FTP Protocol Specifications

FTP Protocol Specifications

To understand the essence of the FTP protocol, you need to look at the history of the emergence of a worldwide network. As you know, at the very beginning the web was a not so popular and a limited accessible computer network, which began to be used to organize and host static pages of sites and exchange information (transfer files) between individual computers.

In the process of forming a global network, its structure is constantly changing, the number of users is expanding, new services and corresponding protocols appear.

File Transfer Protocol (FTP) is a file transfer protocol, one of the first and main protocols of the TCP / IP family, which provides the ability to send (copy, transfer) files over the Internet from a remote computer to a local one, and vice versa. It is known that programs that use the FTP protocol have become part of separate Internet service and a service that provides access to files of other computers on the network via FTP is of the same name.

The FTP protocol is used, in particular, by the authors of the virtual www-server owners to remotely control and update their contents.

For the FTP application to work, you must have the appropriate programs:

  • FTP client. A browser or a file management program that you can access and FTP server with.
  • FTP server. It’s is a program that runs on a powerful computer – a server, the one that exposes the files to the Internet.

Using the FTPConnection object, you can work with remote computers by performing standard actions with files: download, upload, rename files, access their properties, create directories.

FTP protocol has a generally established specification of commands and responses that programs use for their work.

The user-level FTP protocol operation algorithm consists of several stages:

  • Identification (entering the identifier name and password).
  • Directory selection.
  • Determination of the transfer protocol.
  • Execution of transfer commands.
  • Completion of the procedure.

File management using the FTP protocol depends on the selected four items:

  • File type: ASCII, EBCDIC, local.
  • Format: nonprint, telnet format control, Fortran carriage control (for files such as ASCII and EBCDIC).
  • Structure: file, records, pages.
  • Transmission mode: stream, blocks, compressed.

You must pay attention to compliance with the rules for using file upload modes. If the operating mode is incorrectly selected, the file may not work correctly.

If we are talking about file sharing, then using FTP protocols is convenient only until the number of requests to download the same file in one unit of time, from one source, begins to grow exponentially, which is associated with a huge increase in the percentage of users Internet and rising global traffic. In this regard, servers and server data channels begin to withstand the load, which leads to a decrease in the speed of file distribution.

The disadvantage of the FTP protocol is the transmission between the server and the client of clear text, which does not protect the transmitted information, and therefore cannot be used to transmit confidential information.

Pay attention to the fact that hosting providers like SiteGround and DreamHost are offering reliable hosting for business owners with FTP access.

How to Pick a Reliable Website Hosting (2020 Updated)

How to Pick a Reliable Website Hosting (2020 Updated)

Hosting refers to the place on the server where your site files are stored – databases, content, engine, etc. The functioning of the resource, its stability, and profitability of the business, when it comes to commercial projects, depend on the reliability of the storage and the speed of the servers.

Today we will tell you how to choose a hosting that meets your needs and not to lose money on the way.

What type of hosting providers are out there?

There are three types of them, the difference lies in the degree of service by the hosting company and technical capabilities required from you as the maintainer of your site or business online.

Shared Hosting

In this scenario, sites of different owners are hosted and run on the same server. Technical capacities are distributed among all users and you do not need to configure everything manually. The provider is responsible for ensuring operability.

The pros of shared hosting are as follows:

  • Low prices (the hoster makes a profit from a large number of customers).
  • The ability to contact technical support if problems arise. It’s pretty important and the response speed is always high (at least, for the quality hosting providers like SiteGround or DreamHost) because the hoster is responsible for the operation of the resources of many users.
    If conditionally 1000 sites become unavailable at the same time, this is fraught with loss of the reputation of the provider.
  • Additional functions – checking files for viruses, installing SSL-certificate, CMS, backup, one-click WordPress install (if you don’t know what WordPress is, read our article. Most of the hosting providers today are WordPress hosting out-of-the-box), etc. Many of them are available in one click.
  • Accelerated operation of the resource in some cases. Suppose a server is designed for the uninterrupted functioning of 1000 resources, but only 500 owners use the services of a particular provider. Accordingly, existing sites take extra power from underused resources.
  • Server setup and software updates are the sole concern of the hoster.

Shared hosting solutions got two main disadvantages:

  • The desire of the provider to increase his profits and places on the server more sites than the server can hold, resources wise. For each of the users, this is fraught with performance problems, low page loading speed. The solution is to work with honest hosters for whom reputation is important.
  • “Bad neighbors.” On the same server, along with your, let’s say, online store, you can find online cinemas, casinos, adult-themed resources that somehow violate applicable law. If they are blocked, “law-abiding” projects will suffer. Solution: check in advance what resources are hosted on the same IP, work with hosters who value reputation who do not work with problem clients.

In general, this is a reliable and good hosting, it will suit a beginner who just starting his site and who does not want to understand the intricacies of the settings, and an experienced site owner, for whom saving time is important.

VPS hosting

Implies a virtual dedicated server. You rent part of it and you are not so dependent on your neighbors, because there are also fewer of them.

The benefits of VPS web hosting are as follows:

  • Fully manage the facilities you paid for. Resources not you currently not utilize are not distributed among other clients.
  • You control the operating system and software on the server. Technical support staff can configure hosting for the most comfortable work.
  • Adequate price when it comes to medium or large projects. We recommend choosing this kind of hosting for an online store hosting, corporate portal, forum – resources containing a large number of files and using a lot of disk space. For a Landing Page or single-page, this solution is not rational (just go with shared hosting).
  • There are no restrictions on the number of sites for one account. All limits apply only to capacities. You can place a single large project or many small ones.

There is only one drawback: you will have to delve deeper into the settings or separately pay for technical support services if something goes wrong or additional functionality is required that is not provided for in the selected tariff plan.

Dedicated server

All capacities and equipment are completely yours, there are no neighbors, any settings are possible. The only limiting factor is the high price. However, it makes sense to rent a dedicated physical server only for very large projects, for example, online games.

Practical tips on picking a website hosting

Let’s start by mentioning the top tips you should follow on the way of picking your web hosting solution.

Tips 1 – Project requirements

Think about how much disk space you need. This value is directly dependent on the type of project. For a business card style site, the requirements are minimal while large projects need more resources. This is one of the points that affect the choice. Also, decide if you plan to expand in the future to order the optimal package right away.

Tips 2 – CMS for your site

Look at the technical requirements for hosting on the official site used by the CMS (for example, WordPress websites). For many of the CMS out there, the hosting solutions already provide a one-click installation and maintenance support.

Tips 3 – Dedicated IP

Find out if dedicated IP is provided by the potential website webhosting. This is much more convenient than sharing it with multiple users, moreover, it will protect against unwanted proximity.

Tips 4 – SSL certificate

These days, SSL is pretty much a must-have. Take an interest in the possibility of setting up an SSL certificate – the service is provided on a paid and free basis. Respectable hosting providers are adding the SSL certificate for free, as part of the hosting solution. Try to go with those.

Tips 5 – Separate domain registration

Separate your domain registration from your hosting solution. There are many reasons for that. As for recommended domain registrars, check out our review.

Tips 6 – Site backup

It should be possible to back up your site data so in case of technical issues, you will not lose the site and all the money invested in it.

Tips 7 – Hosting SSD hard drives

Find out what type of drives your provider uses – regular hard drives or SSDs. The latter option is better since it works several times faster. Accordingly, site pages also load at increased speed.

Tips 8 – Web hosting uptime

Pay attention to the uptime of the web hosting provider – it shows the time of smooth operation of the site with technical downtimes. The minimum value is 99.5%. It’s important because, in the case of low uptime, the number of dissatisfied visitors is growing, which negatively affects your business.

Tips 9 – Control panel

Consider the convenience of a control panel installed on the server. The way it’s implemented will affect how much time you spend on administration.

Tips 10 – Geolocation

Ask your provider where the equipment is geographically located. Many companies use server capacities located abroad, explaining this by reliability and stability. However, keep in mind that as the distance between the server and the user increases, the download speed decreases and it doesn’t matter if you need to choose a hosting for your landing page, online store or news publication: the farther the server and the more “heavy” elements on the pages, the longer they load.

Tips 11 – Technical support

Take an interest in the technical support work schedule and questions that you can contact for a quick solution for your website webhosting. Look for 24/7 support.

Differences between Shared Hosting VPS Hosting and Dedicated Server Webhosting
Shared Hosting VS VPS Hosting VS Dedicated Server

Where to find a good website hosting provider?

You can search for a hosting company on thematic platforms, forums, and groups. There are also compiled ratings, but there is no guarantee that the information presented in them is objectives or not sponsored by EIG. There are a number of hosting providers we recommend:

DreamHost website hosting

Check out DreamHost, a non-EIG, with free SSL, and SSD based web hosting solution. Already using them for a couple of years on numerous websites and absolutely satisfied with them. Great uptime and support when I need it. It’s one of the best non-EIG hosting services available.

Also, with 90 days money-back guarantee period, it can feel safe with your money.

Start webhosting with DreamHost >

SiteGround website hosting

SiteGround is a non-EIG hosting solution which positions itself as a company offering high-quality, “well-crafted” hosting solutions. It got more unique developer-oriented features. For example, on “GoGeek” plan they do free PCI compliance and free Git & staging areas.

Start webhosting with SiteGround >

WP Engine website hosting

Web hosting offering by WP Engine is an expensive and premium managed WordPress non-EIG hosting for demanding users such as agencies and enterprises.

Start hosting with WP Engine >

What Are IOPS and How It Affects Your Site Speed

What Are IOPS and How It Affects Your Site Speed

IOPS – the name of the group of performance indicators of the disk subsystem, which stands for Input/output Operations Per Second and it’s meaning is exactly as the definition – the number of input/output operations per second.

It’s important to note that it’s a predefined value by the web hosting you use, which enforces the number of input and output operations that allowed on your hosting server at once. If the allowed threshold is reached, throttling of your server requests will start which in turn, will cause a general slowness t your site performance.

One operation refers to reading or writing a file system block (a file system consists of blocks of a fixed length, for example, 4 kilobytes, and large files consist of many blocks).

Another important indicator is latency (delay, the time it takes to complete one operation, measured in milli-or even microseconds).

On VPS and dedicated servers, there is an opportunity to evaluate these indicators. Sometimes similar configurations (for example, 1 core 2 GHz, 2 GB of RAM) gives IOPS values ​​that differ by an order of magnitude.

This is how stable IOPS look like:

Stable IOPS performance

And a not stable IOPS performance:

Not stable IOPS benchmark

Also, take a note on a limited IOPS benchmark:

Limited IOPS performance

How essential is it for sites and web applications? The answer is not entirely obvious.

Modern sites are systems with a multilayer cache (OS, DBMS, programming language interpreter caches, application-level caches). If you look superficially at disk activity while running some popular CMS, then reading may not be there at all. All that is needed to generate the page is already in RAM. This is normal, and IOPS and latency seem to be less important.

But here are some cases where disk activity can be observed:

  • Separate service or the entire server after a reboot when the cache is not “warmed up”.
  • Large database when not everything fits in buffers and cache.
  • Lots of statics, which does not fit in RAM.
  • Sites with user authorization and personalized pages when the cache efficiency is low.
  • Pages with heavy SQL queries spanning large data sets.
  • Creating backups.
  • Lack of RAM, fast cache flushing.

If you don’t want to encounter this slowness from time to time on different pages, and which are therefore difficult to catch, it is better to control IOPS indicators.

To see how intensively your site is working with disk, you can use the iotop program. Installation on Debian will look as follows:

apt-get update
apt-get install iotop

You can call it like this which will show only processes using the disk and update data every two seconds:

iotop -o -d 2

Here is an example site where everything is in the cache:

Particular attention should be paid to the IO column – this is the fraction of the process execution time spent on disk operations. In the case shown, nothing is read from the disk, but only slightly written to the CMS database (perhaps the session information is updated, and something is logged).

And here is a heavy page:

The script was executed for several seconds, while almost 40% of the time was read from disk. And this is an SSD. There could well be a 504 error on a slow disk or with a serious limit on read speed.

When renting inexpensive VPS, it makes sense to check the drive (and of crouse, avoid EIG servers). For a high-quality VPS hosting server, look into our DreamHost hosting review, and SiteGround hosting review.

How to Buy a Domain Name (+ tip to get it for FREE, 2020 Updated)

How to Buy a Domain Name (+ tip to get it for FREE, 2020 Updated)

If you want to increase your visibility as a business or personal brand, connect with your audience, and fight for your own space on the Internet, you must establish an online presence. In a study by GE Capital Retail Bank, between 70-80% of customers at first search for a company online before visiting its premises or committing to a purchase.

Whereas businesses can get online through social media, having a website is the recommended first step into establishing your brand and business online. The website will act as a hub from where the ‘spokes’ connecting to guest blogs, social networking sites and other online spaces emanate.

The first decade of the 21st century has recorded an explosion of technologies that have taken about 1.5 billion websites online. Some of these are business websites while others are for individuals and non-profits. You must be a part of it if you want to succeed online so let’s learn how to buy a domain registration and even how to register a domain name for free.

Getting A Domain Name – Where It All Begins

While you can build a website on your local machine, you cannot take it online without a domain name. Think of your domain name as your online address where all your resources are located. Therefore, getting a domain name from the best domain name registrar is effectively the first step toward building a website.

Much like your personal name, the domain name is your website identity. While coming up with any name suffices, you’ll want one that truly reflects your activities and what you want your website to be known for. This guide discusses all you need to know about domain names, how to find, register, and maintain them.

The Importance of a Domain Name

Are you probably asking yourself how important is a domain name? Well, there are three critical aspects of domain names that you need to appreciate right from the onset.

  • First and lasting impression – Your domain name is the gateway to your website resources. It has the power to give your visitors a positive lasting impression about your brand or ruin the party.
  • Affects SEO Ratings – While exact match domains (EMDs) such as cleanyourroomflorida.com are no longer an outright ticket to the top of search engine result pages (SERPs) having well-placed keywords in your domain name can boost your ranking efforts.
  • An important tool for brand definition – Getting the domain name right makes it easier for your target audience to identify with your brand and for potential customers to quickly wrap their heads around what your business is all about.

How to Register a Domain Name

To register a domain name, you must first identify an ICANN-accredited domain name registrar. The Internet Corporation for Assigned Names and Numbers (ICANN) is a non-profit organization that plays a unique role in defining how the domain names ecosystem works and evolves. Some of the top domain registrars are:

  • NameCheap – A reliable and cheap Los Angeles-based registrar and web hosting provider. Currently home to 10 million domains.
  • DreamHost – FREE domain name registration with webhosting solution. A reliable web hosting that hosts over 1.5 million websites for more than 400,000 users. Get a FREE domain (for 1 year) from DreamHost.
  • Hover – Registrar with headquarters in Toronto, Canada.It’s a good option, but we suggest to go with NameCheap or DreamHost.

To get a hang of what domain registration is all about, we’ll cover three options one for each of the above registrars.

Register a Domain Name with NameCheap.com

Step 1: Go to NameCheap.com and type your domain name into the search box.

Step 2: When you see that your domain name is available, add it to your cart.

How to Buy a Domain Name
Buying a new domain name on NameCheap

Step 3: Note that WhoIsGuard, which is the domain privacy functionality is free forever, while on other sites it can cost up to $9.99 per year. Great perk by NameCheap (and of course, if for some reason you’re not interested, you can simply un-check the box).

Step 4: You can change the term of the registration (number of years for domain registration). I’m suggesting at least a 3-year period, so you won’t have to worry about renewing after the first year.

If you’re absolutely committed to making your website work over the long term, perhaps you should even select the 5-year term domain registration period.

Now press on Confirm Order, insert your payment method information and you got it, your own domain name!

How do get a domain name
Confirming a domain order on NameCheap

Get a Free Domain with DreamHost

A neat trick that we highly recommend people to use is to get a web hosting and domain together. Because, later on, to make your website work, you’re going to need both of them anyway, so why to enjoy a free domain if you can?

So why DreamHost? It’s a Los Angeles-based hosting provider, that not from the EIG list and has been in the industry for close to 25 years and offers free domain name register for up to 1 year.

The free domain name and hosting will also help you save some time, money and the need to migrate your domain name (name servers) to your web hosting service (when you buy them separately, you need to configure your host with your registrar name servers).

DreamHost.com: Currently offers register for FREE domain name (for 1 year) whoever signs up with their web hosting services. Great deal and if you wandered on how to register free domain name, you got it.

Get a FREE domain name together with web hosting package
Register for a free domain name with DreamHost

Q & A: Registering A Domain

The domain registration process, especially to beginners, comes with lots of what, how and why questions. In this section, we shall cover some of the basic questions that are frequently asked in forums, blogs and emails to registrars.

What is a Domain Name?

A domain name is an address that points to the location of your website and web resources. It is much like a stake on the ground that identifies where your business is on the vast world of the internet. An example of a domain is Namecheap.com or Cnn.com.

Domain names were created to replace or stand in for Internet Protocol (IP) addresses. The internet is a massive network of computers each having a unique identity known as an IP address. For instance, an IP address may read 154.70.55.159

As you can imagine, remembering this number every time you want to visit a website is rather difficult. To help ease the pain and simplify website location, domain names were created. A domain name can have a mixture of numbers and letters such as mysite123.com.

What are Domain Name Extensions?

Domain name extensions also know as Top-Level Domains (TLDs) refer to the part of the domain that comes immediately after the dot. Examples include org, com, and net. There are two basic types of domain name extensions.

  • Generic Top-Level Domain – These domains are universal. They do not fall under any specific country or region. Examples are info, net, come, pro, tax, etc. They are regulated by ICANN policies.
  • Country – Code Top-Level Domains: These are domains associated with a geographical region or country. They have two instead of three letters. Examples are nl, dk, ke, de, and ir.

New general top-level domains have come up such as auction, attorney, associates, accountant, and many others. There are more than 300 such domain extensions. In terms of popularity, .com is the highest followed by .net and .org. They are familiar and easy to recall.

When Should you Register a Domain Name?

As soon as you have an idea or a concept around a certain domain name, go ahead and register it. As of the latest number, the total number of domain names registered was around 350 million. Each day, more than 45,000 .com domain names are snapped up.

It is not a must that you have a business up and running before you can register a domain. The best approach is just to register the name for a year as you explore the possibilities of setting up a website. Most registrars give discounted pricing that you can leverage to ensure you don’t miss out on your favorite name.

What’s the Price of a Domain Name

Domain name pricing varies based on the registrar and the extension. Registrars such as Namecheap are known for their affordable domain names. With 10-$11 per year, you can purchase and maintain a .com domain name. Specialized top-level domain names such as .service and .store and others often come at a higher price.

For the first year, most domain registrars give offers to their customers. You can get a domain for as low as $0.98 which then renews at the normal pricing after the promotional year.

You Need to Have a Website to Register a Domain Name?

No, you don’t. There are several options available such as registering a domain and then building your website later on such as NameCheap we previously recommended. You could also register your domain name and put up a coming soon page or a temporary website. Lots of internet-based entrepreneurs are in the habit of buying domain names as part of their portfolio and then holding them with the intention of trading them at a profit.

How do I Pick the Best Domain Name?

Choosing the best domain name begins with a research process. Although nothing is cast on stone, the following are some tips to help you get the best domain.

  • Get a domain name that is simple to spell and pronounce preferably a short name.
  • Go for a .com TLD because of its familiarity with most users
  • Incorporate your brand name and keywords in the domain. For instance, lawnmowingtexas.com
  • Avoid numbers or hyphens and always stick to letters for ease of recall

Which Domain Name Registrar is the Best?

Best could mean many things to many people but in terms of pricing and domain management features, Namecheap, Inc. is one of the best. It always has ongoing coupons and deep discounts for beginners, consistent pricing on renewals and an easy-to-use dashboard with great support in case you will need one.

If you want to try out with a free domain, go for DreamHost. Remember that you can always transfer your domain to another registrar if you don’t feel comfortable with your current registrar.

Which TLD Should You Buy?

The best domain name extension is .com. It is not only easier to remember but also some keyboards and keypads come with a built-in .com extension to make typing easier for users.

How to Get a Domain Name for Free?

As we wrote previously in the article, you can get a free domain name in case you buy it together with a webhosting, from specific hosting providers that provide this service.

We recommend DreamHost, a reliable and SSD based hosting provider that hosts over 1.5 million websites for more than 400,000 users. That’s your solution on how to get a domain name free. Get a FREE domain (for 1 year) from DreamHost.

Do I Need To Register New Domain Extensions?

You probably familiar with the most common .com, .net, and .org extensions, but there are dozens of more potential extensions available. However, these new domain extensions are hard to remember and difficult to brand.

Whereas new domain name extensions are marketed as being brand targeted, some of them may be hard to remember therefore indirectly affecting your brand.

With that being said, You can have more than one domain extension to safeguard your business against destructive competition.

Can I Buy A Domain Name Permanently?

It is not possible to permanently own a domain name. Domain names are bought on yearly renewable contractual arrangements on the minimum. However, you can prepay for up to 10 years thereby getting the assurance of longterm ownership. So if you wandered on how to buy a domain name permanently, that’s your best way to go.

What happens when my Domain Name Expires?

Domain names expire if there is no payment made on the renewal date. Some registrars give you a grace period before taking the domain name back onto the market.

How is the Domain Name Renewal Process?

When you purchase a domain name, you are given access to a dashboard by the registrar from where you can renew your domain. Instead of doing manual renewals each year, you can decide to turn on the auto-renew feature. Domain registrars normally send you renewal reminders to your registered email.

Can I Reserve A Domain Name Without Buying It?

It is not possible to reserve a domain name. The only option available is to register it and then wait until you are ready to build our website.

How Do I Buy An Existing Domain Name?

If you’ve come up with a perfect name for your website but upon checking the domain name with the registrars you realize that it is already taken up, you still have a chance to get it.

However, you may have to first find out when the domain name was registered, who currently owns it and their contact details. Some sellers may decline your offer to purchase while others may give you an outrageous price. All that notwithstanding, it is worth a try.

Conclusion

Registering a domain is not difficult, you only need to have all your ducks in a row before you begin. Take a bold step, buy your domain and build your website. Some registrars have website builders to help you quickly come up with a fancy website.

As we stated in the beginning, our recommended domain registration options are NameCheap for a reliable and cheap domain registrar with great UI, fast support and great pricing and DreamHost for a FREE domain name registration together with web hosting solution that you would probably need for your site as well.

How to Fix WordPress 500 Internal Server Error?

How to Fix WordPress 500 Internal Server Error?

If you manage a WordPress site, you probably encountered, for at least one time, the WordPress HTTP 500 Internal Server Error. It’s one of the most frequent WordPress errors that makes many beginners and advanced users alike, to panic. But, there is no real need to be in hysteria, it’s solvable.

Let’s stay calm, concentrate and remember that many had exactly the same problem. We have fixed errors like the internal server error, error connecting to a database, white screen of death and many others. We can assure you that they are all fixable. In this article, we will tell you how to get rid of a WordPress internal server error by collecting all possible solutions in one place.

WordPress Internal Server Error 500 Example

Why does Internal Server Error happen in WordPress?

An internal server error occurs not only in WordPress, but it can also happen on any server and it really does not say anything to the developer, just that some internal flow in the server has failed.

Asking how to fix this error is the same as telling the doctor that you feel pain, without saying where exactly. Usually, this error happens due to plugins or themes. It can also happen due to a damaged .htaccess file and PHP memory limit. We also heard that these errors sometimes appear only in the admin panel, while everything else can work fine on the rest of the site.

Checking the integrity of .htaccess file

First of all, you need to check the integrity of the .htaccess file. You can do this by renaming it to something else. To do this, access your site hosting via FTP (let’s hope it’s not an EIG hosting). It is located in the same folder as wp-admin, wp-content, and wp-includes.

Once you rename it, try loading your site again. If the problem is resolved, do not forget to immediately go to the admin panel and go to Settings »Permalinks and click on the Save button. This will generate a new .htaccess file.

PHP memory limit increase

Sometimes WordPress internal errors occur if you run out of PHP memory limit. Read our article on how to increase PHP memory in WordPress. What can be done?

  1. Create an empty php.ini file
  2. Insert the next text into it: memory = 64MB
  3. Save the file
  4. Upload it to the / wp-admin / folder using FTP. Some users told us that this helped them solve the problem.

If increasing your memory limit has solved your problem, then this is only a temporary solution. After all, something is wasting your server memory (and if you got a VPS hosting, it’s a good opportunity to benchmark it). This may be a bad plugin or theme feature. We recommend asking your hosting provider to look in the logs to diagnose the problem.

Deactivate all plugins

If none of this helped, then this error was most likely caused by a specific plugin. It is also possible that some plugins do not fit together. In this case, you need to disable all plugins and then enable them one by one.

Follow our tutorial on how to deactivate all WordPress plugins without WP-Admin.

If disabling all the plugins helped, then you can find out which of the plugins is causing the error. Just activate one plugin each time until the error reappears.

Rebooting wp-admin and wp-include

It’s pretty much a last resort solution, but it might help. Download latest the wp-admin and wp-includes folders from a fresh installation of a WordPress site. Upload them to your site FTP and replace the existing versions with the newest one (don’t forget to backup the previous versions).

This will not delete any information but may solve the problem if which file was damaged.

Ask your hosting about it

If all else fails, then contact your hosting provider. By using server logs you can find out the cause of the error.

Tell us in the comments if this error occurred to you and how you solved it. If you know any way to fix the error, then let us know about it!