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  12 <h1>The rEFInd Boot Manager:<br />Methods of Booting Linux</h1>
  13
  14 <p class="subhead">by Roderick W. Smith, <a
  15 href="mailto:rodsmith@rodsbooks.com">rodsmith@rodsbooks.com</a></p>
  16
  17 <p>Originally written: 3/19/2012; last Web page update:
  18 12/30/2012, referencing rEFInd 0.6.2</p>
  19
  20
  21 <p>I'm a technical writer and consultant specializing in Linux technologies. 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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  86
  87 <hr />
  88
  89 <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>
  90
  91 <hr />
  92
  93 <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>
  94
  95 <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>
  96
  97 <a name="traditional">
  98 <h2>Using a Traditional Linux Boot Loader</h2>
  99 </a>
 100
 101 <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> and <a href="http://www.rodsbooks.com/efi-bootloaders/grub2.html">GRUB 2</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 three 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>
 102
 103 <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>
 104
 105 <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>
 106
 107 <a name="quickstart">
 108 <h2>Using the EFI Stub Loader: A Quick Setup Guide</h2>
 109 </a>
 110
 111 <p>The EFI stub loader is basic and reliable, but it requires some setup to use it on some computers. I describe three methods of using it: 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="#longterm">a long-term setup</a> for those without the ideal setup.</p>
 112
 113 <a name="easiest">
 114 <h3>For Those With Foresight or Luck: The Easiest Method</h3>
 115 </a>
 116
 117 <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, or ext4fs. 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>
 118
 119 <p>If you installed rEFInd 0.6.0 or later with its <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:
 120
 121 <ol>
 122
 123 <li>Copy the relevant driver file for your filesystem and architecture to
 124     the <tt>drivers</tt> or <tt>drivers_<tt class="variable">arch</tt></tt>
 125     subdirectory of the rEFInd installation directory on the ESP. You may
 126     need to create this subdirectory, too.</li>
 127
 128 <li>Create a <tt>refind_linux.conf</tt> file in your <tt>/boot</tt>
 129     directory. The <tt>mkrlconf.sh</tt> script that comes with rEFInd
 130     should do this job, or you can do it manually as described <a
 131     href="#efistub">later.</a></li>
 132
 133 </ol>
 134
 135 <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="#longterm">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>
 136
 137 <a name="testing">
 138 <h3>Testing the EFI Stub Loader</h3>
 139 </a>
 140
 141 <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 17, Ubuntu 12.10, and probably 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>
 142
 143 <ol>
 144
 145 <li>Copy your kernel file (<tt>vmlinuz-*</tt>) and matching initial RAM
 146     disk file (<tt>init*</tt>) from <tt>/boot</tt> to a subdirectory of
 147     <tt>EFI</tt> on your ESP. Your distribution's directory there should
 148     work fine. For instance, typing <tt class="userinput">cp
 149     /boot/vmlinuz-3.6.7-4.fc17.x86_64
 150     /boot/initramfs-3.6.7-4.fc17.x86_64.img /boot/efi/EFI/redhat</tt> might
 151     do the trick on a Fedora system, although you'll probably have to
 152     adjust the version numbers. Note that the filename forms vary from one
 153     distribution to another, so don't worry if yours look different from
 154     these. Be sure that you match up the correct files by version number,
 155     though.</li>
 156
 157 <li>Copy the <tt>/boot/refind_linux.conf</tt> file to the same directory to
 158     which you copied your kernel. If this file doesn't exist, create it by
 159     running (as <tt>root</tt>) the <tt>mkrlconf.sh</tt> script that came
 160     with rEFInd.</li>
 161
 162 <li>Reboot. You should now see a new entry for launching the Linux kernel
 163     that you copied. Try the option. If it works, great. If not, you may
 164     need to adjust your <tt>refind_linux.conf</tt> file. See the <a
 165     href="#efistub">detailed configuration section</a> for a description of
 166     this file's format. If the kernel begins to boot but complains that it
 167     couldn't find its root filesystem, double-check the version numbers on
 168     your kernel and initial RAM disk file, and check the <tt>root=</tt>
 169     option in <tt>refind_linux.conf</tt>.</li>
 170
 171 </ol>
 172
 173 <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>
 174
 175 <a name="longterm">
 176 <h3>Configuring a Maintenance-Free Setup</h3>
 177 </a>
 178
 179 <p>If your <tt>/boot</tt> directory happens to be on an XFS, JFS, or Btrfs 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>
 180
 181 <ol>
 182
 183 <li>Begin with your ESP mounted at <tt>/boot/efi</tt>, which is the most
 184     common location. If it's not mounted there, type <tt
 185     class="userinput">mount /dev/sda1 /boot/efi</tt> to do so (adjusting
 186     <tt>/dev/sda1</tt>, if necessary), or mount it elsewhere and adjust the
 187     paths in the following procedure as necessary.</li>
 188
 189 <li>Check the size of the ESP by typing <tt class="userinput">df -h
 190     /boot/efi</tt>. The ESP must be large enough to hold several Linux
 191     kernels and initial RAM disk files&mdash;100MiB at a bare minimum, and
 192     preferably 200&ndash;500MiB.</li>
 193
 194 <li>Check your <tt>/boot</tt> directory to be sure it contains no links or
 195     other files that rely on Unix/Linux-style permissions or ownership. If
 196     it does, don't proceed, or at least research these files further to
 197     determine if you can work around the need for such permissions and
 198     ownership.</li>
 199
 200 <li>Type <tt class="userinput">cp -r /boot/* /boot/efi</tt>. You'll see an
 201     error message about being unable to copy <tt>/boot/efi</tt> into
 202     itself. Ignore this.</li>
 203
 204 <li>Type <tt class="userinput">umount /boot/efi</tt>.</li>
 205
 206 <li>Edit <tt>/etc/fstab</tt> and change the mount point for
 207     <tt>/boot/efi</tt> to <tt>/boot</tt>. If the ESP isn't present in
 208     <tt>/etc/fstab</tt>, you must create an entry for it, with a mount
 209     point of <tt>/boot</tt>.</li>
 210
 211 <li>Type <tt class="userinput">mount -a</tt> to re-mount everything,
 212     including <tt>/boot</tt>. Check that your normal <tt>/boot</tt> files
 213     are all present, along with the new <tt>/boot/EFI</tt> directory, which
 214     holds what used to be <tt>/boot/efi/EFI</tt>. If something seems to be
 215     missing (other than <tt>/boot/efi</tt> with a lowercase <tt>efi</tt>),
 216     then you should try to correct the problem.</li>
 217
 218 <li>If it doesn't already exist, create a file called
 219     <tt>/boot/refind_linux.conf</tt> and populate it with kernel options,
 220     as described <a href="#refind_linux">later.</a> If this file doesn't
 221     already exist, the easiest way to create it is to run the
 222     <tt>mkrlconf.sh</tt> script that comes with rEFInd 0.5.1 and
 223     later.</li>
 224
 225 <li>Check your <tt>refind.conf</tt> file (presumably in
 226     <tt>/boot/EFI/refind</tt>) to be sure that the
 227     <tt>scan_all_linux_kernels</tt> line is uncommented. If it's not,
 228     uncomment that line.</li>
 229
 230 <li>Optionally, type <tt class="userinput">cp
 231     /boot/EFI/refind/icons/os_<i>name</i>.icns /boot/.VolumeIcon.icns</tt>
 232     to give loaders in <tt>/boot</tt> an icon for your distribution.</li>
 233
 234 <li>Reboot to test that this configuration works.</li>
 235
 236 </ol>
 237
 238 <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>
 239
 240 <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>
 241
 242 <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, or ext4fs; but if you use any of the last five filesystems (four 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>
 243
 244 <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, 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>
 245
 246 <a name="efistub">
 247 <h2>EFI Stub Loader Support Technical Details</h2>
 248 </a>
 249
 250 <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>
 251
 252 <p>With all versions of rEFInd, you can create manual boot loader stanzas
 253 in the <tt>refind.conf</tt> file to identify a Linux kernel and to pass it
 254 all the options it needs. This approach is effective and flexible, but it
 255 requires editing a single configuration file for all the OSes you want to
 256 define in this way. If a computer boots two different Linux distributions,
 257 and if both were to support rEFInd, problems might arise as each one tries
 258 to modify its own rEFInd configuration; or the one that controls rEFInd
 259 might set inappropriate options for another distribution. This is a problem
 260 that's been a minor annoyance for years under BIOS, since the same
 261 potential for poor configuration applies to LILO, GRUB Legacy, and GRUB 2
 262 on BIOS. The most reliable solution under BIOS is to chainload one boot
 263 loader to another. The same solution is possible under EFI, but rEFInd
 264 offers another possibility.</p>
 265
 266 <p>rEFInd 0.2.1 and later supports semi-automatic Linux EFI stub loader detection. This feature works as part of the standard boot loader scan operation, but it extends it as follows:</p>
 267
 268 <ol>
 269
 270 <li>rEFInd looks for boot loaders whose names include the strings
 271     <tt>bzImage</tt> or <tt>vmlinuz</tt> and that end in <tt>.efi</tt>. For
 272     instance, <tt>bzImage-3.3.0.efi</tt> or <tt>vmlinuz-3.3.0-fc17.efi</tt>
 273     would match, and trigger subsequent steps in this procedure. Beginning
 274     with version 0.3.0, if you uncomment the
 275     <tt>scan_all_linux_kernels</tt> option in <tt>refind.conf</tt>, rEFInd
 276     will also scan for kernels <i>without</i> a <tt>.efi</tt> filename
 277     extension. This option is uncommented by default, but if you comment it
 278     out, delete it, or change it to read <tt>scan_all_linux_kernels 0</tt>,
 279     rEFInd won't scan for kernels that lack <tt>.efi</tt> filename
 280     extensions.</li>
 281
 282 <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>
 283
 284 <li>rEFInd looks for an initial RAM disk in the same directory as the
 285     kernel file. A matching initial RAM disk has a name that begins with
 286     <tt>init</tt> and that includes the same version string as the kernel.
 287     The version string is defined as the part of the filename from the
 288     first digit to the last digit, inclusive. Note that the version string
 289     can include non-digits. For instance, the version string for
 290     <tt>bzImage-3.3.0.efi</tt> is <tt>3.3.0</tt>, which matches
 291     <tt>initramfs-3.3.0.bz</tt>; and <tt>vmlinuz-3.3.0-fc17.efi</tt>'s
 292     version string is <tt>3.3.0-fc17</tt>, which matches
 293     <tt>initrd-3.3.0-fc17.img</tt>. Many other matches are possible. If an
 294     initial RAM disk is identified, rEFInd passes a suitable
 295     <tt>initrd=</tt> option to the kernel when it boots.</li>
 296
 297 <p class="sidebar">rEFInd 0.2.1 and 0.2.2 used a filename of <tt>linux.conf</tt> to hold Linux kernel options; however, the Linux kernel developers plan to use this name themselves, so I've switched to <tt>refind_linux.conf</tt> as of rEFInd 0.2.3. Through version 0.4.2, rEFInd still supported the <tt>linux.conf</tt> filename as a backup to <tt>refind_linux.conf</tt>, but as of version 0.4.3, <tt>linux.conf</tt> no longer works, so you should rename rEFInd's <tt>linux.conf</tt> file to <tt>refind_linux.conf</tt> if you're upgrading.</p>
 298
 299 <li>rEFInd looks for a file called <tt>refind_linux.conf</tt> in the same
 300     directory as the kernel file. This file is a practical requirement for
 301     booting from an auto-detected kernel. It consists of a series of lines,
 302     each of which consists of a label followed by a series of kernel
 303     options. The first line sets default options, and subsequent lines set
 304     options that are accessible from the main menu tag's submenu screen. If
 305     you installed rEFInd 0.5.1 or later with the <tt>install.sh</tt>
 306     script, that script created a sample <tt>refind_linux.conf</tt> file,
 307     customized for your computer, in <tt>/boot</tt>. This file will work
 308     without changes on many installations, but you may need to tweak it for
 309     some.</li>
 310
 311 </ol>
 312
 313 <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 kernel. Each entry will implement as many options as there are lines in the <tt>refind_linux.conf</tt> file. 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>
 314
 315 <p>The <tt>scan_all_linux_kernels</tt> option is intended to help users and distribution maintainers when rEFInd is used in conjunction with a Linux filesystem driver for EFI or when the ESP is mounted as the Linux <tt>/boot</tt> partition. In these cases, if all the kernels in Linux's <tt>/boot</tt> directory include EFI stub loader support, rEFInd will automatically detect and use kernels installed in the usual way, such as via an automatic system update. You won't even need to move or rename your kernels. You will need to set up a <tt>refind_linux.conf</tt> file and you may need to install a driver or set the <tt>also_scan_dirs</tt> option in <tt>refind.conf</tt>; but these are one-time requirements. Set up in this way, ongoing maintenance to handle kernel updates drops to zero!</p>
 316
 317 <p>As an example, consider the following file configuration:</p>
 318
 319 <pre class="listing">
 320 $ <b>ls -l /boot/efi/EFI/ubuntu/</b>
 321 total 17943
 322 -rwxr-xr-x 1 root root  4781632 2012-03-18 12:01 bzImage-3.3.0.efi
 323 -rwxr-xr-x 1 root root   131072 2011-10-14 04:10 grubx64.EFI
 324 -rwxr-xr-x 1 root root 13459936 2012-03-18 12:02 initrd.img-3.3.0
 325 -rwxr-xr-x 1 root root      266 2012-03-26 19:39 refind_linux.conf
 326 </pre>
 327
 328 <p>When rEFInd scans this directory, it will find two EFI boot loaders in <tt>EFI/ubuntu</tt>: <tt>grubx64.EFI</tt> and <tt>bzImage-3.3.0.efi</tt>. rEFInd will create two main-menu tags for these two loaders, one of which will launch Ubuntu's standard GRUB and the other of which will launch the 3.3.0 kernel file directly. The <tt>refind_linux.conf</tt> file contains a list of labels and options:</p>
 329
 330 <a name="refind_linux">
 331 <pre class="listing">
 332 "Boot using default options" "root=/dev/sda3 ro quiet splash vt.handoff=7"
 333 "Boot into single-user mode" "root=UUID=1cd95082-bce0-494c-a290-d2e642dd82b7 ro single"
 334 "Boot without graphics"      "root=UUID=1cd95082-bce0-494c-a290-d2e642dd82b7 ro"
 335 # "Boot alternate install"   "root=/dev/sdb9 ro quiet splash vt.handoff=7"
 336 </pre>
 337 </a>
 338
 339 <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>
 340
 341 <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 <tt>initrd.img-3.3.0</tt> 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>
 342
 343     <br /><center><img src="automatic-submenu.png" align="center"
 344     width="376" height="279" alt="rEFInd can load Linux boot options from
 345     a refind_linux.conf file in the Linux kernel's directory."
 346     border=2></center><br />
 347
 348 <p>To assist in initial configuration, rEFInd's <tt>install.sh</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.sh</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>
 349
 350 <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>
 351
 352 <ul>
 353
 354 <li>Your kernels must be compiled with EFI stub loader support.</li>
 355
 356 <li>You can't set a submenu option to boot via a different boot loader,
 357     such as ELILO or GRUB; all the submenu options apply to a single boot
 358     loader&mdash;that is, a single kernel. (rEFInd will still detect other
 359     boot loaders and provide separate main-menu tags for them,
 360     though.)</li>
 361
 362 <li>If an installation includes two or more kernel files, each one receives
 363     its own main-menu entry; you can't combine them together in one menu
 364     item. This is essentially a corollary of the preceding limitation. The
 365     result can be an overburdened main menu if your system has many
 366     kernels.</li>
 367
 368 <li>All the kernels in a given directory use the same
 369     <tt>refind_linux.conf</tt> file. If you need to set different options
 370     for different kernels, you'll need to place those kernels in different
 371     directories.</li>
 372
 373 <li>You must place your kernels in a directory other than the one that
 374     holds the main rEFInd <tt>.efi</tt> file. This is because rEFInd does
 375     not scan its own directory for boot loaders.</li>
 376
 377 </ul>
 378
 379 <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 rather limited (ext2fs/ext3fs, ReiserFS, ISO-9660, and HFS+), but even just one or two options might help a lot if you've got an undersized ESP or if copying your kernel file to the ESP is a hassle you'd rather avoid.</p>
 380
 381 <p>Beginning with version 0.3.1, 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>
 382
 383 <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>
 384
 385 <p>On the whole, this method of configuration 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 any rEFInd 0.2.3 or later installation 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>
 386
 387 <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>
 388
 389 <hr/>
 390
 391 <p>copyright &copy; 2012 by Roderick W. Smith</p>
 392
 393 <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>
 394
 395 <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>
 396
 397 <p><a href="index.html">Go to the main rEFInd page</a></p>
 398
 399 <p><a href="secureboot.html">Learn how to manage Secure Boot</a></p>
 400
 401   <p><a href="http://www.rodsbooks.com/">Return</a> to my main Web page.</p>
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