Changeset 29244b7 for postlfs/filesystems/initramfs.xml
- Timestamp:
- 03/25/2020 09:46:27 PM (4 years ago)
- Branches:
- 10.0, 10.1, 11.0, 11.1, 11.2, 11.3, 12.0, 12.1, kea, ken/TL2024, ken/inkscape-core-mods, ken/tuningfonts, lazarus, lxqt, plabs/newcss, plabs/python-mods, python3.11, qt5new, rahul/power-profiles-daemon, renodr/vulkan-addition, trunk, upgradedb, xry111/intltool, xry111/llvm18, xry111/soup3, xry111/test-20220226, xry111/xf86-video-removal
- Children:
- f716ef4
- Parents:
- 9bd10279
- File:
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- 1 edited
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postlfs/filesystems/initramfs.xml (modified) (3 diffs)
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postlfs/filesystems/initramfs.xml
r9bd10279 r29244b7 16 16 <title>About initramfs</title> 17 17 18 <para>The only purpose of an initramfs is to mount the root filesystem. The 19 initramfs is a complete set of directories that you would find on a normal 20 root filesystem. It is bundled into a single cpio archive and compressed 21 with one of several compression algorithms.</para> 22 23 <para>At boot time, the boot loader loads the kernel and the initramfs image 24 into memory and starts the kernel. The kernel checks for the presence of the 25 initramfs and, if found, mounts it as / and runs /init. The init program is 26 typically a shell script. Note that the boot process takes longer, possibly 27 significantly longer, if an initramfs is used.</para> 28 29 <para>For most distributions, kernel modules are the biggest reason to have an 30 initramfs. In a general distribution, there are many unknowns such as file 31 system types and disk layouts. In a way, this is the opposite of LFS where 32 the system capabilities and layout are known and a custom kernel is normally 33 built. In this situation, an initramfs is rarely needed.</para> 34 35 <para>There are only four primary reasons to have an initramfs in the LFS 36 environment: loading the rootfs from a network, loading it from an LVM 37 logical volume, having an encrypted rootfs where a password is required, or 38 for the convenience of specifying the rootfs as a LABEL or UUID. Anything 39 else usually means that the kernel was not configured properly.</para> 18 <para> 19 The only purpose of an initramfs is to mount the root filesystem. The 20 initramfs is a complete set of directories that you would find on a normal 21 root filesystem. It is bundled into a single cpio archive and compressed 22 with one of several compression algorithms. 23 </para> 24 25 <para> 26 At boot time, the boot loader loads the kernel and the initramfs image 27 into memory and starts the kernel. The kernel checks for the presence 28 of the initramfs and, if found, mounts it as / and runs /init. The init 29 program is typically a shell script. Note that the boot process takes 30 longer, possibly significantly longer, if an initramfs is used. 31 </para> 32 33 <para> 34 For most distributions, kernel modules are the biggest reason to have 35 an initramfs. In a general distribution, there are many unknowns such 36 as file system types and disk layouts. In a way, this is the opposite 37 of LFS where the system capabilities and layout are known and a custom 38 kernel is normally built. In this situation, an initramfs is rarely 39 needed. 40 </para> 41 42 <para> 43 There are only four primary reasons to have an initramfs in the LFS 44 environment: loading the rootfs from a network, loading it from an LVM 45 logical volume, having an encrypted rootfs where a password is required, or 46 for the convenience of specifying the rootfs as a LABEL or UUID. Anything 47 else usually means that the kernel was not configured properly. 48 </para> 40 49 41 50 <sect2 id="initramfs-build"> 42 51 <title>Building an initramfs</title> 43 52 44 <para>If you do decide to build an initramfs, the following scripts 45 will provide a basis to do it. The scripts will allow specifying a 46 rootfs via partition UUID or partition LABEL or a rootfs on an 47 LVM logical volume. They do not support an encrypted root file system 48 or mounting the rootfs over a network card. For a more complete 49 capability see <ulink url="http://www.linuxfromscratch.org/hints/read.html"> 50 the LFS Hints</ulink> or <ulink url="http://fedoraproject.org/wiki/Dracut"> 51 dracut</ulink>.</para> 52 53 <para>To install these scripts, run the following commands as the 54 <systemitem class="username">root</systemitem> user:</para> 53 <para> 54 If you do decide to build an initramfs, the following scripts will 55 provide a basis to do it. The scripts will allow specifying a rootfs 56 via partition UUID or partition LABEL or a rootfs on an LVM logical 57 volume. They do not support an encrypted root file system or mounting 58 the rootfs over a network card. For a more complete capability see 59 <ulink url="http://www.linuxfromscratch.org/hints/read.html"> the LFS 60 Hints</ulink> or <ulink 61 url="http://fedoraproject.org/wiki/Dracut">dracut</ulink>. 62 </para> 63 64 <para> 65 To install these scripts, run the following commands as the 66 <systemitem class="username">root</systemitem> user: 67 </para> 55 68 56 69 <screen role="root"><userinput>cat > /sbin/mkinitramfs << "EOF" … … 434 447 435 448 436 <para>To build an initramfs, run the following as the <systemitem 437 class="username">root</systemitem> user:</para> 449 <para> 450 To build an initramfs, run the following as the <systemitem 451 class="username">root</systemitem> user: 452 </para> 438 453 439 454 <screen role="nodump"><userinput>mkinitramfs [KERNEL VERSION]</userinput></screen> 440 455 441 <para>The optional argument is the directory where the appropriate kernel 442 modules are located. This must be a subdirectory of <filename 443 class='directory'> /lib/modules</filename>. If no modules are specified, 444 then the initramfs is named <emphasis>initrd.img-no-kmods</emphasis>. If a 445 kernel version is specified, the initrd is named 446 <emphasis>initrd.img-$KERNEL_VERSION</emphasis> and is only appropriate for 447 the specific kernel specified. The output file will be placed in the 448 current directory.</para> 449 450 <para>If early loading of microcode is needed (see <xref 451 linkend="cpu-microcode"/>), you can install the appropriate blob or 452 container in <filename class="directory">/lib/firmware</filename>. 453 It will be automatically added to the initrd when running 454 <command>mkinitramfs</command>.</para> 455 456 <para>After generating the initrd, copy it to the <filename 457 class='directory'>/boot</filename> directory.</para> 458 459 <para>Now edit <filename>/boot/grub/grub.cfg</filename> and add a new 460 menuentry. Below are several examples.</para> 456 <para> 457 The optional argument is the directory where the appropriate kernel 458 modules are located. This must be a subdirectory of <filename 459 class='directory'> /lib/modules</filename>. If no modules are specified, 460 then the initramfs is named <emphasis>initrd.img-no-kmods</emphasis>. 461 If a kernel version is specified, the initrd is named 462 <emphasis>initrd.img-$KERNEL_VERSION</emphasis> and is only appropriate 463 for the specific kernel specified. The output file will be placed in the 464 current directory. 465 </para> 466 467 <para> 468 If early loading of microcode is needed (see <xref 469 linkend="cpu-microcode"/>), you can install the appropriate blob or 470 container in <filename class="directory">/lib/firmware</filename>. 471 It will be automatically added to the initrd when running 472 <command>mkinitramfs</command>. 473 </para> 474 475 <para> 476 After generating the initrd, copy it to the <filename 477 class='directory'>/boot</filename> directory. 478 </para> 479 480 <para> 481 Now edit <filename>/boot/grub/grub.cfg</filename> and add a new 482 menuentry. Below are several examples. 483 </para> 461 484 462 485 <screen role="nodump"><userinput># Generic initramfs and root fs identified by UUID … … 481 504 }</userinput></screen> 482 505 483 <para>Finally, reboot the system and select the desired system.</para> 506 <para> 507 Finally, reboot the system and select the desired system. 508 </para> 484 509 485 510 </sect2>
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