I did a do_release_upgrade on my Ubuntu 16.04 (there were errors, in particular some were related to X11 or Xorg) and now I have this at boot:  Help ! EDIT I reinstalled grub from a live Ubuntu and now I have this at boot, still need help!  BOOT INFO is here  BOOT REPAIR report is here  lsb_release -a gives 18.04 Bionic . $ lspci -k | grep -A 2 -i &quot;VGA&quot; gives VGA compatible controller: Intel Corporation HD Graphics 5500 (rev 09) Subsystem: Lenovi HD Graphics 5500 kernel driver in use i915  then: sudo apt-add-repository ppa:ubuntu-x-swat/updates sudo apt-get update &amp;&amp; sudo apt-get upgrade  EDIT 2 I have access to command line via tty1, I tried to reinstall xserver sudo apt-get install --reinstall xserver-xorg but it still boots on the black screen with [ OK ] lines as in the screeshot above. EDIT 3 I tried reinstalling GDM sudo apt purge gdm gdm3 sudo apt install gdm3 ubuntu-desktop sudo dpkg-reconfigure gdm3 #to choose GDM systemctl restart gdm  I also tried startx and I get: X.Org X Server 1.19.6 ... using system config directory &quot;/usr/share/X11/xorg.conf.d&quot; xf86EnableIOPorts: failed to set OIPL for I/O (Operation not permitted) xinit: connection to server lost waiting for X server to shut down. (II) server terminated sucessfully (0). Closing log file.
Just ran the latest batch of updates on 20.04 (Xubuntu), and now I'm getting a GRUB error: symbol 'grub_calloc' not found  I'm dropped into the 'grub rescue' shell, but have no idea what to do there that might be useful. To me, 'symbol not found' implies some sort of build error with the grub package, but I don't really know how grub works. I noticed that this update also included 'firmware', not sure if that could be related. Is my best bet just to boot from a live CD and see if I can roll back the update to grub somehow? Edited to add: OK, thanks to lots of people ! Here's what I think I now understand.  On 'non-UEFI' systems, grub is installed in two separate parts. The first, most basic, part is the part that is started on bootup. But for most of it's functionality, it needs the second part. These parts must be aligned - neither part must require any functionality from the other part which is not actually there. The visible, run-time problem occurs when these parts are not aligned, and the function grub_calloc is not supplied. It's not 100% clear to me if grub_calloc belongs in the second, larger part or the first. I would have expected the second, but the grub build system is a work of considerable art, so I don't know :).  The root cause of the problem is that the grub update has not ensured that both parts have been updated. Ideally, failure to do this should cause grub installation to fail, and the system should be reverted to a safe state. This does not happen. This is actually still a bit of a mystery to me. All that the update needs to do by default is put each part where the current parts are, because obviously that worked. If the install locations/drives are configuration - driven, and one of these locations can't be reached, then somehow a mismatch has arisen between that configuration data and reality. This might not show up as a problem as long as no new dependency was introduced between the parts.   All flavours of solution involve reinstalling grub to ensure that the two parts are aligned. It's not actually necessary to go back to the previous version ( although that will work ), because it's not the grub runtime per se that is broken. There are numerous ways to achieve this, depending on your environment, but running the Boot-repair live disk worked for me. It may be useful, for the purpose of avoiding such a misalignment in future, to ensure that the grub installer on your system is configured to install to the correct devices. This update resolves some important bugs (). If you have reverted grub to resolve this problem, be aware that you are exposed to these issues.
Are amounts of money singular or plural? Are the two sentences correct or is one of them incorrect?     1) Five billion dollars is earmarked for the project.   2) Five billion dollars has been earmarked for the project.   I know dollars are countable. So I think both 'is' and 'has been' are correct here.   Also, do they differ in meaning? Considering that sound can't travel through vacuum. Using Ubuntu 11.10, how do I format an external or USB drive? I don't find an option to 'format' when I right click. In the new version, the drives don't come up on the desktop, but instead come on the Launcher. Icon missing when application is launched I've created an application launcher in /usr/share/applications that launches rdesktop. The file specifies an icon name and I've added the icons to:   /usr/share/icons/HighContrast/48x48/apps /usr/share/icons/HighContrast/22x22/apps /usr/share/icons/HighContrast/256x256/apps /usr/share/icons/HighContrast/32x32/apps /usr/share/icons/HighContrast/scalable/apps-extra /usr/share/icons/HighContrast/24x24/apps /usr/share/icons/HighContrast/16x16/apps /usr/share/icons/hicolor/scalable/apps /usr/share/icons/hicolor/128x128/apps /usr/share/icons/hicolor/16x16/apps   I then drug the launcher to the taskbar and the launcher with the correct logo is visible in the taskbar. However, when I start the task, a new icon is created in the taskbar, a square with a question mark in the center.  What icons do I need and where, so that the taskbar displays the correct icon for the application when it is launched?  The .desktop file contents:   [Desktop Entry] Version=1.0 Terminal=false Icon=mswindows Type=Application Categories=Network; Exec=rdesktop win7shared1 -g 1680x1000  Name=win7shared1 GenericName=rdesktop Comment=Open windows desktop  Keywords=Windows StartupNotify=false How to return value from an asynchronous callback function? Can we decrypt in this order when the message is encrypted twice? I think I remember reading somewhere that the Baire Category Theorem is supposedly quite powerful. Whether that is true or not, it's my favourite theorem (so far) and I'd love to see some applications that confirm its neatness and/or power.  Here's the theorem (with proof) and two applications:    (Baire) A non-empty complete metric space $X$ is not a countable union of nowhere dense sets.  Proof: Let $X = \bigcup U_i$ where $\mathring{\overline{U_i}} = \varnothing$. We construct a Cauchy sequence as follows: Let $x_1$ be any point in $(\overline{U_1})^c$. We can find such a point because $(\overline{U_1})^c \subset X$ and $X$ contains at least one non-empty open set (if nothing else, itself) but $\mathring{\overline{U_1}} = \varnothing$ which is the same as saying that $\overline{U_1}$ does not contain any open sets hence the open set contained in $X$ is contained in $\overline{U_1}^c$. Hence we can pick $x_1$ and $\varepsilon_1 &gt; 0$ such that $B(x_1, \varepsilon_1) \subset (\overline{U_1})^c \subset U_1^c$.   Next we make a similar observation about $U_2$ so that we can find $x_2$ and $\varepsilon_2 &gt; 0$ such that $B(x_2, \varepsilon_2) \subset \overline{U_2}^c \cap B(x_1, \frac{\varepsilon_1}{2})$. We repeat this process to get a sequence of balls such that $B_{k+1} \subset B_k$ and a sequence $(x_k)$ that is Cauchy. By completeness of $X$, $\lim x_k =: x$ is in $X$. But $x$ is in $B_k$ for every $k$ hence not in any of the $U_i$ and hence not in $\bigcup U_i = X$. Contradiction. $\Box$    Here is one application (taken from ):  Claim: $[0,1]$ contains uncountably many elements.  Proof: Assume that it contains countably many. Then $[0,1] = \bigcup_{x \in (0,1)} \{x\}$ and since $\{x\}$ are nowhere dense sets, $X$ is a countable union of nowhere dense sets. But $[0,1]$ is complete, so we have a contradiction. Hence $X$ has to be uncountable.     And here is another one (taken from ):  Claim: The linear space of all polynomials in one variable is not a Banach space in any norm.  Proof: "The subspace of polynomials of degree $\leq n$ is closed in any norm because it is finite-dimensional. Hence the space of all polynomials can be written as countable union of closed nowhere dense sets. If there were a complete norm this would contradict the Baire Category Theorem." GNU find and masking the {} for some shells - which? The man page for GNU find states:    -exec command ;     [...] The  string `{}'  is  replaced  by the current      file name being processed everywhere it occurs in the      arguments to the command, not just in arguments where      it is alone, as in some  versions  of  find.     Both  of  these  constructions might need to be escaped      (with a `\') or quoted to protect them from expansion      by the shell.     That's from the man to find (GNU findutils) 4.4.2.   Now I tested this with bash and dash, and both don't need to have the {} being masked. Here is a simple test:  find /etc -name "hosts" -exec md5sum {} \;    Is there a shell, for which I really need to mask the braces? Note, that it doesn't depend upon whether the file found contains a blank (invoked from bash):   find ~ -maxdepth 1 -type d -name "U*" -exec ls -d {} \;  /home/stefan/Ubuntu One   This changes if the found file is passed to a subshell:  find ~ -maxdepth 3 -type d -name "U*" -exec bash -c 'ls -d {}' \;  ls: cannot access /home/stefan/Ubuntu: No such file or directory ls: cannot access One: No such file or directory   which can be solved by:  find ~ -maxdepth 3 -type d -name "U*" -exec bash -c 'ls -d "$0"' {} \;   in contrast to:   find ~ -maxdepth 3 -type d -name "U*" -exec bash -c 'ls -d "{}"' \;  /home/stefan/Ubuntu One   but that's not what the man page is talking about, is it? So which shell treats {} in a different way? Is there a better way than simply trying to open the file?  int exists(const char *fname) {     FILE *file;     if ((file = fopen(fname, "r")))     {         fclose(file);         return 1;     }     return 0; } Journey Builder: Error binding data bound member I am having issues with input in VMware Workstation Player 12 in windowed mode or on multiple screens. When typing something in the VM and moving mouse cursor out of the VM without clicking on anything (for example on the second screen with host OS), the typing in that VM stops until I move the cursor back into VM.  Can this feature be disabled somehow so I am able to type in the virtual machine even when cursor is outside of it?  Both guest and host are Win10 x64 OS. Why are cancer rates low in large animals? Large animals generally have more cells and live longer than smaller animals. For example,  live up to 200 years and weigh up to 100 tonnes, as opposed to humans (living ~ and weigh ~) and  (10–25 g, &lt;1 year in the wild). Hence, whales have an immense number of cells and those cells are subjected to environmental carcinogenic influences (chemicals, UV) for a longer period of time.   Cancer is caused by random mutations and those random mutations are basically stochastic processes. Given their long life span and larger number of cells, shouldn't larger animals have a substantially higher chance to develop cancer? In fact, story goes that bowhead whales in fact only , and less so compared to humans? I just did a clean installation of Ubuntu 18.04.1 on a tablet which was previously running Ubuntu 17.10. Back then just after the installation the screen was rotated, but I was able to get it to work (I think it was running on Wayland).  Now with 18.04.1 the situation is similar: when Ubuntu first boots the login screen is upside-down, but that's not a problem. This time, after login, the screen is correctly oriented but the mouse cursor is upside down and mouse movements are inverted with respect to both axes. The problem is that when I try to click on something the click is registered on the position on the other side of the screen (symmetrically with respect to the center).   It almost seems like the screen (desktop, application, etc.) is correctly displayed, with also the mouse positioned correctly and moving as it should, but then the mouse cursor which is shown to the user is inverted, like if the screen had been inverted just before drawing the cursor.  I already tried the answers I could find, but none worked for me. Anyone have an idea of what's going on?  Thanks How would I import/export Blender's preferences? How can I obtain the limit of the series     $$\sum_{n=1}^{\infty} \frac{2^{[\sqrt{n}]}+2^{-[\sqrt{n}]}}{2^n}$$   Where $[\ \ ]$ is . Using CLI, how do I change the user's profile picture? A similar task for changing the desktop background, can be achieved using the following script:   FILE="/backgrounds/background.png" gsettings set org.gnome.desktop.background picture-uri "$FILE"   How would I achieve the same result, but with the user's avatar/profile picture? Arbitrary precision spline interpolation I want to search for what += means, but Google won't return any documents.  Also when I come across some PHP code I don't understand I can't search for the keywords as written.  How can I search for these special characters or include these special characters in a search. In C++, sizeof('a') == sizeof(char) == 1. This makes intuitive sense, since 'a' is a character literal, and sizeof(char) == 1 as defined by the standard.  In C however, sizeof('a') == sizeof(int). That is, it appears that C character literals are actually integers. Does anyone know why? I can find plenty of mentions of this C quirk but no explanation for why it exists. How to determine equality for two JavaScript objects?