Navigating Challenges with Proxmox PCI Passthrough
Exploring the capabilities of Proxmox PCI passthrough can be both exciting and challenging. This powerful feature allows virtual machines to directly access hardware devices, greatly enhancing performance. However, it can also introduce complex issues, as I discovered during my recent experience with passing through a SATA controller. In this post, I’ll guide you through my troubleshooting journey and the steps I took to resolve these issues effectively.
Table of Contents
Proxmox PCI Passthrough: A Troubleshooting Journey
PCI passthrough is a powerful feature of Proxmox that allows VMs to directly access hardware devices. While it can significantly enhance performance, it also comes with risks, as I discovered during a recent attempt to pass through a SATA controller to a VM. This post details my experience and the steps I took to resolve the issues that arose.
The Problem
To improve performance for one of my virtual machines, I decided to add a SATA controller via PCI passthrough. However, this change quickly led to serious issues:
- Proxmox began to crash immediately after the VM with the passthrough device started.
- I lost access to the Proxmox web GUI and console.
- Rebooting the server did not help, as the VM would start automatically and crash the system again.
Troubleshooting Steps
Initial Diagnosis and Attempts
Realizing that the automatic startup of the VM was causing Proxmox to crash, my initial attempts focused on trying to access the Proxmox interface quickly after a reboot. Unfortunately, each time the VM started, the system would lock up before I could make any changes.
Booting into Ubuntu for Recovery
With no success accessing Proxmox directly, I turned to an Ubuntu live USB. Booting into Ubuntu allowed me to mount the Proxmox root filesystem and attempt to fix the issue from there. Here’s a detailed look at what I did:
Mounting the Proxmox Filesystem
# List all partitions to identify the Proxmox root partition
sudo lsblk
# Assuming the root partition is /dev/sda3 (this may vary)
# Create a mount point
sudo mkdir /mnt/proxmox-root
# Mount the Proxmox root filesystem
sudo mount /dev/sda3 /mnt/proxmox-root
# Bind mount necessary filesystems
sudo mount --bind /dev /mnt/proxmox-root/dev
sudo mount --bind /proc /mnt/proxmox-root/proc
sudo mount --bind /sys /mnt/proxmox-root/sys
Disabling Proxmox Services
To prevent the VMs and other services from starting automatically, I disabled several Proxmox services:
# Chroot into the Proxmox environment
sudo chroot /mnt/proxmox-root
# Disable Proxmox services
systemctl disable pve-guests
systemctl disable pve-cluster
systemctl disable pvedaemon
systemctl disable pveproxy
systemctl disable pvestatd
systemctl disable pve-firewall
Locating and Modifying Configuration Files
Next, I modified the Proxmox service file to prevent VMs from starting automatically:
# Open the service file for editing
nano /lib/systemd/system/pve-guests.service
# Comment out the lines responsible for starting and stopping VMs
# ExecStart=/usr/bin/pvesh ...
# ExecStop=/usr/bin/pvesh ...
# Save and exit the file
# Press Ctrl + O, Enter to save and Ctrl + X to exit
Rebooting and Fixing the VM
After disabling the services and modifying the service file, I rebooted the server into Proxmox. This time, Proxmox started without automatically launching the VMs, allowing me to access the web GUI. I immediately removed the problematic PCI device from the VM settings.
Reverting the Service Changes
With the issue resolved, I reverted the changes I made to the pve-guests.service file by uncommenting the previously commented lines:
# Re-enter the chroot environment if needed
sudo chroot /mnt/proxmox-root
# Open the service file again
nano /lib/systemd/system/pve-guests.service
# Uncomment the lines
ExecStart=/usr/bin/pvesh ...
ExecStop=/usr/bin/pvesh ...
# Save and exit the file
# Press Ctrl + O, Enter to save and Ctrl + X to exit
Re-enabling Proxmox Services
Finally, I re-enabled the previously disabled Proxmox services:
# Re-enable Proxmox services
systemctl enable pve-guests
systemctl enable pve-cluster
systemctl enable pvedaemon
systemctl enable pveproxy
systemctl enable pvestatd
systemctl enable pve-firewall
Unmounting and Rebooting
After making the necessary changes, I unmounted the filesystems and rebooted the server:
# Exit the chroot environment
exit
# Unmount the filesystems
sudo umount /mnt/proxmox-root/dev
sudo umount /mnt/proxmox-root/proc
sudo umount /mnt/proxmox-root/sys
sudo umount /mnt/proxmox-root
# Reboot the server
sudo reboot
Outcome
After these steps, Proxmox was back to normal. Fortunately, despite the multiple forced shutdowns and reboots, no damage was done to the disks, and the system was stable once more. This experience highlighted several important lessons for anyone managing a Proxmox environment.
Key Takeaways
- Preparation: Always have a backup plan and ensure you have live boot media available for emergencies. This can save a lot of time and stress in case of critical issues.
- Recovery Options: Booting into a different OS like Ubuntu can provide the necessary access to fix critical issues when the primary system is unresponsive.
- Caution with Passthrough: Be cautious when configuring PCI passthrough. Thoroughly research and understand the hardware and Proxmox settings to avoid potential crashes.
- Service Management: Knowing how to disable and manage system services can prevent automatic actions that might lead to system crashes. It’s crucial to understand how to stop and start services safely.
- System Monitoring: Regularly monitor your system’s health and ensure that you have tools like SMART monitoring in place to catch potential disk issues early.
By sharing this experience, I hope to provide some insights and potential solutions for anyone facing similar challenges. Persistence and systematic troubleshooting can help you overcome even the most frustrating technical issues. If you have similar experiences or tips, feel free to share them in the comments below. Let’s help each other navigate these tricky situations!
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