Lot of articles recommend deactivating ssh for root user with PermitRootLogin no in /etc/ssh/sshd_config. There is also a lot of questions on serverfault about implementing root ssh deactivation.   But what is motivation for that?  It makes the attacker to guess the user name in addition. But shouldn't the cryptographic strength of public-private keys and RSA encryption be enough?  I am asking not just out of curiosity, but because using non-root user : pipelining (compatibility) or allow_world_readable_tmpfiles(security).
I have recently found an argument against disabling a root user login in Linux at   I assume that, if everybody uses a public key authentication, there's no risk at losing the root password.  Is it always better to disable the root login via ssh?
What command(s) would you use to extract all of the usernames from a database called /etc/passwd and then sort this output alphabetically in reverse order? I am writing a client-side Swing application (graphical font designer) on Java 5. Recently, I am running into java.lang.OutOfMemoryError: Java heap space error because I am not being conservative on memory usage. The user can open unlimited number of files, and the program keeps the opened objects in the memory. After a quick research I found  and others saying on Windows machine the JVM defaults max heap size as 64MB.  Given this situation, how should I deal with this constraint?  I could increase the max heap size using command line option to java, but that would require figuring out available RAM and writing some launching program or script. Besides, increasing to some finite max does not ultimately get rid of the issue.  I could rewrite some of my code to persist objects to file system frequently (using database is the same thing) to free up the memory. It could work, but it's probably a lot work too.  If you could point me to details of above ideas or some alternatives like automatic virtual memory, extending heap size dynamically, that will be great. Why is there an unexplainable gap between these inline-block div elements? "is" vs "are" when followed by a number I read the following sentence on YouTube and initially thought it was grammatically incorrect:     Here are 10 minutes of the movie Black Hawk Down!   I thought "are" should have been "is" but then I realized minutes is plural so the plural form, are, is used correctly. I also thought how most people would naturally say "Here is ten dollars in change" but is the use of the singular form, is, correct since dollars is plural?   Am I misunderstanding a rule? I used the inbuilt dataset stackloss here. I used following R code for creating the multiple regression model.  &gt; head(stackloss)   Air.Flow Water.Temp Acid.Conc. stack.loss   1        80         27         89         42   2        80         27         88         37   3        75         25         90         37   4        62         24         87         28   5        62         22         87         18   6        62         23         87         18  &gt; fit &lt;- lm(stack.loss ~ .,data=stackloss) &gt; plot(fit)   And when I plot the model, the four following graphs are displayed.      How to interpret these graphs? What are the significance of these graphs? How to use these graphs? (exercise from Tao's analysis book) Proof of a lemma relating to power set of X How to determine the cause of MacBook battery not charging? I see that the question &quot;why is my MacBook not charging?&quot; gets asked a lot. The problem is, there are multiple reasons. Possible points of failure are: charger, cable, magsafe connector, DC input board, logic board, battery. (Have I missed any?). What is the best sequence for a user to follow, to diagnose the problem? By way of example, here are the first steps that I usually try:  Make sure the charger is working. Either use your charger on a different Mac, or test a spare charger with your Mac.  Check the connection. There might be gunk in your port that's stopping the connector from lying flat.  Try resetting the SMC and PRAM.  If the computer boots, run Coconut Battery to determine battery status.   This is where I get a bit stuck. For example, I have a machine here that boots fine when plugged in, but not from battery. Disconnecting the MagSafe causes the machine to switch off. Sounds like it's a dead battery, except that Coconut reports the battery as detected, in good condition, but not charging. What steps should I take next? Specifically, I'm asking for a generic algorithm to help determine the source of the fault (preferably without swapping out lots of components one by one)? Noticed in :         is 320, shown 322. Also locked in 2013.  And then :         has a score of 179, shown 180.  has a score of 123, shown 122.  Neither of these posts got any votes recently. Does causation imply correlation? Correlation does not imply causation, as there could be many explanations for the correlation. But does causation imply correlation? Intuitively, I would think that the presence of causation means there is necessarily some correlation. But my intuition has not always served me well in statistics. Does causation imply correlation? Sorting list based on values from another list How to get the file name and a line number of a function call? I've bent (again) my derailleur hanger. It's a replaceable hanger but for this summer I can't get an original one and I know that the non-original one I can get is made in a harder material and could possibly damage the frame.  So I'm left with the choice of straightening this light aluminium alloy thing. How do I do that without breaking/weakening it? I listened to this on audiobook and it was great.  The premise was a human ends up travelling to an alien planet. The aliens have a perimeter to their 'base' that is under constant attack from the planet's animals. It is revealed towards the end that there is some sort of signal being transmitted that is making all the animals and plant life attack a certain point on the planet (where the aliens are).   Other major plot points I remember: The human traveller falls in love with an alien. The aliens have a sort of virtual training environment that simulates life outside the perimeter, where plants attack you etc. There is a secondary alien group that the human ends up with, and although they are rivals to other group, they have a trade set up.   Any help much appreciated! Thanks. Can I remove a digital signature from a DLL? How can I count all the lines of code in a directory recursively? ggmap: create circle symbol where radius represents distance (miles or km) The result of ls * , ls ** and ls *** I know using the command ls will list all the directories. But what does the ls * command do ? I used it and it just lists the directories. Does the star in front of ls mean how deep it will list the directories? Let $U = \{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12\}$, and $f$ be a function from $U$ into $U$.   Finally, let $F : P(U) \to P(U)$ be the function defined by  $$F(X) = \{f(x) | x \in X\}$$  For instance, if $f(x) = 13 − x$, and $X = ${1, 3, 4, 7}, then $$F(X) = \{f(1), f(3), f(4), f(7)\} = \{12, 10, 9, 6\}$$  Show that $F(A−B)$ is not necessarily a subset of $F(A)−F(B)$.    I am having trouble showing an example. Let's say:  $A = \{1,3\} , B = \{2,3\}$  $F(A) = \{f(1),f(2)\} = \{12,11\}$  $F(B) =\{f(2),f(3)\} = \{11,10\}$  Now, $F(A-B) = \{12,10\}$  $F(A)-F(B) = \{12\}$.  Hence, $\{12,10\} \nsubseteq \{12\}$ &lt;-- hmm..  By definition if $A \nsubseteq B$, there exist an $x \in A$ such that $x \notin B$. From my example, we have $x=10 \in A $ but $\notin B$. Is that sufficient?     I'm confused between the difference of $F(A-B)$ and $F(A)-F(B)$. Can I use a variable which has a non-linear relationship to the dependent variable in logistic regression? Let's say I am building a logistic regression model where the dependent variable is binary and can take the values $0$ or $1$. Let the independent variables be $x_1, x_2, ..., x_m$ - there are $m$ independent variables. Let's say for the $k$th independent variable, the bivariate analysis shows a U-shaped trend - i.e., if I group $x_k$ into $20$ bins each containing roughly equal number of observations and calculate the 'bad rate' for each bin - # observations where y = 0 / total observations in each bin - then I get a U shaped curve.  My questions are:   Can I directly use $x_k$ as input while estimating the beta parameters? Are any statistical assumptions violated which might cause significant error in estimating the parameters? Is it necessary to 'linearize' this variable through a transformation (log, square, product with itself, etc.)? When I get a third party app it says it needs to be verified before I can use it but when I go to settings to verify I tap verify and nothing happens. Is there something I can do so I don’t have to constantly reinstall my apps?