A Linux Container (LXC) in a locked state prevents any further operations, such as starting, pausing, or deleting the container, according to the Proxmox VE error “CT is locked (snapshot-delete)”. As part of our Proxmox Support, Bobcares provides answers to all of your questions.

Overview

1. Fixing Proxmox VE error “CT is locked (snapshot-delete)”
2. What are the Error Impacts?
3. Causes & Fixes of the Error
4. Prevention Steps
5. Conclusion

Fixing Proxmox VE error “CT is locked (snapshot-delete)”

A locked Linux Container (LXC) prevents any further activities, including starting, halting, or deleting the container. We can see this in the error message. Usually, an unfinished or unsuccessful backup procedure that required taking a snapshot of the container is the reason behind this lock. The error appear as follows:

This message suggests a problem with the removal of a snapshot of the backup process is the reason of the container lock.

What are the Error Impacts?

• Container Inaccessibility: Until the lock is released, the container cannot be launched, stopped, or managed.

• Backup Failures: Because the container is in lock state, backup jobs may continually fail.

• Resource Usage: Since the snapshot might still be storing resources, the locked state may result in needless resource usage.

Causes & Fixes of the Error

1. Failed Backup Operation: A backup operation failed, locking the container.

Fix:

To unlock the container, we use this command (replace with our container’s ID):

pct unlock

Delete the Failed Snapshot:

pct delsnapshot vzdump

Then, make sure the configuration file is correct and in the right directory:

Path: /etc/pve/nodes//lxc/.conf

If it’s incorrect, move or rename it to the correct location.

2. Configuration File Issues: The container’s configuration file is missing or in the wrong place.

Fix:

Check File Path and ensure it’s in /etc/pve/nodes//lxc/.

If the file is in the wrong directory, move it:

mv /etc/pve/nodes/node1/qemu-server/101.conf /etc/pve/nodes/node1/lxc/101.conf

3. Network and Cluster Issues: Network problems or cluster quorum loss can lock containers.

Fix:

Verify network settings:

ip addr show

Check multicast settings:

ip maddr show

Check Cluster Health:

View cluster status:

pvecm status

Verify quorum:

pvecm nodes

4. Manual Intervention: Interrupting a backup job manually can leave the container locked.

Fix:

Unlock the Container:

pct unlock

Check Task Logs:

pve task log

Identify the failure point to prevent future issues.

Prevention Steps

1. We must often backup logs to catch any errors early and prevent containers from becoming locked.

2. Maintain stable network and storage solutions to prevent errors during backup operations.

3. We must avoid stopping backup jobs manually unless absolutely necessary, as this can leave containers in a locked state.

4. We can also use the correct tools for managing containers (pct for LXC) and virtual machines (qm for KVM).

5. Keep Proxmox VE and its components up to date to benefit from bug fixes and improvements.

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Conclusion

When a backup process fails or leaves a snapshot incomplete, a container lock happens, according to this Proxmox error. Until we finish the issue, this stops more operations on the container. Using the pct unlock command to unlock the container and the pct delsnapshot command to remove any failed snapshots will resolve the issue. Such problems can be avoided by making sure the configuration file path is right and by keeping the network circumstances stable. Proxmox can also be kept up to date and monitored often to assist prevent these mistakes.