Category Archives: Proxmox

Allowing OpenVPN to create tun device on LXC / Proxmox

Due to built-in security of LXC, trying to setup a tunnel interface inside a container is by blocked by default.

ERROR: Cannot open TUN/TAP dev /dev/net/tun

To allow this for a specific container in Proxmox, we need to make a few tweaks to allow this interface to work in a specific container (we don’t want to allow all containers to be able to setup a tunnel – hackers can hide their tracks using it).

How to do this:

ADD these lines to /etc/pve/lxc/<container-id>.conf

lxc.cgroup.devices.allow = c 10:200 rwm
lxc.hook.autodev = sh -c "modprobe tun; cd ${LXC_ROOTFS_MOUNT}/dev; mkdir net; mknod net/tun c 10 200; chmod 0666 net/tun"


OPNsense firewall on Proxmox fix ‘no internet’

Quick post to note how I determined and then fixed the internet access issue I was having when I installed OPNsense on Proxmox.

OPNsense virtual machine is configured with VirtiO network drivers.

Other than the obvious “I can’t access anything on the internet” or can’t reach external IP addresses problem I looked at troubleshooting via nmap – because the devices on the network could ping externally ( and also resolve DNS requests.

In a broken state you may see ‘tcpwrapper’ when testing a known host serving HTTP, like so:

root@test:~# nmap -p 80 -sV

Starting Nmap 7.40 ( ) at 2018-11-17 17:54 UTC

Nmap scan report for (

Host is up (0.010s latency).


80/tcp open  tcpwrapped

Service detection performed. Please report any incorrect results at .

Nmap done: 1 IP address (1 host up) scanned in 7.91 seconds

To fix this issue, ensure that “Disable hardware checksum offload” is  enabled in the OPNsense interface, then reboot the firewall for changes to take effect.

After a reboot, doing another test via nmap will actually respond with HTTP fingerprints, as expected and internet is back.

root@test:~# nmap -p 80 -sV

Starting Nmap 7.40 ( ) at 2018-11-17 18:00 UTC

Nmap scan report for (

Host is up (0.0096s latency).


80/tcp open  http    gws

1 service unrecognized despite returning data. If you know the service/version, please submit the following fingerprint at :



































Service detection performed. Please report any incorrect results at .

Nmap done: 1 IP address (1 host up) scanned in 52.89 seconds


Fix zfs-mount.service failing after reboot on Proxmox

In my new homelab migration to Proxmox I came across a bug that will prevent you from being able to mount all your ZFS mount points and be a pain in the ass even more if you host containers in that folder.
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LXC allow non-root users to bind to port 80 (couchpotato example)

A follow-up to my last post dealing with unprivileged port access on linux containers.

This time, I have a couchpotato container that I want to change its default port from 5050 to port 80, so that it is as simple as http://mycouch/ to access from the local network.
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Install proxmox on a partition instead of a full-disk

By default, installing Proxmox with ZFS during the installation process will force you to use the entire disk for the root zpool. For most installs this is good enough. However, I like to do things differently sometimes.

I have a pair of Samsung 840 Pro 256GB SSDs that I wanted to use for my new homelab that I am currently building (moving from vmware to proxmox). You may be wondering why I want to install the operating system on a partition instead of an entire disk. Several reasons:
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Troubleshooting networking issues after fresh install of proxmox VE 4.4

Writing a quick troubleshooting guide and informative post to address an issue I came across when installing Proxmox VE 4.4 on two of my machines.

On servers with more than two network interfaces Debian/Proxmox renames all interfaces and does not properly detect eth0 as the on-board ethernet as many other linux flavors. This may cause a mild headache if you just installed Proxmox with static IP addresses using the installer and upon reboot you can’t access any network resources. Continue reading

Virtualization hypervisor and containers all in one

I’m a big fan of virtualization, the ability to run multiple platforms and operating systems (called guests) in a single server (called host) is probably one of the best computing technologies of the past 10 years.

Personally, I have been using virtualization circa 2004. It all took off after 2006 when chip manufacturer’s started bundling virtualization technologies in their processors (Intel VT-x or AMD-v). The reason why “cloud” computing is so popular can also be attributed to virtualization.

In a container world…

However, in the past couple of years a new technology has been making making the rounds everywhere, the words “containers”, “docker”, “orchestration” is picking up steam in the past year. They say that containers are changing the landscape for system administrators and application developers.

Claims that containers can be built and deployed in seconds, share a common storage layer and allow you to resize the container in real-time when you need more performance or capacity are really exciting concepts and I think the time is now for me to jump in and learn a thing of two about this new technology when its hot a new. Continue reading

Add additional IP’s on different subnets using same Ethernet card on PVE

To do this, we need to add a custom route to the server, we need to add the network and netmask addresses, to test and see if it works:

route add -net netmask dev vmbr0

if it works, add the following to your /etc/network/interfaces file

iface vmbr0 inet static

bridge_fd 0
up route add -net netmask dev vmbr0
down route del -net netmask dev vmbr0

did not work? Remove route with:

route del -net netmask dev vmbr0