Ignore:
Timestamp:
04/21/2014 09:44:04 PM (10 years ago)
Author:
Bruce Dubbs <bdubbs@…>
Branches:
10.0, 10.0-rc1, 10.1, 10.1-rc1, 11.0, 11.0-rc1, 11.0-rc2, 11.0-rc3, 11.1, 11.1-rc1, 11.2, 11.2-rc1, 11.3, 11.3-rc1, 12.0, 12.0-rc1, 12.1, 12.1-rc1, 7.6, 7.7, 7.8, 7.9, 8.0, 8.1, 8.2, 8.3, 8.4, 9.0, 9.1, arm, bdubbs/gcc13, ml-11.0, multilib, renodr/libudev-from-systemd, s6-init, trunk, xry111/arm64, xry111/arm64-12.0, xry111/clfs-ng, xry111/lfs-next, xry111/loongarch, xry111/loongarch-12.0, xry111/loongarch-12.1, xry111/mips64el, xry111/pip3, xry111/rust-wip-20221008, xry111/update-glibc
Children:
5af3f9e
Parents:
c65dd23e
Message:

Rewrite and reorganize Chapter 7.
Update systemd customization.

git-svn-id: ​http://svn.linuxfromscratch.org/LFS/trunk/BOOK@10542 4aa44e1e-78dd-0310-a6d2-fbcd4c07a689

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1 edited

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  • chapter07/symlinks.xml

    rc65dd23e rbf58c1e  
    99  <?dbhtml filename="symlinks.html"?>
    1010
    11   <title>Creating Custom Symlinks to Devices</title>
     11  <title>Managing Devices</title>
     12
     13  <sect2>
     14
     15    <title>Network Devices</title>
     16
     17    <para>Udev, by default, names network devices according to Firmware/BIOS
     18    data or physical characteristics like the bus, slot, or MAC address.  The
     19    purpose of this naming convention is to ensure that network devices are
     20    named consistently and not based on the time the network card was
     21    discovered.  For example, on a computer having two network cards made by
     22    Intel and Realtek, the network card manufactured by Intel may become eth0
     23    and the Realtek card becomes eth1. In some cases, after a reboot the cards
     24    get renumbered the other way around.</para>
     25   
     26    <para>In the new naming scheme, typical network device names would then
     27    be something like enp5s0 or wlp3s0.  If this naming convention is not
     28    desired, the traditional naming scheme or a custom scheme can be
     29    implemented.</para>
     30
     31    <sect3>
     32      <title>Disabling Persistent Naming on the Kernel Command Line</title>
     33   
     34      <para>The traditional naming scheme using eth0, eth1, etc can be
     35      restored by adding <userinput>net.ifnames=0</userinput> on the
     36      kernel command line.  This is most appropriate for those systems
     37      that have only one ethernet device of the same type.  Laptops
     38      often have multiple ethernet connections that are named eth0 and
     39      wlan0 and are also candidates for this method.  The command line
     40      is passed in the GRUB configuration file.
     41      See <xref linkend="grub-cfg"/>.</para>
     42    </sect3>
     43
     44    <sect3>
     45      <title>Creating Custom Udev Rules</title>
     46   
     47      <para>The naming scheme can be customized by creating custom Udev
     48      rules.  A script has been included that generates the initial rules.
     49      Generate these rules by running:</para>
     50
     51<screen role="nodump"><userinput>bash /lib/udev/init-net-rules.sh</userinput></screen>
     52
     53      <para> Now, inspect th
     54      <filename>/etc/udev/rules.d/70-persistent-net.rules</filename> file, to
     55      find out which name was assigned to which network device:</para>
     56
     57<screen role="nodump"><userinput>cat /etc/udev/rules.d/70-persistent-net.rules</userinput></screen>
     58
     59      <note><para>In some cases such as when MAC addresess have been assigned to
     60      a network card manually or in a virtual environment such as Qemu or Xen,
     61      the network rules file may not have been generated because addresses
     62      are not consistently assigned.  In these cases, this method cannot
     63      be used.</para></note>
     64 
     65      <para>The file begins with a comment block followed by two lines for each
     66      NIC. The first line for each NIC is a commented description showing its
     67      hardware IDs (e.g. its PCI vendor and device IDs, if it's a PCI card),
     68      along with its driver in parentheses, if the driver can be found. Neither
     69      the hardware ID nor the driver is used to determine which name to give an
     70      interface; this information is only for reference. The second line is the
     71      Udev rule that matches this NIC and actually assigns it a name.</para>
     72 
     73      <para>All Udev rules are made up of several keys, separated by commas and
     74      optional whitespace. This rule's keys and an explanation of each of them
     75      are as follows:</para>
     76 
     77      <itemizedlist>
     78        <listitem>
     79          <para><literal>SUBSYSTEM=="net"</literal> - This tells Udev to ignore
     80          devices that are not network cards.</para>
     81        </listitem>
     82        <listitem>
     83          <para><literal>ACTION=="add"</literal> - This tells Udev to ignore this
     84          rule for a uevent that isn't an add ("remove" and "change" uevents also
     85          happen, but don't need to rename network interfaces).</para>
     86        </listitem>
     87        <listitem>
     88          <para><literal>DRIVERS=="?*"</literal> - This exists so that Udev will
     89          ignore VLAN or bridge sub-interfaces (because these sub-interfaces do
     90          not have drivers). These sub-interfaces are skipped because the name
     91          that would be assigned would collide with their parent devices.</para>
     92        </listitem>
     93        <listitem>
     94          <para><literal>ATTR{address}</literal> - The value of this key is the
     95          NIC's MAC address.</para>
     96        </listitem>
     97        <listitem>
     98          <para><literal>ATTR{type}=="1"</literal> - This ensures the rule only
     99          matches the primary interface in the case of certain wireless drivers,
     100          which create multiple virtual interfaces. The secondary interfaces are
     101          skipped for the same reason that VLAN and bridge sub-interfaces are
     102          skipped: there would be a name collision otherwise.</para>
     103        </listitem>
     104        <listitem>
     105          <para><literal>NAME</literal> - The value of this key is the name that
     106          Udev will assign to this interface.</para>
     107        </listitem>
     108      </itemizedlist>
     109 
     110      <para>The value of <literal>NAME</literal> is the important part. Make sure
     111      you know which name has been assigned to each of your network cards before
     112      proceeding, and be sure to use that <literal>NAME</literal> value when
     113      creating your configuration files below.</para>
     114
     115    </sect3>
     116
     117    <sect3>
     118      <title>Custom Naming in Systemd</title>
     119   
     120      <para>Network interface names can also be customized with a set of
     121      files spcific to systemd.  A file with a name such as 10-eth0.link
     122      in the /etc/systemd/network directory can set an interface name. All
     123      files in the directory will be applied in lexical order.  Files
     124      in the /lib/systemd/network directory with the same name as those
     125      in /etc/systemd/network will be overridden.  See the man page
     126      for systemd.link for a full explanation.</para>
     127
     128      <para>An example file looks like:</para>
     129
     130<screen role="nodump">[Match]
     131MACAddress=12:34:56:78:9a:bc
     132Driver=brcmsmac
     133Path=pci-0000:02:00.0-*
     134Type=wlan
     135Virtualization=no
     136Host=my-laptop
     137Architecture=x86-64
     138
     139[Link]
     140Name=wireless0
     141MTUBytes=1450
     142BitsPerSecond=10M
     143WakeOnLan=magic
     144MACAddress=cb:a9:87:65:43:21</screen>
     145
     146    <para>The [Match] section specifies when to apply the rule.  In
     147    the example above, the entries can be shortened to the minimum
     148    needed to uniquely identify the network device.  Similarly,
     149    the [Link] section only needs to specify the changes from the
     150    default that are desired.  In many cases, the only thing needed is
     151    the Name entry.</para>
     152
     153    </sect3>
     154
     155  </sect2>
    12156
    13157  <sect2>
    … …  
    109253    after a reboot the order changes to the opposite one.
    110254    For all classes of hardware except sound cards and network cards, this is
    111     fixable by creating udev rules for custom persistent symlinks.
     255    fixable by creating Udev rules for custom persistent symlinks.
    112256    The case of network cards is covered separately in
    113257    <xref linkend="ch-scripts-network"/>, and sound card configuration can
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