify the root (<tt>/</tt>) partition via the <a
200 href="http://www.freedesktop.org/wiki/Specifications/DiscoverablePartitionsSpec/">Discoverable
201 Partitions Spec,</a> if your disk uses the appropriate type codes. A
202 <tt>refind_linux.conf</tt> file remains desirable, though, and is
203 necessary in some situations.</li>
204
205 </ul>
206
207 <p>When you reboot, you should see rEFInd options for your Linux kernels. If they work, your job is done, although you might want to apply some of the tweaks described in the <a href="#reconfigure">maintenance-free setup</a> section. If you have problems, you may need to adjust the <tt>refind_linux.conf</tt> file, as described in the <a href="#efistub">detailed configuration section.</a></p>
208
209 <a name="testing">
210 <h3>Preparing a Test Configuration</h3>
211 </a>
212
213 <p>If you're not sure you want to use the EFI stub loader in the long term, you can perform a fairly quick initial test of it. This procedure assumes that you have access to a 3.3.0 or later Linux kernel with EFI stub support compiled into it. (Fedora since version 17, Ubuntu since 12.10, and most other distributions ship with such kernels.) Creating this configuration poses no risk to your current boot options, provided you don't accidentally delete existing files. The procedure for a quick test is:</p>
214
215 <ol>
216
217 <li>Copy your kernel file (<tt>vmlinuz-*</tt>) and matching initial RAM
218 disk file (<tt>init*</tt>) from <tt>/boot</tt> to a subdirectory of
219 <tt>EFI</tt> on your ESP. Your distribution's directory there should
220 work fine. For instance, typing <tt class="userinput">cp
221 /boot/vmlinuz-4.2.5-300.fc23.x86_64
222 /boot/initramfs-4.2.5-300.fc23.x86_64.img /boot/efi/EFI/fedora</tt> might
223 do the trick on a Fedora system, although you'll probably have to
224 adjust the version numbers. Note that the filename forms vary from one
225 distribution to another, so don't worry if yours look different from
226 these. Be sure that you match up the correct files by version number,
227 though.</li>
228
229 <li>Copy the <tt>/boot/refind_linux.conf</tt> file to the same directory to
230 which you copied your kernel. If this file doesn't exist, create it by
231 running (as <tt>root</tt>) the <tt>mkrlconf</tt> script that came
232 with rEFInd. This step may not be strictly necessary if <tt>/boot</tt>
233 is an ordinary directory on your root (<tt>/</tt>) partition.</li>
234
235 <li>Reboot. You should now see a new entry for launching the Linux kernel
236 that you copied. Try the option. If it works, great. If not, you may
237 need to adjust your <tt>refind_linux.conf</tt> file. See the <a
238 href="#efistub">detailed configuration section</a> for a description of
239 this file's format. If the kernel begins to boot but complains that it
240 couldn't find its root filesystem, double-check the version numbers on
241 your kernel and initial RAM disk file, and check the <tt>root=</tt>
242 option in <tt>refind_linux.conf</tt>.</li>
243
244 </ol>
245
246 <p>You can continue to boot your computer with this type of configuration; however, the drawback is that you'll need to copy your kernel whenever it's updated. This can be a hassle. A better way is to configure you system so that the EFI, and therefore rEFInd, can read your Linux <tt>/boot</tt> directory, where most Linux distributions place their kernels.</p>
247
248 <a name="reconfigure">
249 <h3>If You Need to Reconfigure Your Partitions....</h3>
250 </a>
251
252 <p>If your <tt>/boot</tt> directory happens to be on an XFS or JFS partition that the EFI can't read, or it's tucked away in an LVM or RAID configuration that the EFI can't read, you won't be able to use the <a href="#easiest">easiest solution.</a> Fortunately, this problem can be overcome with relatively little fuss. Several variant procedures are possible, but I begin by describing one that will almost always work, although it's got some important caveats (described at the end). You should perform the following steps as <tt>root</tt>, or precede each of these commands with <tt>sudo</tt>:</p>
253
254 <ol>
255
256 <li>Begin with your ESP mounted at <tt>/boot/efi</tt>, which is the most
257 common location. If it's not mounted there, type <tt
258 class="userinput">mount /dev/sda1 /boot/efi</tt> to do so (adjusting
259 <tt>/dev/sda1</tt>, if necessary), or mount it elsewhere and adjust the
260 paths in the following procedure as necessary.</li>
261
262 <li>Check the size of the ESP by typing <tt class="userinput">df -h
263 /boot/efi</tt>. The ESP must be large enough to hold several Linux
264 kernels and initial RAM disk files&mdash;100MiB at a bare minimum, and
265 preferably 200&ndash;500MiB.</li>
266
267 <li>Check your <tt>/boot</tt> directory to be sure it contains no links or
268 other files that rely on Unix/Linux-style permissions or ownership. If
269 it does, don't proceed, or at least research these files further to
270 determine if you can work around the need for such permissions and
271 ownership.</li>
272
273 <li>Type <tt class="userinput">cp -r /boot/* /boot/efi</tt>. You'll see an
274 error message about being unable to copy <tt>/boot/efi</tt> into
275 itself. Ignore this.</li>
276
277 <li>Type <tt class="userinput">umount /boot/efi</tt>.</li>
278
279 <li>Edit <tt>/etc/fstab</tt> and change the mount point for
280 <tt>/boot/efi</tt> to <tt>/boot</tt>. If the ESP isn't present in
281 <tt>/etc/fstab</tt>, you must create an entry for it, with a mount
282 point of <tt>/boot</tt>.</li>
283
284 <li>Type <tt class="userinput">mount -a</tt> to re-mount everything,
285 including <tt>/boot</tt>. Check that your normal <tt>/boot</tt> files
286 are all present, along with the new <tt>/boot/EFI</tt> directory, which
287 holds what used to be <tt>/boot/efi/EFI</tt>. If something seems to be
288 missing (other than <tt>/boot/efi</tt> with a lowercase <tt>efi</tt>),
289 then you should try to correct the problem.</li>
290
291 <li>If it doesn't already exist, create a file called
292 <tt>/boot/refind_linux.conf</tt> and populate it with kernel options,
293 as described <a href="#refind_linux">later.</a> If this file doesn't
294 already exist, the easiest way to create it is to run the
295 <tt>mkrlconf</tt> script that comes with rEFInd 0.5.1 and
296 later.</li>
297
298 <li>Check your <tt>refind.conf</tt> file (presumably in
299 <tt>/boot/EFI/refind</tt>) to be sure that the
300 <tt>scan_all_linux_kernels</tt> line is uncommented. If it's not,
301 uncomment that line.</li>
302
303 <li>Optionally, type <tt class="userinput">cp
304 /boot/EFI/refind/icons/os_<i>name</i>.icns /boot/.VolumeIcon.icns</tt>
305 to give loaders in <tt>/boot</tt> an icon for your distribution.</li>
306
307 <li>Reboot to test that this configuration works.</li>
308
309 </ol>
310
311 <p>Recall that in step #4, you <i>copied</i> the contents of <tt>/boot</tt> (as a safety measure), but you did not move them. Therefore, you ended up with two copies of your kernels and other <tt>/boot</tt> directory contents, with one copy hiding the other when you mounted the ESP at <tt>/boot</tt>. Once you've booted successfully and are sure all is working well, you can recover some disk space by unmounting <tt>/boot</tt> and deleting the contents of the underlying <tt>/boot</tt> directory on your root (<tt>/</tt>) filesystem. Be sure that the <tt>/boot</tt> partition is unmounted before you do this, though! Also, be sure to leave the <tt>/boot</tt> directory itself in place, even if it has no contents; the directory is needed as a mount point for the <tt>/boot</tt> partition. Note that GRUB 2 may stop working if you delete its files from the root filesystem's <tt>/boot/grub</tt> directory, so if you want to keep GRUB around, you should re-install it with the separate <tt>/boot</tt> partition mounted.</p>
312
313 <p>Once this task is done, updates to your kernel will automatically be stored in the root directory of your ESP, where rEFInd will automatically detect them. Thus, the boot configuration becomes maintenance-free. The procedure as just described has some drawbacks, though. By placing your kernels in the root directory of your ESP, you render them vulnerable to any other OS with which you might be dual-booting. Your ESP must also be large enough to hold all your kernels. If you dual-boot with multiple Linux distributions, they might conceivably overwrite each others' kernels, and distinguishing one from another becomes more difficult.</p>
314
315 <p>For these reasons, a variant of this procedure is desirable on some systems. Most of the steps are similar, but in this variant, you create a separate <tt>/boot</tt> partition that's independent of the ESP. This partition can use FAT, HFS+, ReiserFS, ext2fs, ext3fs, ext4fs, or Btrfs; but if you use any of the last six filesystems (five on Macs), you must install the matching EFI filesystem driver that ships with rEFInd. Creating the filesystem will normally require you to shrink an existing partition by a suitable amount (200&ndash;500MiB). Mount your new <tt>/boot</tt> partition at a temporary location, copy or move the current <tt>/boot</tt> files into it, unmount it, and add it to <tt>/etc/fstab</tt> as <tt>/boot</tt>.</p>
316
317 <p>If your distribution already uses a separate <tt>/boot</tt> partition, but if it uses XFS or some other unsuitable filesystem, you can back it up, create a fresh FAT, HFS+, ReiserFS, Btrfs, ext2, ext3, or ext4 filesystem on it, and restore the original files. You'll probably need to adjust the UUID value in <tt>/etc/fstab</tt> to ensure that the computer mounts the new filesystem when you boot. If you use a separate non-ESP <tt>/boot</tt> partition, you'll probably want to continue mounting the ESP at <tt>/boot/efi</tt>.</p>
318
319 <a name="efistub">
320 <h2>EFI Stub Loader Support Technical Details</h2>
321 </a>
322
323 <p>The Linux <a href="http://www.rodsbooks.com/efi-bootloaders/efistub.html">EFI stub loader</a> is a way to turn a Linux kernel into an EFI application. In a sense, the kernel becomes its own boot loader. This approach to booting Linux is very elegant in some ways, but as described on the page to which I just linked, it has its disadvantages, too. One challenge to booting in this way is that modern Linux installations typically require that the kernel be passed a number of options at boot time. These tell the kernel where the Linux root (<tt>/</tt>) filesystem is, where the initial RAM disk is, and so on. Without these options, Linux won't boot. These options are impossible for a generic boot loader to guess without a little help. It's possible to build a kernel with a default set of options, but this is rather limiting. Thus, rEFInd provides configuration options to help.</p>
324
325 <p>With all versions of rEFInd, you can create manual boot loader stanzas
326 in the <tt>refind.conf</tt> file to identify a Linux kernel and to pass it
327 all the options it needs. This approach is effective and flexible, but it
328 requires editing a single configuration file for all the OSes you want to
329 define in this way. If a computer boots two different Linux distributions,
330 and if both were to support rEFInd, problems might arise as each one tries
331 to modify its own rEFInd configuration; or the one that controls rEFInd
332 might set inappropriate options for another distribution. This is a problem
333 that's been a minor annoyance for years under BIOS, since the same
334 potential for poor configuration applies to LILO, GRUB Legacy, and GRUB 2
335 on BIOS. The most reliable solution under BIOS is to chainload one boot
336 loader to another. The same solution is possible under EFI, but rEFInd
337 offers another possibility.</p>
338
339 <p>rEFInd supports semi-automatic Linux EFI stub loader detection. This
340 feature works as part of the standard boot loader scan operation, but it
341 extends it as follows:</p>
342
343 <ol>
344
345 <li>rEFInd looks for boot loaders whose names include the strings
346 <tt>bzImage</tt> or <tt>vmlinuz</tt>. For instance,
347 <tt>bzImage-3.19.0.efi</tt> or <tt>vmlinuz-4.2.0</tt> would match, and
348 trigger subsequent steps in this procedure. The
349 <tt>scan_all_linux_kernels</tt> option in <tt>refind.conf</tt> controls
350 the scanning for kernels whose names do not end in <tt>.efi</tt>; if
351 this option is set to <tt>false</tt>, kernel filenames must end in
352 <tt>.efi</tt> to be picked up by rEFInd. This option is set to
353 <tt>true</tt> by default, but you can change it if you don't want to
354 scan all Linux kernels.</li>
355
356 <li>If a file's name ends in <tt>.efi.signed</tt>, any other file with an
357 otherwise-identical name that <i>lacks</i> this extension is excluded.
358 This peculiar rule exists because Ubuntu delivers two
359 copies of every kernel, one with and one without this extension. The
360 one with the extension is signed with a Secure Boot key; the one
361 without it is not so signed. Thus, if both files are present, the one
362 without the key won't boot on a computer with Secure Boot active, and
363 either will boot if Secure Boot is inactive. Thus, rEFInd excludes the
364 redundant (unsigned) file in order to help keep the list of boot
365 options manageable.</li>
366
367 <p class="sidebar">A kernel whose filename lacks a version string matches an initial RAM disk that also lacks a version string in its filename. Note that you can reliably use only <i>one</i> kernel and initial RAM disk per directory that lack version numbers in their filenames.</p>
368
369 <li>rEFInd looks for an initial RAM disk in the same directory as the
370 kernel file. A matching initial RAM disk has a name that begins with
371 <tt>init</tt> and that includes the same version string as the kernel.
372 The version string is defined as the part of the filename from the
373 first digit to the last digit, inclusive. Note that the version string
374 can include non-digits. For instance, the version string for
375 <tt>bzImage-3.19.0.efi</tt> is <tt>3.19.0</tt>, which matches
376 <tt>initramfs-3.19.0.bz</tt>; and
377 <tt>vmlinuz-4.2.5-300.fc23.x86_64</tt>'s version string is
378 <tt>4.2.5-300.fc23.x86_64</tt>, which matches
379 <tt>initrd-4.2.5-300.fc23.x86_64.img</tt>. Many other matches are
380 possible. If an initial RAM disk is identified, rEFInd passes a
381 suitable <tt>initrd=</tt> option to the kernel when it boots.</li>
382
383 <li>rEFInd looks for a file called <tt>refind_linux.conf</tt> in the same
384 directory as the kernel file. It consists of a series of lines,
385 each of which consists of a label followed by a series of kernel
386 options. The first line sets default options, and subsequent lines set
387 options that are accessible from the main menu tag's submenu screen. If
388 you installed rEFInd with the <tt>refind-install</tt>
389 script, that script created a sample <tt>refind_linux.conf</tt> file,
390 customized for your computer, in <tt>/boot</tt>. This file will work
391 without changes on many installations, but you may need to tweak it for
392 some.</li>
393
394 <li>If rEFInd can't find a <tt>refind_linux.conf</tt> file in the directory
395 that holds the kernel, the program looks for a file called
396 <tt>/etc/fstab</tt> on the partition that holds the kernel. If this
397 standard Linux file is present, rEFInd uses it to identify the root
398 (<tt>/</tt>) filesystem and creates two sets of Linux kernel boot
399 options: One set launches the kernel normally, but with minimal
400 options, and the other set launches the kernel into single-user mode.
401 This step can get a computer to boot without any rEFInd-specific
402 configuration files, aside from <tt>refind.conf</tt> in rEFInd's own
403 directory, but only if <tt>/boot</tt> is not a separate partition. The
404 intent is to facilitate the use of rEFInd as an emergency boot manager
405 or to help users who must install rEFInd from OS X or Windows. Note
406 that rEFInd uses <tt>/etc/fstab</tt> only if <tt>refind_linux.conf</tt>
407 is <i>not</i> found.</li>
408
409 <li>If rEFInd can't find a <tt>refind_linux.conf</tt> file or an
410 <tt>/etc/fstab</tt> file, it tries to identify the Linux root
411 (<tt>/</tt> filesystem by looking for a partition with a GUID type code
412 matching that specified for the root (<tt>/</tt>) filesystem in the <a
413 href="http://www.freedesktop.org/wiki/Specifications/DiscoverablePartitionsSpec/">Freedesktop.org
414 Discoverable Partitions Specification.</a> These type codes are as yet
415 seldom used, but if and when they become common, they should help a lot
416 for situations similar to those of the preceding case, but when a
417 separate <tt>/boot</tt> partition is used.</li>
418
419 </ol>
420
421 <p>The intent of this system is that distribution maintainers can place their kernels, initial RAM disks, and a <tt>refind_linux.conf</tt> file in their own subdirectories on the ESP, on EFI-accessible <tt>/boot</tt> partitions, or in <tt>/boot</tt> directories on EFI-accessible Linux root (<tt>/</tt>) partitions. rEFInd will detect these kernels and create one main menu entry for each directory that holds kernels; or if <tt>fold_linux_kernels</tt> is set to <tt>false</tt>, one menu entry for each kernel. Each entry will implement as many options as there are lines in the <tt>refind_linux.conf</tt> file (multiplied by the number of kernels, if <tt>fold_linux_kernels</tt> is <tt>true</tt>). In this way, two or more distributions can each maintain their boot loader entries, without being too concerned about who maintains rEFInd as a whole.</p>
422
423 <p>As an example, consider the following (partial) file listing:</p>
424
425 <pre class="listing">
426 $ <b>ls -l /boot/vmlin*</b>
427 total 17943
428 -rw-r--r-- 1 root root 5271984 Aug 7 10:18 /boot/vmlinuz-3.16.7-24-default
429 -rw-r--r-- 1 root root 5271536 Oct 23 17:25 /boot/vmlinuz-3.16.7-29-default
430 </pre>
431
432 <p>When rEFInd scans this directory, it will discover two kernels in <tt>/boot</tt>. Assuming <tt>fold_linux_kernels</tt> is its default of <tt>true</tt>, rEFInd will create one main-menu tag for these two kernels. A <tt>refind_linux.conf</tt> file in this directory should contain a list of labels and options:</p>
433
434 <a name="refind_linux">
435 <pre class="listing">
436 "Boot with standard options" "ro root=UUID=084f544a-7559-4d4b-938a-b920f59edc7e splash=silent quiet showopts "
437 "Boot to single-user mode" "ro root=UUID=084f544a-7559-4d4b-938a-b920f59edc7e splash=silent quiet showopts single"
438 "Boot with minimal options" "ro root=UUID=084f544a-7559-4d4b-938a-b920f59edc7e"
439 # This line is a comment
440 </pre>
441 </a>
442
443 <p>Ordinarily, both fields in this file must be enclosed in quotes. If you have to pass an option that includes quotes, you can do so by doubling up on them, as in <tt>"root=/dev/sdb9 my_opt=""this is it"""</tt>, which passes <tt>root=/dev/sdb9 my_opt="this is it"</tt> to the shell. You can include as much white space as you like between options. You can also place comments in the file, or remove an option by commenting it out with a leading hash mark (<tt>#</tt>), as in the fourth line in this example.</p>
444
445 <p>In the preceding example, the first line sets the options that rEFInd passes to the kernel by default (along with the name of the discovered initrd file, since its version string matches that of the kernel). The next two lines set options that you can obtain by pressing Insert, F2, or + on the main menu, as shown here:</p>
446
447 <br /><center><img src="automatic-submenu.png" align="center"
448 width="622" height="210" alt="rEFInd can load Linux boot options from
449 a refind_linux.conf file in the Linux kernel's directory."
450 border=2></center><br />
451
452 <p>Note that in this example, the default kernel (the one with the most recent time stamp) appears first on the list, with the labels specified in <tt>refind_linux.conf</tt>. Subsequent kernels (just one in this example) appear below it, with the same labels preceded by the kernel filename. If you were to set <tt>fold_linux_kernels false</tt>, each kernel would get its own entry on the main menu, and each one's submenu would enable options for launching it alone.</p>
453
454 <p>To assist in initial configuration, rEFInd's <tt>refind-install</tt> script creates a sample <tt>refind_linux.conf</tt> file in <tt>/boot</tt>. This sample file defines three entries, the first two of which use the default GRUB options defined in <tt>/etc/default/grub</tt> and the last of which uses minimal options. The first entry boots normally and the second boots into single-user mode. If you want to create a new file, you can use the <tt>mkrlconf</tt> script that comes with rEFInd. If you pass it the <tt>--force</tt> option, it will overwrite the existing <tt>/boot/refind_linux.conf</tt> file; otherwise it will create the file only if one doesn't already exist.</p>
455
456 <p>From a user's perspective, the submenus defined in this way work just like submenus defined via the <tt>submenuentry</tt> options in <tt>refind.conf</tt>, or like the submenus that rEFInd creates automatically for Mac OS X or ELILO. There are, however, limitations in what you can accomplish with this method:</p>
457
458 <ul>
459
460 <li>Your kernels must be compiled with EFI stub loader support. (This is
461 almost always true of distribution-provided kernels these days.)</li>
462
463 <li>You can't set a submenu option to boot via a different boot loader,
464 such as ELILO or GRUB; all the submenu options apply to a single boot
465 loader&mdash;that is, a single kernel. (rEFInd will still detect other
466 boot loaders and provide separate main-menu tags for them,
467 though.) Folded kernel entries are an exception to this rule.</li>
468
469 <li>All the kernels in a given directory use the same
470 <tt>refind_linux.conf</tt> file. If you need to set different options
471 for different kernels, you'll need to place those kernels in different
472 directories.</li>
473
474 <li>You must place your kernels in a directory other than the one that
475 holds the main rEFInd <tt>.efi</tt> file. This is because rEFInd does
476 not scan its own directory for boot loaders.</li>
477
478 </ul>
479
480 <p>Ordinarily, a kernel booted in this way must reside on the ESP, or at least on another FAT partition. On a Macintosh, though, you can use HFS+ to house your kernel files. In fact, that may be necessary; my Mac Mini hangs when I try to boot a Linux kernel via an EFI stub loader from the computer's ESP, but it works fine when booting from an HFS+ partition. If you use <a href="drivers.html">EFI drivers,</a> though, you can place your kernel on any filesystem for which an EFI driver exists. This list is currently good (ext2fs/ext3fs, ext4fs, ReiserFS, Btrfs, ISO-9660, HFS+, and NTFS in rEFInd, plus more from other sources), so chances are you'll be able to use this method to boot your kernel from your root (<tt>/</tt>) partition or from a <tt>/boot</tt> partition.</p>
481
482 <p>rEFInd sorts boot loader entries <i>within each directory</i> by time stamp, so that the most recent entry comes first. Thus, if you specify a directory name (or a volume label, for loaders stored in a volume's root directory) as the <tt>default_selection</tt>, rEFInd will make the most recent loader in the directory the default. This can obviate the need to adjust this configuration parameter when you add a new kernel; chances are you want the most recently-added kernel to be the default, and rEFInd makes it so when you set the <tt>default_selection</tt> in this way. If you <i>don't</i> want the latest kernel to become the default, you can use <tt>touch</tt> to give the desired kernel (or other boot loader) in the directory a more recent time stamp, or you can set <tt>default_selection</tt> to a value that uniquely identifies your desired default loader. One caveat you should keep in mind is that the EFI and Windows interpret the hardware clock as local time, whereas Mac OS X uses <a href="http://en.wikipedia.org/wiki/Coordinated_Universal_Time">Coordinated Universal Time (UTC)</a>. Linux can work either way. Thus, time stamps for boot loaders can be skewed by several hours depending on the environment in which they were created or last modified.</p>
483
484 <p class="sidebar"><b>Tip for distribution maintainers:</b> If you maintain an <tt>EFI/<tt class="variable">distname</tt></tt> directory for your kernels, you can place your version of rEFInd in a directory called <tt>EFI/<tt class="variable">distname</tt>/refind</tt>. This will avoid collisions with duplicate rEFInd installations from other distributions.</p>
485
486 <p>On the whole, auto-detecting kernels and passing boot options using <tt>refind_linux.conf</tt> has a lot going for it. For distribution maintainers, if you place your Linux kernel files (with EFI stub support) on the ESP, with suitable filenames, matching initial RAM disk files, and a <tt>refind_linux.conf</tt> file, then rEFInd should detect your files, even if the user installs another distribution with another rEFInd that takes over from yours. (If the user, or this other rEFInd installation, disables auto-detection, this won't work.)</p>
487
488 <p>For end users, this method is simpler than maintaining manual configurations in <tt>refind.conf</tt> (or equivalents for ELILO or GRUB). To install a new kernel, you need only copy it and its initial RAM disk, under suitable names, to a scanned directory on the ESP. There's no need to touch any configuration file, provided you've already set up <tt>refind_linux.conf</tt> in your kernel's directory. You will, however, have to adjust <tt>refind_linux.conf</tt> if you make certain changes, such as if your root directory identifier changes.</p>
489
490 <hr/>
491
492 <p>copyright &copy; 2012&ndash;2015 by Roderick W. Smith</p>
493
494 <p>This document is licensed under the terms of the <a href="FDL-1.3.txt">GNU Free Documentation License (FDL), version 1.3.</a></p>
495
496 <p>If you have problems with or comments about this Web page, please e-mail me at <a href="mailto:rodsmith@rodsbooks.com">rodsmith@rodsbooks.com.</a> Thanks.</p>
497
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