diff --git a/chapter09/symlinks.xml b/chapter09/symlinks.xml index 24ebf537d..86528ba69 100644 --- a/chapter09/symlinks.xml +++ b/chapter09/symlinks.xml @@ -17,27 +17,28 @@ Udev, by default, names network devices according to Firmware/BIOS data or physical characteristics like the bus, slot, or MAC address. The purpose of this naming convention is to ensure that network devices are - named consistently and not based on the time the network card was - discovered. For example, on a computer having two network cards made by - Intel and Realtek, the network card manufactured by Intel may become eth0 - and the Realtek card becomes eth1. In some cases, after a reboot the cards - could get renumbered the other way around. + named consistently, not based on when the network card was + discovered. In older versions of Linux—on a computer with two + network cards made by Intel and Realtek, for instance—the + network card manufactured by Intel might have become eth0 + while the Realtek card became eth1. After a reboot, the cards + would sometimes get renumbered the other way around. - In the new naming scheme, typical network device names would then - be something like enp5s0 or wlp3s0. If this naming convention is not - desired, the traditional naming scheme or a custom scheme can be + In the new naming scheme, typical network device names are + something like enp5s0 or wlp3s0. If this naming convention is not + desired, the traditional naming scheme, or a custom scheme, can be implemented. Disabling Persistent Naming on the Kernel Command Line - The traditional naming scheme using eth0, eth1, etc can be + The traditional naming scheme using eth0, eth1, etc. can be restored by adding net.ifnames=0 on the - kernel command line. This is most appropriate for those systems - that have only one ethernet device of the same type. Laptops - often have multiple ethernet connections that are named eth0 and - wlan0 and are also candidates for this method. The command line - is passed in the GRUB configuration file. + kernel command line. This is most appropriate for systems + that have just one ethernet device of a particular type. Laptops + often have two ethernet connections named eth0 and + wlan0; such laptops can also use this method. The command line + is in the GRUB configuration file. See . @@ -56,23 +57,22 @@ cat /etc/udev/rules.d/70-persistent-net.rules - In some cases such as when MAC addresses have been assigned to - a network card manually or in a virtual environment such as Qemu or Xen, - the network rules file may not have been generated because addresses + In some cases, such as when MAC addresses have been assigned to + a network card manually, or in a virtual environment such as Qemu or Xen, + the network rules file may not be generated because addresses are not consistently assigned. In these cases, this method cannot be used. - The file begins with a comment block followed by two lines for each + The file begins with a comment block, followed by two lines for each NIC. The first line for each NIC is a commented description showing its hardware IDs (e.g. its PCI vendor and device IDs, if it's a PCI card), - along with its driver in parentheses, if the driver can be found. Neither + along with its driver (in parentheses, if the driver can be found). Neither the hardware ID nor the driver is used to determine which name to give an interface; this information is only for reference. The second line is the udev rule that matches this NIC and actually assigns it a name. - All udev rules are made up of several keys, separated by commas and - optional whitespace. This rule's keys and an explanation of each of them - are as follows: + All udev rules are made up of several keywords, separated by commas and + optional whitespace. Here are the keywords, and an explanation of each one: @@ -88,10 +88,10 @@ DRIVERS=="?*" - This exists so that udev will ignore VLAN or bridge sub-interfaces (because these sub-interfaces do not have drivers). These sub-interfaces are skipped because the name - that would be assigned would collide with their parent devices. + that would be assigned would collide with the parent devices. - ATTR{address} - The value of this key is the + ATTR{address} - The value of this keyword is the NIC's MAC address. @@ -102,7 +102,7 @@ skipped: there would be a name collision otherwise. - NAME - The value of this key is the name that + NAME - The value of this keyword is the name that udev will assign to this interface. @@ -110,7 +110,7 @@ The value of NAME is the important part. Make sure you know which name has been assigned to each of your network cards before proceeding, and be sure to use that NAME value when - creating your configuration files below. + creating your network configuration files. @@ -118,10 +118,10 @@ - CD-ROM symlinks + CD-ROM Symlinks Some software that you may want to install later (e.g., various - media players) expect the /dev/cdrom + media players) expects the /dev/cdrom and /dev/dvd symlinks to exist, and to point to a CD-ROM or DVD-ROM device. Also, it may be convenient to put references to those symlinks into /etc/fstab. Udev @@ -139,15 +139,15 @@ ata_id or scsi_id programs, depending on which type of device you have. - There are advantages to each approach; the correct approach to use - will depend on what kinds of device changes may happen. If you expect the + There are advantages to each approach; the correct approach + depends on what kinds of device changes may happen. If you expect the physical path to the device (that is, the ports and/or slots that it plugs into) to change, for example because you plan on moving the drive to a different IDE port or a different USB connector, then you should use the by-id mode. On the other hand, if you expect the device's - identification to change, for example because it may die, and you would - replace it with a different device with the same capabilities and which - is plugged into the same connectors, then you should use the + identification to change, for example because it may die, and you intend + to replace it with a different device that + plugs into the same connectors, then you should use the by-path mode. If either type of change is possible with your drive, then choose a @@ -198,13 +198,13 @@ this is only an issue if you need the symlinks on both systems to point to the same device. If you need that, then inspect (and possibly edit) the generated /etc/udev/rules.d/70-persistent-cd.rules - file after booting, to make sure the assigned symlinks match what you need. + file after booting, to make sure the assigned symlinks match your needs. - Dealing with duplicate devices + Dealing with Duplicate Devices As explained in , the order in which devices with the same function appear in @@ -214,7 +214,7 @@ /dev/video1 refers to the tuner, and sometimes after a reboot the order changes. For all classes of hardware except sound cards and network cards, this is - fixable by creating udev rules for custom persistent symlinks. + fixable by creating udev rules to create persistent symlinks. The case of network cards is covered separately in , and sound card configuration can be found in BLFS.