Understanding lsblk and udev

Oct 13, 2025 by leolavanderia.com.br 132 views

Introduction

When working with complex storage systems, such as ZFS pools, it's essential to have a clear understanding of the devices attached to your system. In this article, we'll explore a common issue where lsblk can see all drives attached, but udev only shows half of them. We'll delve into the possible causes, including conflicting identifiers, and provide solutions to help you resolve this issue.

Understanding lsblk and udev

lsblk

lsblk is a command-line tool that provides a list of all block devices (disks, partitions, and RAID devices) attached to your system. It's a powerful tool for identifying and managing storage devices. lsblk uses the libblkid library to gather information about the devices, which makes it a reliable source for device identification.

udev

udev is a device manager for Linux that manages device events and provides a way to identify devices using unique identifiers. udev uses a database of device rules to match devices with their corresponding identifiers. When a device is attached or detached, udev updates the database to reflect the changes.

The Issue: Conflicting Identifiers

When you run lsblk, you can see all the drives attached to your system, including the Terramaster D8 Hybrid DAS connected via USB with 4x HDD and 4x NVME drives. However, when you run udevadm info -a -p /dev/sdX, where sdX is the device file of one of the drives, you only see half of the drives listed.

This issue can be caused by conflicting identifiers between lsblk and udev. lsblk uses the libblkid library to identify devices, while udev uses its own database of device rules. If the identifiers used by lsblk and udev are different, it can lead to inconsistent results.

Possible Causes

1. Device Name Conflicts

One possible cause of conflicting identifiers is device name conflicts. If two or more devices have the same name, it can lead to confusion and inconsistent results. For example, if you have two devices with the same name, sda and sdb, it can cause udev to only show one of the devices.

2. Device Rule Conflicts

Another possible cause of conflicting identifiers is device rule conflicts. If two or more device rules match the same device, it can lead to inconsistent results. For example, if you have two device rules that match the same device, one with a udev rule and another with a lsblk rule, it can cause udev to only show one of the devices.

3. Device Database Corruption

A corrupted device database can also cause conflicting identifiers. If the udev database is corrupted, it can lead to inconsistent results. For example, if the database is missing or corrupted, it can cause udev to only show half of the devices.

Solutions

1. Check Device Names

To resolve device name conflicts, you can check the device names using lsblk and udevadm. Run the following commands:

lsblk -o NAME
udevadm info -a -p /dev/sdX

This will show you the device names used by lsblk and udev. If you see any conflicts, you can try renaming the devices using udevadm.

2. Check Device Rules

To resolve device rule conflicts, you can check the device rules using udevadm. Run the following command:

udevadm info -a -p /dev/sdX

This will show you the device rules that match the device. If you see any conflicts, you can try modifying the rules using udevadm.

3. Rebuild Device Database

To resolve device database corruption, you can try rebuilding the device database using udevadm. Run the following command:

udevadm trigger

This will rebuild the device database and update the device rules.

Conclusion

In this article, we explored the issue of lsblk seeing all drives attached but udev only showing half of them. We discussed the possible causes, including conflicting identifiers, and provided solutions to help you resolve this issue. By checking device names, device rules, and rebuilding the device database, you can resolve this issue and ensure that udev shows all devices attached to your system.

Additional Tips

1. Use `udevadm` to Manage Devices

udevadm is a powerful tool for managing devices. You can use it to trigger device events, rebuild the device database, and modify device rules.

2. Use `lsblk` to Identify Devices

lsblk is a reliable tool for identifying devices. You can use it to list all devices attached to your system and identify their properties.

3. Use `udevadm` to Debug Issues

udevadm provides a way to debug issues with device identification. You can use it to troubleshoot device name conflicts, device rule conflicts, and device database corruption.

Q&A: Troubleshooting Conflicting Identifiers

In our previous article, we explored the issue of lsblk seeing all drives attached but udev only showing half of them. We discussed the possible causes, including conflicting identifiers, and provided solutions to help you resolve this issue. In this article, we'll answer some frequently asked questions (FAQs) related to this issue.

Q: What are the possible causes of conflicting identifiers?

A: The possible causes of conflicting identifiers include device name conflicts, device rule conflicts, and device database corruption.

Q: How can I check device names?

A: You can check device names using lsblk and udevadm. Run the following commands:

lsblk -o NAME
udevadm info -a -p /dev/sdX

This will show you the device names used by lsblk and udev.

Q: How can I check device rules?

A: You can check device rules using udevadm. Run the following command:

udevadm info -a -p /dev/sdX

This will show you the device rules that match the device.

Q: How can I rebuild the device database?

A: You can rebuild the device database using udevadm. Run the following command:

udevadm trigger

This will rebuild the device database and update the device rules.

Q: What are the benefits of using `udevadm`?

A: udevadm is a powerful tool for managing devices. It provides a way to trigger device events, rebuild the device database, and modify device rules. Using udevadm can help you troubleshoot device identification issues and ensure that udev shows all devices attached to your system.

Q: What are the benefits of using `lsblk`?

A: lsblk is a reliable tool for identifying devices. It provides a way to list all devices attached to your system and identify their properties. Using lsblk can help you troubleshoot device identification issues and ensure that udev shows all devices attached to your system.

Q: How can I debug issues with device identification?

A: You can debug issues with device identification using udevadm. Run the following command:

udevadm info -a -p /dev/sdX

This will show you the device rules that match the device and help you troubleshoot device identification issues.

Q: What are the common mistakes to avoid when troubleshooting device identification issues?

A: Some common mistakes to avoid when troubleshooting device identification issues include:

Not checking device names and device rules
Not rebuilding the device database
Not using udevadm to trigger device events
Not using lsblk to identify devices

By avoiding these common mistakes, you can troubleshoot device identification issues more effectively and ensure that udev shows all devices attached to your system.

Conclusion

In this article, we answered some frequently asked questions (FAQs) related to the issue of lsblk seeing all drives attached but udev only showing half of them. We discussed the possible causes, including conflicting identifiers, and provided solutions to help you resolve this issue. By following these tips and solutions, you can troubleshoot device identification issues and ensure that udev shows all devices attached to your system.

Additional Tips

1. Use `udevadm` to Manage Devices

udevadm is a powerful tool for managing devices. You can use it to trigger device events, rebuild the device database, and modify device rules.

2. Use `lsblk` to Identify Devices

lsblk is a reliable tool for identifying devices. You can use it to list all devices attached to your system and identify their properties.

3. Use `udevadm` to Debug Issues

udevadm provides a way to debug issues with device identification. You can use it to troubleshoot device name conflicts, device rule conflicts, and device database corruption.

By following these tips and solutions, you can troubleshoot device identification issues and ensure that udev shows all devices attached to your system.