Why isn't $1 \to \mathbb{Z}_2 \to \mathbb{Z}_4 \to \mathbb{Z}_2 \to 1$ a split extension?
Exact sequence splits?
Ubuntu 14.04 System Logging I've set up an Ubuntu 14.04 Server (from an Ubuntu 12.04 Server) but today I wanted to look in the auth.log but this file is not used. It seems that ´syslog´ was deleted.  How does Ubuntu 14.04 log? I need this for a server.  Thank you. In order to animate a character so that it grabs an object an throws it, I added a Child-Of constrained and keyframed its influence. In the F-curve Editor I can't set the curve which controls the influence to interpolation-mode Constant without changing the other curves (Which should be linear or bezier).   How can the interpolation mode of a curve changed independently? What does each AMS package do? In my view, any document with a substantial amount of mathematics should load the packages from AMS-TeX. Hence, most of my document's preambles contain  \usepackage{amsmath, amsthm, amssymb, amsfonts}   (I could add to that the non-AMS mathtools, etc.). What do each of those packages do? Do I really need to list all of them, or do some of them load others? In particular, does any package load all of them, so that I can simply type  \usepackage{ams-everything}   shorter than the current list? How can I diagnose and repair missing drive space? What geometric object is given by this equation? What geometric object is given by this equation?  $x^2+y^2+z^2+2xy+2xz+2yz-x-y-z-6=0$  Maple says it's a hyperboloid of one sheet, but is there a way to show it without going the long way by using the principal axis theorem? Run TTY script every time I open a GUI terminal When I log in to a TTY I get the following nice text:  Ubuntu 16.04.03 LTS Log-in: username Password: Last log-in date/time Welcome to Ubuntu 16.04.03 LTS   * Documentation:  * Management:  * Support:  9 packages to update 4 updates are security updates   I would like the last 2 lines repeated every time I open a GUI terminal for all users in the adm group (but will settle for having the entire thing displayed each and every time I open a GUI Terminal for all users)  I tried the obvious:  fab-root@fab-ux-predator:~ $ cd /etc/update-motd.d/ fab-root@fab-ux-predator:/etc/update-motd.d $ ./90-updates-available  fab-root@fab-ux-predator:/etc/update-motd.d $ cat /var/lib/update-notifier/updates-available cat: /var/lib/update-notifier/updates-available: Permission denied fab-root@fab-ux-predator:/etc/update-motd.d $   What am I missing?  P.S. Obviously I can chmod o+r the file, but how future-proof would that be? I am making a test where I am asked to add the missing words.     [...] chair is [...] useful piece of furniture.    I would have said that a is the missing word in both the cases, but the test says the words I should have added are the and a respectively.     [...] last time I saw [...] bear, I was travelling in [...] Europe.   I would have added: nothing, a, nothing. The correct answer is: the, a, nothing.  Why is the the correct article to use in both the sentences? Extract URLs from text in PHP I'm looking for a source/spec that can tell me what CSS properties can applied to which HTML elements.  For instance, the css property; "overflow".  I know I can apply this to div, p, textarea but what other elements can I apply this too?  Is there a spec somewhere I can reference? Now that I'm looking into home automation, I'm thinking about automatically cutting off the fridge power from 3am ~ 5am. Given that modern refrigerators are well insulated, it should be able to withstand 2 hours of non powered cooling.  If I proceed with this project, will I see a big reduction in my monthly electrical bill? MD5 Hash outputs not produced Are there any hash outputs not produced by the MD5 hash function? I need to use it as a placeholder for an empty hash while comparing two hashes. Busy Device on Umount I often experience a problem to umount a directory:  umount /mnt/dir umount: /mnt/dir: device is busy   There are many reasons why the device is busy. Sometimes there are processes running which have open locks on it, sometimes there are other directories mounted on top of /mnt/dir.  My question:  What are the steps to check why a directory couldn't be unmounted.  I know there are many reasons, but it's ok if you explain a specific solution.  [EDIT]  [X]  running processes on mounted volumes.   [X] another volume is mounted on top of a volume we want to unmount   [_] NFS locks the volume we want to unmount How to add days to current Date using JavaScript. Does JavaScript have a built in function like .Net's AddDay? How can author deal with late reviews? Another problem I personally struggle with in peer-review publication process is the situation when review takes really, really, really long. The precise definition of "long" is probably very area-specific: for example a paper in Maths will probably took longer to review than one in Physics. Many well-established journals and major publishers, sadly, prefer not to specify the "rules of the game" precisely, particularly how long the review process should normally take. Fortunately, I quite often serve as a referee with the very same journals and know the amount of time I am given to write a review. Unfortunately, when I am an author, I do not observe these deadlines to be always met. For example, a notable U.S. publisher would ask a reviewer to send a review in 2 months; but in practice a first review of my paper once took as long as 8 months.  As a rule of thumb, I usually start writing to editors with questions about "the status of my paper" in X+1 months time, when X is a deadline time for a reviewer to submit a review. This strategy is not particularly successful &mdash; what I usually get is a recommendation to be more patient. Since there is no "official" deadline time announced, there is no formal ground for complaints here.  Of course, such delays lead to a whole bunch of funny situations, particularly if a preprint is put online (e.g., on arXiv) and the results are presented in some conferences. Follow-ups with no official paper to cite, grant applications in which you can not justify by a solid publication, good research but bad bibliometrics or CV, to name just a few.   Could you recommend an efficient way to deal with this problem? How do I Sort a Multidimensional Array in PHP How to Set a Short User Password in macOS Mojave and Later (10.14+) I just installed macOS Mojave and put in my usual short desktop-only password I've been using for years (yes, you read that right). Now though, the operating system rejects setting a password less than 4 characters. It also does not allow having no password at all.  I am completely comfortable using the shell if need be.  How can I change the password policy to allow quite short passwords? How do I delete all empty directories in a directory from the command line? Say I have a directory named foo/. This folder includes subdirectories. How can I delete all the empty directories in one command? Is it appropriate to ask questions about software licenses/licensing on ? Or is the appropriate place  ? Or is there no appropriate site currently and we should suggest such a site on ? I have notifications in the OSX Notification Center, as for most of my apps I am using the setting, "Show in Notification Centre: 10 Recent Items" This is a good setting but rather than have a very full Notification Center, I would still like to clear it from time to time with 1 click.  I am using Yosemite 10.10.3 Blocking web sites with Windows Firewall