I ran something like:  sudo chmod -R 777 /.     In my Ubuntu 16.04 LTS it shows many errors on display, but anyway, the damage was done. Now I can't use sudo  sudo: error en /etc/sudo.conf, línea 0 mientras carga plugin 'sudoers_policy' sudo: /usr/lib/sudo/sudoers.so sólo tener permisos de escritura por el propietario sudo: error fatal, no se puede cargar los plugins   And besides of that I'm nervous about what else I have broken.  Is there a way to reestablish the right permissions of the system files?  I apologise for the English, that is not my native language.
I accidently ran  sudo chmod 755 -R /   instead of  sudo chmod 755 -R ./   I stopped it after few seconds, but now there is some problems such as  sudo: must be setuid root   How can I revert permissions back?
I have two layers, one (A) has point features and the other (B) has polygons.  How do I produce a new table with some (the ID) or all the fields from the A table and some (the area code) or all from the B table where the B polygon contains the A point?  I am using QGIS. How to show that $\lim_{n \to +\infty} n^{\frac{1}{n}} = 1$? "Who to follow" or "whom to follow"? has a "who to follow" button on the upper side of the screen. Shouldn't it be "whom to follow"?   suggests that whom is the correct usage in a case like this. How to turn off Wireless power management permanently ubuntu 18.04 LTS bluetooth [0cf3:3004] discovery not working How do I set up SIP voice calling in Empathy? I would like to use Empathy for Internet voice chat, but I do not see an option under the Empathy Accounts menu to create a SIP account.  How do I set up Internet voice calling in Empathy? I do not have enough time to bake my bread.  Can I refrigerate it or let it sit on the counter and bake it later in the day? I'd like to be able to find out which process is currently using a certain port in Linux. Is there any way to do this? $|A \cup B| = \mathfrak{c}$, then $A$ or $B$ has cardinality $\mathfrak{c}$. Sum of nth roots of unity Question: If $c\neq 1$ is an $n^{th}$ root of unity then, $1+c+...+c^{n-1} = 0$  Attempt: So I have established that I need to show that $$\sum^{n-1}_{k=0} e^{\frac{i2k\pi}{n}}=\frac{1-e^{\frac{ik2\pi}{n}}}{1-e^{\frac{i2\pi}{n}}} =0$$ by use of the sum of geometric series'. My issue is proceeding further to show that this is indeed true. I need to build a function which parses the domain from a URL.  So, with   http://google.com/dhasjkdas/sadsdds/sdda/sdads.html   or  http://www.google.com/dhasjkdas/sadsdds/sdda/sdads.html  it should return google.com  with   http://google.co.uk/dhasjkdas/sadsdds/sdda/sdads.html  it should return google.co.uk. What translation occurs when writing to a file that was opened in text mode that does not occur in binary mode? Specifically in MS Visual C.  unsigned char buffer[256]; for (int i = 0; i &lt; 256; i++) buffer[i]=i; int size  = 1; int count = 256;   Binary mode:  FILE *fp_binary = fopen(filename, "wb"); fwrite(buffer, size, count, fp_binary);   Versus text mode:  FILE *fp_text = fopen(filename, "wt"); fwrite(buffer, size, count, fp_text); Can't install jdk on Fedora with yum nor with rpm Solve for $f(x)$ if $f(f(x))=6x-f(x)$ If $f: [0,\infty) \rightarrow [0,\infty)$ and   $f(f(x))=6x-f(x)$ $f(x)&gt;0$ $  \forall x \in (0,\infty) $   Find f(x) I am trying to setup a dual screen configuration on debian 8 jessie with Gnome.  My computer has 3 graphical outputs : 2 displayport and 1 HDMI. I can't manage to have two of this 3 outputs to work simultaneously.  output of xrandr is (with the other display on displayport):  xrandr: Failed to get size of gamma for output default Screen 0: minimum 1680 x 1050, current 1680 x 1050, maximum 1680 x 1050 default connected primary 1680x1050+0+0 0mm x 0mm 1680x1050      0.00* `   output of xrandr is (with hdmi working):  xrandr: Failed to get size of gamma for output default Screen 0: minimum 1920 x 1080, current 1920 x 1080, maximum 1920 x 1080 default connected primary 1920x1080+0+0 0mm x 0mm 1920x1080      0.00*   I also tried to use both displayport but it does not work either.  output of lshw -c videò:  *-display UNCLAIMED         description: VGA compatible controller    product: Intel Corporation    vendor: Intel Corporation    physical id: 2    bus info: pci@0000:00:02.0    version: 06    width: 64 bits    clock: 33MHz    capabilities: pciexpress msi pm vga_controller bus_master cap_list    configuration: latency=0    resources: memory:f6000000-f6ffffff memory:e0000000-efffffff  ioport:f000(size=64)   (with both screens connected via displayport)  output of lspci -v -s0:0:2.0  00:02.0 VGA compatible controller: Intel Corporation Device 1912 (rev 06) (prog-if 00 [VGA controller]) Subsystem: Dell Device 06b9 Flags: bus master, fast devsel, latency 0, IRQ 255 Memory at f6000000 (64-bit, non-prefetchable) [size=16M] Memory at e0000000 (64-bit, prefetchable) [size=256M] I/O ports at f000 [size=64] Expansion ROM at &lt;unassigned&gt; [disabled] Capabilities: &lt;access denied&gt; Why is 'that' sometimes optional before dependent clauses? How do I remove login credentials (emails or OpenIDs) from my account?     For more information, see "" in the . I have a dataset for which I have multiple sets of binary labels. For each set of labels, I train a classifier, evaluating it by cross-validation. I want to reduce dimensionality using principal component analysis (PCA). My question is:  Is it possible to do the PCA once for the whole dataset and then use the new dataset of lower dimensionality for cross-validation as described above? Or do I need to do a separate PCA for every training set (which would mean doing a separate PCA for every classifier and for every cross-validation fold)?  On one hand, the PCA does not make any use of the labels. On the other hand, it does use the test data to do the transformation, so I am afraid it could bias the results.  I should mention that in addition to saving me some work, doing the PCA once on the whole dataset would allow me to visualize the dataset for all label sets at once. If I have a different PCA for each label set, I would need to visualize each label set separately. How to text-to-speech output using command-line? How to get speech output from entered text by using command-line?  Also facility to change speech rate, pitch, volume etc using simple command. What does string theory predict for the singularity inside a black hole? The usual explanation for what's going on inside a black hole goes something like "General Relativity predicts a singularity with infinite curvature, but when matters gets so tightly compressed we should expect quantum effects to become important, so the singularity will probably be blurred". Authors then proceed to say that we need a quantum theory of gravity to answer such things, and quickly abandon the subject.  Well, while we don't have an experimentally confirmed quantum theory of gravity, we do have a speculative one, string theory. What does it say about singularities? Are they smeared out like the books say? Do they remain points (or rings for a rotating black hole) with infinite curvature and density? Do we not know?