From APUE     There are  rules for who can change the IDs. Let’s consider only the   user ID for now. (Everything we describe for the user ID also applies   to the group ID.)         If the process has superuser privileges, the setuid function sets the real user ID, effective user ID, and saved set-user-ID to uid.   If the process does not have superuser privileges, but uid equals either the real user ID or the saved set-user-ID, setuid sets only the   effective user ID to uid. The real user ID and the saved set-user-ID   are not changed.   If neither  of  these  two  conditions  is  true, errno is  set  to EPERM and -1 is returned.      What does it mean by "a process have or does not have superuser privileges"?  Is it defined as whether the real user ID of the process is root or not?
Real UID, effective UID, and some systems even have a "saved UID". What's the purpose of all these, especially the last one?
$P(\limsup A_n)=1 $ if $\forall A \in \mathfrak{F}$ s.t. $\sum_{n=1}^{\infty} P(A \cap A_n) = \infty$ Let $\mathfrak{F} = (A_n)_{n \in \mathbb{N}}$. Prove that $P(\limsup A_n)=1$ if $\forall A \in \mathfrak{F}$ s.t. $P(A) &gt; 0, \sum_{n=1}^{\infty} P(A \cap A_n) = \infty$. (Side question 1 Is second Borel-Cantelli out because we don't know if the $A_n$'s are independent?)  Suppose $\forall A \in \mathfrak{F}$ s.t. $P(A) &gt; 0, \sum_{n=1}^{\infty} P(A \cap A_n) = \infty$, but $P(\limsup A_n)&lt;1$. My prof gave us this convenient hint: Show $\exists M &gt; 0$ s.t. $P(\bigcap_{j=M}^{\infty} A_j^{c}) &gt; 0$.  $1 &gt; P(\limsup A_n)$  $1 - P(\limsup A_n) &gt; 0$  $P(\liminf A_n^{c}) &gt; 0$  By definition of $\liminf A_n^{c}$, $\exists M &gt; 0 $ s.t. $P(\bigcap_{j=M}^{\infty} A_j^{c}) &gt; 0$. (Side questions 2 and 3 Isn't this =1? ...Wait, is that what we're trying to prove? Haha)  $\to 1 - P(\bigcup_{j=M}^{\infty} A_j) &gt; 0$  $\to 1 &gt; P(\bigcup_{j=M}^{\infty} A_j)$  Main question: Now I guess we have to come up with some A s.t.  $\to 1 &gt; P(\bigcup_{j=M}^{\infty} A_j) \geq \sum_{n=1}^{\infty} P(A \cap A_n)$, or is there something else to do? How to graphically represent a language Is 'clamp' a formally recognized mathematical function? I was surprised to find the clamp function absent from  and . Is this mainly a concept particular to computer programming? Is it known by another name in mathematics? I'll be editing the Wikipedia shortly to include a reference to this function but I want to make sure I'm not omitting some synonymous terms I'm currently unaware of.  $$   \operatorname{clamp}(x) = \max( a , \min( x , b ) ) \in [a,b] $$ Better way of saying "those who are curious"? list all suggested packages for currently installed packages Latexmk can't see a dependency on a .fmt format file When I signed up I received a welcome message specifically indicating I should take the tour to earn my first badge:     Clicking the message takes me directly to the .  However, as   , the 'Informed' badge is not active here on meta.  Shouldn't the wording of the welcome message be altered if a user signs up on a site which does not use this badge? Using OPENQUERY to execute a script I have a SQL Server 2008 instance which I want to use to import data from an Oracle server.  I have set up a linked server that works correctly when running simple queries like SELECT * FROM table. However, if I declare a variable or loop through the rows in a table or anything else inside the OPENQUERY, I get errors.  Is it possible to do this using OPENQUERY? Do I need additional permissions? I recently installed an SSD and AFAIK Ubuntu makes a weekly FSTrim on SSD's that support it.  Is there a log file of this trims? Find equation of a plane that passes through point and contains the intersection line of 2 other planes Find equation of a plane that passes through point P $(-1,4,2)$ that contains the intersection line of the planes  $$\begin{align*} 4x-y+z-2&amp;=0\\ 2x+y-2z-3&amp;=0 \end{align*}$$  Attempt: I found the the direction vector of the intersection line by taking the cross product of vectors normal to the known planes. I got $\langle 1,10,6\rangle$. Now, I need to find a vector normal to the plane I am looking for. To do that I need one more point on that plane. So how do I proceed? Is there a route that would allow travel to the US from the UK or Schengen area, given the US travel ban? I'm a European citizen living in the US on a work visa. Due to some unfortunate circumstances, I need to urgently visit my home country. However I would like to get back to the US after my visit is complete. Flying from the US to Europe is not a problem as there are still daily flights between some city pairs. However going back could be tricky, as  anyone who has been in the Schengen area in the past 14 days from re-entering the country.   Is there a flight route that would let me from Europe to some country, stay there for 14 days and then fly to the US? Canada is out, as they've banned international visitors. Mexico seems to keep their border open, but I  any direct European flights from their airports. Almost every other country either suspended flights or doesn't allow foreign nationals to enter. Does $\lim_{h\rightarrow 0}\ [f(x+h)-f(x-h)]=0$ imply that $f$ is continuous? Consider an inviscid Burgers equation:  $u_t + u u_x = 0.$  With the initial data:  $ u(x,0) = \left\{ \begin{array}{ll}              0  \quad  &amp; \text{if} \quad x &lt; 0, \\[0.5em]              1  &amp; \text{if} \quad x &gt; 0.\end{array} \right. $  Possible weak solutions to this problem include, for example:  $ u_1(x,t) = \left\{ \begin{array}{ll}              0  \quad  &amp; \text{if} \quad x &lt; t/2, \\[0.5em]              1  &amp; \text{if} \quad x &gt; t/2.\end{array} \right. \hspace{10mm} $   $ u_2(x,t) = \left\{ \begin{array}{lll}              0  \quad  &amp; \text{if} \quad x &lt; 0, \\[0.5em]                      x/t &amp; 0 &lt; x &lt; t,\\[0.5em]              1  &amp; \text{if} \quad x &gt; t.\end{array} \right. $  Every material that provides such examples states that it is easy to check that these are both solutions of our problem. I do not see how that is done.  I know how to obtain the equation:  $ \int_{0}^\infty \int_{-\infty}^\infty [ q \phi_t + f(q) \phi_x ] dx dt + \int_{-\infty}^\infty q(x,0) \phi(x,0) dx = 0,  $  But I do not see how to "test" if the weak solutions provided above satisfy this. I tried writing the solutions as Heavside functions and integrating them, but I am not sure how to handle an arbitrary test function.  I assume there are some solution I could construct that would not be the weak solution to our initial data, how to check that? Am I going to have trouble flying without my full name on the ticket? In my passport, my name is Firstname middlename1 middlename2 lastname, and in the ticket is LASTNAME/FIRSTNAME MR.  Will be a problem? I'll travel from Brazil to Bali, Indonesia and according to the agency I bought the ticket from, there's no problem and it's common.  The airline is Qatar Airlines and I have looked , which says that the passenger name can't be changed after the booking has finished.  But I don't know if it is a problem. Block network access of a process? CSS bug with printing site pages (now with 100% more suggested fix included!) How to resolve conflicting distributions in apt-get When doing an apt-get update/upgrade I see that warning  W: Conflicting distribution: https://downloads.plex.tv/repo/deb public InRelease (expected public but got )   I was upgrading to Ubuntu Zesty 17.04 before and do not know how to fix the above. Already have seen ? but there are no suggested fixes for that.  Maybe one of you can give some hints? Thanks! How would Gauss' law hold in time varying electric fields? Can a possessive S be attached to nouns that are not human beings (or animals)? Can a possessive S be attached to nouns that are not human beings (or animals)?  For example, instead of saying "the back of the chair", can I say "the chair's back"?   I remember learning that not everything can get a possessive s, but this issue is not clear to me. What levels-up Psi-abilities?