Using Uuids To Mount Devices; Naming Devices With Udev; Understanding Uuids; Using Uuids To Assemble Or Activate File System Devices - Novell LINUX ENTERPRISE SERVER 10 - STORAGE ADMINISTRATION GUIDE 7-2007 Administration Manual

Using UUIDs to Mount Devices

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This section describes 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 31
Section 3.2, "Understanding UUIDs," on page 31
Section 3.3, "Using UUIDs in the Boot Loader and /etc/fstab File (x86)," on page 32
Section 3.4, "Using UUIDs in the Boot Loader and /etc/fstab File (IA64)," on page 33
Section 3.5, "Additional Information," on page 34

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.

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 31
Section 3.2.2, "Finding the UUID for a File System Device," on page 32
3.2.1 Using UUIDs to Assemble or Activate File System
Devices
The UUID is always unique to the partition and does not depend on the order in which it appears or
where it is mounted. With certain SAN devices attached to the server, the system partitions are
renamed and moved to be the last device. For example, if root (/) is assigned to /dev/sda1
(http://reactivated.net/writing_udev_rules.html).
Using UUIDs to Mount Devices
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