Suppose I have a trusted ISO Ubuntu 18.04 image on a USB stick. I have a brand new notebook and boot it from the USB stick. The notebook is connected through Wi-Fi with an unknown or untrusted internet provider ( suppose I am in a Wi-Fi Caffé), so I cannot trust dynamic DNS I got through DHCP.  AFAIK, when installing and upgrading packages, secure apt is used, so downloaded packages are signed and their signatures are checked by the public keys previously loaded in the ISO image.  I conclude that under this situation the installation is secure, regardless of the reliability of the DNS you are using.    Are my assumptions true?    Note: Although this question has been marked as a duplicate one of  , it is slightly different because it has to do more with a brand new installation than with upgrading packages of an installed system, and my question is originally concerned with DNS reliability instead of HTTP vs HTTPS protocol. Nevertheless, as fas as both cases use apt in a secure way, relying on public key infrastructure, the answer for both of them is the same.
Are repository updates secure?  As a bear of little brain from the developer side, I cannot understand why the repository list is http://security.ubuntu.com and the other http(unsecured) sites listed in /etc/apt/sources.list.  Without a certificate chain match this appears as "ask any responder for a list of packages to update" instead of "ask the ubuntu.com site..."  Can any network choose to spoof the update sites, and is this a common practice to provide a locally cached and vetted copy?
Restore Missing "Settings" (gnome-control-center) Icon in Ubuntu 18.04 I have been running Ubuntu 18.04 for a couple of weeks. I upgraded from 16.04 and all went smoothly.   I am not sure what I changed, but this morning I noticed that the "Settings" Icon that launches gnome-control-center is missing from "Show Applications" and the applications menu as well. When I searched from "Show Applications" for gnome-control-center or just settings, nothing showed up.   So, I figured I must have accidentally removed it and figured a reinstall of the package would resolve the issue. I have searched and found several postings where this worked. I tried:  sudo apt install gnome-control-center   And then rebooted - which reinstalled the gnome-control-center and I could then launch it from the command line. However, there was still no Settings Icon in any of the menus.   I also tried many other suggestions including:  sudo apt-get install --reinstall gnome-control-center sudo apt-get install ubuntu-desktop sudo apt install ubuntu-desktop --reinstall sudo apt-get install unity-control-center   However, none of these has been successful in restoring the icon into "Show Applications" or any applications menu.   Anyone have any suggestions on something I haven't tried? Would be much appreciated.  Or, is there a way to just manually recreate the icon?   Output of locate gnome-control-center.desktop:  /usr/share/applications/gnome-control-center.desktop  /home/dccrens/.local/share/applications/gnome-control-center.desktop /home/dccrens/.gnome/apps/gnome-control-center.desktop   I am running Ubuntu 18.04 desktop on kernel 4.15.0-45-generic. Is it possible to find a smooth function $p$ such that $$p(x)=0 \text{ if } x\le -1$$ $$p(x)=0 \text{ if } x&gt; 0$$ $$0\le p(x) \le 1 \text{ if } -1&lt;x&lt;1$$ $$p(x) = 1 \text{ if } -\frac{1}{2}\le x \le \frac{1}{2}$$ Hint: The following function has continuous derivatives of all orders $$f(x) = 0 \text{ if } x\le 0$$ $$f(x) = e^{-\frac{1}{x^2}} \text{ if } x&gt;0$$  My thought: Considering the left-half of the function $p$, I tried something like $e^{-\frac{1}{\tan^2(x\pi)}}$. The shape looks good but I am not sure about the smoothness at $-1$ and $-\frac{1}{2}$. For $x=-1$, since $\tan$ is infinitely differentiable so we have smoothness there. But for $x=-\frac{1}{2}$, I am not sure about the smoothness after &quot;gluing&quot; with $y=1$. Checking via ArcPy if ArcMap is in edit session? Are there network-wide reputation leagues? I would love to see which people have the most network-wide reputation, how can I see that? It is my understanding that I can disable my touchscreen by adding Option "Ignore" "on" to this file                                /usr/share/X11/xorg.conf.d/10-evdev.conf   Section "InputClass"           Identifier "evdev touchscreen catchall"           MatchIsTouchscreen "on"           MatchDevicePath "/dev/input/event*"           Driver "evdev"           EndSection   so it would look like this   Section "InputClass"           Identifier "evdev touchscreen catchall"           MatchIsTouchscreen "on"           MatchDevicePath "/dev/input/event*"           Driver "evdev"           Option "Ignore" "on"           EndSection   What would happen if I simplied changed MatchIsTouchscreen to "off"?   Section "InputClass"           Identifier "evdev touchscreen catchall"           MatchIsTouchscreen "off"           MatchDevicePath "/dev/input/event*"           Driver "evdev"           EndSection   Would this disable my touchscreen? Speed of light when accelerating I'm studying special relativity and saw the 2 postulates of Einstein. The most remarkable one for me is the universal speed of light. Einstein postulated that the speed of light in vacuum is the same for all inertial observers, regardless of the motion of the source. But what if we are accelerating and we are changing from one inertial frame to another, how will we observe the speed of light? Is it still the same? I suggest it's not? Because I alread saw a small introduction to general relativity where the light will bend in a gravitational field and therefore also when you accelerate. So does the speed of light change because it bends? pgrouting unexpected output Xbox Game bar after uninstalling UWP and disabling UAC It looks like the  update  from Microsoft.  I have  and  UWPs as much as I can, along with Cortana and Edge.  Yet today I saw a weird green bar popup saying something about "Press Win + G to bring up the game bar".  I figured it would have to do with the Xbox UWP app, which I have previously uninstalled.  I presume this is UWP functionality, but I'm not sure how to find out for certain.  Can this app or program exist outside of the UWP ecosystem?  Is it a part of the Xbox app?  What method(s) are there to remove it?  Is there a prophylactic to prevent such things in the future?  I'm currently stuck in Windows Home, even though I  (not me, but gives you context).  I will be fixing that sometime soon. How to redirect output to a file and stdout In bash, calling foo would display any output from that command on the stdout.  Calling foo &gt; output would redirect any output from that command to the file specified (in this case 'output').  Is there a way to redirect output to a file and have it display on stdout? As it was suggested  I am using cat command to concatenate several .mp3 files into one .mp3 file. Imagine, I have following .mp3 files in the current folder: 001001.mp3 001002.mp3 001003.mp3 001004.mp3 001005.mp3  or, like this: 096001.mp3 096002.mp3 096003.mp3 096004.mp3  I need to concatenate these .mp3 files in there ascending sequence, i.e.  001001.mp3+001002.mp3+001003.mp3+etc. In order to join these .mp3 files into one I am executing following command in the current folder: cat *.mp3 &gt; final.mp3  I tested the final .mp3 file and it is what I am expected, but I need to be sure that above command picks files in there ascending sequence. Can I be sure that above command always concatenates files in the ascending sequence? Thank you Sir! I'm looking for an algorithm which when given a latitude and longitude pair and a vector translation in meters in Cartesian coordinates (x,y) would give me a new coordinate. Sort of like a reverse Haversine. I could also work with a distance and a heading transformation, but this would probably be slower and not as accurate. Ideally, the algorithm should be fast as I'm working on an embedded system. Accuracy is not critical, within 10 meters would be good. I am reading George Gamow's book  and a certain assertion Gamow makes seems a little startling considering what I already know of the subject of infinite cardinality.     But the number of all geometrical points, though larger than the number of integer and fractional numbers, is not the largest one known to mathematicians. In fact it was found the variety of all possible curves, including those of the most unusual shapes, has a larger membership than the collection of all geometric points, and thus has to be described by the third number in the infinite sequence. [Gamow, 22]   He later does explicitly say the number of all possible curves is $\aleph_2$. But nowhere else can I find reference to this being true, nor does he provide any sort of reasoning to its validity.  My question is how can you prove the set of all possible curves is of cardinality $\aleph_2$ and not $\aleph_1$ or $\aleph_0$? The basic 6T structure used for storing data is same as one used in "Positive Feedback Differential Voltage Sense Amplifier", then how come while the data is stored in SRAM memory cell it doesn't get amplified? For every set $A$, the empty set is a subset of $A$. The empty set is a set. Therefore, the empty set has a cardinality $\geq 1\ldots$ I have only recently been exposed to sets. According to , as seen on the first bullet mark of the link, $ \forall A: \emptyset \subseteq A$  Does this mean that $\emptyset$ is an element of all sets? (This is False, thank you those that answered)  Is the empty set also a set itself?  Assuming these statements are true, then the empty set therefore an element of the empty set. This does not sound right, please clarify for me. Thank you. List sorting by custom field I dont know how to sort a list of SObject Case.  I have a List&lt;Case&gt; newCases which i iterate over in for cycle, where i save Cases to my new List&lt;Case&gt; casesList.  for (Case newCase : newCases) {             if(newCase.Case_Content__c == '111' &amp;&amp; newCase.Status == '24'){                 String cuid = newCase.CUID__c;                 cuidSet.add(cuid);                 casesList.add(newCase);                 casesList.sort(); //TODO sorting by CUID__c             }         }   What i need to do is, to sort this new list by field CUID__c. So the Cases with same CUID are together.  Thank you for any help :) $|G|>2$ implies $G$ has non trivial automorphism Well, this is an exercise problem from Herstein which sounds difficult:   How does one prove that if $|G|&gt;2$, then $G$ has non-trivial automorphism?   The only thing I know which connects a group with its automorphism is the theorem, $$G/Z(G) \cong \mathcal{I}(G)$$ where $\mathcal{I}(G)$ denotes the Inner- Automorphism group of $G$. So for a group with $Z(G)=(e)$, we can conclude that it has a non-trivial automorphism, but what about groups with center? This is my code:  import datetime today = datetime.date.today() print(today)   This prints: 2008-11-22 which is exactly what I want.  But, I have a list I'm appending this to and then suddenly everything goes "wonky". Here is the code:  import datetime mylist = [] today = datetime.date.today() mylist.append(today) print(mylist)   This prints the following:   [datetime.date(2008, 11, 22)]   How can I get just a simple date like 2008-11-22? Permanently blocking a domain in iptables Suppose I want to block Facebook permanently. To do this, I have followed following processes:     #host -t a www.facebook.com   Sample output:     www.facebook.com has address 69.171.224.40   Find CIDR     #whois 69.171.224.40 | grep CIDR   Sample output:     CIDR:           69.171.224.0/19   To prevent outgoing access to www.facebook.com  Approach 1:     #iptables -I FORWARD -p tcp -d 69.171.224.0/19 -j DROP   Approach 2:     #iptables -I FORWARD -p tcp -d www.facebook.com -j DROP   Both Approaches work well. In approach 1, IP address may be changed so it will not block Facebook permanently. I don't know about approach 2 whether it will block Facebook permanently or not. If above approaches are not right way to block a domain permanently, how can I do it? prove/disprove Big-Oh I have the following function f(n), and I want to prove/disprove that it is O(n$^2$): \begin{cases}     4[sum(n/2,n)],&amp; \text{if n is even } \\     2n-1+sum(n-3,n),              &amp; \text{otherwise} \end{cases} (it should be 2 n-1, so a space between 2 and n) where sum( j,k ) is a ‘partial arithmetic sum’ of the integers from j up to k, that is \begin{cases}     0&amp; \text{if j&gt;k } \\     j + (j+1) + (j+2) + ... + k,              &amp; \text{otherwise} \end{cases} e.g. sum(3,4) = 3 + 4 = 7, etc. Note that sum(j,k) = sum(1,k) – sum(1,j-1) How do I prove or disprove that this is O(n$^2$)? I use a Windows 10 machine remotely at work. Both the local and remote machine are in the same ISP network (not same local network, but same ISP). I've been using it like that for almost a year now and I had never experienced absolutely any issues.  Until recently. I don't know if anything specific triggered this behavior, but I feel that it started happening after I upgraded the remote to W10 1903. I later upgraded the local one as well and I feel that it only made the problem worse (but I don't really have any data).  From time to time, the session will freeze - the image stops updating. However, what I type and mouse clicks are still being sent. No error message is shown whatsoever, the image simply freezes. To make it work again, I have to close and re-open the session. Everything that I had typed and/or clicked while it was frozen is there.  Is there any way I can debug this?