Fix TUN/TAP not available on Synology NAS

If you’re looking into running OpenVPN on your Synology NAS, you may have come across the following error:

ERROR: Cannot open TUN/TAP dev /dev/net/tun: No such file or directory (errno=2)

Let’s see how to fix it.

Check the tun module status

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Check if you have the tun module installed:

❯ lsmod | grep tun

If the result comes out empty, try installing it:

❯ insmod /lib/modules/tun.ko

If everything went fine, move on to the next test.

Test if the tun.ko module works

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Now let’s make sure the tun.ko module works as expected:

❯ mkdir /dev/net
❯ mknod /dev/net/tun c 10 200
❯ chmod 600 /dev/net/tun
❯ cat /dev/net/tun

If the result of the cat command was File descriptor in bad state, it means the module has been correctly installed.

Make tun.ko module persistent

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The module installation needs to be made persistent otherwise on every Synology restart, you’ll have to repeat the insmod command.

Create the following file to run on every system boot:

❯ cat <<EOF > /usr/local/etc/rc.d/tun.sh
#!/bin/sh -e

insmod /lib/modules/tun.ko
EOF

Make the script executable:

❯ chmod a+x /usr/local/etc/rc.d/tun.sh

Reboot your Synology NAS or execute the script manually once. Done!