UDev Configuration

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UDev guarantees persistent device names across reboots regardless of their order of discovery. This is vital for ASM storage devices. UDev also ensures the devices have the correct ownership\permissions for ASM. The following covers using Oracle Linux 7.x UDev to manage disks for ASM.

UDev is an alternative to Oracle's ASMLib and does not require additional kernel modules or a specific kernel version. UDev also has a smaller footprint than ASMLib.

Furthermore, Oracle fully supports the Linux 7.x method detailed here using UDev via SYMLINK method as opposed to the Linux 6.x legacy method of using the mapper architecture (per 3-17731438021).

ASMLib has been deprecated in favor of ASMFD in Oracle 12.2 and later.

If you are using VMWare you may need to do this to display the UUID.


The scenario below shows implementing for 3 disks.

Add Option to scsi_id.config

 echo options=-g>>/etc/scsi_id.config

This ensures the SCSI devices are configured as trusted.

Get Device ID

 /usr/lib/udev/scsi_id -g -u -d /dev/sdb
  • Do this for each disk (sdb,sdc,sdd...).

Create 99-oracle-asmdevices.rules

Create\Edit: /etc/udev/rules.d/99-oracle-asmdevices.rules

For each disk:

  • Set RESULT to the Device ID string from above.
  • Set\increment the SYMLINK name for each disk.
 PROGRAM=="/usr/lib/udev/scsi_id -g -u -d /dev/$parent",

The above goes on one line.

3 Disk Template

  • KERNEL=="sd*1",SUBSYSTEM=="block",PROGRAM=="/usr/lib/udev/scsi_id -g -u -d /dev/$parent",RESULT=="TBD",SYMLINK+="asm-disk01",OWNER="grid",GROUP="asmadmin",MODE="0660"
  • KERNEL=="sd*1",SUBSYSTEM=="block",PROGRAM=="/usr/lib/udev/scsi_id -g -u -d /dev/$parent",RESULT=="TBD",SYMLINK+="asm-disk02",OWNER="grid",GROUP="asmadmin",MODE="0660"
  • KERNEL=="sd*1",SUBSYSTEM=="block",PROGRAM=="/usr/lib/udev/scsi_id -g -u -d /dev/$parent",RESULT=="TBD",SYMLINK+="asm-disk03",OWNER="grid",GROUP="asmadmin",MODE="0660"

Replace TBD with matching Device ID.

Reload Partition Tables

 /sbin/partprobe /dev/sdb1
 /sbin/partprobe /dev/sdc1
 /sbin/partprobe /dev/sdd1

Test UDev

 udevadm test /block/sdb/sdb1|more
 udevadm test /block/sdc/sdc1|more
 udevadm test /block/sdd/sdd1|more

Restart Udev Service

udevadm control --reload-rules

Check Ownership and Permissions

The symlinks are owned by root, but devices will be owned by grid:asmadmin

  • ls -al /dev/asm*
  • ls -rlt /dev/sd?1

Example Output

[root@lnx01 ~]# ls -al /dev/asm*
lrwxrwxrwx 1 root root 4 Jun 19 12:52 /dev/asm-disk01 -> sdb1
lrwxrwxrwx 1 root root 4 Jun 19 12:54 /dev/asm-disk02 -> sdc1
lrwxrwxrwx 1 root root 4 Jun 19 12:58 /dev/asm-disk03 -> sdd1

[root@lnx01 ~]# ls -rlt /dev/sd?1 
brw-rw---- 1 grid asmadmin 8, 17 Jun 19 12:52 /dev/sdb1
brw-rw---- 1 grid asmadmin 8, 33 Jun 19 12:54 /dev/sdc1
brw-rw---- 1 grid asmadmin 8, 49 Jun 19 12:58 /dev/sdd1

Next Node

Repeat the above procedure for all other RAC node systems. Use the Device ID as displayed from first system.


After configuring UDev it is a good idea to reboot all nodes and ensure all the disks look OK via:

  • ls -al /dev/asm*
  • ls -rlt /dev/sd?1

During the GI installation set the ASM_DISKSTRING initialization parameter to /dev/asm-disk* to identify the ASM disks.

Display Disk Info

Commands to view UDev related disk info.

 lsscsi -is
 lshw -class disk
 inxi -Dxx

yum install inxi -y


Special thanks to Chris Jolliffe for sharing this!

  1. Power down VM, right click and select edit settings.
  2. Select the options tab and click on General under Advanced.
  3. Click the Configure Parameters Button and verify that the disk.EnableUUID parameter is not present
  4. If present, change Value to “true”, if not present select, the Add Row button and enter the Name disk.EnableUUID and Value true.
  5. Click ok, and ok, and power on the vm.
  6. Now check the scsi_id by /usr/lib/udev/scsi_id -g -u -d /dev/sdb

This method can also be used for VMWare.


To undo the changes:

  1. Remove /etc/udev/rules.d/10-local.rules and /dev/<YourDiskName>
  2. Run systemctl restart systemd-udevd.