Tips and tricks: What is devlabel, and how do I use it?

Devlabel is a script which manages symbolic links to storage devices on your system. This is accomplished by utilizing the inherent unique identifiers (UUID) that each device should have in order to maintain a correctly pointing symlink in the event that the device name changes (eg. /dev/sdc1 becomes /dev/sdd1).

By adding entries using devlabel, users can instead reference all devices by their symlink and no longer have to worry about what the true name of their device is. Devlabel works with both IDE and SCSI storage.

Devlabel first tries to find the uuid of the partition that you are attempting to add to devlabel by using the /usr/bin/partition_uuid program. Partition UUIDs are supported currently under ext2, ext3, xfs, jfs and ocfs. If no partition UUID can be found (or if it is not a partition you are adding) devlabel will then attempt to find either a SCSI uuid or IDE identifier.

To determine the unique identifier associated with a SCSI device, devlabel uses the program /usr/bin/scsi_unique_id. If this program cannot determine a unique identifier for your block device then the device cannot be used with devlabel.

Example usage of the devlabel command can be found below:

• Add a device to be managed by devlabel

  devlabel add -d  -s
  

• Remove a devlabel symlink

  
  devlabel remove -s
  

• Report the status of all devlabel symlinks

  devlabel status
  

• Get the UUID of a particular device

  devlabel printid -d 
  

Once a devlabel has been configured files such as /etc/fstab can be modified to reflect these changes and point to the symlink rather than the physical device itself.

The configuration file for devlabel is /etc/sysconfig/devlabel. This file tracks all the current device symlinks. It is not recommended to edit this file by hand.

The devlabel command is available from the devlabel package for Red Hat Enterprise Linux 3 and onwards.
For further information see the Red Hat Enterprise Linux System Administration Guide http://www.redhat.com/docs/manuals/enterprise/RHEL-3-Manual/sysadmin-guide/ch-devlabel.html

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