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@@ -93,40 +93,52 @@
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</sect3>
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<sect3>
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- <title>Udev Bootscript</title>
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-
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- <para>The <command>/etc/rc.d/init.d/udev</command> initscript takes care of creating
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- device nodes when Linux is booted. The script unsets the uevent handler
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- from the default of <command>/sbin/hotplug</command>. This is done
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- because the kernel no longer needs to call out to an external binary.
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- Instead <command>udevd</command> will listen on a netlink socket for
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- uevents that the kernel raises. Next, the bootscript copies any static
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- device nodes that exist in <filename
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+ <title>Udev Bootscripts</title>
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+
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+ <para>The <command>/etc/rc.d/init.d/udev</command> initscript takes care
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+ of creating device nodes when Linux is booted. The script unsets the
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+ uevent handler from the default of <command>/sbin/hotplug</command>.
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+ This is done because the kernel no longer needs to call out to an
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+ external binary. Instead <command>udevd</command> will listen on a
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+ netlink socket for uevents that the kernel raises. Next, the bootscript
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+ copies any static device nodes that exist in <filename
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class="directory">/lib/udev/devices</filename> to <filename
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- class="directory">/dev</filename>. This is necessary because some devices,
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- directories, and symlinks are needed before the dynamic device handling
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- processes are available during the early stages of booting a system, or
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- are required by <command>udevd</command> itself. Creating static device
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- nodes in <filename class="directory">/lib/udev/devices</filename> also
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- provides an easy workaround for devices that are not supported by the
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- dynamic device handling infrastructure. The bootscript then starts the
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- Udev daemon, <command>udevd</command>, which will act on any uevents it
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- receives. Finally, the bootscript forces the kernel to replay uevents for
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- any devices that have already been registered and then waits for
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+ class="directory">/dev</filename>. This is necessary because some
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+ devices, directories, and symlinks are needed before the dynamic device
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+ handling processes are available during the early stages of booting a
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+ system, or are required by <command>udevd</command> itself. Creating
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+ static device nodes in <filename
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+ class="directory">/lib/udev/devices</filename> also provides an easy
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+ workaround for devices that are not supported by the dynamic device
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+ handling infrastructure. The bootscript then starts the Udev daemon,
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+ <command>udevd</command>, which will act on any uevents it receives.
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+ Finally, the bootscript forces the kernel to replay uevents for any
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+ devices that have already been registered and then waits for
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<command>udevd</command> to handle them.</para>
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+ <para>The <command>/etc/rc.d/init.d/udev_retry</command> initscript takes
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+ care of re-triggering events for subsystems whose rules may rely on
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+ filesystems that are not mounted until the <command>mountfs</command>
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+ script is run (in particular, /usr and /var may cause this). This script
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+ runs after the <command>mountfs</command> script, so those rules (if
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+ re-triggered) should succeed the second time around. It is configured
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+ from the <filename>/etc/sysconfig/udev_retry</filename> file; any words
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+ in this file other than comments are considered subsystem names to
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+ trigger at retry time. (To find the subsystem of a device, use
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+ <command>udevadm info --attribute-walk</command>.)</para>
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+
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</sect3>
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<sect3>
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<title>Device Node Creation</title>
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- <para>To obtain the right major and minor number for a device, Udev relies
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- on the information provided by <systemitem
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+ <para>To obtain the right major and minor number for a device, Udev
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+ relies on the information provided by <systemitem
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class="filesystem">sysfs</systemitem> in <filename
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class="directory">/sys</filename>. For example,
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<filename>/sys/class/tty/vcs/dev</filename> contains the string
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- <quote>7:0</quote>. This string is used by <command>udevd</command>
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- to create a device node with major number <emphasis>7</emphasis> and minor
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+ <quote>7:0</quote>. This string is used by <command>udevd</command> to
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+ create a device node with major number <emphasis>7</emphasis> and minor
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<emphasis>0</emphasis>. The names and permissions of the nodes created
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under the <filename class="directory">/dev</filename> directory are
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determined by rules specified in the files within the <filename
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Bruce Dubbs