Make Alt + Tab behavior in Ubuntu 18.04 same as in Ubuntu 16
How do I easily switch between windows rather than applications in GNOME Shell?
Monday morning mistake: sudo rm -rf --no-preserve-root / Please note: The answers and comments to this  question contains content from another, similar question that has received a lot of attention from outside media but turned out to be hoax question in some kind of viral marketing scheme. As we don't allow ServerFault to be abused in such a way, the original question has been deleted and the answers merged with this question.      Here's a an entertaining tragedy. This morning I was doing a bit of maintenance on my production server, when I mistakenly executed the following command:  sudo rm -rf --no-preserve-root /mnt/hetznerbackup /  I didn't spot the last space before / and a few seconds later, when warnings was flooding my command line, I realised that I had just hit the self-destruct button. Here's a bit of what burned into my eyes:  rm: cannot remove `/mnt/hetznerbackup': Is a directory rm: cannot remove `/sys/fs/ecryptfs/version': Operation not permitted rm: cannot remove `/sys/fs/ext4/md2/inode_readahead_blks': Operation not permitted rm: cannot remove `/sys/fs/ext4/md2/mb_max_to_scan': Operation not permitted rm: cannot remove `/sys/fs/ext4/md2/delayed_allocation_blocks': Operation not permitted rm: cannot remove `/sys/fs/ext4/md2/max_writeback_mb_bump': Operation not permitted rm: cannot remove `/sys/fs/ext4/md2/mb_stream_req': Operation not permitted rm: cannot remove `/sys/fs/ext4/md2/mb_min_to_scan': Operation not permitted rm: cannot remove `/sys/fs/ext4/md2/mb_stats': Operation not permitted rm: cannot remove `/sys/fs/ext4/md2/trigger_fs_error': Operation not permitted rm: cannot remove `/sys/fs/ext4/md2/session_write_kbytes': Operation not permitted rm: cannot remove `/sys/fs/ext4/md2/lifetime_write_kbytes': Operation not permitted # and so on..   I stopped the task and was relieved when I discovered that the production service was still running. Sadly, the server no longer accept my public key or password for any user via SSH.  How would you move forward from here? I'll swim an ocean of barbed wire to get that SSH-access back.  The server is running Ubuntu-12.04 and hosted at Hetzner. I have just started special theory of relativity. The limiting speed known as speed of light fascinated me most. I asked my teacher:      Consider two massless objects moving in the same direction at the speed of light. What would be their relative velocity w.r.t each other?   My teacher tells me that their relative velocity would be zero. But then the speed of light is universal constant regardless of the motion of its frame of reference, so shouldn't their relative velocity be $c$? What is their relative velocity and how? Do objects moving at the speed of light obey law of addition of velocities? Implement MicroController Power Switch and re-use the button for other features This is similar to other questions, but I feel it is different because of the reuse of the "power" button.   I want a "latching" Momentary Power button.  Behavior:   User Pushes momentary button, holds down as long as necessary and the device powers up. Between Power On and Off the same button will be re-used for other functions  When it is held down for 5 +/- seconds the MicroController will turn itself off.    Design Constraints:   Battery provides between 3.7V to 2.9V during it's usable life The Voltage regulator requires Vin +/- 0.3V on the Enable Pin, 3.1V output. MicroController operates at 3.1V MicroController Output Pin High state is 2.7V Max   Debouncing: In this case I'm not concerned about debouncing the switch, if the user doesn't hold it down long enough for the MicroController to set it's Digital Output pin  High the device doesn't power on.  I've worked up the following schematic, which kind of works.    It assumes 3.7V from the battery. Uses an Analog Input for the Power button, which then uses the variation in voltage to determine if the button has been pressed. In the current design the difference is 0.12 V (from 3.4 to 3.52), but the MicroController has a 12 bit ADC so that shouldn't be a problem, in addition I can adjust the sensitivity range of the ADC.   Questions:  What is the difference between reality and the simulator?  Is there a better way?  How can I get a greater voltage difference on the button input? I've tried many different combinations but they increase the voltage range above the 3.6V Input High Maximum specified in the datasheet.  I'm not excited about the "Leakage current" when the uC Controlled Power Pin is Low, any suggestions?   Thank you for any ideas/suggestions/answers. Show that both mixed partial derivatives exist at the origin but are not equal $$f(x,y) = \begin{cases} \displaystyle \frac{xy(x^2-y^2)}{x^2+y^2} &amp; \text{if } (x,y) \neq (0,0), \\ 0 &amp; \text{if } (x,y) = (0,0). \end{cases}$$ I tried finding both mixed partial derivatives but they ended up being the same for that function. I must be failing to take into account something dealing with the fact that it is piece-wise. I still need to show the mixed partial derivatives exist. How can I do all of this? Upgrade High-Trust Addin/App from 2013 to 2016 I have a SharePoint 2013 environment with several High-Trust Addins. This must now be upgraded to SharePoint 2016.  My Questions:   I was unable to find any documentation on the required steps. Links are welcome. Do i have to migrate App-Management Service and Subscription Settings Service?  don't even mention them.   say yes, but linked background is no longer available.  , i had to create a New-SPTrustedSecurityTokenIssuer. In this step, a RegisteredIssuerName had to be specified. This IssuerName consists of the Realm and the .   I think IssuerID can and should be migrated to SharePoint 2016, as it it also defined inside the High-Trust app. What about the Realm? This is by default the same value as FarmID. If i migrate this value, i have to change the Realm in SharePoint 2016. Or should i create the TST with a new Realm and existing IssuerID? I work sometimes till 4 am and my friends and the rest of the world obviously don't know in advance that I don't want to be called at 8 am.  Is there an app or setting that can allow me to have an emergency override list of people I need to be woken up for if a possible emergency arises but ignore all other calls until I wake up?    I'm familiar with the Do Not Disturb option, but it has limitations that it blocks all calls. What if there is an emergency at night?  What if I want to allow certain callers during the Do not Disturb time? Is there a way to have an emergency list that allows calls during silent? Could not get lock /var/lib/apt/lists/lock when I try to apt-get update I'm getting the below error,  E: Could not get lock /var/lib/apt/lists/lock - open (11: Resource temporarily unavailable) E: Unable to lock directory /var/lib/apt/lists/ "ImportError: No module named _struct" configuring python-minimal When I run sudo apt-get upgrade, the dpkg error appears and interupts the process.  Error details:  Setting up python-minimal (2.7.3-0ubuntu7.1) ... Traceback (most recent call last):   File "/usr/local/lib/python2.7/runpy.py", line 162, in _run_module_as_main     "__main__", fname, loader, pkg_name)   File "/usr/local/lib/python2.7/runpy.py", line 72, in _run_code     exec code in run_globals   File "/usr/local/lib/python2.7/compileall.py", line 16, in &lt;module&gt;     import struct   File "/usr/local/lib/python2.7/struct.py", line 1, in &lt;module&gt;     from _struct import * ImportError: No module named _struct dpkg: error processing python-minimal (--configure):  subprocess installed post-installation script returned error exit status 255 dpkg: dependency problems prevent configuration of python:  python depends on python-minimal (= 2.7.3-0ubuntu7.1); however:   Package python-minimal is not configured yet.   And this problem leads to a series of dependency problems when processing the following packages:    python  gwibber-service  libgwibber3  libgwibber-gtk3  gwibber  gwibber-service-facebook  gwibber-service-identica  gwibber-service-twitter  python-all  python-dev  python-all-dev  python-apt  python-problem-report  python-apport  python-libxml2  unity-lens-gwibber  unity-scope-video-remote   Finally, nothing I can do for this problem. And several days later, the root directory is full and I even could not uninstall any software because of this problem. Keeping tables/figures close to where they are mentioned Is there any package or a method to force LaTeX to keep floating environments like table and figure closer to where they are declared? Can someone give me some example code that creates a surface with a transparent background in pygame? Is "Michael here" correct? What's the best way to do a backwards loop in C/C#/C++? I need to move backwards through an array, so I have code like this:  for (int i = myArray.Length - 1; i &gt;= 0; i--) {     // Do something     myArray[i] = 42; }   Is there a better way of doing this?  Update: I was hoping that maybe C# had some built-in mechanism for this like:  foreachbackwards (int i in myArray) {     // so easy }   Update 2: There are better ways. Rune takes the prize with:  for (int i = myArray.Length; i-- &gt; 0; ) {         //do something } //or for (int i = myArray.Length; i --&gt; 0; ) {     // do something }   which looks even better in regular C (thanks to Twotymz):  for (int i = lengthOfArray; i--; ) {         //do something } Cleaning polygon after using dissolve to repair geometry in QGIS? I'm trying to obtain the boundaries of shapefile, thus to clean the inside as a matter of speaking. While I had expected that dissolve while get me a proper polygon, unfortunately it still has some remainders. How could I get rid of them?  Does QGIS have a tool similar to Repair Geometry?  Here's the source    Result below: How to differentiate a given inner product (CSIR DEC(2018) Let $A$ be a $n \times n$  invertible  matrix.Define a function $F:\mathbb{R}^{n} \times \mathbb{R}^{n} \rightarrow \mathbb{R}$ by $F(x,y)=\langle Ax,y\rangle$. Let $DF(x,y)$ denotes the derivative of $F$ at $(x,y)$ which is a linear transformation from $\mathbb{R}^{n} \times \mathbb{R}^{n} \rightarrow \mathbb{R} $. Then      1) if $x\neq 0$,then  $DF(x,0)\neq 0$      2) if $y\neq 0$,then  $DF(0,y)\neq 0$      3)  if $(x,y)\neq (0,0)$,then $DF(x,y)\neq 0$      4) if $x=0 \; or \;y=0$,then $DF(x,y)= 0$   I don't even know how to start the solution and also how to take derivative in higher dimensions.  Please help!  Thank you. Exponential of the differential operator I am not sure whether this question is even well-posed. But today I learnt that $e^Df(x) = f(x+1)$ where $D$ is differential operator and  $$e^D \triangleq \sum_{i=0}^{\infty} \frac{D^i}{i!}.$$  (ref. )  So I was curious as to whether the differential equation  $$\frac{df(t)}{dt} = e^Df(t) = f(t+1)$$  has any solutions apart from $f = 0$? I frequently prefer to look for questions on superuser .    I have never been able to determine how these search results are ordered.  Typically, search results are returned in order of relevance and the search help says they are "weighted heavily towards question title matches", but in this case, you would think that the search would order them based on whatever tab is currently selected (newest, hot, active)?  I ordinarily never stray outside of 'newest', but it's clear the results are not sorted by age. I'm using Linux Mint. My login shell (cat /etc/passwd | grep myUserName) is bash.  After I start my graphical desktop environment and run a terminal emulator from it, I can see that .bash_profile is not sourced (environment vars that are exported in it are unset). But if I log in from a text console (ctrl+alt+F1) or manually run bash -l from the terminal emulator, .bash_profile works fine.  Am I wrong when I think that .bash_profile should be sourced when X starts and all export'ed vars should be available in the terminal, running from X?  P.S. Placing everything in .bashrc and sourcing it from .bash_profile is not good idea (): environment stuff should be sourced only once. Where do I suggest new Stack Exchange sites? Is there an appropriate place to suggest new Stack Exchange based sites, perhaps a place for them to be voted upon?  I wish there was a Stack Exchange site for Aviation (both real-life and simulated). I have filed my 2012 tax return jointly with my wife, along with my wife's ITIN application, back in late March.  In April, I got a letter for IRS ITIN department saying that we should send my wife's original passport to them. So we sent my wife's passport on May 15th. USPS tracking number confirmed that IRS received it on May 20th.  However, last week (end of June) we have received another letter from IRS ITIN department saying that our ITIN application has been rejected, rejected because we have not sent the original identification document that they requested!  Okay, let's put our tax return and ITIN aside. Where is my wife's passport? Right now my wife does not have her personal identification, nor proof of legal status in U.S. Could IRS have lost it?  I tried to call the IRS several times. One time I waited for 1 hour and 20 minutes to talk to a person, and that person said he has only 10 minutes to talk before he has to leave. He said they'll investigate and someone(?) will call us back soon, but never called back. I wrote them a letter, but no response. I tried calling several times more, but machine is saying 'sorry too many calls right now, we can't accept your call'.  What can I do? What would happen if you used a dead person's hair in Polyjuice Potion?