kernfs.xml 4.6 KB

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  1. <?xml version="1.0" encoding="ISO-8859-1"?>
  2. <!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
  3. "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
  4. <!ENTITY % general-entities SYSTEM "../general.ent">
  5. %general-entities;
  6. ]>
  7. <sect1 id="ch-tools-kernfs">
  8. <?dbhtml filename="kernfs.html"?>
  9. <title>Preparing Virtual Kernel File Systems</title>
  10. <indexterm zone="ch-tools-kernfs">
  11. <primary sortas="e-/dev/">/dev/*</primary>
  12. </indexterm>
  13. <para>Various file systems exported by the kernel are used to communicate to
  14. and from the kernel itself. These file systems are virtual in that no disk
  15. space is used for them. The content of the file systems resides in
  16. memory.</para>
  17. <para>Begin by creating directories onto which the file systems will be
  18. mounted:</para>
  19. <screen><userinput>mkdir -pv $LFS/{dev,proc,sys,run}</userinput></screen>
  20. <sect2>
  21. <title>Creating Initial Device Nodes</title>
  22. <para>When the kernel boots the system, it requires the presence of a few
  23. device nodes, in particular the <filename
  24. class="devicefile">console</filename> and <filename
  25. class="devicefile">null</filename> devices. The device nodes must be
  26. created on the hard disk so that they are available before the kernel
  27. populates <systemitem class="filesystem">/dev</systemitem>), and
  28. additionally when Linux is started with
  29. <parameter>init=/bin/bash</parameter>. Create the devices by running the
  30. following commands:</para>
  31. <screen><userinput>mknod -m 600 $LFS/dev/console c 5 1
  32. mknod -m 666 $LFS/dev/null c 1 3</userinput></screen>
  33. </sect2>
  34. <sect2 id="ch-tools-bindmount">
  35. <title>Mounting and Populating /dev</title>
  36. <para>The recommended method of populating the <filename
  37. class="directory">/dev</filename> directory with devices is to mount a
  38. virtual filesystem (such as <systemitem
  39. class="filesystem">tmpfs</systemitem>) on the <filename
  40. class="directory">/dev</filename> directory, and allow the devices to be
  41. created dynamically on that virtual filesystem as they are detected or
  42. accessed. Device creation is generally done during the boot process
  43. by Udev. Since this new system does not yet have Udev and has not yet
  44. been booted, it is necessary to mount and populate <filename
  45. class="directory">/dev</filename> manually. This is accomplished by bind
  46. mounting the host system's <filename class="directory">/dev</filename>
  47. directory. A bind mount is a special type of mount that allows you to
  48. create a mirror of a directory or mount point to some other location. Use
  49. the following command to achieve this:</para>
  50. <screen><userinput>mount -v --bind /dev $LFS/dev</userinput></screen>
  51. </sect2>
  52. <sect2 id="ch-tools-kernfsmount">
  53. <title>Mounting Virtual Kernel File Systems</title>
  54. <para>Now mount the remaining virtual kernel filesystems:</para>
  55. <screen><userinput>mount -v --bind /dev/pts $LFS/dev/pts
  56. mount -vt proc proc $LFS/proc
  57. mount -vt sysfs sysfs $LFS/sys
  58. mount -vt tmpfs tmpfs $LFS/run</userinput></screen>
  59. <!--
  60. <variablelist>
  61. <title>The meaning of the mount options for devpts:</title>
  62. <varlistentry>
  63. <term><parameter>gid=5</parameter></term>
  64. <listitem>
  65. <para>This ensures that all devpts-created device nodes are owned by
  66. group ID 5. This is the ID we will use later on for the <systemitem
  67. class="groupname">tty</systemitem> group. We use the group ID instead
  68. of a name, since the host system might use a different ID for its
  69. <systemitem class="groupname">tty</systemitem> group.</para>
  70. </listitem>
  71. </varlistentry>
  72. <varlistentry>
  73. <term><parameter>mode=0620</parameter></term>
  74. <listitem>
  75. <para>This ensures that all devpts-created device nodes have mode 0620
  76. (user readable and writable, group writable). Together with the
  77. option above, this ensures that devpts will create device nodes that
  78. meet the requirements of grantpt(), meaning the Glibc
  79. <command>pt_chown</command> helper binary (which is not installed by
  80. default) is not necessary.</para>
  81. </listitem>
  82. </varlistentry>
  83. </variablelist>
  84. -->
  85. <para>In some host systems, <filename>/dev/shm</filename> is a
  86. symbolic link to <filename class="directory">/run/shm</filename>.
  87. The /run tmpfs was mounted above so in this case only a
  88. directory needs to be created.</para>
  89. <screen><userinput>if [ -h $LFS/dev/shm ]; then
  90. mkdir -pv $LFS/$(readlink $LFS/dev/shm)
  91. fi</userinput></screen>
  92. </sect2>
  93. </sect1>