Command 'sudo' not found I tried to install sudo with apt install sudo but it won't work. I got these errors: E: Could not open lock file /var/lib/dpkg/lock-frontend - open (13: Permission denied)   E: Unable to acquire the dpkg frontend lock (/var/lib/dpkg/lock-frontend), are you root?  I am always required to give root access whenever i want to open some files in the terminal but i can't do that without sudo
Can sudo be reinstalled after being removed? This seems to be a chicken-egg problem. The most common task using sudo is installing and removing software.  sudo apt-get purge &lt;appname&gt;   But sudo itself can be removed.  sudo apt-get purge sudo # Do not run this command on production computers!   This is where the fun comes  ubuntu@ubuntu:~$ sudo bash: /usr/bin/sudo: No such file or directory   Although it's obvious that no person in his right mind will purge sudo (other than me), someone can be fooled to run this command (not directly, in its hex mode, or whatever it's called) or a person could SSH in disguised as tech guru and do the mess.  So is there a way of reinstalling sudo?
How can I get form data with JavaScript/jQuery? Show a message if directly accessing a deleted answer or comment Currently, if you access a deleted question you will get a short message informing you that the question has been deleted. However, if you click on a direct link to a deleted answer or comment (which you can get via notifications), nothing is displayed.  This is naturally quite confusing as you will get the message about a new answer or comment via notifications, click on the link and simply see nothing.  Therefore, I propose to display some sort of message to the user, informing her/him that the answer or question has been deleted. Note that this is different from always showing a deleted answer/comment, as I specifically request it in case you access the specific URL.  One example for a comment would be:   One example for a deleted answer is:   This question is related to ,  but requests a feature to circumvent the problem altogether. Exponent and abelian groups What is inverse CDF Normal Distribution Formula Let $M$ be a positive, continuous martingale that converges a.s. to zero as $t$ tends to infinity. I now want to prove that for every $x&gt;0$ $$ P\left( \sup_{t \geq 0 } M_t &gt; x \mid \mathcal{F}_0 \right) = 1 \wedge \frac{M_0}{x}. $$ My approach: I thought that rewriting the conditional probability to an expectation would help so we obtain that we must prove: $$ \mathbb{E} \left[ 1_{\sup_{t \geq 0 } M_t &gt; x}  \mid \mathcal{F}_0 \right] = 1 \wedge \frac{M_0}{x}.$$ A hint to me was given that I should consider stopping the process when it gets above $x$. Thus a stopping time that would do this is $\tau = \inf\{t\geq 0 : M_t&gt;x\}$. But now I'm stuck as I want to apply optional sampling results but we have an indicator which complicates things. How could I proceed from this? Any help is appreciated! This is an attempt to write a canonical QA for this issue, as per the Meta post:   I expect it to be periodically edited with the goal of becoming a comprehensive information resource.  I have a MacBook Pro that has a key(Shift, Return,   Command, P, etc.) that doesn’t respond when pressed or is stuck in the down position.    It's possible that my favorite beverage was spilled (or some other liquid damage).  It's also possible that I have no idea what happened.  It was working yesterday and suddenly today it's no longer working.  Is there any way to bypass or remap the key?  Can I  have the system ignore it completely?  (This question can also apply to external USB keyboards or the Bluetooth keyboards) I am trying to calculate the last two digits of $3^{400}$, but working $\bmod {100}$ is proving intractable. I did the last digit case pretty handily, and now I'm stuck at last two. Friendly error page to replace WSOD This should be the easiest thing to do, but for some reason I just can't get it done.  I'm trying to get a friendly static error page to replace nasty 500 scenarios. For now I'm just trying to replicate a 500 situation on my local machine (Drupal 7 running on MAMP) by throwing in some crap characters on the top of my template.php in my theme, which does trigger a 500 situation, but for some reason the ErrorDocument directive in my .htaccess or Apache config file has no effect.  What I'm doing is quite simply this:  ErrorDocument 500 /500.html   And I have the simplest ever static html-page in the root of my site with the name of 500.html.  Still, when I intentionally break template.php, I get the dreaded White Screen Of Death instead of my nice friendly error page.  What am I doing wrong here? I've done this a billion times in non-Drupal setups but just can't get my head around this one. Let's say that I have a folder, within my Documents folder, that has files I want no one to access without a password.  Is there a way to lock down that folder so that it's password protected / encrypted?  In fact, is it possible to password-protect any individual folder? Over on another network site, a helpful user corrected the grammar of .  The answer now says     I believe it's valid.   where I originally wrote     I believe it valid.   Is the original sentence gramamatically (or at least idiomatically) correct or do I absolutely need a form of 'to be' here? (What's more, is 'to be' a copula or an auxiliary verb if used like this?)  I am quite certain that I have seen sentences like the original one in the past, but I am uncertain where. Given that I am frequently exposed to the somewhat made-up English of authors in the fields of sci-fi and fantasy, I might have fallen into a trap here.  Edit: I don't doubt that the correction is valid and enhances readability. The Monty Hall Problem - where does our intuition fail us? After the  of registering an account to book train tickets online using my British VISA card, I finally got into a position of being able to book a ticket, but what it appears to be telling me is that I'm only being added to a wait list, which I assume means my tickets aren't confirmed.  Can someone explain how the wait list works, and what my chances are of getting on the train successfully?    It currently says the wait list is 7 The train is the Mandor Express, from Delhi to Jodhpur on the 18th of Nov   Update: So I got the train! Although it didn't get confirmed until a few hours before it was due to leave. Find the number of solutions of $\sin x+2 \sin 2x- \sin 3x=3$ I've been wondering what makes the  such an important model. What I came up with:   It is a (relatively) simple system, making it a perfect example for physics students to learn principles of classical and quantum mechanics. The harmonic oscillator potential can be used as a model to approximate many physical phenomena quite well.   The first point is sort of meaningless though, I think the real reason is my second point. I'm looking for some materials to read about the different applications of the HO in different areas of physics. Which is more appropriate in the following sentence?     "I asked him to not judge her according to (or: based on) her beauty"   vs     "I asked him not to judge her according to (or:based on) her beauty"   or maybe you wouldn't choose either of the above, but something else? Preparing CSV files for use in ArcGIS Desktop? Is it acceptable to begin a declarative sentence with "Am"? I want to know firstly if it's grammatically correct to start a declarative sentence with "Am". For example:     Am excited about the game today.   Secondly, if it is grammatically incorrect, then I wanted to ask how much "head room" there is for the above usage. I can't think of an example now, nor find one here at english.stackexchange. However I imagine there are usages of the english language that grammatically are illegal, yet have somehow become accepted as colloquial or idiomatic perhaps. doing comparison if else in JasperReports I want to append several shapefiles in QGIS. The ftools 0.6.1 add-on is installed.   But under Vektor>Datenmanagement-Werkzeuge>Shapedateien zu einer zusammenführen (=append shapefiles) is only the possiblility to choose the Eingabedatei (input file) and the Ausgabedatei (output file) but not a further Datei (file) for the append itself? (Even though there are  several shapefiles in the same folder)  //Furthermore the icon "In neue Projektion exportieren" (export to new projection) is also not appearing under the: Vektor>Datenmanagement-Werkzeuge? Do I need a further add-on?//  Has anyone an idea why I can't choose a shapefile for the appending?  Thanks in advance! phil Math.cos() gives wrong result