Archive of October 2021

Fix Printer Spooler service cannot start issue on Windows 7 system

One of my old classmates asked me to fix the issue that her computer cannot print anything. Thanks to TeamViewer, I could connect to her computer then fix the issue. I found that the Printer Spooler service is down and could not start. When you start it, it started and then automatically shuts down in 2 seconds. Google helped me.

For this case, in short: Remove all files in C:\Windows\system32\spool\PRINTERS directory

After that, the service could start, and all printers came back and worked.

Fritz 7490: Root cause for Port mapping failure issue on a vagrant virtual machine


The root cause is that the default route was not set to the router's IP address.

My journey to resolve the issue:

The issue is that port mapping can work with my raspberry pi while it couldn't work with a virtual machine in the same LAN. I firstly think it must be a bug from the router. I upgrade the router to its latest firmware, but it still doesn't work. I google back and forth, I learned much from all kinds of answers, but they were just not my case. I almost decided to give up.

Then I found the following answer from E. van Putten, he answered this question and nobody gave his answer a "Like"!!!

In case you landed on this page because you can't reach a server running inside a Xen Guest from the internet (but can connect locally), then read on...

  1. The fritzbox can get confused by different OS'es appearing from the same MAC-address etc. (could happen while you are setting up / experimenting with Xen)
  2. The fritzbox has seemingly duplicate entries in the list, but with different settings, you need to delete the portmap from the incorrect entry, cleanup the list and reapply the portmap settings.
  3. It might be that your guest OS has no default gateway IP-address set. You'd expect a default gateway set to the local IP-address of your fritzbox. The symptoms of a missing default gateway is that your LAN PCs can access the server running inside the guest just fine, but external users from the internet cannot connect.

He gave three possible causes, and my case is the third one! here's my solution

opts = {
    :name => "yt-gateway",
    :ip => "",
    :mem => "1024",
    :cpu => "1"
Vagrant.configure("2") do |config| = "bento/ubuntu-20.04"
  config.vm.hostname = opts[:name] :public_network, ip: opts[:ip], bridge: "eno1"
  config.vm.provision "shell", run: "always", inline: "route add default gw || true"
  config.vm.provider "virtualbox" do |v| = opts[:name]
    v.customize ["modifyvm", :id, "--memory", opts[:mem]]
    v.customize ["modifyvm", :id, "--cpus", opts[:cpu]]
    v.customize ["modifyvm", :id, "--name", opts[:name]]

I love you E. van!

Setup PiVPN on a Vagrant virtual machine that is running Ubuntu 20.04

PiVPN should be easy to setup at any debian/ubuntu family distribution. However, my case wasn't.

  1. The first issue I met is Can't call method "set" on an undefined value at /usr/share/perl5/Debconf/ line 126, line 5., and I found a useful anwser from, which is
apt-get install --reinstall debconf

it worked! though I don't know the root cause.

  1. The second issue is rather weird, it simple stuck after showing ::: Backing up the openvpn folder... message. What's wrong with that on earth? Unfortunately, I couldn't find anything useful from google/stackoverflow.... I have to find out the root cause by myself.

ps -ef command shows there is a wget -qO- process running. Why it is running so long and looks never end? I copied the wget command and run it manually. aha, I found the cause!

--2021-10-10 23:01:15--
Resolving (
Connecting to (||:443... connected.
HTTP request sent, awaiting response... 302 Found
Location: [following]
--2021-10-10 23:01:15--
Resolving ( 2606:50c0:8002::154, 2606:50c0:8003::154, 2606:50c0:8001::154, ...
Connecting to (|2606:50c0:8002::154|:443... ^C

You could see, all of the IP addresses wget used are in IPV6 format while my network doesn't support IPV6 . So it is easy to fix. According to this question from stackoverflow, I added the following line at the end of /etc/wgetrc and the issue has gone!

inet4_only = on