9p / virtfs : new files in shared folder don’t belong to the expected user and group

For the last two days I tried to share a folder between the host and a guest virtual machine, both running the latest Debian Stretch.

The folder I wish to share is owned by the myuser, group mygroup on the host hard drive (/srv/sharedfolder). Since the guest is a LAMP server running Nextcloud I wish to access and write to this shared folder as www-data:www-data.

So I created a libvirt’s filesystem with the Default driver and Mapped mode :

<filesystem type='mount' accessmode='mapped'>     <source dir='/srv/sharedfolder'/>     <target dir='sharedfolder'/>     <alias name='fs0'/>     <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x0'/> </filesystem> 

Mapped seems to be the good choice as written at suse.com :

The user credentials and the client-user’s credentials are saved in extended attributes. This model is recommended when host and guest domains should be kept completely isolated.


On the host side :

  • user and group at /etc/libvirt/qemu.conf are set to myuser and mygroup
  • the shared folder has been “chmoded” with chmod 775

On the guest side :

  • the mountpoint of the shared folder belong to www-data:www-data
  • fstab (with kernel.org as reference) :

    sharedfolder /srv/sharedfolder 9p trans=virtio,version=9p2000.L,rw,nofail 0 0


So far, I can read and write the shared folder as www-data, so the mission seems to be accomplished.

But when a new file is created on the host file by myuser within the shared folder the new file is seen as owned by myuser:myuser by the guest (whereas i expected it would be owned by www-data:www-data).

So what should I do ? Thanks in advance.

Galois group to Sextic Polynomial with Two Real Roots

I have the following polynomial $ $ f(x,Q)=0.064x^6+0.96x^4+4.8x^2-(13.824Q)x+8=0$ $ where the variable $ Q$ is in the range $ ]1,2\pi]$ . This polynomial is obtained from an equation that describes a nozzle. From the theory I know there are certainly two positive real roots: I have done the check for different values of $ Q$ and Wolfram confirms it.

I need the formula to get the two real positive solutions by only changing the value of $ Q$ : then I have to implement this formula in MATLAB. For what I have written above I think the sextic has a solvable Galois group so can be exactly expressed in terms of radicals.

I am an aerospace engineer and to be honest I don’t know where to start with Galois theory.

A question on verifying the mixing time of finite groups such as the Rubik’s Cube Group

I’m interested in some questions about the computational complexity of bounding the mixing time of random walks on Cayley-graphs of finite groups like that of the Rubik’s Cube Group $ G$ . Determining that $ 20$ is the diameter (God’s number) of the Rubik’s Cube Group under the half-turn metric with Singmaster generating set $ s=\langle U, U’, U^2, D, D’, D^2,\cdots\rangle$ was a wonderful result. I’m curious about follow-up questions, such as determining how many half-turn twists would it take to get the cube fully “mixed” to $ \epsilon$ -close to the uniform stationary distribution $ \pi$ , say in the variational distance sense.

For example, noting that there are $ 18$ moves in the half-turn metric, and calling $ n$ the mixing time, can we say something like:

For all but a very small number of elements of $ g\in G$ , are there very close to $ \frac{18^n}{\vert G \vert}$ ways of writing $ g$ as words of length $ \le n$ ?

My intuition is that, after the cube is fully mixed with $ n$ moves, there should not be a large special subset $ A\subset G$ of elements that need a lot more or a lot less than $ 18^n$ ways of writing them, starting from the solved position. On the other hand, if the cube has only been scrambled with $ m\lt n$ twists, then there should be a large subset $ A$ that has elements that are in some sense maybe only writable with no more than $ \frac{18^m}{2\vert G \vert}$ different words of length $ \le m$ .

I think we can combine approximate counting techniques to parlay such gaps into an Arthur-Merlin protocol to verify the mixing time is $ \ge n$ :

  • Arthur chooses a random element of $ g$ , a random hash $ h$ mapping words of $ G$ onto a set of size $ \frac{18^n}{\vert G \vert}$ , and a random image $ y$ of $ h$
  • Merlin tells Arthur a word $ W$ of length up to $ n$ that, when applied to the starting position of the cube, equals $ g$
  • The word $ W$ must also satisfy $ h(W)=y$ – indicating that there are likely a lot of words of length $ \le n$ that equal $ g$
  • Arthur repeats with Merlin to amplify as needed

Because, for groups I think, the mixing time is at least the diameter, this also may provide an Arthur-Merlin approach to bound the diameter of a large group.

New girl gamer in our D&D group is causing weird tension – what to do?

I’m concerned because a new player just joined our D&D 5e group and is super flirty with all the male players (both in person and as her character – she’s a bard). And the problem is that she’s changed the whole vibe of our gaming group. We used to be a really cohesive team, and now almost every decision takes ages to make because the guys are defending all her stupid ideas and not acting from their characters’ perspectives. Even our online chats with the DM are strangely sexual now.

The new player is completely NEW to D&D (a complete beginner), and we only met her recently when the DM said she could join the group. Our group is not a friends-group; we met through a gaming group online. The DM likes to get people interested in D&D, so that’s how she got in the door. Our group is aged in their 20s; I think (3 of us are over 35). We have mixed genders and mixed ethnicities (though most Australians). Most players are beginners (except 2 of us who grew up playing D&D in the 80s- I’m 1 of such).

I am a female player in the group, but it’s not an issue of jealousy for me. If she’s super flirty, it reflects badly on her, and in any case, if she “succeeds” in finding a partner, it doesn’t bother me. I don’t care if people date in our group (we already have a couple in the group).

The issue is that, since she joined our campaign, our team dynamic (in game) has changed. One such problem is that her character is a level 1, and we’re all higher levels, so we’re constantly trying to “save” her. I find it really annoying that the guys act all “smitten” and can’t see she just has changed our group dynamic. It’s a rift, and I don’t know what to do to fix it.

I have mentioned my problem with this to the DM, who suggests we play harder campaigns. But the DM has not made any decision to kill her character off either way. Do we kill her? Or level her up? Or…?

The net problem is that decisions are taking too long, and the dynamic of the group is leaning on sexual-tension instead of gameplay.

Please share how you have seen a similar problem resolved using our site’s Good Subjective/Bad Subjective guidelines; specifically, back up your answer with relevant experience or citations. An “idea you think might be good” without any evidence isn’t a good answer.

How to set up G Suite for large group of transient users for low-level document access?

I am the board chair and de-facto IT person at a small youth development non-profit. We have recently switched to G Suite for email and cloud file storage. We have 3 “classes” of user: staff, board, and youth. Staff have individual accounts within our G Suite environment. Board members have private gmail accounts that are given access to Team Drives, etc. My question is about Youth.

We have about 60 teenagers participating in our programs every year. We would like them to have access to various documents in the field via chromebooks we have available. This group has unreliable access to internet and email at home, so using personal accounts is untenable. The group also has high turnover, and so creating 60 individual user accounts and keeping that user list up to date would be onerous.

The seemingly obvious solution is to create a single user, “youth” and give access to that account to our program staff so they can log into a Team Drive, for example, on a chromebook, hand it to one of our youth, and they can access whatever documents they need to.

I understand that G Suite is based on the assumption that every user is an individual human being, and many features don’t really work well when that assumption is broken. However, in this scenario, I can’t really think of another simple way to accomplish what I need. Is there a better way to do this? Are there any unintended consequences of doing it this way that I should be aware of?

Thanks for your help and advice! -Leif

Prove that $\frac{x+y}{1+xy}$ is an Abelian Group

Let $ I=\left]-1,\ 1\right[$ be an interval, and $ \left(I,\ \star\right)$ be a magma such that:

$ $ \left(\forall\ \left(x,\ y \right) \in I^2\right)\ x \star y=\frac{x+y}{1+xy}$ $

I need to prove that $ \left(I,\ \star\right)$ is an Abelian group.

A simple way to prove it is by checking that the magma $ \left(I,\ \star\right)$ satisfies the group axioms including commutativity.

Based on the following statement I would like to approach that problem:

Let $ f$ be a homomorphism from $ \left(X,\ \perp \right)$ to $ \left(I,\ \star\right)$ , then the algebraic structure of $ \left(I,\ \star\right)$ is exactly the algebraic structure of $ \left(X,\ \perp \right)$

So I would like to find out a usual Abelian group – ex. $ \left(\mathbb{R},\ +\right)$ – and a homomorphism $ f$ from that group to $ \left(I,\ \star\right)$ .

Assume that $ f$ is a homomorphism from $ \left(X,\ \perp \right)$ to $ \left(I,\ \star\right)$ , then

$ $ \left(\forall\ \left(x,\ y \right) \in X^2\right)\ f\left(x \perp y \right)= f\left(x\right) \star f\left(y \right)$ $

$ $ \Leftrightarrow f\left(x \perp y \right)= \frac{f\left(x\right) + f\left(y \right)}{1+f\left(x\right) \cdot f\left(y \right)}$ $

I got stuck on that. Could anyone support me with some hints how to get it done.

Gmail Forward email to group, with recipients replying to specific person

I forward a LOT of emails every day. Most of the time, people reply to who they need to. Example. “Do you need money?” Email. Forward to people who need money. But I don’t need them to reply to me, I need them to reply to Mr. Money.

I hope this makes sense. But if you click “reply” in the email you received from me, I get the reply. It would be nice to have it go to another specific email which changes with almost every forward. In Mozilla’s version of email Thunderbird, you can set a specific reply to email address. But due to security, they don’t allow Thunderbird used here.

Failure to create availability group

I”m having a problem creating a new Availability group in a windows cluster. I have 3 nodes in the cluster. Two nodes are running as a FCI and a single stand-alone node that’s a member of the windows cluster.

Msg 19405, Level 16, State 17, Line 2 Failed to create, join or add replica to availability group ‘SQL Cluster 2’, because node ‘DRNode’ is a possible owner for both replica ‘DRNode’ and ‘SQL Instance’. If one replica is failover cluster instance, remove the overlapped node from its possible owners and try again.

I’ve fixed this issue by removing the DRNode from being a possible owner of the SQL FCI, but the issue persists. Do I need to restart the role to make it effective?

I’ve confirmed in PS that it’s correct.

 PS C:\Windows\system32> get-clusterownernode -resource "SQL Network  Name (FCI Name)"  ClusterObject                                               OwnerNodes -------------                                               ----------  SQL Network Name (FCI Name)                                 {Node1, Node2}