I guess that my mail server is unprotected and spammers are using my mail server to spam myself
Fighting Spam - What can I do as an: Email Administrator, Domain Owner, or User?
Age replacement policy for hard disks and SSDs at servers I'm planing an age replacement policy for our storage and servers. Most of them are for DBs and some for images (static content) so yes, they have an huge I/O everytime.  Also, we use Samsung 840 Pro SSDs for the RAID Controllers (PERC H700i) as CacheCade.  Are you guys managing the replacement of old hard drives and solid state drives? Noether's Theorem: Lie groups vs. Lie algebras; finite vs. infinitesimal symmetries I've had a brief look through similar threads on this topic to see if my question has already been answered, but I didn't find quite what I was looking for, perhaps it is because I'm finding it hard to put words on my question and I hope that you will be able to help me ask it clearly.  I'm trying to link what I know from mathematics to what we are writing in physics for Noether's theorem. If I understand correctly we are looking at the symmetries of the action i.e. under which symmetry groups is it invariant. Noether's theorem allows us to calculate a conserved current in the case of a continuous symmetry (Lie groups), by means of so-called infinitesimal symmetries which I believe to be elements of the Lie algebra (so the tangent space to the neutral element) of the Lie group.  I'm guessing that if the action is invariant under the symmetry then it's "variation" should be 0 when we vary the system (space-time coordinate, or field) using this symmetry; it is exactly this step that I would like to understand better, how can I formalize this step correctly mathematically? How should I understand this variation, and how does it's calculation give rise to the elements of the Lie algebra? How are digital movies sent to a movie theater? For many years, movies were stored on rolls of film that were physically mailed to theaters. Now, most theaters project their movies digitally. But how are these digital movies sent to the theater?   Do they mail a hard drive to the theater? Do they give the theater a username and password to a super secret website where they can download it? How does it get there? If $f:\mathbb{R}\rightarrow \mathbb{R}$ is differentiable and $\lim_{x\to \infty } f^\prime(x)=0$ show that $\lim _{x\to \infty } (f(x+1)-f(x))=0$. Having some trouble proving this:     If $f:\mathbb{R}\rightarrow \mathbb{R}$ is differentiable and $\lim_{x\to \infty } f^\prime(x)=0$ show: $\lim _{x\to \infty } (f(x+1)-f(x))=0$   Attempt: from $\int \lim _{x\rightarrow \infty } f^\prime(x) \mathrm{d}x=0$ we can say that $f^\prime(x)=const$ would we then have to show that  $\lim _{x\to \infty } (f(x+1))$ is also a constant? From there if we show that both are equal then the difference is zero. I am on the right track?  Thank you for the help. What is a session 0? What is a "Session 0"?   When is it done? What does it contain? Is it recommended, if not mandatory? What is each person's role (DM/GM, players, etc.)? What topics are best discussed there?   Usually with my groups, we go directly to the meat of the game right after the character creation, but I see a lot of answers that basically say "you should have a session 0", but it's never explained what it is made of, so it's kind of an enigma for me. Man travelling alone across a planet, thinks about a fearsome creature that he hears behind him About fifteen years ago I read a short story about a man on a planet (possibly Mars or the Moon), travelling alone between bases. It's written in the first person and as he's walking across the planet, he's thinking to himself about this fearsome creature that preys on people. It sneaks up on them, makes some noise and then attacks them. Just as he turns the final corner of the canyon he was walking through and sees the door to the other base, he hears the creature behind him making its noise and the story ends.  It was in a short story collection but I don't remember the name of the story or the book it was in. Any help would be much appreciated. Why pendulum does not follow SHM for larger angular displacement? Considering an ideal case(neglecting drag of air, damping etc.), a pendulum follows SHM if the angular displacement is small (upto 10 degrees). But, for large angular displacement(more than 10 degree), it does not follow SHM. Why? What force cause the pendulum not to follow SHM? What should be done with questions that have been resolved as a comment instead of an answer? I'm trying to go through and provide answers to every unanswered question (search &quot;closed:0 answers:0&quot;), somewhat following the spirit that was blogged about at  .  However, I'm finding this much more difficult than it needs to be, as many of the questions have already been answered without the use of an &quot;answer&quot; - but instead, in the form of a comment by either the OP or another poster. I wouldn't mind reading through and skipping these, as long as there was some appropriate action I could take to at least assist with preventing these questions from being seen again from the same query - either by myself or another SO member.  Is there such an appropriate action?  Should we vote to close?  If so, using what reason? Even if I vote to close, what are the chances that 4 other users will also view the question and also vote to close?  (i.e., will my individual vote even do any good?  Is there any report to show recent close votes, so that others may also review and contribute supporting close votes?) Should we post some sort of an answer - even just something to the effect of &quot;this was already answered by the OP's own comment to his answer (above)&quot;? Would something like this be appropriate to flag for moderator attention, and let the moderators deal with it?  (Or would this be considered too trivial?) Should we rename the question title to something standard that can be used in a search exclusion?  (Maybe &quot;SOLVED:&quot;?)  Basically, how can I help to denote questions as &quot;This question is no longer in active search of an answer - though better answers may still be appreciated.&quot;? I've already reviewed , which was closed as a duplicate of  - but this requires effort on part of a user who may very likely no longer be active. Otherwise, is there something I should be doing to improve my search to filter out these types of questions? I've run across this many times, so I don't consider it to be a rare issue.  However, the last question like this I just ran across, prompting this question, was .  In this case, the question was self-answered by the OP in the form of a comment, this question is the OP's only question, the OP has no other visible activity on SO, and the OP hasn't been seen on SO since he registered and posted the question 5 months ago. Another one I just ran across is .  However, here the &quot;answer&quot; comment was posted by a reputable and recently active SO member.  Should I leave a comment directed at him, asking him to re-post his comment as an answer, or should I post my own answer echoing his comment?  (Or something else?) Yet another is .  Interestingly, the OP actually self-edited the question to include the &quot;SOLVED:&quot; prefix on to the question, instead of posting his resolving comment as an answer (and ideally accepting it) as he was asked to do by another comment.  This brings up another good idea - is there a &quot;standard&quot; we should use to rename the titles on these &quot;resolved but unanswered&quot; posts that could be used as a search exclusion?  (Also added to the above list.) Can the Force be used to fly? In The Empire Strikes Back Yoda uses the Force to lift Luke's X-Wing out of the water and put it on land.  In Attack of the Clones and in many instances in the second series of The Clone Wars, Anakin (and others) use the Force to jump higher than they could otherwise, or to jump from very high locations, but I don't think I've ever seen the Force used for outright self-levitation.  But if Yoda could lift the X-Wing, shouldn't a strong Jedi be able to lift himself and, essentially, fly with the help of the Force? Why can't variables be declared in a switch statement? Create an encrypted ZIP file in Python Permanently mounting loop device I created a file   touch /datastore/virtual/pseudoblock   created a loop device with it  sudo losetup /dev/loop0 /datastore/virtual/pseudoblock   (although I got a warning about its size)  and then initialized it with random data  dd if=/dev/urandom of=/dev/loop0 bs=1M count=100   My questions are  a) why is it not displayed yet in my block devices' list?  NAME                     MAJ:MIN RM   SIZE RO TYPE  MOUNTPOINT sdb                        8:16   0 489.1G  0 disk   ├─sdb2                     8:18   0   488M  0 part  /boot ├─sdb3                     8:19   0 488.1G  0 part   │ └─sdb3_crypt           253:0    0 488.1G  0 crypt  │   ├─ubuntu--vg-root    253:1    0 472.2G  0 lvm   / │   └─ubuntu--vg-swap_1  253:2    0  15.9G  0 lvm   [SWAP] └─sdb1                     8:17   0   512M  0 part  /boot/efi sda                        8:0    0 931.5G  0 disk   └─sda1                     8:1    0 931.5G  0 part     └─sda1_crypt           253:3    0 931.5G  0 crypt      └─store--vg-store1tb 253:4    0 931.5G  0 lvm   /datastore   b) how can I permanently mount it via /etc/fstab since I cannot get its UUID?  $ blkid /dev/mapper/sdb3_crypt: UUID="fSHjbj-51K2-QfhI-G0Wb-o3lN-4pE1-BB4wCP" TYPE="LVM2_member" /dev/mapper/ubuntu--vg-root: UUID="9e452886-4d8g-fj54-854c-80bc171826e8" TYPE="ext4"   working on   $ lsb_release -a No LSB modules are available. Distributor ID: Ubuntu Description:    Ubuntu 16.04.5 LTS Release:    16.04 Codename:   xenial   with  $ uname -a Linux pkara-pc01 4.15.0-42-generic #45~16.04.1-Ubuntu SMP Mon Nov 19 13:02:27 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux I am aware of what hyperfocal distance is and the general principles behind it. However, most of the tutorials I have seen and read regarding it make use of lenses with focus distance indicators. Unfortunately, neither of my lenses (Nikkor 18-55mm &amp; 35mm f1.8) have indicators.  I have read that you can 'cheat' and simply focus a third of the way into the shot (which I have done previously simply by spot-focusing on the lowest focus point in my VF). I also assume you could pace out the distance and note an object to focus on when you get back to the camera (though that might be easier said than done).  Does anyone have any suggestions on how to achieve maximum sharpness from front to back without focus distance markers. A new lens is not an option; global economic crisis and all that! It seems that they can all mean "easily provoked to anger"  irascible：Easily provoked to outbursts of anger; irritable.  fractious：Irritable; argumentative; quarrelsome.  irritable：1.Capable of being irritated. 2.Easily exasperated or excited.  atrabilious：1.Characterized by melancholy. 2.ill-natured; malevolent. which vectors are perpendicular to each other?  $\vec a = (1, -2, 3)$, $\vec b = (5, 4, 1)$, $\vec c = (1, 0, -5)$  Do i just take the dot product of 2 of them. If the dot product they are at $90^\circ$? But how do i know if there perpendicular? How can I move my /home directory to another partition if it's already part of the / partition? I have a wonderful running Maverick Meerkat install going on right now. I want to move my /home to another partition as per many suggestions.   How can I go about doing this without reinstalling the entire Ubuntu system? Can I simply create the partition with gparted and then change the mount point of /home in fstab to reflect it or is it a bit more difficult? Getting a File's MD5 Checksum in Java I am looking to use Java to get the MD5 checksum of a file.  I was really surprised but I haven't been able to find anything that shows how to get the MD5 checksum of a file.  How is it done? Ethernet device not managed I am using Ubuntu 16.10 and recently I have not been able to connect to internet using Ethernet. The network manager shows device not managed. The WiFi network is working fine.      I've tried the solution from this questionn  with no use.  My /etc/network/interfaces file:  # interfaces(5) file used by ifup(8) and ifdown(8) auto lo iface lo inet loopback   My /etc/NetworkManager/NetworkManager.conf file:  [main] plugins=ifupdown,keyfile,ofono dns=dnsmasq  [ifupdown] managed=true   Output of nmcli d:  DEVICE  TYPE      STATE      CONNECTION  wlp2s0  wifi      connected  eduroam     enp8s0  ethernet  unmanaged  --          lo      loopback  unmanaged  -- I am trying to construct a theoretical Diffie-Hellman key exchange protocol. However, i cannot understand the difference between choosing an additive group or a multiplicative group. I believe an additive would make it much more simple, but would a multiplicative group make it more difficult to break? What would be the difference between the use of those 2 kinds of number groups? If $\forall x \in R, x^2-x \in Z(G)$, than $R$ is commutative Let $R$ be a ring such that for every $x\in R$ we have $x^2-x \in Z(G)$. Show that $R$ is a commutative ring.    My thoughts  What should I do? I could show that every $y \in R$ could be written in the shape $x^2-x$ but I don't know if that is true. We know that  $y \cdot(x^2-x) \ = \ (x^2-x)\cdot y$ for any $x,y \in R$, but that doesn't mean that $xy = yx$. Please give me a hint