Server Bug Fix: OpenVPN connection issue on Azure VM

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I had many un succesfull attempts at installing openvpn access server on a VM but everytime the Issue is same. I connect to my VPN after installing but when I go to any website it says “ERR_NAME_NOT_RESOLVED”. Please tell me what is the Issue and I had install openvpn via this link: https://medium.com/@evgenijrenke/configure-openvpn-access-server-on-azure-6e6120bacddf. T had even tried to flush my Windows DNS but of no use.
Please Help!

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Math Genius: Simplified tensor formula

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A is a fourth-order tensor, B is a second-order tensor, and C is a second-order tensor
$$mathbf{A}:mathbf{B}cdotmathbf{C}=[quad ]:mathbf{B}$$
$$mathbf{B}cdotmathbf{C}=[quad ]:mathbf{B}$$
$$mathbf{B}cdotmathbf{C}=[quad ]:mathbf{C}$$
What is the expression in brackets?Can you derive it step by step?thank you very much!

Write the first equation in index notation (employing Einstein summation)
$$eqalign{
A_{ijkl}:B_{kp}C_{pl} &= left(A_{ijkl}C^T_{lp}right):B_{kp} \
}$$

The term in parentheses is mystery tensor, i.e.
$$T = Acdot C^T$$
The second and third equations can be written as
$$eqalign{
B_{ij}C_{jk} &= left(B_{ij}C_{jk};M_{lp}right):B_{lp} \
B_{ij}C_{jk} &= left(B_{ij}C_{jk};N_{lp}right):C_{lp} \
}$$

So any matrix $M$ which satisfies $M:B=1$ will solve the first equation, i.e.
$$T=(Bcdot C)star M$$
where $(star)$ denotes the dyadic product.

Similarly, any $N$ which satisfies $N:C=1$ solves the second equation, i.e.
$$T=(Bcdot C)star N$$
Here are some concrete examples. Let $M$ be a matrix in which all of the elements are zero except for $M_{11}=B_{11}^{-1}$. A second solution would take $M_{12}=B_{12}^{-1}$.

Another type of solution takes a random matrix $R$ and scales it to satisfy the constraint
$$M=frac{R}{R:B}=frac{R}{{rm Tr}(RB^T)}
quadimpliesquad M:B = 1$$

Obviously, there are an infinite number of solutions to the last two equations.

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Server Bug Fix: Oracle VM and live storage migration (like storage vMotion on VMware), is it possible?

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I have to migrate VMs to new storage for a client. Hypervisor is Oracle VM, versions 3.3 & 3.4. Haven’t access to the machines yet, I’m searching for info for live storage migration on this platform, Oracle VM.

In Oracle docs, Oracle VM 3.4 docs this doesn’t seem possible (only if the VM is stopped). In Oracle VM datasheet it mentions, Storage live VM migration, perform live migrations of running virtual machines that have virtual disks on local storage.

So I am confused. Does anybody have any experience of live storage migration on Oracle VM, versions 3.3 & 3.4?

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Ubuntu HowTo: Lenovo Touchpad issue 20.04

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I decided to swap from Windows to Ubuntu 20.04 (I’m a newbie) and I found a problem with the touchpad.

uname -r gives: 5.4.0-33-generic

xinput gives:

⎡ Virtual core pointer                      id=2    [master pointer  (3)]
⎜   ↳ Virtual core XTEST pointer                id=4    [slave  pointer  (2)]
⎜   ↳ PS/2 Logitech Wheel Mouse                 id=15   [slave  pointer  (2)]
⎣ Virtual core keyboard                     id=3    [master keyboard (2)]
    ↳ Virtual core XTEST keyboard               id=5    [slave  keyboard (3)]
    ↳ Power Button                              id=6    [slave  keyboard (3)]
    ↳ Video Bus                                 id=7    [slave  keyboard (3)]
    ↳ Video Bus                                 id=8    [slave  keyboard (3)]
    ↳ Power Button                              id=9    [slave  keyboard (3)]
    ↳ Sleep Button                              id=10   [slave  keyboard (3)]
    ↳ Lenovo EasyCamera: Lenovo EasyC           id=12   [slave  keyboard (3)]
    ↳ Ideapad extra buttons                     id=13   [slave  keyboard (3)]
    ↳ AT Translated Set 2 keyboard              id=14   [slave  keyboard (3)]

It shows the touchpad as PS/2 Logitech Wheel Mouse.

xserver-xorg is already the newest version (1:7.7+19ubuntu14).

What I’ve tried:

I installed first the binary:

xserver-xorg-input-synaptics_1.9.1-1ubuntu1_amd64.deb

No problems, but the touchpad still not working.

I’d appreciate help to fix this issue; I know that it is known issue, and probably the solution is in front of me, but you can appreciate I’m new to Ubuntu.

I’ve removed xserver-xorg-input-synaptics, unplugged the auxiliary mouse and restart the laptop.

The touchpad is recognised and the main functions working.

Thanks Pilot6 for the help.

The ONLY way I can get my trackpads to function properly on my Thinkpad t469 and t15 is to install xserver-xorg-input-synaptics

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Making Game: I need to get pip but don’t have disutils

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I need to get disutils.util to unpackage things that I try to get using pip. The problem is I don’t have pip and I don’t have permission to use sudo or basically anything.

I searched and searched but I couldn’t find a solution that worked.

I’m on Linux the 18.04 LTS I have python 3.

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Linux HowTo: Adding a key with “ssh-add” works but passing it with “-i” doesn’t

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I have a case like follows:

ssh -J${some-jump-host} -i some-key.pem [email protected]${some-ip}

which does not ask for the key password for some-key.pem but directly fail as it is not authenticated.

However, if I do:

ssh-add -K some-key.pem
ssh -J${some-jump-host} [email protected]${some-ip}

this asks the password when adding the key, then it works.

I have

$ cat ~/.ssh/config
Include ~/ssh_config

Host *
    UseKeychain yes
    StrictHostKeyChecking no
    User my-username

IdentityFile path-to-an-irrelevant-key
IdentityFile path-to-some-other-irrelevant-key
ServerAliveInterval 60
ServerAliveCountMax 10
StrictHostKeyChecking no
UserKnownHostsFile=/dev/null
ForwardAgent yes
ForwardX11 yes

in ~/ssh_config we just define some hosts and proxy jumps, and this:

Host *
    User my-username
    PKCS11Provider /Library/OpenSC/lib/opensc-pkcs11.so
    ForwardAgent yes 
    StrictHostKeyChecking no
    UserKnownHostsFile=/dev/null 

so my question is, why ssh seem to be ignoring the key when it is passed with -i?

Note:
this is the relevant output of the -vvv for the case with -i

debug1: Will attempt key: some-key.pem  explicit
debug2: pubkey_prepare: done
debug3: send packet: type 5
debug3: receive packet: type 7
debug1: SSH2_MSG_EXT_INFO received
debug1: kex_input_ext_info: server-sig-algs=<rsa-sha2-256,rsa-sha2-512>
debug3: receive packet: type 6
debug2: service_accept: ssh-userauth
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug3: send packet: type 50
debug3: receive packet: type 53
debug3: input_userauth_banner
Authorized uses only. All activity may be monitored and reported.
debug3: receive packet: type 51
debug1: Authentications that can continue: publickey
debug3: start over, passed a different list publickey
debug3: preferred publickey,keyboard-interactive,password
debug3: authmethod_lookup publickey
debug3: remaining preferred: keyboard-interactive,password
debug3: authmethod_is_enabled publickey
debug1: Next authentication method: publickey

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Math Genius: Meaning of the slash “/” in $mathbb{Z}/pmathbb{Z}$

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What the meaning of the slash “/” in expression like this: $mathbb{Z}/pmathbb{Z}$ ? I know that it is called “a quotient ring”, but quotient reminds division. It’s an operator somewhat related to division?

I’m an engineer trying to fully understand the abstract algebra behind error correction codes. May you leave a suggestion of a book for non-mathematicians that explain this topic in an easy manner?

If $R$ is a ring and $J$ a two-sided ideal of $R$, the quotient ring $R/J$ consists of the equivalence classes $x + J$ for $x in R$, where $x sim y$ if $x – y in J$.
This is a ring with operations $(x+J) + (y+J) = (x+y)+J$ and $(x+J)(y+J) = xy + J$.

In the case of $mathbb Z / pmathbb Z$, $pmathbb Z$ consists of the multiples of $p$ and the equivalence relation is congruence mod $p$. Thus $mathbb Z/pmathbb Z$ consists of the congruence classes mod $p$.

In $Bbb Z$ ,we define the equivalence relation $R$ by $x ;R; y iff x-y$ is a multiple of $p $.

$Bbb Z/p Bbb Z $ is the set of equivalence classes.

$$Bbb Z/3Bbb Z={overline {0},overline {1},overline {2}}. $$

$$overline {3}=overline {0}. $$

Risking self-praise, I might recommend my own course notes (formerly a book published by a traditional publisher) “Coding Notes” at http://www.math.umn.edu/~garrett/coding/CodingNotes.pdf There are also the rather telegraphic overheads for a course I taught many times on that subject using those notes/book, at http://www.math.umn.edu/~garrett/coding/

This course (and the book/notes) was meant to be intelligible to people who’d not studied any abstract algebra before, and, in particular, to engineering and computer science people, in addition to math majors in the relatively early part of their undergrad education.

So, in particular, these notes are very down-to-earth, and talk in a way precisely meant to be intelligible to engineering and computer science people… who may have a “different dialect” in mathematics.

So, no, not abstract, yet mathematically accurate, and aimed at coding-theory issues. (Though not really high-end, and certainly no longer up-to-date.)

The generic notation for the quotient of a set $X$ by an equivalence relation $cal R$ is: $; X/cal R$.

As the equivalence relation here can be defined as $;xcal R yiff x-yin pmathbf Z$, the ideal $pmathbf Z$ is taken as the name of the relation and used in the notation of the quotient set.

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Code Bug Fix: Device Proximity LED for barcode

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The fact is that old scanners do not read the generated 1D barcode from the phone screen. And I started looking for another option and came across Beaming Barcode Technology, and here.

I wanted to get the SDK for Android, I did not find it anywhere. I tried to decompile the old APK, to no avail.

After searching, I realized that they were bought by Samsung.

But for some reason they don’t talk about it anywhere, there are no questions in StackOverflow about this technology, or about the implementation of a smartphone Proximity sensor to generate a barcode.

Question:

Does this technology really work?

If so, how do you implement this yourself with a sensor?

Perhaps the technology could be thought of as LoopPay(SamsungPay) in magnetic stripe cards.
Samsung Paid Around $250 Million for LoopPay, Its Apple Pay Competitor
Samsung Pay

The magnetic stripe card is highly compatible with the physical specifications regarding the reading method, and it was effective to some extent even with technologies such as LoopPay.
However, there may be countries or regions that are technically possible but are not serviced due to differences in rules or business practices.

On the other hand, the basics of barcode scanners are to illuminate a barcode and convert the light that can be reflected and detected to be recognized, but there are various methods and shapes.
Mechanism of barcode scanning

By analogy with LoopPay, isn’t it a method of simulating this reflected light with the light emission of the LED of the smartphone and making it look like it has read a barcode?
The sensor is the barcode scanner of the POS terminal, so the sensor may not be needed on the smartphone side.

That’s why there are no questions or articles about proximity sensors or any sensors.

However, as mentioned above, barcode scanners are not as limited in standards as magnetic stripe readers, and there are various methods and shapes of barcode scanners in the world.

The technology you asked may work, but if it works, it will have limited scope.
It is unlikely that it will spread in a practical range.

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Server Bug Fix: Vyos: Redirect All Users Web Request to Webpage When Internet is Down

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We are a small company and are currently using Vyos router for our internet connection.
I would like to know if it is possible to redirect all the users web requests to a static web page whenever the internet goes down so that the users can know that there is a problem with the router itself which can make my work a lot easier.
My idea is something that is pretty similar to how plug and play routers function.

I know how to make a webpage on my Vyos but i’m not sure how to redirect all the web traffic to it when it can’t reach the internet.

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Making Game: Is there a way of converting a hierarchical list into a table in Word?

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I have a list like:

  • Top Level 1
    • Sub Level 1
      • Sub Sub Level 1
      • Sub Sub Level 2
    • Sub Level 2
      • Sub Sub Level 3

(but bigger)

Is there a way I can convert the above into a table that looks like:

Top Level 1 | Sub Level 1 | Sub Sub Level 1
            |             | Sub Sub Level 2
            | Sub Level 2 | Sub Sub Level 3

Word doesn’t have this functionality in particular, I’m afraid.

Word does not do this.

But I do have a solution using Excel that you can paste back into Word.

My solution uses a simple search and replace
and a native Text to Columns in a spreadsheet software.

Generic solution

Step 1) Search and replace all the spaces/ tabs that make your hierarchy with the bullet. (In Word or in Excel or anywhere or plain text editor).
You’ll end up with something like this

∙ item 1
∙∙ item 2
∙∙∙ item 3

Step 3) Paste into a spreadsheet and use the Text to Columns feature and split in on your bullet character. Done!

My specific workflow using my apps of choice

Step 1) Copy paste the list from Workflowy as a plain text into Vscode. This results in a markdown style list.

- item 1
  - item 2
    - item 3

Step 2) Search and replace every two spaces and replace them with -

- item 1
-- item 2
--- item 3

Step 3) Copy paste into OpenOffice/ Excel. Use the Text to Columns feature and split in on -. Done! You get your table!

Workaround:

  1. In Word, go to New Number Format under Numbering.
  2. After the number, provide a distinct special
    character.
  3. Do this for all hierarchical levels.
  4. Copy and paste the entire content to Excel or Google Sheet along
    with the numbers and special characters. It will copy to a single
    column.
  5. Write a formula using Find or Search to copy only the cells with the
    specific Special Character for a specific hierarchy.
  6. Do this for all hierarchical levels.

BulletsToTable.com

I had the same problem – I make my notes as heirarchical lists in MS OneNote but sometimes want to show them as tables. This web app makes quick work of what you asked, just paste in your list!

Edit: Demo GIF here to show it in action

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