IconsPage/hdd.png Linux now prefers to use UUID (Universally Unique Identifier), LABEL, or symlinks to identify media storage devices on a system. Directly using /dev/hd*# or /dev/sd*# is no longer preferred since these device assignments can change between system boots:

  • all filesystems should be specified by UUID=<id> or LABEL=<name> for each partition.

  • all physical devices should be specified by a symlink, like /dev/cdrom for a cd drive and /dev/disk/by-id/... for each physical hard drive.

IconsPage/editor.png The files for which UUID is most critical:

  • /boot/grub/menu.lst

  • /etc/fstab

  • /etc/initramfs-tools/conf.d/resume

This page uses the terminal a lot, so if you are new to this, see UsingTheTerminal.

The Fstab page provides some excellent examples of UUID in action.

Finding UUIDs

IconsPage/note.png UUIDs can be determined using the blkid command. This command lists UUIDs for all attached devices (mounted or not).

IconsPage/example.png Here are examples (your output will be different, but similarly formatted). The command:

sudo blkid

produces an output similar to:

  •  /dev/sda1: TYPE="ntfs" UUID="72C0DE8EC0DE57C5" LABEL="windows" 
     /dev/sda2: UUID="30fcb748-ad1e-4228-af2f-951e8e7b56df" SEC_TYPE="ext2" TYPE="ext3" 
     /dev/sda5: TYPE="swap" UUID="8c4e69f8-5074-42c0-8134-0b2429c4c02c" 
     /dev/sdb1: SEC_TYPE="msdos" UUID="4848-E35A" TYPE="vfat" 

Alternatively you can list them from their listing in your root filesystem:

ls -l /dev/disk/by-uuid/

produces an output similar to:

  •  total 0
     lrwxrwxrwx 1 root root 10 2008-06-04 03:10 30fcb748-ad1e-4228-af2f- 951e8e7b56df -> ../../sda2
     lrwxrwxrwx 1 root root 10 2008-06-07 16:51 4848-E35A -> ../../sdb1
     lrwxrwxrwx 1 root root 10 2008-06-04 03:10 72C0DE8EC0DE57C5 -> ../../sda1
     lrwxrwxrwx 1 root root 10 2008-06-04 03:10 8c4e69f8-5074-42c0-8134-0b2429c4c02c -> ../../sda5

Converting to UUIDs

IconsPage/info.png IconsPage/note.png If you are using Ubuntu 6.06 Dapper Drake LTS, you can use these commands to "upgrade" to UUIDs. All other supported versions of Ubuntu automatically use UUIDs, so this is not necessary. You may be interested in having a look, anyway.

Fstab

For /etc/fstab:

sudo rm /etc/fstab.pre-uuid
sudo /var/lib/dpkg/info/volumeid.postinst configure

Grub

For /boot/grub/menu.lst:

sudo update-grub

Resuming from Hibernation

For /etc/initramfs-tools/conf.d/resume, there is no automatic procedure. You must manually verify that RESUME=UUID=<some_UUID> where <some_UUID> matches the UUID for the swap line in your /etc/fstab file.

First check the contents of the files:

cat /etc/initramfs-tools/conf.d/resume
cat /etc/fstab | grep swap

If the UUIDs do not match or do not exist in the resume file, open it for editing one of the following:

gksudo gedit /etc/initramfs-tools/conf.d/resume
sudo nano -Bw /etc/initramfs-tools/conf.d/resume

Now add the correct UUID to the resume file in the format

  •  RESUME=UUID=<swap_UUID>

Save and close.

After any adjustment, run:

sudo update-initramfs -u

Using LABEL

IconsPage/note.png Labels can be very useful for external media, like flash drives and USB hard drives since these are generally automounted by hal (Hardware Abstraction Layer). If a device has a label, it will be mounted at the /media/<label> location and appear with the label on the desktop.

IconsPage/tip.png For help with labeling devices, see RenameUSBDrive.

Symlinks

Symlinks (symbolic links) are used to make it easier to identify a device. For example /dev/cdrom can link to /dev/scd0. These are normally created by udev which is the device manager program used in the Linux 2.6 kernel series. We will not cover creating your own symlinks here (may be added later).

IconsPage/example.png Other examples of symlinks include /dev/floppy to /dev/fd0 or /dev/dvd to /dev/scd1 .

You can view the linked device on a symlink with the ls command, like so:

ls -l /dev/cdrom

produces an output similar to:

  •  lrwxrwxrwx 1 root root 4 2008-06-22 17:31 /dev/cdrom -> scd0

This tell us that /dev/cdrom is a symlink to the device /dev/scd0 .

To view the physical device identifiers (like for a hard drive, not to be confused with a disk's partitions), the command:

ls -l /dev/disk/by-id/

produces an output similar to:

  •  total 0
     lrwxrwxrwx 1 root root  9 2008-06-22 10:30 ata-Hitachi_HTS541080G9AT00_MPB4PAX6H6B68G -> ../../sda
     lrwxrwxrwx 1 root root 10 2008-06-22 10:30 ata-Hitachi_HTS541080G9AT00_MPB4PAX6H6B68G-part1 -> ../../sda1
     lrwxrwxrwx 1 root root 10 2008-06-22 10:30 ata-Hitachi_HTS541080G9AT00_MPB4PAX6H6B68G-part2 -> ../../sda2
     lrwxrwxrwx 1 root root 10 2008-06-22 10:30 ata-Hitachi_HTS541080G9AT00_MPB4PAX6H6B68G-part3 -> ../../sda3
     lrwxrwxrwx 1 root root 10 2008-06-22 10:30 ata-Hitachi_HTS541080G9AT00_MPB4PAX6H6B68G-part5 -> ../../sda5
     lrwxrwxrwx 1 root root  9 2008-06-22 17:31 ata-LEXAR_ATA_FLASH_13523623189499090034 -> ../../sdb
     lrwxrwxrwx 1 root root 10 2008-06-22 17:31 ata-LEXAR_ATA_FLASH_13523623189499090034-part1 -> ../../sdb1
     lrwxrwxrwx 1 root root  9 2008-06-22 10:30 scsi-1ATA_Hitachi_HTS541080G9AT00_MPB4PAX6H6B68G -> ../../sda
     lrwxrwxrwx 1 root root 10 2008-06-22 10:30 scsi-1ATA_Hitachi_HTS541080G9AT00_MPB4PAX6H6B68G-part1 -> ../../sda1
     lrwxrwxrwx 1 root root 10 2008-06-22 10:30 scsi-1ATA_Hitachi_HTS541080G9AT00_MPB4PAX6H6B68G-part2 -> ../../sda2
     lrwxrwxrwx 1 root root 10 2008-06-22 10:30 scsi-1ATA_Hitachi_HTS541080G9AT00_MPB4PAX6H6B68G-part3 -> ../../sda3
     lrwxrwxrwx 1 root root 10 2008-06-22 10:30 scsi-1ATA_Hitachi_HTS541080G9AT00_MPB4PAX6H6B68G-part5 -> ../../sda5
     lrwxrwxrwx 1 root root  9 2008-06-22 17:31 scsi-1ATA_LEXAR_ATA_FLASH_13523623189499090034 -> ../../sdb
     lrwxrwxrwx 1 root root 10 2008-06-22 17:31 scsi-1ATA_LEXAR_ATA_FLASH_13523623189499090034-part1 -> ../../sdb1

Note that each partition (called part#) identifies with their parent device - this is because they exist on that physical piece of hardware. You will also notice that the drives and partitions appear twice, the first time as ata and the second time as scsi. I am unclear as to why this is, but I believe it is related to IDE hard drives being identified to the system as SCSI drives (because of ide-scsi emulation?).

Other Resources

IconsPage/resources.png Here are some other useful and related pages.

UsingUUID (last edited 2014-03-31 03:29:21 by drax)