When I want to run “sudo apt upgrade”, this error shows up: You don’t have enough free space in /var/cache/apt/archives.  Then, I run this code: sudo apt autoclean   and also sudo apt clean  and also sudo apt-get autoclean  However, nothing changes and the same error appears again when upgrading.
When I run the command to install the package solr-jetty, I am told   You don't have enough free space in /var/cache/apt/archives/   Here's the result of the df -H command:    I have installed Ubuntu with VirtualBox on my Mac.  How can I fix this problem?
Setting up a bicycle for someone with restricted knee articulation My father, now in his 70's, had a left knee replacement several years ago. He has limited movement in that knee - probably about 85 degrees on a good day. His knee can extend fully, but cannot bend as much as it should. As a result, he cannot pedal a bike he cannot get his left leg over the top of the pedal stroke.   He is desperate to get back onto a bike, he knows he won't be ripping up the road and winning races like the old days, but wants the freedom to go for a slow easy rides.    Does anyone have suggestions as to a solution to the problem. We don't mind spending money if we know the solution will work, but he can't afford to throw big money at wild ideas that may or may not work. If we find a solution, a new bike is likely.   We have access several mountain bikes in a range of sizes to trail ideas, and we have all the tools and skills to build bikes up from parts and rearrange things as needed.    EDIT: Thanks everyone - all great suggestions. What am am going to do is got tto the LBS and get hold of a cheap set of short cranks for around $30- probably from a kids bike, in the 120-150 size range, and see if he can ride that. Depending how he goes, I'll try a standard right crank and a short left crank. If all else fails, we will go for the Power Cranks   UPDATE: In case anyone else has similar problems. Got some 152mm cranks for $30. Set an old  mountain bike up with the seat as far back as possible. The old man is able to ride reasonably comfortably, now has a smile from ear to ear - any suggestions how to remove it - doesn't fit with the grumpy old man image :)   Has got me wondering how many people with minor knee problems would benefit from short(er) cranks....... How to convert a std::string to const char* or char*? If $x$ and $y$ are irrational, is $x + y$ irrational? Is $x - y$ irrational? How to format table with long column head entries? Given a continuous random variable $X$ and the pdf find.... There is a pattern excercise:  First pattern: We have $X$ and the probability density function is usually:  $$ f(x) = \begin{cases}   {ax+bx^2} &amp;  {0\lt x \lt 1} \\   0 &amp; \text{else}   \end{cases} $$  Then we are given $E|X| = 0.6$   And usually asks to find:  a) $P\{X&gt;0.5\}$  b) $Var(X)$    Second pattern:  $$ f(x) = \begin{cases}   {cx^4} &amp;  {0\lt x \lt 2} \\   0 &amp; \text{else}   \end{cases} $$  Where c is a constant. Find:  a) Mean value of $X$  b) Variance of $X$     Third pattern (it's more like a reverse problem):  We are given $Y= \sqrt{X}$, find it's cumulative distribution function (CDF) and  it's probability density function (pdf).    Update:  The third one is transferred to a .  This is not homework. I'm self-studying and in need of some help. Thank you. What is the acceptable similarity in a mathematics PhD dissertation when checking by Turnitin? I have checked the originality of my PhD thesis in mathematics using . The similarity was 31%. Is this percentage acceptable by most committees? How can I run a DSLR from AC power? My wife has a Nikon D3100 that I've been using to film, but the battery typically won't last through long shoots.  I've gathered from searching around that I can't charge the camera with USB, but I wondered if there's ANY way to do that. It seems at least possible that an adapter could exist that would fill in for the battery and plug into the wall, but I haven't been able to find such a thing.  Is there such a product or technique? It would be nice to not buy a second battery, I'm really hoping for a "set it and forget it" solution. How to view and export database content? I'm trying to view the actual entries, not the backend identifiers.  &gt; db.&lt;collection&gt;.find({"_id": "486b4ca55b144b119f4551417c5798c8"}).pretty()  {     "_id" : "486b4ca55b144b119f4551417c5798c8",     "date" : ISODate("2017-04-20T05:47:06.176Z"),     "content" : ObjectId("58f84b5a0318762cb6e230a6"),     "digest" : "d064a874c872d75f6ab67c04d8b79b26f65f9b4f",     "short" : "5f9b4f",     "size" : 2374694 }   Also tried mongoexport:  $ mongoexport --host 127.0.0.1 --port &lt;port&gt; -o test --pretty --db &lt;database&gt; --collection &lt;collection&gt;   This also shows backend data. I just want to see what was uploaded to the database. The actual content itself. I'm trying to use the Html.DropDownList extension method but can't figure out how to use it with an enumeration.  Let's say I have an enumeration like this:  public enum ItemTypes {     Movie = 1,     Game = 2,     Book = 3 }   How do I go about creating a dropdown with these values using the Html.DropDownList extension method?  Or is my best bet to simply create a for loop and create the Html elements manually? What is the difference between test set and validation set? How can I determine whether my processor is 32-bit or 64-bit? My processor is AMD Phenom 8450 triple-core. When should "farther" and "further" be used? Why does the Replace() string method not modify my string variable? LWC: Difference between "window" and "this" I am trying to understand what exactly is the difference between window and this in the context of a LWC component.  According to this  the Locker intercepts calls to the Window and uses Secured Window instead which acts as:     Secure wrapper for the window object, which represents a window containing a DOM document.   As for this what I  was:     To add an event listener to an element that a template doesn’t own,   call addEventListener directly: this.addEventListener()   What does salesforce mean by an element that a template doesn't own? Isn't window an element that the template doesn't own? Experience using dropdowns in-line of sentence "mad lib" style Do you have experience implementing text inputs or drop-downs in-line with other text or forms? Is this approach any better than just creating a separate field/label?  In the example below the user has the option to indicate when to be reminded again (in one, two, or three days). When they are reminded of an assignment, they simply get an email or text message. I have the following text:    A   Hello   world   B   Hello   world   C   Hello   world   I know that I can replace Hello by Hi using sed:  sed 's/Hello/Hi/g' -i test   but this replace each Hello with Hi:    A   Hi   world   B   Hi   world   C   Hi   world   what I really want is to replace only the Hello after B:    A   Hello   world   B   Hi   world   C   Hello   world   so I have tried this:  sed 's/"B\nHello"/"B\nHi"/g' -i test   but nothing happened, How can I do this?  Note: There are some white-spaces on the beginning of each line of the file. Do harmonic numbers have a “closed-form” expression? Convert a string to an enum in C# What's the best way to convert a string to an enumeration value in C#? I have an HTML select tag containing the values of an enumeration. When the page is posted, I want to pick up the value (which will be in the form of a string) and convert it to the corresponding enumeration value. In an ideal world, I could do something like this: StatusEnum MyStatus = StatusEnum.Parse(&quot;Active&quot;);  but that isn't a valid code. Prima facie this is impossible but perhaps someone has some kind of hack to do it. This is one of the last things holding me back from switching to Gmail from Pine.  To be clear, bouncing a message is like forwarding but leaving all the headers intact. It sort of amounts to spoofing the email, which perhaps is why Gmail doesn't support it. To the recipient of a bounced email, it seems as if they were just BCC'd. I can copy, move, create, and delete them. I can rename them using the REN command from a command prompt. I cannot rename folders through Windows Explorer anywhere on my machine, including on other drives.   When I try to do so, I receive an error titled "Rename Folder" that says "Can't find the specified file. Make sure you specify the correct path and file name." Then when I click Try Again or Cancel, I get another error titled "Rename" that says "The file or folder does not exist."  As far as I can tell, nothing else is wrong with my computer, but I'm pulling my hair out trying to fix this problem. I don't know for sure if superuser is the right place to ask this question, but feel free to redirect me.  Summary of Failed Attempts:   Booted into Safe Mode  Made a New User Account System Restore Point (two days ago, 9 days ago)  Deleting / Restoring / Modifying FolderDescriptions registry entries SFC /scannow  Removing windows update KB2984006  Scanned for viruses using Nod32  Scanned for malware using MalwareBytes   Details:  Tried rolling back to two different system restore points, both immediately before I observed the problem and one release prior to that.  Tried restoring FolderDescriptions registry entries as found here:   Booting in safe mode as suggested here:   SFC /scannow as suggested here:   Tried removing registry keys and windows update KB2984006 as suggested here:   Tried exporting folderdescriptions from other machine and importing as suggested here:   Compared my exported registry with other machine's exported registry for both:  HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\FolderDescriptions HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Windows\CurrentVersion\Explorer\FolderDescriptions   My FolderDescriptions branch of the registry in both cases are binary equal to those exported from my wife's Windows 8.1 laptop which works fine.