We have a new documentation site for cPanel & WHM! You can find our new documentation site at docs.cpanel.net.

We will continue to maintain our API documentation on this server.

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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 tells DNS servers the identity of your server, which allows visitors to find your server on the Internet.

Absolute Domain Name

See Fully Qualified Domain Name.

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 (WHM >> 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.

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.

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.

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 Machine Instance (AMI) images. Amazon Linux is functionally compatible with the Red Hat Enterprise Linux (RHEL) 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)

An instant messaging program that AOL discontinued on December 15, 2017. We removed AIM in cPanel & WHM version 70.


A web server software that receives requests from browsers and serves web pages to the browsers. For more information, visit the Apache website.

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 in cPanel's Apache Handlers interface (cPanel >> Home >> Advanced >> Apache Handlers). For more information, read Apache's handler documentation.

Apache SpamAssassin

An application that filters 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. You can enable this service for users in WHM's Tweak Settings interface (WHM >> Home  >> Server Configuration >> Tweak Settings).

API Token

An authorization key hash that allows you to grant third-party users permission to run API functions with WHM account data. You can manage API tokens in WHM's Manage API Tokens interface (WHM >> Home >> Development >> Manage API Tokens). For more information, read our Guide to API Authentication - API Tokens in WHM documentation.

Application Key (Appkey)

A value that uniquely identifies each application within the cPanel interface. No two items in the cPanel interface share the same app_key value. For more information, read our Guide to cPanel Interface Customization - Appkeys documentation.

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, L.L.C provides APIs that you can use to customize and integrate with cPanel, WHM, and Manage2. For more information, read our Developer Documentation documentation.

American Standard Code for Information Interchange (ASCII)

A traditional character encoding standard that represents text in electronic communications. UTF-8 encoding has surpassed ASCII as the modern standard for character encoding.


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.


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


Autoresponders allow you to automate replies to incoming email. You can configure automatic email response messages in cPanel's Autoresponders interface (cPanel >> Home >> Email >> Autoresponders).


A feature in WHM that provides free, Domain-Validated SSL certificates to users' domains. The system periodically inspects users' installed certificates and replaces those that are about to expire or that are insufficient to provide a baseline level of security. This feature is available in WHM's Manage AutoSSL interface (WHM >> Home >> SSL/TLS >> Manage AutoSSL).

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. Also referred to as outscatter, misdirected bounces, blowback, and collateral spam.


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

  • We recommend that cPanel users store a backup copy of their website on a 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, such as a web page, image, video, or audio file, the server transfers that file to the visitor’s computer. Bandwidth refers to 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)

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. This is also referred to as named. For more information, visit the BIND website.

Blackhole (Black Hole)

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


A method of access control that access privileges to a defined list of users, programs, or network addresses. In cPanel & WHM, this term can refer to:

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

See Greylisting and Whitelist.


A blocker is a condition the system discovers which does not allow the system to perform a version update. The update process performs compatibility checks before it upgrades to a new version. For more information, read our Upgrade Blockers documentation.

Bounce Message

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


An application that requires would-be senders to reply to a verification email in order to filter spam through challenge-response verification. The system only accepts the original email after the sender replies to the verification message. You can configure these settings in cPanel's  BoxTrapper interface (cPanel >> Home >> Email >> BoxTrapper).

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 notification 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.


Modifications to the cPanel interface's appearance in order to match your company's logo and brand. Branding changes include updates to image assets or text labels. For more information, read our Guide to cPanel Interface Customization - Branding documentation.

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, L.L.C 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).


.crt File

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


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 (WHM >> Home  >> DNS Functions >> Edit DNS Zone) and disk usage cache data in WHM's Tweak Settings interface (WHM >> Home >> Server Configuration >> Tweak Settings).

Cascading Style Sheets (CSS)

A style sheet language written in markup language that describes how a document, often in HTML, should appear. CSS standards are regulated by the World Wide Web Consortium (W3C)

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. For more information, visit the CentOS Project website.

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 (CA)

An entity that issues digital certificates for server verification.

Certificate Authority Authorization Record (CAA)

A DNS record that allows you to specify which CA will issue an SSL certificate for a domain. If no CAA record exists for a domain, all CAs can issue a SSL certificate for a domain. For more information, read Wikipedia's article about DNS Certification Authority Authorization.

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.

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. You can manage CSRs in the Certificate Signing Requrest (CSR) section of cPanel's SSL/TLS interface (cPanel >> Home >> Security >> SSL/TLS).

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.

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.

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. UTF-8 and ASCII are popular character sets. For more information, read Wikipedia's 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.


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 and eliminates the need for manual updates.
  • Configuration clusters allow the system to replicate settings from a primary server to secondary servers.
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.

Common Gateway Interface (CGI)

A protocol that allows a web server to communicate with scripts and other software. 

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. For more information, visit the CVE website.


A computer program that translates source code that developers wrote into a language that a computer can read. This helps to protect your server from attacks and vulnerability exploits. Use WHM's Compiler Access interface (WHM >> Home >> Security Center >> Compiler Access) to manage your system's complier access.

Comprehensive Perl Archive Network (CPAN)

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


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


The companion software to WHM, which cPanel, L.L.C 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 (cPanel >> Home >> Security >> SSL/TLS Wizard) uses the cPanel Market to sell SSL certificates. For more information about custom cPanel Market provider modules, read our Guide to cPanel Market Provider Modules documentation.

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, 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 (cPanel >> 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. For more information, read our cPHulk Brute Force Protection documentation.


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, in percentage format. For more information, read the Troubleshooting High Server Loads on Linux Servers forum article.

Cron Job

A script or task that the system executes at a scheduled interval. These commands exist in the crontab Unix configuration file. Users can manage cron jobs with cPanel's Cron Jobs interface (cPanel >> Home >> Advanced >> Cron Jobs). Server administrators can manage cron jobs with WHM's Configure cPanel Cron Jobs interface (WHM >> Home >> Server Configuration >> Configure cPanel Cron Jobs).

Cross-Site Request Forgery Attack (XSRF or CSRF)

A type of malicious attack that forces a user to execute unauthorized commands, usually through a link, to exploit a trusted website. To help prevent these attacks, cPanel & WHM requires every request to contain a unique per-session security token. Also referred to as one-click attacks or session riding.

ConfigServer Security & Firewall (CSF)

A stateful firewall, login/intrusion detection, and security plugin for Linux-based servers. For more information, visit the CSF website.


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 Product Versions and the Release Process documentation.



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, L.L.C uses to describe a feature that we no longer support or will remove in an upcoming release. For more information, read our cPanel Deprecation Plan documentation.

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.

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.

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.

Directory Harvest Attack (DHA)

A brute force attack technique by which spammers attempt to find valid email addresses through guesswork and various permutations of common addresses.

Disk Space Quota

A limit that hosting providers place on the amount of disk space that an account may use. Users can locate their usage data in cPanel's Disk Usage interface (cPanel >> Home >> Files >> Disk Usage). Server administrators manage users' disk space quotas in WHM's Quota Modification interface (WHM >> Home >> Account Functions >> Quota Modification).

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.

DNS Zone

An administrative space or portion of the Domain Name System (DNS). This space directs Internet traffic to the correct location. For example, example.com is a DNS zone whose servers direct its Internet traffic. Server administrators can manage the server's DNS zones in the DNS Functions section of the WHM Features List interface.

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.

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 Connect

GoDaddy® created the Domain Connect standard in order to simplify the configuration of DNS records. Normally, to connect to a third-party service provider, such as Microsoft Office365®, site administrators would need to enter a large amount of potentially-confusing DNS entries. However, with Domain Connect, they can allow the service provider to communicate with their server and configure the necessary DNS entries for them.

Domain Name

The name that a site owner gives to a website, which appears in the website’s URL and email addresses. Generally, domains use the example.com format, where example is the domain name and com is the top-level domain. Also known as a 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 example.com when they type example2.com.

Domain Name System (DNS)

The component of the Internet that converts human-readable domain names (for example, www.example.com) into computer-readable IP addresses (for example,

  • A DNS record can specify which mail servers exist for a given domain. These records also identify which nameservers contain authoritative information about your domains and services.
  • The nameserver software on your server manages nameserver records. cPanel & WHM offers three nameserver software options: BIND, NSD, and MyDNS.


    We deprecated the MyDNS and NSD nameservers in cPanel & WHM version 78 and plan to remove them a future release. We strongly recommend that you migrate to PowerDNS. For more information, read our cPanel Deprecation Plan.

Domain-Validated (DV) Certificate

A digital certificate used for SSL/TLS verification. The certificate authority (CA) verifies that the applicant controls the DNS domain via email, phone, or other method. These certificates are the least secure level of domain validation, since the CA does not attempt to verify who the domain owner actually is.

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.

Domain-based Message Authentication, Reporting, and Conformance (DMARC)

An email authentication method used with DKIM and SPF that allows senders and receivers to more easily determine whether an email message originated from the sender. For more information, read dmarc.org's Overview documentation.


An open-source mail server software that has optimal security. For more information, visit the Dovecot website.


A version of cPanel that allows you to run a dedicated physical nameserver. This version of cPanel is extremely minimal, and only replicates DNS zones to your other servers. For more information, read our cPanel DNSOnly™ documentation.


EasyApache (EA)

A part of cPanel & WHM that installs, modifies, and validates your Apache web server, PHP, 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.

End of Life (EOL)

The stage of software's lifecycle when the author no longer provides security updates or bug fixes. When a version of cPanel, LLC's software, an operating system, or third-party software that ships with cPanel & WHM reaches EOL, we can no longer guarantee support for that version of software.

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

Pages that display warning messages when visitors encounter problems while they try to access your site. You can customize these pages in cPanel's Error Pages interface (cPanel >> Home >> Advanced >> Error Pages). For more information, read our HTTP Error Codes and Quick Fixes documentation.


A free mail transfer agent software that is highly flexible and easily configurable. 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 Fourth Filesystem (ext4)

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

Extended HELO (EHLO)

An Extended Simple Mail Transfer Protocol (ESMTP) command that an email server or client sends to identify itself when it connects with another email server. This command initiates the process of sending an email and follows with the server sending its domain name. The ESMTP command notifies the receiving server or client that the sending server supports ESMTP extensions.


Extended SMTP (ESMTP)

An extension of the original Simple Mail Transfer Protocol (SMTP)'s protocols. ESMTP sends an EHLO request to an email server or client to identify the server's supported protocol. The server returns a list of its available ESMTP commands.

Extended Third Filesystem (ext3)

A journaled filesystem that Linux servers often use.

Extended Validation (EV) Certificate

A digital certificate used for SSL/TLS verification, where the certificate authority (CA) verifies the owner of a domain with a comprehensive identity validation process. These certificates enable HTTPS on a user's web browser address bar and state the name of the verified owner. These certificates are the most secure level of domain validation.

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.


cPanel & WHM version 66 deprecated XML output for cPanel API 1, cPanel API 2, UAPI, WHM API 0, and WHM API 1.

  • Calls for XML API output will return a deprecation warning.
  • We plan to remove XML output entirely in a future version of cPanel & WHM.

For more information, read our cPanel Deprecation Plan documentation.

External Authentication

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



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.

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 MacOS®).


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 with the Global Email Filters interface (cPanel >> Home >> Email >> Global Email Filters), or customize them for each individual account with the Email Filters interface (cPanel >> Home >> Email >> Email 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.


A firewall tool for Linux operating systems that dynamically manages network and firewall zones and defines the trust levels of network connections or interface. For more information, visit the firewalld website.

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 can result in data loss.


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. However, if 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 host.example.com. format, with a trailing dot. For the purposes of cPanel, a final dot is unnecessary, but the domain name must contain at least two dots. You must write FQDNs in lowercase letters. Also referred to as an absolute domain name. 


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.

General Availability (GA)

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

Generators (Web Statistics Generators)

Software applications that compile log 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: AnalogAWStats, and Webalizer. Server administrators can manage their server's web statistics and software in WHM's Statistics Software Configuration interface (WHM >> Home >> Server Configuration >> Statistics Software Configuration).

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.

See Forceful Reboot.


A service that protects a server against unwanted email or spam. When you enable greylisting in WHM's Greylisting interface (WHM >> Home >> Email >> 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.

See Blacklist and Whitelist.

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.



A file that resides in a specific directory and contains the directory's configuration information. The .htaccess file may also contain authentication instructions.


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


Simple Mail Transfer Protocol (SMTP) command that an email server or client sends to identify itself when it connects with another email server. This command initiates the process of sending of an email and follows with the server sending its domain name. Older email clients use this command because these clients do not require service extensions.


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 in cPanel & WHM that allows users to check email through a browser. For more information, visit the Horde Webmail website.


The unique, human-recognizable name for a server across the Internet (for example, host.example.com). System administrators can specify or change a server’s hostname with WHM’s Change Hostname interface (WHM >> 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.


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

Hypertext Markup Language (HTML)

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

Hypertext Transfer Protocol (HTTP)

The primary application method (protocol) by which you exchange or transfer data (hypertext) over the web.



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

Identity Provider (IdP)

A third-party authority (for example, OpenID Connect) that offers user authentication you can use to log in to other sites or services.

Include (file)

A file that a program automatically adds within another file. Include files can add custom content to the header or footer of the cPanel interface. Server administrators can use the include command to add a series of specifications to the Apache configuration file (httpd.conf) or use WHM's  Include Editor interface (WHM >> Home >> Service Configuration >> Apache Configuration). For more information, read our Guide to cPanel Interface Customization - UI Includes documentation.

Index Page

The default page, generally index.htmlindex.htm or index.php, that visitors view 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's Indexes interface (cPanel >> Home >> Advanced >> Indexes).

Internet Message Access Protocol (IMAP)

One of the two most widely-used email transfer methods, the other being POP3. 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. For more information, read our Guide to IPv6 documentation.
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. 

Internet Relay Chat (IRC)

An application layer protocol of real-time online communication that allows both group discussion and one-to-one messaging, as well as data transfer.


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


A user space utility program that allows server administrators to configure the Linux kernel firewall data tables. For more information, visit the iptables website.


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. These small applications, which run within the context of a browser, are called applets.

JavaScript Object Notation (JSON)

A file format that uses human-readable text to store and exchange data. JSON contains data objects in attribute-value pairs and array data types. cPanel & WHM uses JSON for API output and some internal data storage. It is much easier to use than the XML format, which we deprecated from our API libraries.



The central component of a 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.

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 (WHM >> Home >> Server Configuration >> Tweak Settings) to select 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.

For more information, read our The cPanel Log Files documentation.

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 Product Versions and the Release Process and cPanel & WHM Long-Term Support documentation.


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 (WHM >> Home >> DNS Functions >> Edit MX Entry).

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 in flat files. You can manage maildir with WHM's Mailbox Conversion interface (WHM >> Home >> Email >> Mailbox Conversion).

See mdbox.

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, L.L.C 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, L.L.C 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 and database editing tools. For more information, visit the MariaDB website.

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.


A format that stores multiple messages in a file and uses a simple index convention. You can manage mdbox with WHM's  Mailbox Conversion interface (WHM >> Home >> Email >> Mailbox Conversion). For more information, visit Dovecot's mdbox website.

See maildir.


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, http://host.example.com/~username). We recommend that you disable mod_userdir in WHM's Apache mod_userdir Tweak interface (WHM >> Home >> Security Center >> Apache mod_userdir Tweak) because the system accounts for bandwidth per-host rather than per-user.


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 (WHM >> 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 and 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). Several types of nameserver exist.

  • Local — Local nameservers are authoritative nameservers. They reside on the same server that hosts the nameserver's cPanel accounts.
  • Clustered — Clustered nameservers exist in a collection of nameservers that all share information and authoritative nameserver status. These nameservers prevent down time. If one server fails, additional servers are available to perform the necessary functions.


    Do not confuse a DNS cluster with a configuration cluster

  • Private or Custom — This type of nameserver is a custom-branded or vanity alternative name for the authoritative nameserver.
  • Remote — Remote nameservers are authoritative nameservers that a separate server hosts.
Network Address Translation (NAT)

The remapping of one IP address space to another by modifying the network address information of packets' IP headers while in transit across a router. This method allows for the use of a single IP address on an entire private network.

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.

Network Information Service (NIS)

A client-server directory service protocol that distributes information across or within networks.

nfs statd

A process that mounts NFS file systems.


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

See UID.


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.


A feature that uses PHP to deny users the ability to open files that are outside of their home directories. You can modify this feature in the Editor Mode section of WHM's MultiPHP INI Editor interface (WHM >> Home >> Software >> MultiPHP INI Editor).

OpenID® Connect (OIDC)

A standard for third-party authentication. cPanel & WHM's External Authentication feature uses OpenID Connect to communicate with third-party authentication providers. For more information, visit the OpenID Connect website.

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 (RHEL), and CloudLinux operating systems.

Option Module (optmod)

An Apache configuration option that add features to the EasyApache system. For more information, read our Custom Modules documentation.

Organizational Validation (OV) Certificate

A digital certificate used for SSL/TLS verification, where the CA verifies the owner of a domain through a vetting process. These certificates enable HTTPS on a user's web browser address bar, and state that the site is secure with a Secure Site Seal. These certificates are more secure than a DV certificate, but not as secure as an EV certificate



A package may refer to:

  1. The set of resource limits that hosting providers assign to a user’s account. System administrators can create, edit, and delete packages in WHM's Packages section of the WHM Feature List interface.
  2. A collection of software that is bundled together for distribution and installation. cPanel, L.L.C 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. This makes your website available from another domain name. For example, both http://www.cpanel.net/ and http://www.cpanel.com/ point to the same website, because cpanel.com is a parked domain for cpanel.net. In cPanel, we refer to parked domains as aliases.

Passive Mode (PASV)

A mode for FTP connections that initiate connections from the client side. You can 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 that cause alerts.


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

Perl Module

A component of software in the Perl programming language that developers commonly reuse. For example, a developer can use a calendar module in a program so that they do 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. 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 perform useful functions for your website. You can install PEAR packages in cPanel's PHP PEAR Packages interface (cPanel >> Home >> Software >> PHP PEAR Packages) or in WHM's Module Installers interface (WHM >> 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 the PECL website.

PHP FastCGI Process Manager (PHP-FPM)

An alternative PHP FastCGI implementation that improves performance of PHP scripts on servers. For more information, visit the PHP-FPM website.

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. Server administrators can access this feature in the SQL Services section of the WHM Feature List. For more information, visit the phpMyAdmin website.


A plugin modifies an interface's features or functionality. You can write plugins for the cPanel or WHM interfaces.

Plus Addressing

Subaddressing (plus addressing) adds a word after your email account username. This feature allows you to sort your mail in a certain way. For example, consider the email address John@example.com. A plus address could be John+list@example.com. Notice the plus ( + ) symbol and the word list that follows the John username. Your email account recognizes these messages and places them in the list mailbox. If the mailbox does not exist, your account will sort this message to the inbox mailbox. The server can even create new folders for plus addressed messages.


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.

Portable Operating System Interface (POSIX)

A standardized collection of commands for the Unix operating system.


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


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, the other being IMAP. POP3 copies every message in an email account to a local computer and then deletes these messages from the mail server. The system does not send information back to the email account about message replies or forwarding. For more information, read our IMAP vs. POP3 documentation.

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

A server that 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.

See Private Key.


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 (WHM >> 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. To set up quotas for your users, you must first use WHM’s Initial Quota Setup interface (WHM >> Home >> Server Configuration >> Initial Quota Setup). Use WHM's Quota Modification interface (WHM >> Home >> Account Functions >> Quota Modification) to modify a user's disk space quota.


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 (WHM >> Home >> Service Configuration >> Exim Configuration Manager).

Red Hat® Enterprise Linux® (RHEL)

A commercial Linux operating system distribution. CentOS is functionally compatible with this 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 example.com when they type example2.com. cPanel allows website owners to set up either temporary or permanent redirects. Users can manage their redirects with cPanel's Redirects interface (cPanel >> Home >> Domains >> Redirects).

See 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 (WHM >> 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 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 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. You can manage account restoration in WHM's Restore a Full Backup cpmove File interface (WHM >> Home >> Backup >> Restore a Full Backup/cpmove File).

Restricted Restore

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

See Restoration.

Reverse DNS lookup (rDNS)

A process that uses pointer records (PTR) to convert IP addresses (for example, to domain names (for example, www.example.com). For more information about rDNS, read our How to Configure Reverse DNS for BIND in WHM documentation.


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


This may refer to:

  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. See UID.
  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. For more information, visit the Roundcube website.

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 (WHM >> Home >> Software >> EasyApache (Apache Update)) 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.

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

TLS is a newer 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 (WHM >> Home  >> SSL/TLS >> Install a SSL Certificate on a Domain) to allow SSL/TLS to protect the site.


As of cPanel & WHM version 68, we only support Transport Layer Security (TLS) protocol version 1.2

  • We will only support applications that use TLSv1.2.
  • We strongly recommend that you enable TLSv1.2 on your server. 

Self-Signed Certificate

An SSL certificate that does not verify the identity of the server because it is signed by the same entity whose identity it certifies. Browsers generally warn users about the authenticity of self-signed certificates. You can create a self-signed SSL certificate in WHM's Generate an SSL Certificate and Signing Request interface (WHM >> Home >> SSL/TLS >> Generate an SSL Certificate and Signing Request).

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 Red Hat Bugzilla case about SPF record errors.

Server Contact

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

Server Profile

A collection of server roles that allow you to optimize a server to perform a specific task or function. For example, the Mail Node profile allows you to provide only the services and cPanel features that allow the system to serve mail. In cPanel & WHM version 76 and later you can select a server profile in WHM's Server Profile interface (WHM >> Home >> Server Configuration >> Server Profile). For more information, read our How to Use Server Profiles documentation.

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 Roles

A collection of services that provide specific server functionality. For example, the DNS role allows users to create and edit Domain Name System (DNS) zone files. This role consists of the bindnamedndspdns, and powerdns services. Server profiles use roles to provide services that allow you to configure a server for a specific task. For more information, read our How to Use Server Profiles documentation.

Server Side Includes (SSI)

A simple, server-based scripting language primarily used for the Internet, generally written to include the contents of multiple files for a web page on a web server. SSI only supports text format.

Service Manager

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

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.

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's Shell Fork Bomb Protection interface (WHM >> Home >> Security Center >> Shell Fork Bomb Protection) 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.

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).

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. You can create these directories in WHM's Skeleton Directory interface (WHM >> Home >> Account Functions >> Skeleton Directory).

Smart Host

A type of email 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.


A GUI-based virtual private server (VPS) management system. For more information visit the SolusVM website.


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


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 (WHM >> 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. For more information, read our Spam Filters documentation.

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. For more information, read our Spam Filters documentation.


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.


A webmail client that allows users to check their email through browsers. We deprecated SquirrelMail and its functionality in cPanel & WHM version 76 and removed it in cPanel & WHM version 78.

SSL Certificate

An electronic document that 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 Product Versions and the Release Process documentation.


A style uses CSS, images, and other assets to modify the appearance of the entire cPanel or WHM interface without changes to its functionality or features. For more information, read our cPanel Style Development documentation.


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


cPanel account users can create subaccounts that use the same login and password information for email, FTP, and Web Disk services. The system maintains password synchronization between each of the subaccount's allowed services. Users can manage subaccounts with cPanel's User Manager interface (cPanel >> Home >> Preferences >> User Manager).


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.


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 documentation or visit the Template Toolkit website.

Terabyte or Tebibyte (TB or TiB)

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.


A skeletal framework of interfaces, over which the system applies one of that theme's styles. cPanel & WHM currently ships with one default cPanel theme and one default WHM theme, as well as Webmail and login themes. You can manage your themes with WHM's Theme Manager interface (WHM >> Home >> Themes >> Theme Manager).


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 secretly performs malicious functions.

Trust Key Relationship

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

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. Users can configure their 2FA in cPanel's Two-Factor Authentication interface (cPanel >> Home >> Security >> Two-Factor Authentication). Server administrators can manage 2FA in WHM's Two-Factor Authentication interface (WHM >> Home >> Security >> Two-Factor Authentication).


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. Notable UIDs include:

  • 0 — root, the top-level system user. 


    To find all of the users with this UID, run the following command:

    grep :x:0: /etc/passwd
  • 99 — nobody, the default executor of CGI scripts, if suEXEC is disabled.


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

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.

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.

Unix Time

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

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.


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.


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


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®, Chrome, and Safari®.

Web Disk

A cPanel feature that allows website owners to drag and drop files to manipulate them through cPanel's  Web Disk interface (cPanel >> Home >> Files >> Web Disk).

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.

WebHost Manager (WHM)

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


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. For more information, read our Webmail documentation.

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.


This may refer to:

  • For BoxTrapper, a list of approved email senders. BoxTrapper automatically delivers messages from senders who are on the whitelist directly to the inbox. For more information, read our BoxTrapper documentation.
  • For cPHulk, a list of approved IP addresses. cPHulk always allows logins to your server from IP addresses on the whitelist. For more information, read our cPHulk Brute Force Protection documentation.

See Blacklist and Greylist.


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 cpanel.net returns the ownership information for cPanel.

Wildcard Certificate

A certificate that allows you to secure a domain with an unlimited number of subdomains, but each subdomain requires a dedicated IP address.


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 (WHM >> Home  >> Server Configuration >> Tweak Settings).


An open-source microkernel-designed hypervisor that allows for many instances of an operating system or different operating systems to run on a single host at the same time. For more information, visit the Xen website.


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 example.com, 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.