Mounting Evms File System Devices By Uuids; Naming Devices With Udev; Understanding Uuids - Novell LINUX ENTERPRISE SERVER 10 - STORAGE ADMINISTRATION GUIDE FOR EVMS Administration Manual

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Mounting EVMS File System

Devices by UUIDs

This section discusses the optional use of UUIDs instead of device names to identify file system

devices in the boot loader file and the /etc/fstab file.

Section 3.1, "Naming Devices with udev," on page 29

Section 3.2, "Understanding UUIDs," on page 29

Section 3.3, "Using UUIDs in the Boot Loader and /etc/fstab File (x86)," on page 30

Section 3.4, "Using UUIDs in the Boot Loader and /etc/fstab File (IA64)," on page 31

3.1 Naming Devices with udev

In the Linux 2.6 and later kernel, udev provides a userspace solution for the dynamic /dev

directory, with persistent device naming. As part of the hotplug system, udev is executed if a device

is added or removed from the system.

A list of rules is used to match against specific device attributes. The udev rules infrastructure

(defined in the /etc/udev/rules.d directory) provides stable names for all disk devices,

regardless of their order of recognition or the connection used for the device. The udev tools

examine every appropriate block device that the kernel creates to apply naming rules based on

certain buses, drive types, or file systems. For information about how to define your own rules for

udev, see

Writing udev Rules

Along with the dynamic kernel-provided device node name, udev maintains classes of persistent

symbolic links pointing to the device in the /dev/disk directory, which is further categorized by

the by-id, by-label, by-path, and by-uuid subdirectories.

NOTE: Other programs besides udev, such as LVM or md, might also generate UUIDs, but they

are not listed in /dev/disk.

For more information about udev(8), see its man page. Enter the following at a terminal console

prompt:

man 8 udev

3.2 Understanding UUIDs

A UUID (Universally Unique Identifier) is a 128-bit number for a file system that is unique on both

the local system and across other systems. It is a randomly generated with system hardware

information and time stamps as part of its seed. UUIDs are commonly used to uniquely tag devices.

Section 3.2.1, "Using UUIDs to Assemble or Activate File System Devices," on page 30

Section 3.2.2, "Finding the UUID for a File System Device," on page 30

(http://reactivated.net/writing_udev_rules.html).