[ab4fdfc] | 1 | <?xml version="1.0" encoding="UTF-8"?>
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[6732c094] | 2 | <!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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| 3 | "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
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[e73e361] | 4 | <!ENTITY % general-entities SYSTEM "../../general.ent">
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| 5 | %general-entities;
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| 6 | ]>
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| 7 |
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| 8 | <sect1 id="postlfs-devices" xreflabel="About Devices">
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| 9 | <?dbhtml filename="devices.html"?>
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| 10 |
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| 11 |
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| 12 | <title>About Devices</title>
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| 13 |
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| 14 | <indexterm zone="postlfs-devices">
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| 15 | <primary sortas="e-etc-udev-rules">/etc/udev/rules.d</primary>
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| 16 | </indexterm>
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| 17 |
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[81a73ed8] | 18 | <para>
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| 19 | Although most devices needed by packages in BLFS and beyond are set up
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| 20 | properly by <application>udev</application> using the default rules
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| 21 | installed by LFS in <filename
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| 22 | class="directory">/etc/udev/rules.d</filename>, there are cases where
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| 23 | the rules must be modified or augmented.
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| 24 | </para>
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[e73e361] | 25 |
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| 26 | <sect2>
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| 27 | <title>Multiple Sound Cards</title>
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| 28 |
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[81a73ed8] | 29 | <para>
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| 30 | If there are multiple sound cards in a system, the "default"
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| 31 | sound card becomes random. The method to establish sound card order
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| 32 | depends on whether the drivers are modules or not. If the sound card
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| 33 | drivers are compiled into the kernel, control is via kernel command line
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| 34 | parameters in <filename>/boot/grub/grub.cfg</filename>. For example,
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| 35 | if a system has both an FM801 card and a SoundBlaster PCI card, the
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| 36 | following can be appended to the command line:
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| 37 | </para>
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[e73e361] | 38 |
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| 39 | <screen><literal>snd-fm801.index=0 snd-ens1371.index=1</literal></screen>
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| 40 |
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[81a73ed8] | 41 | <para>
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| 42 | If the sound card drivers are built as modules, the order can be
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| 43 | established in the <filename>/etc/modprobe.conf</filename> file with:
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| 44 | </para>
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[e73e361] | 45 |
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| 46 | <screen><literal>options snd-fm801 index=0
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| 47 | options snd-ens1371 index=1</literal></screen>
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| 48 |
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| 49 | </sect2>
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| 50 |
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[d20c871] | 51 | <sect2 id="usb-device-issues">
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| 52 | <title>USB Device Issues</title>
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| 53 |
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[81a73ed8] | 54 | <para>
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| 55 | USB devices usually have two kinds of device nodes associated with them.
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| 56 | </para>
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| 57 |
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| 58 | <para>
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| 59 | The first kind is created by device-specific drivers (e.g.,
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| 60 | usb_storage/sd_mod or usblp) in the kernel. For example, a USB mass
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| 61 | storage device would be /dev/sdb, and a USB printer would be
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| 62 | /dev/usb/lp0. These device nodes exist only when the device-specific
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| 63 | driver is loaded.
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| 64 | </para>
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| 65 |
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| 66 | <para>
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| 67 | The second kind of device nodes (/dev/bus/usb/BBB/DDD, where BBB is
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| 68 | the bus number and DDD is the device number) are created even if the
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| 69 | device doesn't have a kernel driver. By using these "raw" USB device
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| 70 | nodes, an application can exchange arbitrary USB packets with the
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| 71 | device, i.e., bypass the possibly-existing kernel driver.
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| 72 | </para>
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| 73 |
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| 74 | <para>
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| 75 | Access to raw USB device nodes is needed when a userspace program is
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| 76 | acting as a device driver. However, for the program to open the device
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| 77 | successfully, the permissions have to be set correctly. By default, due
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| 78 | to security concerns, all raw USB devices are owned by user root and
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[e77b014] | 79 | group root, and have 0664 permissions (the read access is needed, e.g.,
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[81a73ed8] | 80 | for lsusb to work and for programs to access USB hubs). Packages (such
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| 81 | as SANE and libgphoto2) containing userspace USB device drivers also
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| 82 | ship udev rules that change the permissions of the controlled raw USB
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| 83 | devices. That is, rules installed by SANE change permissions for known
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| 84 | scanners, but not printers. If a package maintainer forgot to write
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| 85 | a rule for your device, report a bug to both BLFS (if the package is
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| 86 | there) and upstream, and you will need to write your own rule.
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| 87 | </para>
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| 88 |
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| 89 | <para>
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| 90 | Before Linux-2.6.15, raw USB device access was performed not with
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| 91 | /dev/bus/usb/BBB/DDD device nodes, but with /proc/bus/usb/BBB/DDD
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[e77b014] | 92 | pseudofiles. Some applications still use only
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| 93 | this deprecated technique and can't use the new device nodes. They
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| 94 | cannot work with Linux kernel version 3.5 or newer. If you need to
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| 95 | run such an application, contact the developer of it for a fix.
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[81a73ed8] | 96 | </para>
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[d20c871] | 97 |
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| 98 | </sect2>
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| 99 |
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[e73e361] | 100 | <sect2>
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[826bacb5] | 101 | <title>Udev Device Attributes</title>
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[9f12e36] | 102 |
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[81a73ed8] | 103 | <para>
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| 104 | Fine-tuning of device attributes such as group name and permissions
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| 105 | is possible by creating extra <application>udev</application> rules,
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| 106 | matching on something like this. The vendor and product can be found by
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| 107 | searching the <filename class='directory'>/sys/devices</filename>
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| 108 | directory entries or using <command>udevadm info</command> after the
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| 109 | device has been attached. See the documentation in the current
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| 110 | <application>udev</application> directory of <filename
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| 111 | class='directory'>/usr/share/doc</filename> for details.
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| 112 | </para>
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[9f12e36] | 113 |
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[fdf8b6d0] | 114 | <screen><literal>SUBSYSTEM=="usb_device", SYSFS{idVendor}=="05d8", SYSFS{idProduct}=="4002", \
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| 115 | GROUP:="scanner", MODE:="0660"</literal></screen>
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| 116 |
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[81a73ed8] | 117 | <note>
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| 118 | <para>
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| 119 | The above line is used for descriptive purposes only. The
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| 120 | scanner <application>udev</application> rules are put into place when
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| 121 | installing <xref linkend='sane'/>.
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| 122 | </para>
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| 123 | </note>
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[9f12e36] | 124 |
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[e73e361] | 125 | </sect2>
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| 126 |
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| 127 | <!--
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| 128 | <sect2>
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| 129 | <title>Multiple Network Interfaces</title>
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| 130 |
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| 131 |
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| 132 | </sect2>
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| 133 | -->
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| 134 |
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[fe142cc] | 135 | <!-- These instructions are invalid on systemd because we don't use bootscripts.
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| 136 | In addition, we should probably verify that these are valid on SysV too.-->
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| 137 |
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| 138 | <sect2 revision="sysv">
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[e73e361] | 139 | <title>Devices for Servers</title>
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| 140 |
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[81a73ed8] | 141 | <para>
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| 142 | In some cases, it makes sense to disable
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| 143 | <application>udev</application> completely and create static devices.
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| 144 | Servers are one example of this situation. Does a server need the
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| 145 | capability of handling dynamic devices? Only the system administrator
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| 146 | can answer that question, but in many cases the answer will be no.
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| 147 | </para>
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| 148 |
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| 149 | <para>
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| 150 | If dynamic devices are not desired, then static devices must be
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| 151 | created on the system. In the default configuration, the
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| 152 | <filename>/etc/rc.d/rcS.d/S10udev</filename> boot script mounts a
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| 153 | <systemitem class="filesystem">tmpfs</systemitem> partition over the
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| 154 | <filename class="directory">/dev</filename> directory. This problem can
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| 155 | be overcome by mounting the root partition temporarily:
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| 156 | </para>
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| 157 |
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| 158 | <warning>
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| 159 | <para>
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| 160 | If the instructions below are not followed carefully, your
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| 161 | system could become unbootable.
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| 162 | </para>
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| 163 | </warning>
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[9f12e36] | 164 |
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[e73e361] | 165 |
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| 166 | <screen><userinput>mount --bind / /mnt
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| 167 | cp -a /dev/* /mnt/dev
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[f41f8b6] | 168 | rm /etc/rc.d/rcS.d/{S10udev,S50udev_retry}
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[e73e361] | 169 | umount /mnt</userinput></screen>
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| 170 |
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[81a73ed8] | 171 | <para>
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| 172 | At this point, the system will use static devices upon the next
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| 173 | reboot. Create any desired additional devices using
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| 174 | <command>mknod</command>.
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| 175 | </para>
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| 176 |
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| 177 | <para>
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| 178 | If you want to restore the dynamic devices, recreate the
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| 179 | <filename>/etc/rc.d/rcS.d/{S10udev,S50udev_retry}</filename> symbolic
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| 180 | links and reboot again. Static devices do not need to be removed
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| 181 | (console and null are always needed) because they are covered by the
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| 182 | <systemitem class="filesystem">tmpfs</systemitem> partition. Disk
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[f911e63] | 183 | usage for devices is negligible (about 20–30 bytes per entry).
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[81a73ed8] | 184 | </para>
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[e73e361] | 185 |
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| 186 | </sect2>
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| 187 |
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[e104a36] | 188 | <sect2 id="dev-dvd">
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| 189 | <title>Devices for DVD Drives</title>
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| 190 |
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[81a73ed8] | 191 | <para>
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[8558044] | 192 | If the initial boot process does not set up the
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[81a73ed8] | 193 | <systemitem>/dev/dvd</systemitem> device properly, it can
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| 194 | be installed using the following modification to the default udev rules.
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| 195 | As the <systemitem class="username">root</systemitem> user, run:
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| 196 | </para>
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[e104a36] | 197 |
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| 198 | <screen><userinput>sed '1d;/SYMLINK.*cdrom/ a\
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| 199 | KERNEL=="sr0", ENV{ID_CDROM_DVD}=="1", SYMLINK+="dvd", OPTIONS+="link_priority=-100"' \
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| 200 | /lib/udev/rules.d/60-cdrom_id.rules > /etc/udev/rules.d/60-cdrom_id.rules</userinput></screen>
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| 201 |
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| 202 | </sect2>
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| 203 |
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[e73e361] | 204 | </sect1>
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