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A (Address) Entry

A record that resides on your server and that contains your server’s hostname and IP address. The “A” entry is essential because it tells DNS servers the identity of your server, which allows visitors to find your server on the Internet.

Access Control List (ACL)

Permissions that a server's owner grants to a reseller. You can define ACLs in the Edit Privileges section of WHM's Reseller Center interface (Home >> Resellers >> Reseller Center).


Access Control Lists are not the same as Account Creation Limits. 


A record that allows you to access privatized information. For example, your cPanel account allows you to manage your website. In cPanel & WHM, other instances of the term “account” occur in email and FTP.

Account-Level Filter

A rule that determines where to deliver email that was delivered to a domain's main email account and that meets certain criteria. 

Account Suspension

The restriction of an account, usually due to nonpayment. Hosting providers can suspend accounts until they receive payment, and then unsuspend the account. Suspended accounts retain all of their data, but visitors cannot access their websites. For more information, read our What Happens When You Suspend an Account documentation.

Addon Domain

An additional domain name that a cPanel account owns. The system stores each addon domain in its own directory, which website owners can configure. This allows website owners to manage multiple domains from a single cPanel account. You must register addon domains with a domain name registrar.

Addons (cPAddons)

Additional services, which cPanel usually provides, for your users (for example, blogs, message boards, and shopping carts).

Amazon Linux

Amazon's Linux operating system distribution for Amazon Machine Instance (AMI) images. Amazon Linux is functionally compatible with the Red Hat® Enterprise Linux® operating system.


A program that provides information about the visitors to a website in both graphical and statistical views. For more information, visit the Analog website.

Anonymous FTP

A process through which visitors who do not have FTP accounts may upload and download files to and from a website. Although it poses security risks, anonymous FTP is convenient if the site owner wishes to make files publicly available to download. When you set up anonymous FTP, you must change file permissions and directory access permissions in order to protect any sensitive information.

AOL Instant Messenger (AIM)

A widely-used instant messaging program. WHM can notify you by AIM if there is a problem with your server. For more information, visit the AIM website.


A web server software that receives requests from browsers and serves web pages to the browsers. 

Apache Handler

A record that determines how the Apache software processes a specific type of file. By default, Apache only handles certain file types. You can configure Apache handlers for other file types with cPanel. For more information, read Apache's handler documentation.

Apache SpamAssassin™

An application that can filter suspected spam. You can configure Apache SpamAssassin to filter spam more or less aggressively, based on the user's needs. For more information, visit the Apache SpamAssassin website. Server administrators can use WHM's Tweak Settings interface (Home >> Server Configuration >> Tweak Settings) to enable this service for their users.

Application Key (Appkey)

A value that uniquely identifies each application within the cPanel interface. No two items in the cPanel interface share the same appkey.

Application Programming Interface (API)

A set of programming standards and tools that third-party or internal developers can use to interact with a software application. cPanel, Inc. provides several APIs that you can use to customize and integrate with cPanel, WHM, and Manage2. For more information, read our SDK documentation.

American Standard Code for Information Interchange (ASCII)

A common character set that uses the English alphabet.


A daemon for the at command in Linux operating systems, which performs scheduled tasks.


A process that allows you to confirm the identity of someone with whom the server shares sensitive information. On the web, authentication usually involves either a username and password set or a public and private key pair.

Authoritative Nameserver

A nameserver that returns responses to queries for one or more DNS zones. Name Server (NS) records point to the domain's authoritative nameserver. These nameservers do not cache DNS information for related domains.


Autoresponders allow you to automate replies to incoming email. In cPanel, this feature can confirm the receipt of mail, or inform correspondents that the recipient is unavailable (for example, while on vacation).


A process that sets up users' Outlook® or Outlook Express accounts to receive their cPanel email. For more information, read our AutoConfig and Autodiscover documentation.

AWStats (Advanced Web Statistics)

A program that provides information about the visitors to a website. AWStats presents information in both graphical and statistical views. For more information, visit the AWStats website.




Backscatter is the term for bounced email messages (or failed Delivery Status Notifications) that were erroneously sent to a domain when the domain's name was forged as the sender of spam. Use SPF on your mail server to reduce backscatter.


A copy of your website’s files, directories, databases, and email configurations.

  • We recommend that cPanel users store a backup copy of your website on your personal computer.
  • We recommend that system administrators create server and account backups often.

The amount of data that a server transfers. Every time a visitor views a file, whether it is a web page, image, video, or audio file, the server transfers that file to the visitor’s computer. Bandwidth is the total size of all of the files that the system transferred to visitors’ computers. Hosting providers often limit a site owner's bandwidth, because it can affect the performance of the server.

Bandwidth Limit

A limit that hosting providers impose on the amount of data (bandwidth) that an account may transfer per month.


Images that appear on a website, often as advertisements at the top or bottom of a page. Many banners alternate with each successive visit to the page.

Bayes Testing (Bayesian Spam Filtering)

Bayesian spam filtering is a method by which you can filter spam based on statistics. This method uses tokens (generally words) in emails to determine whether an incoming message is spam. This technique relies on Bayesian statistics. Bayesian classifiers correlate the use of tokens with spam and non-spam emails to calculate a probability that an email is or is not spam.

Berkeley Internet Name Domain (BIND)

The most prominently-used DNS server software, it is also referred to as named. For more information, visit the BIND website.


One of the options for how to handle mail that the default or catch-all email addresses of cPanel users receive. The blackhole option discards mail after the server accepts it. For this reason, it may result in additional spam that your users receive, and it places a larger load on your server than the fail option.

  • For BoxTrapper, a list of rejected email senders. BoxTrapper automatically deletes any messages from senders who are on the blacklist.
  • For cPHulk, a list of rejected IP addresses. cPHulk never allows logins to your server from IP addresses on the blacklist.
  • For Exim, a list of IP addresses from which the system drops SMTP connections unconditionally.

A blocker is a check that the system performs performed before a version change takes place. This check reviews your system for possible compatibility issues with a desired upgrade.

Bounce Message

An email reply that informs a sender that there was a problem with email delivery.


A cPanel-included application that requires would-be senders to reply to a verification email in order to filter spam (also known as challenge-response verification). The system only accepts the original email after the sender replies to the verification message.

BoxTrapper Blacklist

A list of email addresses from which the BoxTrapper application automatically blocks incoming mail. cPanel automatically sends a configurable warning message on receipt of mail from a blacklisted address.

BoxTrapper Ignore List

A list of email addresses from which the BoxTrapper application automatically blocks incoming mail. cPanel does not send a warning message on receipt of mail from an address that the BoxTrapper application ignores.

BoxTrapper Whitelist

A list of email addresses from which the BoxTrapper application automatically accepts incoming mail.

Brute Force Attack

A type of attack wherein the attacker enters a large number of combinations of characters, in an attempt to decrypt a key. WHM includes cPHulk, a protection system that allows you to lock out brute force attackers after a specified number of failed attempts.


See Feature.


A copy of cPanel & WHM that uses a specific version number. cPanel, Inc. releases all cPanel & WHM builds in different stages through Release Tiers.


A unit of measure for digital memory storage. One byte represents a group of eight bits (binary digits).




Stored information that the server accesses, instead of the information source, to save bandwidth and time. You can configure DNS record caches in WHM's Edit DNS Zone interface (Home >> DNS Functions >> Edit DNS Zone). You can configure disk usage cache data in WHM's Tweak Settings interface (Home >> Server Configuration >> Tweak Settings).

Catch-All Address (Default Address)

The email address to which cPanel & WHM routes any email message that email accounts that do not exist on a domain sent.


An open-source Linux operating system distribution. CentOS is functionally compatible with the Red Hat® Enterprise Linux® operating system.

Certificate (Public Key Certificate)

An electronic document that states the identity of a server so that end users know that they communicated with the correct website.

Certificate Authority

An entity that issues digital certificates for server verification.

Certificate Authority Bundle (CA Bundle)

A file that contains details about an SSL certificate, such as its issuer and that issuer's certificates and chain of trust. Browsers include a built-in list of trusted certificate authorities, and compare this list against the CA bundle to determine whether to trust an authority.

Common Gateway Interface (CGI)

A protocol that allows a web server to communicate with scripts and other software. cPanel’s deprecated x3 theme's CGI Center interface (Home >> Software and Services >> CGI Center) provides an array of CGI scripts that allow website owners to generate and manage useful features for websites (for example, guestbooks, clocks, hit counters, countdown clocks, and banner ads).


The CGI Center interface (Home >> Software and Services >> CGI Center) only exists for the cPanel x3 theme. You cannot create new CGI scripts with the cPanel Paper Lantern theme.

CGI Script Alias

A feature of Apache that creates the cgi-bin directory. This is a special directory that contains files that Apache executes as CGI scripts.

Chain Of Trust

A record of which certificate authorities have vouched for the authenticity of other certificate authorities. In order for a certificate authority to sell certificates, another certificate authority must vouch for them.

Character Set

A code that pairs a sequence of characters with a set of numbers, which allows a computer to store and transmit the characters. ASCII is one popular character set. Several character sets exist for Cyrillic and Asian alphabets. For more information, read the Wikipedia article about character sets.

Classless Inter-Domain Routing (CIDR)

A routing method that allows you to create routable subnets with finer granularity than the traditional network classes. CIDR notation is the combination of an IP address and an abbreviated subnet mask. This mask consists of a slash (/) and the number of bits (which is between 0 and 32). Larger numbers indicate smaller network segments. For example, the CIDR notation corresponds to an IP address of and a subnet mask of, with a total of eight addresses in the segment.

Command Line Interface (CLI)

A means of communication with a computer, in which you type commands. On Unix systems, this is also often called a shell.


Any application that accesses a service on another computer. Browsers such as Google Chrome are web clients. FTP clients include FileZilla and Cyberduck.


A group of linked servers. cPanel & WHM has two separate clustering options:

  • DNS clusters keep DNS records synchronized among a group of computers. This eliminates the need for manual updates. 
  • Configuration clusters allow the system to replicate settings from a master server to slave servers.

A computer program that translates source code that people (developers) wrote into a language that a computer can read. As a security measure, WHM allows you to disable your web server’s compilers for most users.


Mail server software, known for its IMAP component. For more information, visit the Courier website.

Comprehensive Perl Archive Network (CPAN)

The main repository of Perl modules (pieces of Perl software). The CPAN library contains over 12,000 modules, most of which are free. cPanel & WHM allows you to search CPAN and install Perl modules.


The companion software to WHM, which cPanel, Inc. designs to simplify website maintenance for website owners.

cPanel Market

A system that administrators can use to sell products from various vendors (for example, the cPanel Store) through the cPanel & WHM interface. For example, cPanel's SSL TLS Wizard interface (Home >> Security >> SSL/TLS Wizard) uses the cPanel Market to sell SSL certificates.

cPanel Store

Our online store, through which customers can purchase various services and products such as licenses, support, and SSL certificates.


Your login credentials for cPanel's Store, our ticket system, and Manage2. You can use your cPanelID as an External Authentication method.


cPanel's WebDAV daemon, which provides access to cPanel's Web Disk interface (Home >> Files >> Web Disk).


A WHM feature that helps protect your web server from malicious users who try to gain unauthorized access through brute force attacks.


A copy of a user’s website, which you can create when you run the /usr/local/cpanel/scripts/pkgaccount script. The cpmove file is useful as a backup, and you can manually upload it to restore the user’s web files.


cPanel Service Daemon, the software that runs cPanel & WHM on your server.

CPU Load

The amount of processing ability that programs on your server currently consume, as a percentage. For more information, read the our Troubleshooting High Server Loads on Linux Servers forum article.

Cron Job

A command that the system executes at regular intervals. These commands exist in the crontab Unix configuration file.

Cross-Site Request Forgery Attack (XSRF or CSRF)

To exploit a trusted website, this attack forces a user to execute unauthorized commands, usually through a link. To help prevent XSRF attacks, cPanel & WHM requires every request to contain your unique per-session security token.

.crt File

The file for an SSL certificate, which is an electronic document that ties a public key to a trusted entity. This electronic document is a key piece in the authentication process.

Certificate Signing Request (CSR)

A request that you send to a certificate authority for an identity certificate. cPanel can generate a CSR for you, but because authorities vary with regard to the information that they require, check their requirements before you apply for a certificate.

Cascading Style Sheets (CSS)

A style sheet programming language that describes how a document, often in HTML, should appear.

Change Log

A record of the changes that each development or production release of cPanel & WHM includes. For more information, read our Change Log documentation.


The Common Unix Printing System Daemon, which the web server uses to print. We strongly recommend that you disable the cupsd daemon because it is vulnerable to attacks.


One of cPanel & WHM's release tiers. Versions on this tier are tested and verified, but may not contain all of the proposed functionality of a release. For more information, read our cPanel & WHM Product Versions and the Release Process documentation.

Common Vulnerabilities and Exposures (CVE) System

An archive of publicly-known security threats, vulnerabilities, and exposures. The CVE system assigns numbers (CVE identifiers), which provide a reference point when you evaluate the coverage and effectiveness of security tools and services.




A computer program that runs as a background process. The user cannot view or directly control this process.

Data Center

A facility that houses servers. A data center is generally a safe place to keep a server because it typically includes backup power supplies, multiple communication connections, and environmental controls.


A term that cPanel, Inc. uses to describe a feature that we no longer support, or will remove in an upcoming release.

Directory Harvest Attack (DHA)

A technique that spammers employ, in which they attempt to find valid email addresses through guesswork and various permutations of common addresses.

Dictionary Attack

A method in which a malicious user tries to guess a password with words from a dictionary. This attack is similar to a brute force attack.

Directory (Folder)

A repository for files, analogous to a file folder on a personal computer. In website management, a directory contains the website's files.

Disk Space Quota

A limit that hosting providers place on the amount of disk space that an account may use.

Distribution (Distro)

A particular package or bundle of software applications. Generally, a distribution of software includes all of the necessary components to run the software successfully.

Document root

The directory that contains a domain's publicly-available web files. Your primary domain's document root typically defaults to the public_html directory. The document root directories of any addon domains or subdomains depend on your server's settings.

Domain Name System (DNS)

The component of the Internet that converts human-readable domain names (for example, into computer-readable IP addresses (for example,, in the case of

DNS Zone

An administrative space or portion of the Domain Name System. This space directs Internet traffic to the correct location. For example, is a DNS zone whose servers direct its Internet traffic.

DNS Zone File

A file on your server that primarily maps IP addresses to domain names. A correctly-configured zone file must exist in order for visitors to access your server from the Internet.


A program that manages DNS services and DNS clustering.


The name that a site owner gives to a website, which appears in the website’s URL and email addresses. Generally, domains use the format, where example is the domain name and com is the top-level domain.

Domain Forwarding (Redirect)

A technique that allows you or your users to automatically send visitors to a domain when they access another domain. For example, a user may reach when they type

DomainKeys Identified Mail (DKIM)

An email authentication method which attempts to verify that a message actually came from the domain it appears to have originated from.


Mail server software that has optimal security. For more information, visit the Dovecot website.

Digital Signature Algorithm (DSA)

A method that you can use to generate public and private keys for the encryption of data. The U.S. government developed this algorithm.



EasyApache (EA)

A part of cPanel & WHM that installs, modifies, and validates your Apache web server, PHP, Tomcat, and other components. For more information, read our EasyApache documentation.


One of cPanel & WHM's release tiers. Versions on this tier have only had rudimentary testing and are subject to further modification. We do not recommend this tier for production servers. For more information, read our Product Versions and the Release Process documentation.

Entropy Banner Manager

A cPanel-included script that allows you to manage rotating banner images on your website.

Entropy Search

A cPanel-included script that creates a search engine for your website.

Environment Variables

Values that advanced administrators place within specific files on the server to change the behavior of Apache and PHP. For more information, read our EasyApache documentation.

Error Pages

These pages display warning messages when visitors encounter problems while they try to access your site. cPanel allows you to configure the error messages that display for your site. For more information, read our HTTP Error Codes and Quick Fixes documentation.


Mail server software that you can configure easily. For more information, visit the Exim website.


An unstable feature or setting that may cause unintended consequences. Exercise extreme caution if you enable an EXPERIMENTAL feature or setting.

  • These features may not function with other features or settings.
  • These features are not currently effective security controls.
  • EXPERIMENTAL features do not qualify for our security bounty.

 For information about an EXPERIMENTAL feature’s compatibility, read our Change Logs documentation.

Extended Third Filesystem (ext3)

A journaled filesystem that Linux servers often use.

Extended Fourth Filesystem (ext4)

A journaled filesystem that Linux servers often use. ext4 is the successor to the ext3 filesystem.

External Authentication

This feature allows system administrators to grant users the ability to access their cPanel accounts with an external account provider, such as your cPanel ID or Google.

Extensible Markup Language (XML)

A language that allows developers to create documents that are both human- and machine-readable. Several of cPanel & WHM's APIs include the option for XML output.




An option that you can use to handle mail that the default or catch-all email addresses of cPanel users receive. The fail option returns all mail that the default address receives as undeliverable.


See Bug.


The system that the operating system uses to manage files and directories. If your server uses multiple partitions, each partition might use a different filesystem. Different versions of cPanel & WHM on different operating systems support the ext3, ext4, and XFS® filesystems. 


In cPanel, a tool that processes mail based on your preferences. For example, a filter can automatically discard spam or save mail from a specified sender to its own folder. In cPanel, you can apply filters to the main email account on a domain (Account Level Filters), or customize them for each individual account (User Level Filters).


A security application that protects servers from intrusion by hackers. For example, CSF is a popular firewall for Linux systems. Linux systems also include a built-in firewall, iptables.

Forceful Reboot

One of the two methods that you can use to restart your server. This method forces the server to restart regardless of any errors that it encounters. Only use a forceful reboot if you cannot reboot gracefully, because it may cause data loss.

FormMail Clone

Software that imitates the function of FormMail. FormMail creates an email message from data that a user enters in the text boxes on a web page, and sends the message to the intended recipient.


A tool that allows you to forward a copy of every email message that you receive to another address. When a forwarder exists, you still receive mail at the original recipient address. If, however, you create a forwarder before you create the original address, the system will forward messages to the end address but not to the original address, because it does not exist.

Fully Qualified Domain Name (FQDN)

A name that uniquely defines a domain’s location. The FQDN generally uses the format, with a trailing dot. For the purposes of cPanel, a final dot is not necessary, but the domain name must contain at least two dots. You must write FQDNs in lowercase letters.

File Transfer Protocol (FTP)

A method that you can use to transfer files from one computer to another. cPanel & WHM includes an FTP server that website owners can configure. You must install an FTP client on the local computer in order to send files to and receive files from the FTP server. Some FTP clients include FileZilla (for Windows®, Linux, and Unix), and Cyberduck (for Mac®).



Gem (RubyGem)

A piece of software in the Ruby language. The central repository for these pieces of software is called RubyGems. For more information, visit the RubyGems website.

Generators (Web Statistics Generators)

Pieces of software that compile statistics for your web server. For example, they can report the amount of bandwidth that each domain has transferred. cPanel & WHM includes three statistics generators: Analog, AWStats, and Webalizer.

General Availability (GA)

A stage of the software release cycle. When the product reaches this stage, we recommend it for widespread production usage.

Gigabyte or Gibibyte (GB or GiB)

A unit of measure for digital memory storage. Generally, for the purposes of this documentation, one gigabyte is one gibibyte, equal to 1,024 Megabytes, 1,048,576 Kilobytes, or 1,073,741,824 bytes.

GNU Privacy Guard (GnuPG)

A suite of tools that you can use for data encryption and signing. Generally, you will use these tools for signing emails. For more information, visit the GnuPG website.

Graceful Reboot

The preferred way to restart your server. This method stores new system information before the server shuts down.


A service that protects a server against unwanted email or spam. When you enable greylisting, the mail server temporarily rejects any email from a sender that the server does not recognize. If the email is legitimate, the originating server attempts to send it again after a delay. After sufficient time passes, the server accepts the email.

GUID (Globally Unique Identifier)

A value that the system uses to identify a resource, similar to UUID.


A program that compresses files for disk space conservation, minimizes transfer times, and makes the transfer of multiple files easier. The compressed files use the filename extension .gz. Unix and Linux systems often use gzip with the tar command to create a tarball file, which uses the .tar.gz file extension.



Home Directory

A cPanel account’s highest-level directory, which contains all of the files and directories that the account's websites use. Visitors cannot view the files in a home directory unless they reside in the public_html directory or one of its subdirectories.

Horde Webmail

A webmail client that cPanel & WHM includes. A webmail client allows users to check email through a browser.


The unique, human-recognizable name for a server across the Internet. For example, System administrators can specify or change the server’s hostname with WHM’s Change Hostname interface (Home >> Networking Setup >> Change Hostname). The server hostname is distinct from your domain name.

Hotlink (Inline Link)

A direct link that embeds a file (such as an image or video) from your site into another website. When another site embeds your files, it uses your bandwidth to serve those files.


A file that resides in a specific directory, and contains configuration information that applies to that directory. The .htaccess file may also contain authentication instructions.

Hypertext Markup Language (HTML)

The language in which website owners write most pages on the Internet.


A file that resides in a specific directory, along with an .htaccess file. The .htpasswd file contains encrypted password information when the owner has set up authentication for the directory.

Hyptertext Transfer Protocol (HTTP)

The primary method (protocol) by which you transfer data over the web.


The configuration file for the Apache web server. For more information, visit the Apache website.




An instant messaging service. You may choose to receive updates from your server through ICQ. For more information, visit the ICQ website.

Identity Provider

A third-party authority that you can use to log in to other sites or services.

Include (file)

A file that a program automatically includes within another file. In WHM, you can add a series of specifications to your Apache configuration file (httpd.conf) through the include command.

Index Page

The page, generally index.htmlindex.htm or index.php, that visitors view by default when they access a website directory. If no index page exists for the specified directory, the visitor sees a list of files in that directory, unless you disable indexing in cPanel.

Internet Message Access Protocol (IMAP)

One of the two most widely used email transfer methods. IMAP synchronizes email account information with the mail server on a regular basis. If a user logs in to multiple computers to check email, IMAP allows the user to see which messages they have viewed, replied to, or forwarded. 

Internet Protocol (IP)

The main protocol that relays information across the internet. This protocol uses IP addresses to deliver information from one host to another. cPanel & WHM supports two versions of Internet Protocol:

  • IPv4 is an older version that uses 32-bit IP addresses. This version has limited availability, but is more widely used and accessible.
  • IPv6 is a newer version that uses 128-bit IP addresses. This version has vast availability of addresses, but requires an IPv6-enabled network and server.
Internet Protocol (IP) Address

A number that identifies a computer on a network, which makes it possible for other computers to find and communicate with it. 

Internet Service Provider (ISP)

The company or organization that provides your access to the internet. 


A loader that, if enabled, can load PHP for cPanel. For more information, visit the IonCube website.

Internet Relay Chat (IRC)

A method of real-time online communication that allows both group discussion and one-to-one messaging, as well as data transfer.



Jailed Shell

A CLI configuration that restricts users’ access rights. The system limits shell sessions to a filesystem that does not contain the home directories of other cPanel users on the system.


A computer programming language that many web applications use. cPanel uses Java to provide the Java Telnet feature. These small applications, which run within the context of a browser, are called applets.

JavaScript Object Notation (JSON)

A language that allows developers to create documents that are both human- and machine-readable. JSON is often easier to use than XML. Several of cPanel & WHM's APIs include the option for JSON output.




A central component of your server’s operating system. The kernel manages communications between the user and the server’s resources, such as its processor and the memory.


In cryptography, keys encrypt or decrypt information. Keys are an important part of encryption and security, and you should guard them appropriately. Key files use the .key filename extension.

Kilobyte or Kebibyte (KB or KiB)

A unit of measure for digital memory storage. Generally, for the purposes of this documentation, one kilobyte is a kebibyte, equal to 1,024 bytes.

Known Netblock

A Class C address space that contains an address from which a user has successfully logged in.




An acronym for the combination of Linux, Apache, MySQL, and PHP. This is a common combination of software for web servers.


A visitor who uses another person’s password to access a restricted area of a website. cPanel allows you to redirect likely offenders or disable accounts with compromised passwords in order to prevent leeches.


A term for an old software program or computer system that is still in use, or for a previous version of a cPanel or WHM feature.


A Unix-based, open-source operating system.


The part of a system that loads a program. Use WHM's Tweak Settings interface (Home >> Server Configuration >> Tweak Settings) to choose the loader that cPanel & WHM uses for PHP. 

Local Host

The computer that you currently work on.

Local User

A user who accesses a service on the machine on which the service exists, as opposed to remotely.


A file that the server automatically creates, which records activities that specific programs and applications on the server perform. For example, error logs list the errors that visitors have encountered on websites that Apache generates.

Log Files

The following list includes many of cPanel & WHM's log files:

  • /usr/local/apache/logs/access_log — A record of the IP addresses of visitors who accessed sites on your server.
  • /usr/local/cpanel/logs/cpdavd_error_log — A record of errors that the cpdavd daemon encountered.
  • /usr/local/cpanel/logs/cphulkd_errors.log — A record of errors that cPHulk's cphulkd daemon encountered.
  • /usr/local/apache/logs/error_log — A record of errors that the Apache web server encountered.
  • /usr/local/cpanel/logs/license_log — A record of errors that cPanel & WHM encountered when it checked its license.
  • /usr/local/cpanel/logs/login_log — A record of failed login attempts.
  • /usr/local/cpanel/logs/stats_log — A record of the activities of the cpanellogd daemon, which compiles your server’s web statistics.
  • /usr/local/cpanel/logs/tailwatchd_log — A record of errors that the tailwatchd daemon encountered. This daemon monitors your server’s logs.
Long-Term Support (LTS)

One of cPanel & WHM's release tiers. Versions on this tier receive important updates and fixes only. For more information, read our cPanel & WHM Product Versions and the Release Process and cPanel & WHM Long-Term Support documentation.



Mail Server Name Indication (Mail SNI)

Allows clients to request a specific hostname at the beginning of the handshake process. In our documentation, SNI refers to this protocol in relation to Apache, while Mail SNI refers to this protocol in relation to Exim.

Mail Transfer Agent (MTA)

A program that sends and receives email messages.


A format that stores email as individual messages with unique filenames. Maildir is cPanel & WHM's default mail storage format.

Mail Exchanger (MX) Entry

A record that specifies where the system sends email for a domain, because it contains the mail server’s IP address. When you use an email scanning service or custom mail delivery, the server administrator may need to change the MX record for a domain in WHM's  Edit MX Entry interface (Home >> DNS Functions >> Edit MX Entry).

Mailing List

A list of email addresses that mailing list members can use to communicate. Alternatively, you can use a mailing list to send email messages to a large group of people. cPanel & WHM uses the Mailman program for mailing list software.


Mailing list software that sends email messages to a group of specified email addresses. For more information, visit the Mailman website.


A cPanel, Inc. website that allows you to perform license-related tasks. Hosting providers log in to Manage2 to add, update, or remove cPanel product licenses, or to manage and pay invoices from cPanel, Inc. For more information, read our Manage2 documentation.


A relational database management tool and server, as well as the type of database it manages. Databases are an integral part of web applications, such as bulletin boards and blogs.  cPanel & WHM provides an integrated MariaDB interface as well as MariaDB database editing tools. 

Megabyte or Mebibyte (MB or MiB)

A unit of measure for digital memory storage. Generally, for the purposes of this documentation, one megabyte is a mebibyte, equal to 1,024 Kilobytes, or 1,048,576 bytes.


An Apache module that allows visitors to enter your hostname, a tilde (~), and the website owner's username in order to view a website (for example, ). We recommend that you disable mod_userdir in WHM's Security Center interface (Home >> Security Center) because the system attributes bandwidth that this method uses when a visitor accesses the site to the hosting provider’s main domain, and skips bandwidth monitoring systems. For more information, visit the Apache website.


In encryption algorithms like RSA, the modulus is the number that both the private and public keys have in common. The plural of modulus is moduli. You can view a key’s modulus in WHM's SSL Storage Manager interface (Home >> SSL/TLS >> SSL Storage Manager).


In general computing, to mount a file system is to make it accessible to users. In a Unix or Linux operating system, you can use the mount command to tell the operating system that a file system or device is ready to use and to affix that system or device to a certain directory.

Multipurpose Internet Mail Extensions (MIME) Type

A component of a file that identifies the file type, so that browsers handle it correctly. cPanel & WHM allows you to specify which application to use to open files with a specific extension.

Multi Router Traffic Grapher (MRTG)

Software that allows you to monitor network traffic. For more information, visit the MRTG website.


A relational database management tool and server, as well as the type of database it manages. Databases are an integral part of web applications, such as bulletin boards and blogs. cPanel & WHM provides an integrated MySQL interface as well as MySQL database editing tools. 




A physical computer that contains a list of domain names and their IP addresses. These computers allow visitors to access a domain through its IP address. Nameserver software gathers data about domains over time. Because of this, changes to DNS records may require 48 hours or more to reach all of the nameservers on the Internet (propagate).

Network File System (NFS)

Allows users to access remote files as though the hardware that they access to manipulate the file was part of the local machine.

nfs statd

A process that mounts NFS file systems.

Network Information Service (nis)

A directory protocol that distributes information across or within networks.


A Unix or Linux system account with the UID of 99. This system account executes CGI and PHP scripts if suEXEC is disabled.


A DNS server daemon. For more information, visit the NSD website.



Open Relay

A mail server configuration that allows anyone to send mail through the server. For security reasons, we strongly recommend that you do not allow your server to operate as an open relay.

OpenID Connect

A standard for third-party authentication. cPanel & WHM's External Authentication feature uses OpenID Connect to communicate with third-party authentication providers.


A feature that uses PHP to deny users the ability to open files that are outside of their home directories. You can enable this feature in WHM’s  PHP open_basedir Tweak interface (Home >> Security Center >> PHP open_basedir Tweak).

Operating System (OS)

The background software that runs all of the other software applications on your system. The OS is a required part of any server. cPanel & WHM supports specific versions of the CentOS, Red Hat® Enterprise Linux, and CloudLinux™ operating systems.

Option Module (opt mod)

An Apache configuration option that advanced administrators can add to the EasyApache (Apache Update) interface.



  1. The set of resource limits that hosting providers assign to a user’s account. You can create, edit, and delete packages in WHM's Packages section (Home >> Packages).
  2. A collection of software that is bundled together for distribution and installation. cPanel, Inc. provides various third-party software, such as FTP and MySQL, as RPM packages that the rpm.versions system manages. For more information, read our rpm.versions documentation.
Parked Domain

A second domain that points to a primary domain. When users attempt to access the parked domain, they see the primary website. For example, both and point to the same website, because is a parked domain for

Passive Mode (PASV)

A mode for FTP connections that initiate connections from the client side. You may use this mode if a user has problems when they attempt to connect to an FTP server through a firewall.

Passive OS Fingerprinting (p0f)

A service that reports the visitor's operating system and other information for email notifications. This information will help you quickly identify visitors who trigger events which cause alerts.


A version of MySQL, which the Percona company enhances and maintains.


A useful programming language for web applications. Perl applications are commonly found as, and .cgi files and may require Perl modules. You can install Perl modules from cPanel's Perl Modules interface (Home >> Software >> Perl Modules) or WHM's Install a Perl Module interface (Home >> Software >> Install a Perl Module).

Perl Module

A piece of software in the Perl language. Modules are common pieces of software that developers reuse. For example, a developer can use a calendar module in a program, and then will not need to write a new set of functions to display calendars.

Perpetual Development

A stage of the software release cycle, in which software remains at the alpha or beta development stage for an indefinite period of time. Developers often use this stage to release new features early in order to encourage wide-spread testing and feedback by early adopters. Perpetual development software is not subject to the same quality standards as General Availability releases.


A computer scripting language that many web-based applications use. PHP applications commonly use the .php.php4, or .php5 file extensions. Some PHP applications require PEAR packages.

PHP Extension and Application Repository (PEAR)

A repository of PHP code. cPanel allows you to search for and install PEAR packages that consist of PHP programs, which can perform useful functions for your website. You can install PEAR packages in cPanel's  PHP PEAR Packages interface (Home >> Software >> PHP PEAR Packages) or in WHM's  Module Installers interface (Home >> Software >> Module Installers).

PHP Extension Community Library (PECL)

A repository for C extensions (pieces of software) for use in PHP. For more information, visit PHP's PECL website.

PHP FastCGI Process Manager (PHP-FPM)

An alternative FastCGI implementation that improves performance of PHP scripts on servers.

PHP Package

A piece of software that uses the PHP language.


A graphical application that allows server administrators to manipulate and manage MySQL databases over the Internet. For more information, visit the phpMyAdmin website.


An authentication method for mail servers. This method allows a user who received mail through POP3 or IMAP to send mail for 30 minutes without the need to reauthenticate through SMTP.


A service that maps program numbers to network addresses on a server (often, rpc.portmap or portmap).

Portable Operating System Interface (POSIX)

A standardized collection of commands for the Unix operating system.


A database management system that is similar to MySQL. For more information, visit the PostgreSQL website.

Post Office Protocol version 3 (POP3)

One of the two most widely used email transfer methods. POP3 copies every message in an email account to a local computer and removes it from the mail server. The system does not send information back to the email account about message replies or forwarding. If an account owner uses multiple computers to check email, we strongly recommend that they use IMAP instead of POP3.

Private Key

A string of characters that a computer uses to encode or decode the encrypted messages that it receives. Encryption schemes use a pair of keys (one public key and one private key) to create a secret code. When you use an encryption scheme, anyone who looks at messages that your computer sent or received cannot determine the contents of those messages without access to the private key. A private key protects your confidential information, and you should safeguard it appropriately.


An instance of a program that runs on your machine.

Process ID (PID)

A unique number that your server assigns to each process that runs.


One of two FTP servers that cPanel & WHM includes. For more information, visit the ProFTPd website.


The spread of a domain’s DNS information across the Internet.

Proxy Server

This server receives requests from users and forwards those requests to other servers.

Public Key

A string of characters that a computer uses to encode or decode the encrypted messages it receives. Typically, you place a public key on a server so that you can establish an encrypted connection to that server.


A subdirectory, inside of your home directory, that contains files that are publicly accessible through FTP. FTP users may also upload files to this directory. This is the default directory that users access when they connect to your site through anonymous FTP.


A subdirectory, inside the home directory, that contains files that are publicly accessible through HTTP. The www directory is a link to the public_html directory. Visitors can view any files and folders in the public_html directory over the Internet, unless the website owner specifically protects them with password protection or the .htaccess file.


One of two FTP servers that cPanel & WHM includes. For more information, visit the Pure-FTPd website.


A programming language that many applications use. When you encounter this term in WHM's Update Preferences interface (Home >> Server Configuration >> Update Preferences), it refers to the Python interpreter, which must be installed on the server before it can run Python programs. For more information, visit the Python website.




Limits to the amount of disk space that a user may use. In order to set up quotas for your users, you must first use WHM’s Initial Quota Setup interface (Home >> Server Configuration >> Initial Quota Setup).



Raw Opts (Custom Configuration Flags)

Lines of data that advanced users can add to a specific file on the server in order to customize Apache's configuration. For more information, read our EasyApache documentation.

Realtime Blackhole List (RBL)

A list of mail servers that are known to send spam. You can subscribe to the list and block incoming mail from such mail servers in WHM's Exim Configuration Editor interface (Home >> Service Configuration >> Exim Configuration Manager).

Red Hat® Enterprise Linux®

A commercial Linux operating system distribution. CentOS is functionally compatible with the Red Hat Enterprise Linux operating system.


A feature that sends users to a different domain than the one that they attempted to access. For example, a user may reach when they type cPanel allows website owners to set up either temporary or permanent redirects. See also domain forwarding.

Referer (HTTP Referer)

A web page that links to a site. This spelling is the industry standard term, though it is based on a misspelling of referrer.

Regular Expressions

Often seen as regex or regexp. Regular expressions allow you to format text so that a specified program can process it and use it to search in a prescribed way. A wildcard character such as an asterisk (*) is an example of a regular expression.


A user who forwards email to a secondary destination. WHM’s View Relayers interface (Home >> Email >> View Relayers) allows you to view users on your server who have relayed mail.


One of cPanel & WHM's release tiers. Versions on this tier are feature-complete and well-tested. For more information, read our cPanel & WHM Product Versions and the Release Process documentation.

Release Candidate (RC)

A stage of the software release cycle, in which feature development is complete and the software passes all known tests. We stage Release Candidates to become the next Production, or General Availability, Release. Release Candidate software may experience limited real-world testing.

Release Tiers

These exist in four types which are, in order from least to most stable, EDGE, CURRENT, RELEASE, and STABLE. For more information, read our cPanel & WHM Product Versions and the Release Process documentation. 


In the hosting industry, resellers use a large amount of resources (bandwidth and disk space) on your server and sell those resources in smaller packages to individual cPanel account holders.


The client side of the DNS system. Resolvers are programs that process DNS queries and work to obtain an IP address from a human-recognizable URL. In Unix and Linux, the /etc/resolv.conf file usually points to a server’s resolvers.


In web hosting, a process that uses backup files to replicate an account on a server. This functionality is useful, for example, to recover damaged files or data, or in the case of a full hardware failure.

Restricted Restore

A feature in WHM that performs additional security checks on backup files, and then restores them to the server.


In computing, a rollback involves the restoration of any part of a system to a previous configuration.

  1. Specific to Unix and Unix-based systems, the system account. The system administrator uses this account, and it carries full privileges to configure a computer system.
  2. The highest-level directory in a Unix or Unix-based system. Generally, we notate this directory with a forward slash (/).
RoundCube Webmail

A webmail client that allows users to check email through an browser rather than an email client.

RPM Package Manager (RPM)

In our documentation, this term may refer to the packaged .rpm file, the software that that file contains, or the package manager itself. For more information, visit the RPM website.


An algorithm that generates public and private keys when to send encrypted data between a local machine and a remote machine. The name of this method is not an abbreviation; it is named after its three inventors.


An object-oriented programming language. System administrators can install and run Ruby programs on cPanel & WHM servers. For more information, read our Guide to Ruby Installations documentation.


A package manager for the Ruby programming language. Developers can use RubyGems as a self-contained format for Ruby programs and libraries.

Ruby on Rails® (RoR)

An open-source framework that runs on the Ruby programming language. 



Script Hooks

A program that an event triggers. WHM's EasyApache (Apache Update) interface allows you to embed custom hook scripts into the Apache configuration process. cPanel & WHM also allows you to create custom script hooks.

Secure Copy Protocol (SCP)

A method that you can use to transfer encrypted files from one computer to another. This method prevents the interception of data.

Secure Shell (SSH)

A network protocol that allows a user to log in to a remote machine securely. cPanel & WHM can create keys to authenticate a user's identity during SSH login, and allows users to manage SSH keys.

Self-Signed Certificate

An SSL certificate that does not verify the identity of the server. This is the equivalent of someone who claims that they are who they say they are. Browsers generally warn users about the authenticity of self-signed certificates.

Sender Policy Framework (SPF)

A feature that allows a recipient server to verify that the domain specified in the From: field really sent the email message. Enable SPF to prevent your server's replies to spam that forged your domain name as part of the sender’s address. SPF only functions if both the sending and receiving mail servers use SPF.


On servers that run CentOS 7, you may see a named warning about the absence of SPF resource records on DNS.

  • This warning is not relevant on CentOS 7 servers, because RFC 7208 deprecated SPF records. CentOS 7 servers use TXT records instead of SPF records.
  • Red Hat 7.1 and CentOS 7.1 both contain bind-9.9.4-23.el7, which is an updated version of BIND that complies with RFC 7208. To resolve this issue, update your operating system to a version that contains the updated version of BIND. For more information, read the the Red Hat Bugzilla case about SPF record errors.

Server Rewriting Scheme (SRS)

A scheme that rewrites the envelope sender of an email so that you can forward mail, but not break SPF.

Server Contact

The server administrator whose contact information you enter in WHM's Basic cPanel & WHM Setup interface (Home >> Server Configuration >> Basic cPanel & WHM Setup).

Server Name Indication (SNI)

Allows clients to request a specific hostname at the beginning of the handshake process. In our documentation, SNI refers to this protocol in relation to Apache, while Mail SNI refers to this protocol in relation to Exim.

Service Manager

In computing, a piece of software that monitors the processes and services on a machine. WHM’s Service Manager interface (Home >> Service Configuration >> Service Manager) allows you to enable and disable services.

Shell (CLI)

Software that allows a user to interact with a computer. Many Unix shells allow the user to run commands.

Shell Fork Bomb

A shell fork bomb is a malicious process that creates a cascade of new processes in order to use a server’s system resources, which, in effect, crashes the server. WHM offers a protective service from shell fork bombs.

Shopping Cart

Software that web servers use to handle ecommerce. A shopping cart allows the shopper to hold items that they wish to purchase while they continue to shop on the website.


A link to an application that allows you to access it from a convenient location, like your computer’s desktop.

Skeleton Directory

A directory that defines which files and subdirectories new accounts own by default. When you create an account, the new user’s account contains an exact copy of the skeleton directory.

Smart host

A type of mail relay server. A smart host permits an SMTP server to send emails to an intermediate mail server before it sends messages to their final destination.

Simple Mail Transfer Protocol (SMTP)

This protocol is the standard by which you transmit email messages across the Internet. Use SMTP to send mail to a mail server’s Mail Transfer Agent (MTA).


PHP loaders that utilize a binary bytecode and, sometimes, multiple levels of encryption. For more information, visit the SourceGuardian website. You can use WHM's Tweak Settings interface (Home >> Server Configuration >> Tweak Settings) to select a PHP loader.


Chiefly, unsolicited email that an automated system sends in bulk. Because recipients consider spam to be a costly nuisance, cPanel & WHM includes features like Apache SpamAssassin and BoxTrapper that can reduce the amount of spam that you receive. Server administrators can use WHM's  Tweak Settings interface (Home >> Server Configuration >> Tweak Settings) to enable these services for their users.

Spam Box

The directory in which Apache SpamAssassin stores spam messages when you enable the Spam Box feature. Generally, the system stores Spam Box messages in the spam folder for the email account.

Spam Score

A value that Apache SpamAssassin assigns to every email message, based on the number of spam-related traits within the message. The higher a message's spam score, the more likely it is to be spam.


An attack in which attackers appear as another user through the falsification of data, in order to conceal their identities. Enable SPF to make it more difficult for spammers to spoof a domain.


A type of file that can incorporate several different images. The cPanel interface uses sprites to decrease load time. When you add an icon, cPanel adds it to the appropriate sprite file.

SQL Database

A type of relational database management system.

SquirrelMail Webmail

A webmail client that allows users to check their email through browsers.

Secure Sockets Layer/Transport Layer Security (SSL/TLS)

TLS is a more recent version of SSL. Both are cryptographic schemes that allow for secure interaction between a browser and a web server. SSL/TLS should protect all sensitive data (for example, credit card numbers) that you transmit over the Internet. Website owners can install an SSL certificate on a website in WHM's Install a SSL Certificate on a Domain interface (Home >> SSL/TLS >> Install a SSL Certificate on a Domain) to allow SSL/TLS to protect the site.

Session (Login Session)

The period of activity between when you log in to and log out of an account or service. Each cPanel & WHM session generates a new security token that is only valid during that session. For more information, read our How to Access cPanel & WHM Services documentation.

SSL Certificate

An electronic document (with the filename extension .crt) which binds a public key to an identity that consists of an email address, company, and location. This electronic document is a key piece in an authentication process.


One of cPanel & WHM's release tiers. Versions on this tier have received considerable public exposure, testing, and verification. For more information, read our cPanel & WHM Product Versions and the Release Process documentation.

Style (Skin)

A set of graphics and settings that determine the appearance of a user’s cPanel interface.


A subsection of a website that exists as a subdirectory in the website owner's home folder. If the domain were, then the subdomain URL would appear as


An Apache feature that allows users to run CGI and SSI applications on the system as themselves. By default, the system account (the nobody account with a UID of 99) executes CGI and SSI.




A program that collates files for transfer or distribution. The system usually compresses files that this program processes into tarballs, which use the .tar file extension.


A file that the tar program collates, and usually compresses.


A network protocol that allows a user to log in to a remote machine user account remotely. Telnet is similar to SSH, but less secure. Do not use Telnet to connect to your website except for testing purposes. Telnet sends login information as plain text, which others can easily intercept.

Template Toolkit (Perl Template Toolkit)

A Perl library template processing system that we use to create templates for all of the cPanel and WHM interfaces. For more information, read our Guide to Template Toolkit in cPanel & WHM documentation or visit the Template Toolkit website.

Terabyte or Tebibyte (MB or MiB)

A unit of measure for digital memory storage. Generally, for the purposes of this documentation, one terabyte is a tebibyte, equal to 1,024 Gigabytes.


In cPanel software, the theme is the larger, skeletal frame work to which the system applies the style.


A smaller version of an image file, which allows you to easily view multiple images. cPanel includes a tool to create thumbnails.

Time to Live (TTL)

A value that specifies how long the system retains a particular record in memory before deletion. 


A small box of information that hovers above an icon when the cursor points at it. 

Trojan Horse (Trojan)

Software that claims to perform one function but actually performs malicious functions secretly.

Trust Key Relationship

A cryptographic scheme that involves a public and private key pair.


The only certificate authority from which you can purchase an SSL certificate within cPanel & WHM. Purchase Trustwave certificates in WHM's Purchase and Install an SSL Certificate interface (Home >> SSL/TLS >> Purchase and Install an SSL Certificate).

Two-Factor Authentication (2FA)

An improved security measure that requires two forms of user identification: a password and a generated security code. When you enable 2FA, an application on your smartphone will supply a generated security code for authorization.



User Datagram Protocol (UDP)

A connectionless transport protocol that works in conjunction with the Internet Protocol (IP). UDP transfers small units of data that require little reassembly, because it does not transmit data packets in a sequential order. It primarily broadcasts messages over a network. DNS lookups use UDP.

User ID (UID)

The unique user number that the system assigns to each user during a session. The following table lists some important UIDs:

0rootThe top-level system user.
99nobodyThe default executor of CGI scripts, if suEXEC is disabled.


The system reserves UIDs 0 through 100 for system accounts like admin and root.

Unix Time

Unix time measures the number of seconds that have passed since the 1st of January, 1970 UTC.

Uniform Resource Identifier (URI)

A string of characters that identifies a website. Some information uses URI synonymously with the terms URL and web address, though technical differences exist between the three terms.

URI Encoding

Encodes information within a Uniform Resource Identifier (URI). In URI encoding, you must convert characters that browsers reserve for URL formatting into percent-encoded characters (for example, encode the forward slash (/) as %2F). For more information, visit URL Encoding at W3Schools.

Uniform Resource Locator (URL)

A string of characters that identifies the location of a website. Some information uses URL synonymously with the terms URI and web address, though technical differences exist between the three terms.


A person who uses a computer to accomplish some purpose.

UUID (Universally Unique Identifier)

A value that the system uses to identify a resource, similar to GUID.




A method to host multiple domains on a single server and sometimes on a single IP address. For more information, visit the Wikipedia article on VirtualHost.

Virtual Private Server (VPS)

A virtualized server. A single physical server can host multiple VPSs, each of which run their own instances of an operating system. This allows each VPS to have a separate root or superuser account, and to operate independently.


A person who views a website.



Web Browser

An application that visitors use to view and interact with sites and pages on the World Wide Web. Examples include Firefox®, Internet Explorer®, and Safari®.

Web Disk

A cPanel feature that allows website owners to drag and drop files to manipulate them.

Web Root

The top-most directory of your website (public_html or www), inside which all of the files and subdirectories for your website reside.

Web Server

A program, such as Apache, which receives requests from clients (browsers), retrieves the requested web pages, and serves them to the clients.


A program that displays various statistics for a website in tables and graphs. For more information, visit the Webalizer website.


Any application that allows website owners to access email through a browser. The main advantage to webmail is the ability to access the email account from any computer on the Internet without the need to install or configure a specific mail program.

Wheel Group

This group of users can execute the su and sudo commands on a Unix-based system, which allows them to become the root user. The su command requires the password for the root user, while the sudo command requires the user’s account password.

  • For BoxTrapper, a list of approved email senders. BoxTrapper automatically delivers messages from senders who are on the whitelist directly to the inbox.
  • For cPHulk, a list of approved IP addresses. cPHulk always allows logins to your server from IP addresses on the whitelist.
WebHost Manager® (WHM)

Companion software to cPanel, which we design for hosting providers, resellers, and system administrators.


A Unix or Linux command that you can execute in a terminal session in order to find out who owns a domain. For example, whois returns the ownership information for cPanel.


For the purposes of cPanel, www is a link to the directory that holds the files that make up your website (~/public_html).



X-source Headers

Pieces of information that the system adds to email messages from a PHP script on your server, which detail the script’s location. Enable these headers to help you locate insecure email scripts that spammers have abused. You can enable these headers in WHM's Tweak Settings interface (Home >> Server Configuration >> Tweak Settings).


A high-performance filesystem for 64-bit servers. Servers that use CentOS 7 or later can use the XFS filesystem with cPanel & WHM.



YAML Ain't Markup Language or Yet Another Markup Language (YAML)

A language that allows developers to create documents that are both human- and machine-readable. Many of cPanel & WHM's configuration files use this format.



Zone (DNS Zone)

An administrative space or portion of the Domain Name System. This space directs Internet traffic to the correct location. An example is, a DNS zone whose servers direct its Internet traffic.

Zone file (DNS Zone File)

A file on your server that primarily maps IP addresses to domain names. A correctly-configured zone file must exist in order for visitors to access your server from the Internet.