🌎 Shane's World

Getting Tailscale to work on my JetKVM

3 min read

Earlier this week I got my JetKVM in the mail. There’s plenty of posts out there about how awesome it is, so I won’t bother to write another post reiterating that. Well, maybe briefly: it is in fact awesome. You should by one.

Remotely accessing my JetKVM

While the folks behind this product seem smart enough, I’m always skeptical about using new cloud services, especially when they have a direct line to my PC. Rather than use their Remote Access feature, I was happy to see that they also had a link in their FAQ pointing to an article on Medium called Installing Tailscale on JetKVM. This unfortunately did not work for me without some minor tweaks.

Getting Tailscale to start automatically

Because JetKVM is built on top of busybox (for better or worse - worse IMHO), it lacks a modern init system. Other than being a good introduction for less experienced folks into how things used to be before systemd, it is a bit of a pain to work with.

Anyway, after using the script shared in the Medium post linked above, the first thing I noticed was that upon reboot my device did not rejoin my tailnet.

After adding some basic logging to the init script, I was able to see that it was crashing due to the TUN device not being available:

wgengine.NewUserspaceEngine(tun "tailscale0") error: tstun.New("tailscale0"): CreateTUN("tailscale0") failed; /dev/net/tun does not exist
flushing log.
logger closing down
logtail: upload: log upload of 942 bytes compressed failed: Post "https://log.tailscale.com/c/tailnode.log.tailscale.io/986ca5896dc4d4b0b3de7618f45bf030588040a882f53c226de82ebe42fc0c5f": context canceled
logtail: dial "log.tailscale.com:443" failed: dial tcp: lookup log.tailscale.com: operation was canceled (in 1.022s), trying bootstrap...
getLocalBackend error: createEngine: tstun.New("tailscale0"): CreateTUN("tailscale0") failed; /dev/net/tun does not exist

Strangely, simply re-running this script resolved the issue and Tailscale started fine. This led me to the realization that the tun kernel module needed to be loaded ahead of time.

Here is my version of the init script that adds some basic logging and checks and ensures that /dev/net/tun exists before trying to start tailscaled:

#!/bin/sh
log="/tmp/ts.log"
 
echo "$(date): S22tailscale script starting with arg: $1" >> $log
 
wait_for_tun() {
  modprobe tun 2>>$log
  for i in $(seq 1 10); do
    [ -e /dev/net/tun ] && return 0
    echo "$(date): /dev/net/tun not ready, retrying..." >> $log
    sleep 1
  done
  echo "$(date): /dev/net/tun still not present after waiting" >> $log
  return 1
}
 
wait_for_network() {
  for i in $(seq 1 10); do
    ip route | grep default >/dev/null && return 0
    echo "$(date): no default route yet, retrying..." >> $log
    sleep 1
  done
  echo "$(date): still no default route after waiting" >> $log
  return 1
}
 
case "$1" in
  start)
    wait_for_tun || exit 1
    wait_for_network || exit 1
    echo "$(date): Starting tailscaled..." >> $log
    TS_DEBUG_FIREWALL_MODE=nftables /userdata/tailscale/tailscaled \
      -statedir /userdata/tailscale-state >> $log 2>&1 &
    ;;
  stop)
    echo "$(date): Stopping tailscaled..." >> $log
    killall tailscaled >> $log 2>&1
    ;;
  *)
    echo "Usage: $0 {start|stop}" >&2
    exit 1
    ;;
esac

Orthogonal issue with non-persistent MAC address

During the process of setting up my JetKVM, I noticed that I was getting a new IP every time the device restarted. The first thing I tried was to give in a static IP through my UniFi console, but was surprised when after a reboot I got yet another IP. This led to me finding this GitHub issuethat has a ton of activity on it. I suspect this will be fixed soon, but in the meantime, this comment had a solution that resolves the issue.

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