OpenVZ kernel does not support TUN/TAP devices

Holmes.Sherlock

Hi,

It's me posting in this forum after a long time.

I registered for a free OpenVZ based VPS (Virtual Private Server) yesterday & tried to configure OpenVPN on it. Earlier, I did the same with a Xen based VPS solution. Everything worked like a charm. When I attempted to start VPN server, below is the error I encountered:

Tue May 22 01:04:47 2012 Note: Cannot open TUN/TAP dev /dev/net/tun: No such file or directory (errno=2)
Tue May 22 01:04:47 2012 Note: Attempting fallback to kernel 2.2 TUN/TAP interface
Tue May 22 01:04:47 2012 Cannot allocate TUN/TAP dev dynamically
Tue May 22 01:04:47 2012 Exiting

I didn't find any TUN/TAP adapter by issuing

ifconfig

To load the TUN module manually, I did this, but nothing was loaded.

modprobe tun

Then I tried to find whether any TUN related module is present in the kernel

lsmod | grep tun

No result returned.

I did all the steps listed here

    Enter mknod /dev/net/tun c 10 200
    Enter chmod 600 /dev/net/tun
    Enter cat /dev/net/tun to test whether the TUN/TAP device is available:
        If you receive the message cat: /dev/net/tun: File descriptor in bad state your TUN/TAP device is ready for use
        If you receive the message cat: /dev/net/tun: No such device the TUN/TAP device was not successfully created: contact VPSLink Support for assistance 

Please note that the TUN/TAP device will be removed if you reinstall your operating system template.

But no luck.

At this point I am sure that the OpenVZ kernel is not complied with the support for required modules. What I am asking is whether there any alternative to having native support for TUN/TAP drivers, i.e. can any third-party drivers be installed for creation of TUN/TAP devices to be used in conjunction with OpenVPN?

Reference 1
Reference 2
Reference 3
OpenVZ-Users-Guide: Page 69

Mimiko

TUN devices a somekind standart. You can search for sources and compile them. Better ask the hosters of VPS to help, as they have power to add such devices.

Holmes.Sherlock

Hi Mimiko, good to see you again. Few months back, I was immensely helped by you & janjust

Mimiko wroteTUN devices a somekind standart.

I didn't get you. Means?

Better ask the hosters of VPS to help, as they have power to add such devices.

Even having root access, can't I add the TUN/TAP support?

Mimiko

The TUN device is a standart device like NUL or COM in the meaning of working. But source code may differ.

In a VPS even if you have root access, the real kernel is protected and for VPS host perspective, for each VPS a clone (or a module) is running, not the real kernel. TUN devices must be closed to kernel, so you can't use it in the VPS without the admins of the VPS host including them in base kernel and allow to share to guest VPS.

Holmes.Sherlock

Mimiko wrote In a VPS even if you have root access, the real kernel is protected and for VPS host perspective, for each VPS a clone (or a module) is running, not the real kernel.

I think, with my little knowledge, that whatever you have written about kernel sharing, is applicable to OpenVZ based virtualization solution, i.e. fits my case.

Xen based platforms, probably, works in a different way where a dedicated kernel is allocated per VM.

yzkwkw

I had almost the same problem. I set up a vps days ago, and i asked the provider to enable tun/tap and they did. after that i installed openvpn on the vps and it worked fine. but yesterday wanted to set the pptpd too, and i asked the provider to enable the ppp module and they also enable it. but then problem came, my openvpn service could not start anymore. the openvpn.log showed that:
------
Note: Cannot open TUN/TAP dev /dev/net/tun: Permission denied (errno=13)
Note: Attempting fallback to kernel 2.2 TUN/TAP interface
Cannot allocate TUN/TAP dev dynamically
Exiting
----------
but i cat the /dev/net/tun it returned:
[root@-]# cat /dev/net/tun
cat: /dev/net/tun: File descriptor in bad state
--------
which meaned it seems to work fine, and the vps tech support did not provide further support.
I could not figure out why. i think maybe there are some bugs in the openvpn? after reenable the tun, it can't regonize it again? or maybe the tun module just not enabled correctly? but the tech support insisted it worked fine.

Mimiko

yzkwkw, ask provider to disable ppp interface, and see what is happening.

When OpenVPN was working only with tun adapter enabled on host, did you ever restarted your VPS? After a restart did tun initialized correctly?

manuel19

You have to ask your Linux VPS provider to install the TUN/TAP drivers.

I was using an OpenVZ server, it doesn't have the TUN/TAP drives, so I wrote a ticket to the Support and they install the TUN/TAP drivers for me.

Hope this help you.

Regards, Manuel.

Holmes.Sherlock

manuel19 wroteYou have to ask your Linux VPS provider to install the TUN/TAP drivers.

I was using an OpenVZ server, it doesn't have the TUN/TAP drives, so I wrote a ticket to the Support and they install the TUN/TAP drivers for me.

Which VPS service are you using?

manuel19

It doesn't matters. Your VPS Provider have the obligation to install something you really want and that is not installed by default in the servers they sell.

If i bought a car to you, the car obliously need 4 tires to run. If the car only have 3, you (the seller) need to buy the other tire, because you are buying a functional car. Any car will run correctly with 3 tires.

So, you provider need to install for you the tire #4, in this case, the TUN/TAP driver.

A normal VPS machine in Linux, need to have installed the TUN/TAP without any extra cost.

canufrank

I know it's way late, but check http://superuser.com/questions/497245/how-to-load-tun-module-in-linux/598412#598412

It worked for me

mkdir -p /dev/net
mknod /dev/net/tun c 10 200

Jeroma11

This is very usefully for me 🙂