Why on Ubuntu 18.04 command "sudo -u username -s" not works as on CentOS 7?
How does sudo handle $HOME differently since 19.10?
Schrödinger Equation for Two Electrons? I'm having trouble finding a simple answer to this question (maybe because there isn't one), but I'm just confused about how the Schrödinger Equation would look for two electrons. I understand that it would exist in 6 dimensional configuration space, but how does the potential look? It's confusing that the potential would be different for each electron depending on where the other one is. What is the difference between private and protected members of C++ classes? What is the difference between private and protected members in C++ classes? I understand from best practice conventions that variables and functions which are not called outside the class should be made private—but looking at my MFC project, MFC seems to favor protected. What's the difference and which should I use? I think sometimes there is a need to post question as anonymous, reason being to avoid linking content of a question with the identity of the questioner. This may not be so evident or required on technical sites like stackoverflow.com but sometimes is a necessity on sites like  or maybe in future depression.stackexchange.com  On such sites user may not want to link his identity to some questions where he may detail about his being over-weight or skinny or maybe some other attribute which he may like to keep private and avoid making his concerns public, but still want to ask a question with valid data.  I am not suggesting that user asking question should not be registered or not responsible for content. I think all down-votes or up-votes should still be attributed to user, but this way most users would not suffer , and reputation could even be used for a bounty. The only change should be that while asking question a valid registered user can hide his identity (the whole user signature block/user card and the reputation should be replaced by "identity-hidden") and that question should not be listed in his public profile.  Anyway identity of questioner doesn't add much value to question. If we think such anonymous question may reduce social nature of Stack Exchange sites, and maybe majority of questions will become anonymous we can curb that by putting a daily or monthly limit per user or put a price of say 50 reputation per anonymous question.  PS: I don't think this is duplicate of        because motive for question and reason for feature request are different, and I propose a different solution too, because creating another account for asking such questions has many problems which having a single account doesn't have    I don't have to manage other account If I keep single account I still may want to keep my details to be linked to my non-anonymous questions I may want to use reputations I earned as bounty for anonymous questions    also allows anonymous questions and may be we can take some hint from there. Do Hogwarts Houses have quotas? Not a year goes by where we don't see at least one person Sorted into each House, and it's usually a fairly even distribution.  The Sorting Hat doesn't get a chance to study the mind of each child before Sorting, so it can't Sort them relative to each other (top X in smarts go to Ravenclaw, 4 bravest to Gryffindor, etc)  What would happen if a Sorting occurred where all the witches/wizards were extremely intelligent?  Would they all get Sorted to Ravenclaw?  What if they were all extremely brave?  What if none of them were particularly smart or courageous, but they all wanted power?  We see that there's a fairly small number of beds per room in each dorm, would the Hat stop Sorting people into a House if it knew the House had no more beds?  If so, could Harry Potter have ended up in Hufflepuff if his last name had been 'Zimmers'? Linux, find all files matching pattern and delete Looking to find all files (recursively) which have an underscore in their file name and then delete them via command line. I have a  to which I'd like to add JPEG and PNG images that I generate on the fly.  All the examples I've seen so far in the , specially in the  use ImageIcons.  I'm generating these images as byte arrays, and they are usually larger than the common icon they use in the examples, at 640x480.   Is there any (performance or other) problem in using the ImageIcon class to display an image that size in a JPanel? What's the usual way of doing it? How to add an image to a JPanel without using the ImageIcon class?   Edit: A more careful examination of the tutorials and the API shows that you cannot add an ImageIcon directly to a JPanel. Instead, they achieve the same effect by setting the image as an icon of a JLabel. This just doesn't feel right... I don't want my users to change the system wallpaper. How do I the lock the wallpaper down? Update  Users are changing wallpaper by right clicking the picture and choosing set as wallpaper. How to restrict this behaviour?  Is it possible to remove Backgrounds Tab from Appearance Preferences? If yes how? Rayleigh-Jeans Law My question is simple, why do we believe  to be absurd? Is the Ultra-violet catastrophe incorrect or is it only because we can not create or know of a perfect emitter? I am a bit confused as to why Quanta was necessary. Consolidate tag wiki excerpt and body contents with regards to suggested edits At the moment, in major part because they are two separate post objects in the system, the excerpt and the body of a tag wiki count as two separate posts with regards to suggested edits in the queue. Mechanically, this is sane, but when it comes to handling the actual queue, it can be confusing. A body edit might consist of little more than a bed of links, which looks bad. But then an excerpt is shown that includes the rest of the data, and since excerpts can be included on the actual wiki page, it makes a lot more sense when they're taken in the same space.  And this is how they are composed, too. The actual edit interface for working on tag wikis has both the excerpt and the body on the same page. In a sense, the excerpt behaves a lot like the "title" of the wiki, if we make a parallel to normal post edits.  Thus, my suggestion (which is to say a suggestion that I repossessed from Robert Cartaino) is that when suggested edits are reviewed for tag wikis, that they be presented in a single unit, treating the excerpt the same as how a title is treated in a question edit. This way, relevant information that is crossed between the two isn't lost because they are reviewed separately. The portion of the tangent to any conic intercepted between the point of contact and the directrix subtends a right angle at the focus of the conic? What happens if my shield breaks? Why do I have to specify runat="server" on all my ASP.NET controls when it is a mandatory attribute and server is the only option available in my limited knowledge of ASP.NET, and I get an error if I don't use it?  I do understand that I can optionally use it on my HTML tags, and I do understand the client/server paradigm and what it is actually specifying.  Is it a redundant tag that could just be implied by the control being an ASP.NET control, or is there an underlying reason? Is 60 minutes enough layover time at Los Angeles International Airport? I am flying in to LAX on American Airlines and have a 60 min layover before I fly out with American Airlines (same ticket).  Will this be enough time? Proving that $\arctan(x)+\arctan(1/x)=\pm \pi/2$, could this line of reasoning possibly be correct? Separate labels in cases What does my internet provider know about my online activities? What does my internet service provider know about my online activites in these cases?   plain server (www, ftp, whatever) connection and provider's DNS secured (e.g. TLS) server connection and provider's DNS plain server (www, ftp, whatever) connection and an non-provider non-logging DNS secured (e.g. TLS) server (www, ftp, whatever) connection and non-provider non-logging DNS   In case 4) does my provider know anything more about my online behaviour than "IP w.x.y.z was assigned to Foo Bar between connect-time and disconnect-time" (i.e. only the duration my router was connected)?  What traffic does need to go through the provider's infrastructure to make my connection work at all? To get rid of dust that had gathered near the fan, I put a vacuum cleaner to the air intake (with the computer turned off).  This removed the dust.  It also caused the fan to rotate at a fairly high speed. Quite faster than normal speed, judging from the sound.  Do I risk destroying stuff by doing this? Two submit buttons in one form I have two submit buttons in a form. How do I determine which one was hit serverside? Is there a system in place to prevent new users asking, answering and accepting answers to each others' off-topic questions? Normally new users are not allowed to up-vote until they gain a bit of reputation by receiving up-votes or accepts from the community of a site.  But this has a weak point that is being exploited:     A number of new users post, answer, and accept each others'    off-topic questions before we can close them (in less than 5 min).    Accepting each others' answers gains them enough reputation to    start up-vote each others' posts.   We are closing them and the moderators clean up afterwards but  this keeps happening over and over again and becoming frustrating  to the extent that I think a systematic solution might be required. Is there a system to prevent this kind of circumvention of  the reputation requirements using accepts by new users?  One possible solution might be to change the system so accepts from users who do not have enough reputation to up-vote  do not give any reputation (at least until the answer gets an up-vote). Windows equivalent of the Linux command 'touch'?