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  • Understanding behaviour of read() and write()

    - by neo730
    hi i am a student and just start learning low level c programming.i tried to understand read() and write() methods with this program. #include <unistd.h> #include <stdlib.h> main() { char *st; st=calloc(sizeof(char),2);//allocate memory for 2 char read(0,st,2); write(1,st,2); } i was expecting that it would give segmentation fault when i would try to input more than 2 input characters.but when i execute program and enter " asdf " after giving " as " as output it executes "df" command. i want to know why it doesn't give segmentation fault when we assign more than 2 char to a string of size 2.and why is it executing rest(after 2 char)of input as command instead of giving it as output only? also reading man page of read() i found read() should give EFAULT error,but it doesn't. I am using linux.

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  • Write a tree class in Java where each level has a unique object type

    - by user479576
    I need to write a tree class in Java where each level has a unique object type. The way it is written below does not take advantage of generics and causes alot of duplicate code. Is there a way to write this with Generics ? public class NodeB { private String nodeValue; //private List<NodeB> childNodes; // constructors // getters/setters } public class NodeA { private String value; private List<NodeB> childNodes; // constructors // getters/setters } public class Tree { private String value; private List<NodeA> childNodes; // constructors // tree methods }

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  • Why won't this piece of my code write to file

    - by user2934783
    I am developing a c++ banking system. I am able to get the float, newbal, values correctly and when I try to write to file, there is no data in the file. else { file>>firstname>>lastname; cout<<endl<<firstname<<" "<<lastname<<endl; cout<<"-----------------------------------\n"; string line; while (getline(file, line)) { //stringstream the getline for line string in file istringstream iss(line); if (iss >> date >> amount) { cout<<date<<"\t\t$"<<showpoint<<fixed<<setprecision(2)<<amount<<endl; famount+=amount; } } cout<<"Your balance is $"<<famount<<endl; cout<<"How much would you like to deposit today: $"; cin>>amountinput; float newbal=0; newbal=(famount+=amountinput); cout<<"\nYour new balance is: $"<<newbal<<".\n"; file<<date<<"\t\t"<<newbal; //***This should be writing to file but it doesn't. file.close(); The text file looks like this: Tony Gaddis 05/24/12 100 05/30/12 300 07/01/12 -300 //Console Output looks like this Tony Gaddis 05/24/12 100 05/30/12 300 07/01/12 -300 Your balance is: #1 How much wuld you like to deposit: #2 Your new balance is: #1 + #2 write to file close file. //exits to main loop:::: How can I make it write to file and save it, and why is this happening. I tried doing it with ostringstream as well considering how I used istringstream for the input. But it didn't work either :\ float newbal=0; newbal=(famount+=amountinput); ostringstream oss(newbal); oss<<date<<"\t\t"<<newbal; I am trying to self teach c++ so any relevant information would be kindly appreciated.

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  • Why do we (really) program to interfaces?

    - by Kyle Burns
    One of the earliest lessons I was taught in Enterprise development was "always program against an interface".  This was back in the VB6 days and I quickly learned that no code would be allowed to move to the QA server unless my business objects and data access objects each are defined as an interface and have a matching implementation class.  Why?  "It's more reusable" was one answer.  "It doesn't tie you to a specific implementation" a slightly more knowing answer.  And let's not forget the discussion ending "it's a standard".  The problem with these responses was that senior people didn't really understand the reason we were doing the things we were doing and because of that, we were entirely unable to realize the intent behind the practice - we simply used interfaces and had a bunch of extra code to maintain to show for it. It wasn't until a few years later that I finally heard the term "Inversion of Control".  Simply put, "Inversion of Control" takes the creation of objects that used to be within the control (and therefore a responsibility of) of your component and moves it to some outside force.  For example, consider the following code which follows the old "always program against an interface" rule in the manner of many corporate development shops: 1: ICatalog catalog = new Catalog(); 2: Category[] categories = catalog.GetCategories(); In this example, I met the requirement of the rule by declaring the variable as ICatalog, but I didn't hit "it doesn't tie you to a specific implementation" because I explicitly created an instance of the concrete Catalog object.  If I want to test the functionality of the code I just wrote I have to have an environment in which Catalog can be created along with any of the resources upon which it depends (e.g. configuration files, database connections, etc) in order to test my functionality.  That's a lot of setup work and one of the things that I think ultimately discourages real buy-in of unit testing in many development shops. So how do I test my code without needing Catalog to work?  A very primitive approach I've seen is to change the line the instantiates catalog to read: 1: ICatalog catalog = new FakeCatalog();   once the test is run and passes, the code is switched back to the real thing.  This obviously poses a huge risk for introducing test code into production and in my opinion is worse than just keeping the dependency and its associated setup work.  Another popular approach is to make use of Factory methods which use an object whose "job" is to know how to obtain a valid instance of the object.  Using this approach, the code may look something like this: 1: ICatalog catalog = CatalogFactory.GetCatalog();   The code inside the factory is responsible for deciding "what kind" of catalog is needed.  This is a far better approach than the previous one, but it does make projects grow considerably because now in addition to the interface, the real implementation, and the fake implementation(s) for testing you have added a minimum of one factory (or at least a factory method) for each of your interfaces.  Once again, developers say "that's too complicated and has me writing a bunch of useless code" and quietly slip back into just creating a new Catalog and chalking any test failures up to "it will probably work on the server". This is where software intended specifically to facilitate Inversion of Control comes into play.  There are many libraries that take on the Inversion of Control responsibilities in .Net and most of them have many pros and cons.  From this point forward I'll discuss concepts from the standpoint of the Unity framework produced by Microsoft's Patterns and Practices team.  I'm primarily focusing on this library because it questions about it inspired this posting. At Unity's core and that of most any IoC framework is a catalog or registry of components.  This registry can be configured either through code or using the application's configuration file and in the most simple terms says "interface X maps to concrete implementation Y".  It can get much more complicated, but I want to keep things at the "what does it do" level instead of "how does it do it".  The object that exposes most of the Unity functionality is the UnityContainer.  This object exposes methods to configure the catalog as well as the Resolve<T> method which is used to obtain an instance of the type represented by T.  When using the Resolve<T> method, Unity does not necessarily have to just "new up" the requested object, but also can track dependencies of that object and ensure that the entire dependency chain is satisfied. There are three basic ways that I have seen Unity used within projects.  Those are through classes directly using the Unity container, classes requiring injection of dependencies, and classes making use of the Service Locator pattern. The first usage of Unity is when classes are aware of the Unity container and directly call its Resolve method whenever they need the services advertised by an interface.  The up side of this approach is that IoC is utilized, but the down side is that every class has to be aware that Unity is being used and tied directly to that implementation. Many developers don't like the idea of as close a tie to specific IoC implementation as is represented by using Unity within all of your classes and for the most part I agree that this isn't a good idea.  As an alternative, classes can be designed for Dependency Injection.  Dependency Injection is where a force outside the class itself manipulates the object to provide implementations of the interfaces that the class needs to interact with the outside world.  This is typically done either through constructor injection where the object has a constructor that accepts an instance of each interface it requires or through property setters accepting the service providers.  When using dependency, I lean toward the use of constructor injection because I view the constructor as being a much better way to "discover" what is required for the instance to be ready for use.  During resolution, Unity looks for an injection constructor and will attempt to resolve instances of each interface required by the constructor, throwing an exception of unable to meet the advertised needs of the class.  The up side of this approach is that the needs of the class are very clearly advertised and the class is unaware of which IoC container (if any) is being used.  The down side of this approach is that you're required to maintain the objects passed to the constructor as instance variables throughout the life of your object and that objects which coordinate with many external services require a lot of additional constructor arguments (this gets ugly and may indicate a need for refactoring). The final way that I've seen and used Unity is to make use of the ServiceLocator pattern, of which the Patterns and Practices team has also provided a Unity-compatible implementation.  When using the ServiceLocator, your class calls ServiceLocator.Retrieve in places where it would have called Resolve on the Unity container.  Like using Unity directly, it does tie you directly to the ServiceLocator implementation and makes your code aware that dependency injection is taking place, but it does have the up side of giving you the freedom to swap out the underlying IoC container if necessary.  I'm not hugely concerned with hiding IoC entirely from the class (I view this as a "nice to have"), so the single biggest problem that I see with the ServiceLocator approach is that it provides no way to proactively advertise needs in the way that constructor injection does, allowing more opportunity for difficult to track runtime errors. This blog entry has not been intended in any way to be a definitive work on IoC, but rather as something to spur thought about why we program to interfaces and some ways to reach the intended value of the practice instead of having it just complicate your code.  I hope that it helps somebody begin or continue a journey away from being a "Cargo Cult Programmer".

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  • Why CoffeeScript is tough to maintain

    - by Renso
    I recently started trying out CoffeeScript only to find out that it caused more headaches. The abstraction level of jQuery was perfect, it did not dictate to coders how to design their code, it just works. However, I recently posted a request to the CoffeeScript team to consider introducing curly braces to help with more complex code to control the flow of logic. For example a if-then-else with many nested levels can be near impossible to debug without tracing through it when using CoffeeScript. Also with IDEs like Visual Studio, regular JavaScript intellicense and auto-formatting make it easy to appropriate indent nested levels without any work on the part of the developer and reading it is not that hard, especially with some extensions that show vertical lines in the code editor to help see what is nested within what part of the code.However with CoffeeScript that is not the case. The samples given in the CoffeeScript web site are of course just simple examples to explain the features and one gets excited pretty quick over the powerful shortcuts. I tried to convert a piece of JavaScript over to CoffeeScript and gave up since you need to first of all remove ALL non CoffeeScript coding constructs for it to even compile. However js2coffee can help with that. However to keep track of nested levels became something that was simply not manageable using CoffeeScript.Furthermore, any coding language that controls the flow of logic by indentation is extremely dangerous for obvious reasons. I liked CoffeeScript a lot, but the fact that the logical flow of the code is controlled by how much you indent code, spaces or tabs, is not reliable as there is no way the programmer has an easy way of knowing what parts of the code will get hit when the code spans a page.When I suggested introducing curly braces in CoffeeScript the team, one contributor advised me that my code needs to be re-designed! Needless to say that is absurd. When I included a piece of the code he asked my if it was legacy code. It's like saying to a Java programmer, sorry you cannot use Java because we don't agree with how you write your code.jashkenas from the CoffeeScript blog gave some great suggestions and made the point that introducing curly braces would be very problematic for them as they use them to denote objects. Makes sense, but I would still love to see some way to replace code flow control with spaces and indentation to something more concrete and human readable.

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  • psql: FATAL: could not write init file

    - by Leonardo M. Ramé
    as the title points out, I'm getting this error when trying to connect to a PostgreSql database from command line, using PostgreSQL. The client machine is an Ubuntu 11.10 x86_64 and the PostgreSQL libraries are from Version 9.1 Server is PostgreSql 8.3. This is the command that I executed: psql -U postgres -d my_database -h 192.168.0.161 -p 5432 -c "select * from xxyy" I get the same results when I use sudo or su postgres. The sad thing is that I can connect without problems using pgAdmin. Any hint?

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  • nginx and php-fpm - Cannot write PHP error log

    - by SteveEdson
    I am using Nginx and PHP-FPM on Linux. I am not sure whether the issue is that PHP is not writing to the location specified in the PHP.ini, or if it just isn't working at all. Some of the logs produced by Nginx and PHP-FPM contain the PHP errors, but they are mixed in with other Nginx log output. When I run phpInfo(), value in the error_log is set to a folder in my home directory, but nothing is ever created. I understand that values in the Nginx conf and PHP-FPM conf can overwrite those set in the PHP.ini, but surely running phpInfo(), would show the final config values? I would like to be able to have 1 folder, with seperate files for the Nginx access and error log as well as PHP errors. Thanks.

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  • ASP.Net application can no longer write to DB after having run out of disk space

    - by remi.despres-smyth
    I'm a software developer troubleshooting a sticky problem on a client's production server, and I've got a bit of a problem. They have a virtual server running Windows Server 2008, SQL Server 2008 R1 and IIS7. It was provisioned with two partitions: one that has the OS (~15 Gig), and the other has IIS' web sites (another ~15 Gig). My application that's running this server has been running perfectly well, up until about an hour ago, when it started throwing System.IO.IOException: "There is not enough space on disk". As soon as my client notified me, I cleared up some space on C:\, emptied the recycle bin, and restarted SQL Server and IIS. The web server came back up and the application was running, but it no longer saves information to the database. No error message is coming up, the application can get information out of the DB, but it can no longer save data back to it. I rebooted the server, to no effect. I spoke with a sys admin at the hosting company, and he says SQL Server appears to have come up fine and the database is not in read-only mode. I confirmed that, as I can add records to tables from SQL Server Management Studio. I looked at the event log immediately after trying to save an edited record in the app, and no new events appear in there that I can tell. I'm assuming this is related to having run out of space, as it was all working fine prior to that, but I'm at a bit of a loss as to what exactly needs a kick in the pants to get going again. Can anyone help me out? What the heck is going on here?

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  • Cannot read/write FTP directory vsftpd on centos 6.0 (empty folder)

    - by adrianTNT
    I have Centos 6.0 and installed vsftp with YUM, I added a user with Webmin panel, set its home dir to "/var/www/html" and its shell to "/bin/sh", user id is 500, user group is same as name: "adrian_ftp". When I start a ftp program it logs in but the remote folder always shows empty. I set directory owner and group to adrian_ftp:adrian_ftp , no change, I also made them 0777, no change. Any ideas? I tried for over 3-4 hours :|

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  • Windows 2003 R2 x86 Mini dump fails to write to disk

    - by Randy K
    I have 3 blade servers that are Blue Screening with a 0xC2 error as far as we can tell randomly. When it started happening I found that the servers weren't set to do provide a dump because they each have 16GB RAM and a 16GB swap file divided over 4 partitions in 4GB files. I set them to provided a small dump file (64K mini dump), but the dump files aren't being written. On start up the server event log is reporting both Event ID 45 "The system could not sucessfully load the crash dump driver." and Event ID 49 "Configuring the Page file for crash dump failed. Make sure there is a page file on the boot partition and that is large enough to contain all physical memory." I understanding is the the small dump shouldn't need a swap file large enough for all physical memory, but the error seems to point to this not being the case. The issue of course is that the max swap file size is 4GB, so this seems to be impossible. Can anyone point me where to go from here?

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  • How to write files in specific order?

    - by Bernie
    Okay, here's a weird problem -- My wife just bought a 2014 Nissan Altima. So, I took her iTunes library and converted the .m4a files to .mp3, since the car audio system only supports .mp3 and .wma. So far so good. Then I copied the files to a DOS FAT-32 formatted USB thumb drive, and connected the drive to the car's USB port, only to find all of the tracks were out of sequence. All tracks begin with a two digit numeric prefix, i.e., 01, 02, 03, etc. So you would think they would be in order. So I called Nissan Connect support and the rep told me that there is a known problem with reading files in the correct order. He said the files are read in the same order they are written. So, I manually copied a few albums with the tracks in a predetermined order, and sure enough he was correct. So I copied about 6 albums for testing, then changed to the top level directory and did a "find . music.txt". Then I passed this file to rsync like this: rsync -av --files-from=music.txt . ../Marys\ Music\ Sequenced/ The files looked like they were copied in order, but when I listed the files in order of modified time, they were in the same sequence as the original files: ../Marys Music Sequenced/Air Supply/Air Supply Greatest Hits ls -1rt 01 Lost In Love.mp3 04 Every Woman In The World.mp3 03 Chances.mp3 02 All Out Of Love.mp3 06 Here I Am (Just When I Thought I Was Over You).mp3 05 The One That You Love.mp3 08 I Want To Give It All.mp3 07 Sweet Dreams.mp3 11 Young Love.mp3 So the question is, how can I copy files listed in a file named music.txt, and copy them to a destination, and ensure the modification times are in the same sequence as the files are listed?

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  • Windows file locks allowing multiple users to write to open file over network

    - by JPbuntu
    I have 6 windows computers (xp,vista,7) that need to access a samba share (Ubuntu 12.04). I am trying to make it so only one client can open a file at a given time. I thought this was pretty standard behavior of file locks, but I can't get it to work. The way it is right now a file can be open by two users, and changed and saved by either one of them. The last file saved overwrites what ever changes the other user made. At first I thought this was a Samba configuration problem, but I get this behavior even between two windows machines. So far I have only tested: Windows Xp Windows Vista Windows XP Samba << Windows Vista and both give the same behavior. When I tested the Samba configuration, I had set strict locking = yes and get errors logged like this: close_remove_share_mode: Could not get share mode lock for file _prod/part_number_list_COPY.xlsx Eventually all of the files are going to be moved onto the Samba share, so that is the configuration I am most concerned about fixing. Any ideas? Thanks in advance. EDIT: I tested an excel file again, and it is now working properly in both above mentioned cases, I am also no longer getting the above mentioned error. I don't know what happened, perhaps a restart fixed it? (also works with strict locking = no) Although I still need to find a solution for the CAD/CAM files we use, the software is Vector and it does not seem to be using file locks. Is there any software that I can use to manage these files, so two people can't open/edit them at a time? Maybe a windows application that forces file locks? Or a dirt simple version control system? (the only ones I have seen at are too complicated for our needs).

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  • Write-but-not-delete permissions on SAMBA

    - by m6a-uds
    Hi! I installed samba on my linux server for public file sharing on the LAN. I works great currently, but I would like to add some security: People from LAN should be able to Read files present and Add new ones, but not delete files. I want to keep this privilege for me ;-) How should-I do this? I have set up a "admin" account having full access even to deletion. There is just left to configure the "guest" acount. Google isn't helping that much right now...

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  • How to install two packages that write the same file

    - by Joel E Salas
    Sirs, a conundrum. I have two packages that each create /usr/bin/ffprobe. One of them is ffmpeg from the Deb Multimedia repository, while the other is ffmbc 0.7-rc5 built from source. The hand-rolled one is business-critical, and we used to just install it from source wherever it was necessary. I can only assume it would clobber the ffmpeg file, and there were never any ill effects. In theory, it should be acceptable for our ffmbc package to overwrite the file from the ffmpeg package. Is there any easy way to reconcile this?

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  • Win7 - DVD drive spins up but fails to read, fails write

    - by MA
    Running Windows 7 x64. DVD drive is a BenQ DC DQ60 ATA dvd-dl rw. Everything functions correctly in linux, and I can boot to cd/dvds, so the drive itself does work. Symptom: when I insert any CD or DVD (burned or retail), the drive spins up the disk, and (usually) displays the disk title in My Computer, but just continues to spin indefinitely. I cannot browse the disk in the drive, install from it, or read anything.

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  • Networking Problem MrxSmb event 50 "Delayed Write Failed" errors occurring all of the sudden

    - by Johnny Musso
    JUST THIS MONTH, we have started getting reports from a number of very stable clients that MrxSmb event id 50 errors keep appearing in their system event logs. Otherwise, they do not appear to have any networking problems except that there is a critical legacy application which seems to either be generating the MrxSmb errors or having errors occur because of them. The legacy application is comprised of 16 bit and 32 bit code and has not been changed or recompiled in many years. It has always been stable on Windows XP systems. The customers that have the problem usually have a small (5 clients or less) peer to peer network with all Windows XP systems. All service packs are loaded on the XP machines. Note: The only thing that seems to correct the problem is disabling opportunistic locking. I don't like this solution because it seems to slow down the network and sometimes causes record locking issues between users (on some networks). Also, this seems to have just started happening - as if a Windows update for XP has caused it? However, I have removed recent updates and it did not correct the issue. Thanks in advance for any help you can provide.

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  • "Path Not Found" when attempting to write to a sub folder within a mapped drive

    - by Adam
    We have an interesting issue with one of our server shares, or possibly, our Win 7 desktops. When our users try to save files in a sub folder, either via copy/paste or through an application, to a mapped drive on our DC they receive an error saying "Path not found". They can however browse this folder and open files from it. This is where the "Path Not Found" error doesn't seem to stack up in my opinion. Users can however save files fine in the root folder of the mapped drive, it appears only to affect sub folders. It seems to be random which users and machines this affects. The users can log on to a different machine and be able to save in sub folders fine, on the same mapped drive. Event viewer hasn't been much help either. Currently, the only solution we have found is to image the machines affected which solves the issue. Our servers are Server 2008 R2 with Win 7 Pro desktops. Any help/pointers/suggestions would greatly be appreciated.

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  • Mac can write to samba share

    - by David
    I have a samba share that works fine for PCs, but we have a mac user who seems to only be able to edit and rename existing files, he cannot add new files. Any ideas? Here is the share setup: path = /media/freeagent/officeshare read only = No guest ok = Yes writeable = yes public = yes

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  • NTFS write speed really slow (<15MB/s) on Ubuntu

    - by Zulakis
    When copying large files or testing writespeed with dd, the max writespeed I can get is about 12-15MB/s on drives using the NTFS filesystem. I tested multiple drives (all connected using SATA) which all got writespeeds of 100MB/s+ on Windows or when formatted with ext4, so it's not an alignment or drive issue. top shows high cpu usage for the mount.ntfs process. AMD dual core processor (2.2 GHz) Kernel version: 3.5.0-23-generic Ubuntu 12.04 ntfs-3g version: both 2012.1.15AR.1 (Ubuntu default version) and 2013.1.13AR.2 How can I fix the writespeed?

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  • Likewise: joined Active Directory but cannot write shares.

    - by Aron Rotteveel
    I have never used a Linux system in an AD environment before and am trying to join my laptop running Ubuntu to join our Active Directory (DC is a Windows Server 2008 machine) using Likewise-open. Using the GUI wizard, I have joined the domain. I can mount network shares using CIFS Problem: I only have read access to our fileserver. What more is needed to get the AD to recognize me as a user who has the appropriate rights? Any help is appreciated.

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  • Motherboard jumper setting: BIOS flash write protection.

    - by Wesley
    I have an ECS P4M800PRO-M478 motherboard and I'm just setting up the jumpers right now, of which there are only two sets. One is the CLR_CMOS jumper, which is set to Normal, of course. However, there is another set called BIOS_WP which controls whether BIOS flash writing is protected or unprotected. Which setting should I have it set at and would this affect any BIOS flashes in the future?

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  • Write permissions LAMP (Debian Lenny)

    - by letseatfood
    I am working on a PHP script that transfers files using FTP functions. It has always worked on my production server (which is a hosting service). The development server I have just setup (I am a novice to servers) is Debian Lenny with Apache2, PHP5, and MySQL5. The file transfer works correctly, but once the file has been written to the server, it has permissions of 600. This makes it impossible for me to view the file (JPEG) in the web browser, as permission is denied. I have scoured the internet and even broken my server installation and reinstalled it trying to figure this out (which has been fun, nonetheless!). I know it is unwise to set 777 permissions on public accessible files, but even that will not solve the problem. The only thing that works is if I chmod 777 thefile.jpg after it has been transferred, which is not a working solution. I tried changing the owner of my site files to www-data per this post, but that also does not work. My user is mike, and it still does not work whether the owner of the files is mike or root. Would somebody point me in the right direction? Thanks! And, of course, let me know if I can clarify anything.

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