I often work on full disk images, I often need to read and write full disk images on not so capable laptops using a USB-3 disk as my temporary medium.  Duplicating a raw image is probably the fastest way, but I have to deal with limited storage space available.  What I need is high throughput and low CPU usage - compression ratio is not that important for me.  I'd like to have a tool that can very lightly compress the images created - mostly encoding empty space on the disk so that I can only store useful data, while making it as fast as possible - hopefully almost as fast as a raw dd duplication.  I tied to use pxz -1, as it can use multiple CPU cores to speed up the compression, hoping for the fastest compression to still be useful. That doesn't however seem to be as fat as I'd like.  Compressing a 500 GB disk image was estimated to take 21 hours:  mint Backup # dd if=/dev/sda bs=100M | pv -ptera -s500G | pxz -1 &gt; Lenovo-Win8-sda.dd.xz 0:09:21 [9.26MiB/s] [6.54MiB/s] [&gt;            ]  0% ETA 21:34:46   No compression at all predicted 3 hours to complete the imaging:  mint Backup # dd if=/dev/sda bs=100M | pv -ptera -s500G &gt; Lenovo-Win8-sda.dd 0:00:20 [80.2MiB/s] [49.8MiB/s] [&gt;           ]  0% ETA 2:50:20   Using lbzip2 -1 for compresson seems to be slightly faster than pxz -1 with ETA at 15 hours, which is still very slow.  mint Backup # dd if=/dev/sda bs=100M | pv -ptera -s500G | lbzip2 -1 &gt; Lenovo-Win8-sda.dd.bz2 0:00:22 [9.07MiB/s] [9.76MiB/s] [&gt;             ]  0% ETA 14:33:38   Are there any faster compression tools for Linux?
Is it possible to speed up the gzip process?  I'm using  mysqldump "$database_name" | gzip &gt; $BACKUP_DIR/$database_name.sql.gz   to backup a database into a directory, $BACKUP_DIR.  the manpage says:     -# --fast --best             Regulate  the  speed  of compression using the             specified digit #, where -1  or  --fast  indi‐             cates  the  fastest  compression  method (less             compression) and -9 or  --best  indicates  the             slowest compression method (best compression).             The default compression level is -6 (that  is,             biased  towards high compression at expense of             speed).    How effective would it be to use --fast? Is this effectively lowering the CPU usage on a modern computer?   My test results  I didn't notice any acceleration:   7 min, 47 seconds (with default ratio -6) 8 min, 36 seconds (with ratio --fast ( = 9 ))   So it seems it takes even longer to use the fast compression?  Only higher compression really slows it down:   11 min, 57 seconds (with ratio --best ( = 1 ))   After getting the Idea with lzop I tested that too and it really is faster:   6 min, 14 seconds with lzop -1 -f -o $BACKUP_DIR/$database_name.sql.lzo
In D&amp;D 5e &quot;&quot; is a condition that can affect a creature during the first round of combat, only until the end of their turn:  [... T]he GM compares the Dexterity (Stealth) checks of anyone Hiding with the passive Wisdom (Perception) score of each creature on the opposing side. Any character or monster that doesn’t notice a threat is surprised at the start of the encounter. If you’re surprised, you can’t move or take an action on your first turn of the combat, and you can’t take a reaction until that turn ends. A member of a group can be surprised even if the other members aren’t. - PHB 189  Does the action that causes the surprise count as part of the round, though? Say Renee, a rogue, achieves a stealth check of 22, easily beating an orc sentry's passive perception. She sneaks directly behind him and stabs him in the back. Surely the orc isn't surprised at all until the dagger hits him (or if Renee misses, she fumbles around behind him or something). What I think it really boils down to in the end is: when is initiative rolled? If (in our example) initiative is rolled before Renee's attack hits (or misses) how can we justify the orc recovering from his surprise before the action that triggered said surprise even occurs, should he roll better than Renee on his initiative? I'd like to go with initiative is rolled immediately following whatever event began the encounter (which could be an attack, but is likely to often be something else wherever surprise isn't intended), but I can't find any documentation to support this stance.  Why Does Anyone Care? There are many reasons you might want someone to be surprised while you're attacking - in this example if Renee is over L3 (and took the Assassin archetype) she'll get 'Assassinate' if the orc is surprised, and 'Death Strike' if she's over L17. That's a lot of potential extra damage!  that if the orc is surprised, Renee will be able to retreat and hide, without having to take the disengage action as her bonus action to avoid an attack of opportunity. Of course, there's no way for her to know whether the orc is surprised or not at that stage, so trying this would be a bit of a gamble... Make clear which profile data is visible to whom Do compound subjects like "everyone ... and everyone..." take singular or plural verb agreement? Here are the examples of compound subjects:      Everything on the bed and everything in the closet was organised   in under an hour.   Everybody who witnessed the shooting and everybody   in the room were interviewed.   Anyone on the soccer team and   anybody on the basketball team was eligible for the scholarship.   Should I also use was instead of were in the second example? Or the first and the third examples are incorrect that I should use were instead of was. A student of mine has been self-studying some elementary number theory. She came by my office today and asked if I had any hints on how to prove the statement      If $m$ is odd then $\gcd(2^m-1,2^n+1)=1$.    It's been a while since I took number theory and I'm not sure what to do. She said she is learning about congruences, primitive roots, and power residues.  She has not taken any group theory. What is time, does it flow, and if so what defines its direction? Can I use one of my attacks to cast a cantrip? In the D&amp;D campaign I am currently participating in, I am playing as a level 5 high elf champion (I actually just reached level 5 at the end of the last session).  As a High Elf, I got a free cantrip at first level, and chose the firebolt cantrip.  Here's what I'm wondering now: for the purposes of the extra attack feature, does firebolt (and similar cantrips) count as an attack? How to arrive at $\int_{0}^{1} f^3(x) \, dx < (\int_{0}^{1} f(x) \, dx)^2$? Define $f : [0,1] \to \mathbb{R} $ differentiable satisfying $f(0)=0$ and $0&lt;f'(x)&lt;1$. Prove:  $\displaystyle\int_{0}^{1} f^3(x) \, dx &lt; \left(\displaystyle\int_{0}^{1} f(x) \, dx\right)^2$ I found the following answer,  Define $F(x)=\displaystyle\int_{0}^{x} f^3(t) \, dt - \left(\displaystyle\int_{0}^{x} f(t) \, dt\right)^2$ We have $$F'(x)=f^3(x)-2 \left(\displaystyle\int_{0}^{x} f(t) \, dt\right)f(x)=f(x)\left[f^2(x)-2 \left(\displaystyle\int_{0}^{x} f(t) \, dt\right)\right]$$ and $$\left[f^2(x)-2 \left(\displaystyle\int_{0}^{x} f(t) \, dt\right)\right]'=2f(x)\left[f'(x)-1\right]$$ from which we can arrive at the conclusion.  But I felt a little confused. In the past I usually proved the inequality by classical inequalities and something like Taylor expansion to use the condition about derivative. But this answer is little out of my expectation. Do we have other proofs or ideas to arrive at $\displaystyle\int_{0}^{1} f^3(x) \, dx &lt; \left(\displaystyle\int_{0}^{1} f(x) \, dx\right)^2$? And other thoughts about solving these types of issues? I think when we talk about $\left(\displaystyle\int_{0}^{1} f(x) \, dx\right)^2 &gt;\ldots \,$ it's a little difficult to deal with. I don't quite know what tools to use. Long story short: since custom flag responses are messages to users like any other (answer, comment, suggested edit, chat message etc.), users should be notified about them!!    A problem I have with flagging, as it currently functions, is that flaggers are not notified about custom responses to flags, when they are given. I really don't care if I don't find out about every last flag of mine, whether it was marked "helpful" or not, but if a moderator went to the effort of typing out a custom response to my flag, explaining why it was or was not helpful, I'd like to see that response. The logical place for this response would be in the messages inbox (the red number thingy in the top left corner), where other responses to user actions (like answers, comments, edits, and chat messages) go.  This may also help to alleviate  of users not realizing that their flags go somewhere -- while I agree with her that "We shouldn't send notifications for [all] flag responses; that would be way too noisy for a lot of people," I think that in the event of a custom response, the flagger should be notified (because some mod thought that this information was relevant to the flagger), and it would not be too noisy because (in my experience1) most flags do not receive a custom response. This could provide one way that flaggers can be made aware of their flagging history.2    1 I don't know who can see this, but  on Mi Yodeya, to date, is 55 flags total (49 helpful), and only one custom response (....that I didn't see for a while, till I checked my flagging history for a different reason).  2 While I don't think that this will replace Monica's suggestion entirely, it would certainly help it a little.    To give credit where credit is due, while I came up with this idea myself, I did notice that someone else had posted about a similar idea earlier in a .  Edit: Just spotted  from the related questions along the side of the page; note that while that proposal is similar to this one, it was about sending all declined flags to the inbox, while I suggested that only the ones with custom responses should make it to the inbox. How to add a PPA on a server? The server version of Ubuntu does not have the  command. How can I add a  (PPA) to the server without this command? How to do research in two very different fields? How to add an edge ring around a hole What is the easiest way to add/extrude an edge loop around the hole in the first image to make it like the second image? Solve $x\equiv 1\pmod2$, $x\equiv 2\pmod3$, $x\equiv 3\pmod4$, $x\equiv 4\pmod5$, $x\equiv 5\pmod6$ and $x\equiv 0\pmod7$ $$\begin{align*} x&amp;\equiv 1\pmod2\\ x&amp;\equiv 2\pmod3\\ x&amp;\equiv 3\pmod4\\ x&amp; \equiv 4\pmod5\\ x&amp;\equiv 5\pmod6\\ x&amp;\equiv 0\pmod7\\ \end{align*}$$  So the solution says we can eliminate $x\equiv 5(\bmod6)$ because the first two cases cover it, but I don't really know how it does. How do we solve it in cases like this where the moduli are not mutually relatively prime. Prove that a polynomial is irreducible or the field contains a $p$th root An exercise from Lang:  Let $k$ be a field. Let $n$ be a nonnegative integer. Consider the polynomial $x^{p^n}-a \in k[x]$. Assume that $\text{char}(k) = p &gt; 0$. Prove that either the polynomial $x^{p^n}-a$ is irreducible over the field $k$ or there exists a $b\in k$ such that $a = b^p$.  How to prove this statement? I am a little bit confused with this statement. Can US stocks list on one stock exchange but trade on other US stock exchanges? I am trying to understand how the US stock market works. From my understanding, there is one stock exchange where a company is &quot;listed&quot;. This stock exchange listing requires the company to adhere to the regulations of the stock exchange where it is listed. Once a company is &quot;listed&quot;, its shares can start to trade on any stock exchange. For example, once a company lists on NASDAQ, its shares can be traded on NASDAQ, NYSE, Boston Stock Exchange, Philadelphia Stock Exchange, National Stock Exchange, EDGX Exchange, EDGA Exchange, NYSE Arca, etc. Is my understanding correct? Is it true that once a stock is listed on a US stock exchange, the stock can then trade on any US stock exchange? Consider the Level 2 quotes for Microsoft (NASDAQ: MSFT). Microsoft is only listed on NASDAQ, but it also trades on the NYSE and other stock exchanges:  My questions are:  Does this mean that companies only need to be listed on one stock exchange in order for their stock to trade on other stock exchanges?  If so, do companies need to adhere to the &quot;listing requirements&quot; of all the stock exchanges where their stock is traded, even though they are not &quot;listed&quot; on those stock exchanges? Does Microsoft have to follow the listing requirements of the NYSE even though it is not listed there?  If stocks can trade on any US stock exchange regardless of which US stock exchange the stock is listed on, why don't NYSE-listed companies reduce their yearly listing fees by listing on NASDAQ instead? I accidentally set an object as camera, how do I undo this? messenger()->addMessage not working after a $form_state->setResponse In the submitForm of a custom form, I have this:    switch ($form_state-&gt;getValue('suscribe')) {   case 0:     $iStatus = 1;     break;   case 1:     $iStatus = 3;     $sFileName = 'sites/default/files/_private/bulletins/' . $form_state-&gt;getValue('adherent')[1] . ".pdf";     $response = new BinaryFileResponse($sFileName);     $response-&gt;setContentDisposition(       ResponseHeaderBag::DISPOSITION_ATTACHMENT,       'bulletin.pdf'     );     $form_state-&gt;setResponse($response);     break; }  $storage = \Drupal::entityTypeManager()-&gt;getStorage('member'); $id = $form_state-&gt;getValue('adherent')[0]; $entity = $storage-&gt;load($id); $entity-&gt;status = $iStatus; $entity-&gt;save();  \Drupal::messenger()-&gt;addMessage($this-&gt;t('Your wish has been recorded.'));   suscribe is a Yes/No radio button. $form_state-&gt;setResponse($response); triggers the automatic download of a pdf document.    The message (Your wish...) is correctly displayed in case 0. In case 1, the message shows only if I refresh the page (or go to another page). How can I have the message displayed without doing another action after submitting the form in case 1?    By the way, database is correctly updated in both cases. I'm using Drupal 8.6.10. Where does the question mark go — inside or outside the parentheses? Let's say I have a generic member in a class or method, like so: public class Foo&lt;T&gt; {     public List&lt;T&gt; Bar { get; set; }          public void Baz()     {         // get type of T     }    }  When I instantiate the class, the T becomes MyTypeObject1, so the class has a generic list property: List&lt;MyTypeObject1&gt;. The same applies to a generic method in a non-generic class: public class Foo {     public void Bar&lt;T&gt;()     {         var baz = new List&lt;T&gt;();                  // get type of T     } }  I would like to know what type of objects the list of my class contains. So what type of T does the list property called Bar or the local variable baz contain? I cannot do Bar[0].GetType(), because the list might contain zero elements. How can I do it? Is PCA still done via the eigendecomposition of the covariance matrix when dimensionality is larger than the number of observations? I have a $20\times100$ matrix $X$, containing my $N=20$ samples in the $D=100$-dimensional space. I now wish to code up my own principal component analysis (PCA) in Matlab. I demean $X$ to $X_0$ first.  I read from someone's code that in such scenarios where we have more dimensions than observations, we no longer eigen-decompose the $X_0$'s covariance matrix. Instead, we eigen-decompose $\frac{1}{N-1}X_0X_0^T$. Why is it correct?  The normal covariance matrix is of size $D\times D$, each element of which tells us the covariance between two dimensions. To me, $\frac{1}{N-1}X_0X_0^T$ is not even of the correct dimensions! It is $N\times N$ matrix, so what would it tell us? Covariance between two observations?! One word/phrase to describe the reaction when you eat a very spicy-hot food I've read the discussion here about .  I've also read this one: .  But I did not find any word or phrase that describes the reaction someone has when eating a too spicy-hot food. You know, they tend to sweat, catch their breath, and even sometimes shed tears; due to the spiciness of the food.  So my questions:        What do you say to describe the reaction someone has when being excitedly "suffered" by a very spicy-hot food? In Indonesian, we would call it kepedasan.   What do you say when you get that thing [the answer to question 1] with you, other than the list I enclose below:                Oh, spicy!     My God, it's spicy-hot!                      Is that it?