Proxmox troubleshooting: fix common VE errors

This Proxmox troubleshooting guide covers the errors admins meet most often and the commands that fix them. Always read the task log first: double-click the failed task at the bottom of the web UI for the full error.

Before you start

• Root shell access through SSH, the web UI shell or IPMI console.
• The VM ID and the exact error text.

"VM is locked"

A backup, snapshot or migration left a lock behind. Make sure no task is still running, then:

qm unlock 105

For containers use pct unlock 105.

Web UI on port 8006 does not load

1. Check the services: systemctl status pveproxy pvedaemon pve-cluster.
2. Restart the proxy: systemctl restart pveproxy.
3. Check root disk space with df -h; a full root filesystem stops cluster services.
4. Check that the firewall still allows your IP on 8006 (firewall setup).

VM fails to start

• "KVM virtualisation configured, but not available": enable VT-x/AMD-V in the BIOS.
• Not enough memory: free RAM on the node or lower the VM's memory; check free -g.
• Storage not available: an NFS share or disk is offline; check Datacenter → Storage.
• ISO missing: the CD drive points to a deleted ISO; set it to Do not use any media.

Storage full

• Check thin pools with lvs and ZFS with zpool list.
• Delete old snapshots and old backups, and enable discard in VMs so freed space returns to the pool.
• A full thin pool can corrupt VMs; act before it reaches 100%.

Cluster without quorum

1. Check with pvecm status.
2. Bring the missing nodes back or fix the corosync network.
3. Only in an emergency, on a single surviving node, lower expected votes with pvecm expected 1 to regain write access; undo the situation properly afterwards.

Lost network after a change

From the console, review /etc/network/interfaces, fix the bridge or IP, and apply with ifreload -a. See bridges and VLANs.

Frequently asked questions

Where are Proxmox logs?

Use journalctl -xe and the task log in the web UI; syslog is under Node → System → Syslog.

Is it safe to restart pveproxy?

Yes, running VMs are not affected.

Why does apt fail with 401?

The enterprise repository is enabled without a subscription (repositories).

Next steps

• Repositories and updates
• Storage types
• High availability