Sudo command wont work
Set myself as owner of /etc with chown command now getting all kinds of errors
What are the advantages of a custom ROM over rooted stock? Why do we say "last night" and not "yesterday night"? As from object, is there a rational reason for saying "last night" rather than  "yesterday night", though you would say "yesterday morning" and "yesterday afternoon"? How to help a toddler overcome the fear of water on head? How close does a particle-antiparticle pair need to be for annihilation to happen? In the experiments for photoelectric emission, the light is incident on one face of the emitting plate, for example the anode, when determining the stopping potential. The electrons are emitted by this face of the plate. Why are the electrons emitted in the direction of the incident light, and not opposite to it?  I have read a little about photons (the key words being, a little), and from what i gather, they have an intrinsic momentum $p=h/\lambda$, which is transferred entirely to the particle that absorbs it (along with the energy $h\nu$). This should imply that the electrons try to move further into the cathode, and not escape it! What is the fault in the reasoning?  Thanks! How to get the caret column (not pixels) position in a textarea, in characters, from the start? How do you get the caret position in a &lt;textarea&gt; using JavaScript?  For example: This is| a text  This should return 7.  How would you get it to return the strings surrounding the cursor / selection?  E.g.: 'This is', '', ' a text'.  If the word “is” is highlighted, then it would return 'This ', 'is', ' a text'. Multiple I2C devices with the same address I have multiple devices with the same address, and only one I2C bus. If I don't want to/can't use an address multiplexer, will the following arrangement work? (sorry for the messy schematic)          &ndash; Schematic created using   SW1 and SW2 are microcontroller I/O, and are pulled low when we don't want to talk to the corresponding IC, and set to high impedance when we do want to talk to that IC. Can anyone see any problems with this, apart from with clock stretching? Assuming you choose diodes with a small voltage drop, like a schottky.  Edit:   Also assuming that the VIH and VIL all worked out with the diode drop and the VOH VOL.   The diodes could also go on the data lines instead, not sure if there would be any benefit/difference (maybe some I2C devices do something special when the clock goes low even if it's not their address? It's probably safer to not clock at all i.e. have the diodes on the clock lines. sed one-liner to delete everything between a pair of brackets? I am working with some text that is full of stuff between brackets [] that I don't want. Since I can delete the brackets myself, I don't need the one-liner to do that for me, but I do need a one-liner that will remove everything between them.  What about parentheses () instead of brackets? I have a number of tiff files named:    sw.001.tif sw.002.tif ...   and I want to remove the .tif at the end of each of the files.  How can I use the rename command to do this? Show that if $f: \mathbb{R} \to \mathbb{R}$ is a continuous injective map, then it is strictly monotonic.    Could someone give me a proof for this? I have the intuition for why it's true - I'm just having trouble expressing that intuition in a rigorous manner. Basically consider two points $x_1, x_2 \in \mathbb{R}$. By the problem statement, $f$ is continuous on $[x_1, \, x_2]$. WLOG, assume that $f$ is strictly increasing. It there exists a point where it is not increasing, then $f$ hits a value twice, and it's not injective. If a car hits a wall at a speed of $v$, and an identical car hits a wall at a speed of $2\,v$, with the kinetic energy equation $E_K = \frac{1}{2}mv^2$ (the speed goes from $v$ to $0$) the second car will lose 4 times the energy, and therefore cause 4 times the damage, but with the force equation $F = ma$ (the car hits the wall and decelerates), it will hit with 2 times the force, and cause 2 times the damage.  How can this be explained? Show that every uncountable set of real numbers has a point of accumulation. I have a SRD-12VDC-SL-C relay with this configuration:  And I want to trigger it with PIR Motion Sensor Detector Module HC-SR501  The problem with direct connection to PIR is, when I connect PIR with 12v DC the Relay remains always ON, i.e. trigger from PIR does not switch it off. And when I connect it via 5V supply the Relay remains always OFF. The trigger output of PIR is 3.3V how can I rectify this problem? by adding some resistor/FETs, or something else. Edit: The voltage at Relay-In(Green) is 10.5V and the relay is OFF it need to go below 9V in order to switch the Relay ON. When I connect it to PIR trigger it goes down to 2.7V (Thus Switching ON the relay, below 9V). And when the PIR trigger of 3.3V comes it goes up to 7.2V but because it is still below 9V) Relay does not switch. How to prove Vandermonde's Identity: $\sum_{k=0}^{n}\binom{R}{k}\binom{M}{n-k}=\binom{R+M}{n}$? How can we prove that     $$\sum_{k=0}^{n}\binom{R}{k}\binom{M}{n-k}=\binom{R+M}{n}?$$   (Presumptive) Source: Theoretical Exercise 8, Ch 1, A First Course in Probability, 8th ed by Sheldon Ross. How do you list the primary key of a SQL Server table? How to generate all permutations of a list? Under what conditions is $AA^T$ invertible? Given a matrix $A$ with dimensions $m \times n$, is $B=AA^T$ invertible if and only if the rows of $A$ are linearly independent?  So far, I've tried writing A as row vectors,   $$A = \begin{bmatrix}v_1\\ v_2\\ \vdots \\ v_m\end{bmatrix}$$  where $B_{i,j} = (v_i v_j) $  The Wikipedia page on the  suggests that the condition I stated above is necessary and sufficient, but does not provide a proof. Does the review queue page show only reviews requiring your action? Does it differ, and when does it? This confusion came up in comments .  On the site I use most actively (RPG.SE), I've noticed that the counts for each review queue appear to only indicate the reviews available to me requiring my action. Just to be clear, I'm talking about this number here:        Since I'm a 10k user, that's pretty easy to tell: even after doing all my reviews, and the review page saying there's 0 items in each queue, I might still have that 10k notice in my top bar saying there's [5] reviews pending, or some other number. So they must still be there, just waiting on other users to finish them, and it just doesn't show them to me. This is fine, I like this behaviour.  However, on Meta SE about an hour ago, there was 1 item in the close vote review queue. I reviewed that item. The count stayed at 1 on the review page. When I clicked to re-enter the queue in case there were new items, I was presented with this:        Another user in that meta question I linked claims this is normal behaviour for them on their own site (Christianity.SE I think?).  What's going on here? Are the review queues supposed to be customised just to what I personally can actually review at the time? Is there a bug, are sites customised differently, or is there just some kind of caching thing leading to a time delay on the review count getting updated? (As they say, it is always caching, but is caching really the culprit here too?) How to really clear the terminal? I can issue the clear command or press Ctrl + L to clear the current Ubuntu terminal, but this just shifts previous output upwards and if you use mouse scroll or PgUP and PgDown keys it's hard to distinguish where the output of previous command ends and output of current command begins.  Is there a way to really clear the terminal so I won't see previous command results? Styling each feature of a layer individually I’ve a PostGIS table which is published as a Geoserver layer. Every feature in the table has some attributes that should style that feature (e.g color, size, opacity, external graphic url, ... etc).  I can create an SLD document and let it read its styling attributes from the table using &lt;PropertyName&gt;, but the problem is more complex than this, for example: some points features need to be styled as a simple circles, while some other need to be styled as external-graphic images. And from the SLD Reference, the SLD PointSymbolizer must have either &lt;Mark&gt; or &lt;ExternalGraphic&gt; element, for that reason I should create two rules one for the simple point symbolizer and the other for the external-graphic point symbolizer, and should add a filter to each rule so that it deals only with the appropriate features, something like:  &lt;FeatureTypeStyle&gt;     &lt;Rule&gt;         &lt;ogc:Filter&gt;             &lt;ogc:PropertyIsEqual&gt;                 &lt;ogc:PropertyName&gt;is-external-graphic&lt;/ogc:PropertyName&gt;                 &lt;ogc:Literal&gt;0&lt;/ogc:Literal&gt;             &lt;/ogc:PropertyIsEqual&gt;         &lt;/ogc:Filter&gt;         &lt;PointSymbolizer&gt;             &lt;Graphic&gt;                 &lt;Mark&gt;                     &lt;WellKnownName&gt;circle&lt;/WellKnownName&gt;                     &lt;Fill&gt;                         &lt;CssParameter name="fill"&gt;                             &lt;ogc:PropertyName&gt;fill-color&lt;/ogc:PropertyName&gt;                         &lt;/CssParameter&gt;                     &lt;/Fill&gt;                 &lt;/Mark&gt;                 &lt;Size&gt;6&lt;/Size&gt;             &lt;/Graphic&gt;         &lt;/PointSymbolizer&gt;     &lt;/Rule&gt;     &lt;Rule&gt;         &lt;ogc:Filter&gt;             &lt;ogc:PropertyIsEqual&gt;                 &lt;ogc:PropertyName&gt;is-external-graphic&lt;/ogc:PropertyName&gt;                 &lt;ogc:Literal&gt;1&lt;/ogc:Literal&gt;             &lt;/ogc:PropertyIsEqual&gt;         &lt;/ogc:Filter&gt;         &lt;PointSymbolizer&gt;             &lt;Graphic&gt;                 &lt;ExternalGraphic&gt;                     &lt;OnlineResource                xlink:type="simple"                xlink:href="smileyface.png" /&gt;                     &lt;Format&gt;image/png&lt;/Format&gt;                 &lt;/ExternalGraphic&gt;                 &lt;Size&gt;6&lt;/Size&gt;             &lt;/Graphic&gt;         &lt;/PointSymbolizer&gt;     &lt;/Rule&gt; &lt;/FeatureTypeStyle&gt;   My question is: Is there any better solution that is more dynamic?