Using UUIDs as label to identify your filesystems

Release:

Red Hat Enterprise Linux

Problem:

Using UUIDs as label to identify your filesystems.

Solution:

What is an UUID?

A universally unique identifier (UUID) is an identifier standard used in software construction, standardized by the Open Software Foundation (OSF) as part of the Distributed Computing Environment (DCE). A UUID is a 16-octet (128-bit) number. In its canonical form, a UUID is represented by 32 hexadecimal digits, displayed in five groups separated by hyphens, in the form 8-4-4-4-12 for a total of 36 characters (32 digits and four hyphens). For example:

550e8400-e29b-41d4-a716-446655440000

There are 340,282,366,920,938,463,463,374,607,431,768,211,456 possible UUIDs (16 to the 32nd power or 2 to the 128th power), or ~3.4 × 1038.

UUID in Linux

In Linux, the ext2/ext3/ext4 filesystem also uses UUID to identify partitions. You are not at the safer side if you are using device node names like /dev/sda1 to refer your file system in your /etc/fstab. This is due to the fact that these device node names can change due to switching of cable or upgrading certain packages. So instead of the device node names you may consider using the UUID or LABELs in non-LVM systems.

Determine what is your current entry of the /etc/fstab by using the below command.

# grep /dev/[hsv]d /etc/fstab

/dev/sda1               /boot                   ext4    defaults        1 2

/dev/sda3               /data                   ext4    defaults        0 2

Replace the device entries which point to the device node names like /dev/sda with the UUID or the Label. In this session we will be considering the UUID. You may use the blkid command for getting the UUID of the concerned devices.

# blkid | grep sd

/dev/sda1: LABEL="/boot" UUID="c9fdb384-19ed-4b94-b29e-23f0f566e970"  TYPE="ext4"

/dev/sda3: UUID="80a27dc2-c309-4cc8-9ceb-3bb1a055cf3d" TYPE="ext4"

Following this example, the above lines from /etc/fstab will look like this after being fixed:

LABEL="/boot"                                 /boot   ext4    defaults        1 2

UUID="80a27dc2-c309-4cc8-9ceb-3bb1a055cf3d"   /data   ext4    defaults        0 2

Check the /etc/grub.conf for the use of device node names for non-LVM device nodes to identify the root file system. If present, change the entry by putting in either the label or the UUID.

Non-recommended Entry:

# grep kernel /etc/grub.conf

    kernel /vmlinuz-2.6.18-308.el5 ro root=/dev/sda2

Recommended Entry:

kernel /vmlinuz-2.6.18-308.el5 ro root=LABEL=/

OR

kernel /vmlinuz-2.6.18-308.el5 ro root=UUID=f52529cb-a959-4a11-8d43-0e4fd8fdecd2

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