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Fix TUN/TAP not available on a 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 try to fix it!

Check the tun module status

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

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

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!