A Virtual Server in Virtualmin means a combination of a system user, a home directory, a
VirtualHost in Apache, a set of entries in the
virtual map database in Postfix, an administrative account in Webmin, a database and database user in MySQL and/or PostgreSQL, and all of the necessary records in BIND.
The home directory for a virtual server named
example.com will generally be found in
/home/example (though this depends on configuration), and nearly all user data, such as mail and website data and applications but not including databases, will be found in this directory.
Virtual Server Owner or Virtual Server Account
The system and Webmin user that owns the Virtual Server. This use is usually named the first part of the domain name of the Virtual Server, but this can be altered during creation. e.g. Here at Virtualmin.com, our virtual server owner account is named
Usermin is the default webmail component of the Virtualmin stack of applications. It runs on port 20000 and uses the HTTPS secure protocol. In addition to reading and composing mail, Usermin allows mailbox users to change their own password, configure mail forwarding, auto-responders, and aliases, and optionally manage databases and upload files.
Webmin is the base upon which Virtualmin is built. It is a general purpose system administration tool that runs on the majority of UNIX-based operating systems. It is Open Source, and is the most popular tool of its kind world-wide.
Virtualmin is a term that is generally used to refer to the full stack of applications that make up a Virtualmin system, including (but not limited to) Webmin with the Virtualmin Virtual Servers module and Virtualmin theme, Usermin, Apache, Postfix or another MTA, databases, BIND and other services. The Virtualmin virtual-server Webmin module is available in both an Open Source version called Virtualmin GPL and a commercial version called Virtualmin Professional. Easy installation of the full Virtualmin stack is available on some platforms. See the download page for more details.
A Sub-Server is a virtual server owned by a pre-existing virtual server. A sub-server can have nearly all of the features of a virtual server, including databases, mailboxes, etc. associated with it. But, ownership and group membership will be tied to the parent virtual server. This type of account should be used when you have many websites that will be maintained by a single account holder.
Virtualmin can impose a number of optional restrictions on the sub-server account type, including limits on number and type of databases, whether the name must be within the parent server DNS zone (e.g. a subdomain name), and whether the parent virtual server administrative account can create their own sub-servers and, if so, how many they can create. Most such limits are imposed during creation based on values found in the Server Template selected for sub-server accounts. The creation limits (e.g. whether and how many sub-servers a virtual server owner is allowed to create) are imposed in the parent virtual server account, and thus appear in the Server Template used for virtual server accounts, rather than sub-server accounts.
An alias server merely acts as a pointer to an existing virtual server. It is generally used to direct connections to one domain name to another. For example, one might have multiple domain names registered, like example.com and example.net. You don't want a different website on each of these names, but you do want them to go somewhere, just in case someone mistypes your address. So, you'd create a canonical virtual server on example.com and create an alias of that virtual server with the name example.net.
Sub-domain is a term that has been, unfortunately, overloaded in the virtual hosting industry, so its usage can be confusing. In Virtualmin, there is a sub-domain account type, that roughly matches accounts of the same name created in cPanel. We do not recommend use of sub-domains, as they merely provide a limited subset of the functionality of a Sub-Server and an odd directory structure. Thus this account type is disabled, by default, in Virtualmin Professional. But, if you or your customers are accustomed to sub-domain account types, you can enable this account type.
Website data for a sub-domain named sub.example.com will generally be found in
/home/example/public_html/sub/ and sub-domains are generally not used for mailboxes or other types of data.
If you are migrating from cPanel, you may wish to read Virtualmin for cPanel Users to help you get a feel for the differences between the two products.