The Geek Diary

CentOS / RHEL : How to find UUID of a device or filesystem

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UUID or universally unique identifier is a useful piece of information. It can be really handy sometimes when the name of the device or file systems are not consistent. Device UUID uniquely identifies the component in the system which is persistent across system reboots.

Device UUID

For CentOS/RHEL 5

# scsi_id -u -g -s /block/sda
35000c50032387713

For CentOS/RHEL 6

# scsi_id --whitelisted /dev/sdd
3600144f0da627ad70000503ad6ce0006

Or:

# udevadm info --query=all --path=/sys/block/sda
P: /devices/pci0000:00/0000:00:01.0/0000:01:00.0/host0/target0:2:0/0:2:0:0/block/sda
N: sda
W: 99
S: block/8:0
S: disk/by-id/scsi-364403a78570b200018ac2cd20575ec04
S: disk/by-path/pci-0000:01:00.0-scsi-0:2:0:0
S: disk/by-id/wwn-0x64403a78570b200018ac2cd20575ec04
E: UDEV_LOG=3
E: DEVPATH=/devices/pci0000:00/0000:00:01.0/0000:01:00.0/host0/target0:2:0/0:2:0:0/block/sda
E: MAJOR=8
E: MINOR=0
E: DEVNAME=/dev/sda
E: DEVTYPE=disk
E: SUBSYSTEM=block
E: MPATH_SBIN_PATH=/sbin
E: ID_SCSI=1
E: ID_VENDOR=LSI
E: ID_VENDOR_ENC=LSI
E: ID_MODEL=MRSASRoMB-4i
E: ID_MODEL_ENC=MRSASRoMB-4i
E: ID_REVISION=2.12
E: ID_TYPE=disk
E: ID_SERIAL_RAW=364403a78570b200018ac2cd20575ec04
E: ID_SERIAL=364403a78570b200018ac2cd20575ec04
E: ID_SERIAL_SHORT=64403a78570b200018ac2cd20575ec04
E: ID_WWN=0x64403a78570b2000
E: ID_WWN_VENDOR_EXTENSION=0x18ac2cd20575ec04
E: ID_WWN_WITH_EXTENSION=0x64403a78570b200018ac2cd20575ec04
E: ID_SCSI_SERIAL=0004ec7505d22cac1800200b57783a40
E: ID_BUS=scsi
E: ID_PATH=pci-0000:01:00.0-scsi-0:2:0:0
E: ID_PART_TABLE_TYPE=dos
E: LVM_SBIN_PATH=/sbin
E: DEVLINKS=/dev/block/8:0 /dev/disk/by-id/scsi-364403a78570b200018ac2cd20575ec04 /dev/disk/by-path/pci-0000:01:00.0-scsi-0:2:0:0 /dev/disk/by-id/wwn-0x64403a78570b200018ac2cd20575ec04

For multipath devices:

# multipath -ll -v
360080e500024a048000004044f3c64ee dm-0 SUN,LCSM100_F
size=95G features='1 queue_if_no_path' hwhandler='1 rdac' wp=rw
|-+- policy='round-robin 0' prio=6 status=active
| `- 7:0:0:0 sdb 8:16  active ready running
`-+- policy='round-robin 0' prio=1 status=enabled
  `- 8:0:0:0 sdk 8:160 active ghost running

Note: the device uuid is fixed value, the uuid of dm-mp device should be identical with the uuid of its paths. In most of situation could not be modified unless the device supports dynamic uuid feature.

Usage:

The device uuid often being used to persistent the device name or dm-mpath name, following example bind the wwid with name oraasm1 persistently.

       multipath {
               wwid                  36006048caf0b141598afa8e2875797a1
               alias                   oraasm1
       }

Note: the partition (such as sda1 sdb1) does not have uuid.

File system uuid

For CentOS/RHEL 5

# blkid /dev/sda1
/dev/sda1: LABEL="/boot1" UUID="ae298adb-1b94-42a0-9dc9-a121c7561a5b" TYPE="ext3" SEC_TYPE="ext2" 
# /lib/udev/vol_id /dev/sda1
ID_FS_USAGE=filesystem
ID_FS_TYPE=ext3
ID_FS_VERSION=1.0
ID_FS_UUID=ae298adb-1b94-42a0-9dc9-a121c7561a5b
ID_FS_LABEL=/boot1
ID_FS_LABEL_SAFE=boot1

Note: the /dev/sdxx must be formated as file system.

Usage:

Could specify uuid in /etc/fstab to bind the device with mount directory persistently.

UUID=xxx-xxx-xxx-xxx            /mount_dir                   ext3    defaults        1 2

Note: file system uuid will be changed after re-create file system.

LVM2 uuid

# pvs -v
  PV         VG   Fmt  Attr PSize  PFree  DevSize PV UUID   
  /dev/sda2  vg0  lvm2 a--  48.81G     0   48.83G xCJzmN-oJmL-kMFl-JCrb-lfoH-movY-6x6K6O
  /dev/sda3  vg0  lvm2 a--  48.81G     0   48.83G 9iXmmM-kKqV-OYDb-eSVN-ymCw-wwVk-uY6fXo
# lvs
  LV       VG   #Seg Attr   LSize   Maj Min KMaj KMin Origin Snap%  Move Copy%  Log Convert LV UUID                               
  lvroot   vg0     3 -wi-ao 146.44G  -1  -1 253  0                                          C0l0R2-KhH8-N7Nk-BhXn-MJhS-35dn-XXdL1B
  lvasmlib vg1     1 -wi-a-   4.88G  -1  -1 253  6                                          5nlcKy-1kvs-l7qb-eIts-tEs6-E2JG-RisWDx
# vgs -v
  VG   Attr   Ext    #PV #LV #SN VSize   VFree  VG UUID                               
  vg0  wz--n- 32.00M   3   1   0 146.44G     0  ereADB-2w9v-O2P9-58OS-RN9Q-t2pV-8wXpSc
  vg1  wz--n-  4.00M   3   3   0 139.71G  9.95G LczKdV-Nq82-lNrr-EmI1-cerd-numb-1qV6m4

Usage:

In some case need recover some pv device, use the –uuid and –restorefile arguments of the pvcreate command to restore the physical volume. The following command restores the physical volume label with the backuped metadata.

# pvcreate --uuid "0YnHNn-1COx-dohx-bwPf-aLyl-pO8F-f5PI5R" --restorefile /etc/lvm/archive/vg0_00000-1324010847.vg /dev/sda2
  Physical volume "/dev/sda2" successfully created

Note: lvm2 uuid will be changed after re-create.

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