When configuring Internet Information Services (IIS), understanding user accounts and permissions is crucial, especially when dealing with directory access. A common point of confusion arises between iis_user (IUSR) and IIS_IUSRS. While both are related to IIS and user identities, they serve distinct purposes. This article clarifies the differences between IUSR and IIS_IUSRS and explains why you might need to “Iis Enable Server Directory Read Iis_user”.
To grasp this, it’s essential to understand the two main identities at play in IIS: the Application Pool Identity and the Anonymous User Identity.
IIS_IUSRS: The Application Pool Identity Group
IIS_IUSRS is a built-in group in IIS that represents IIS Worker Process Accounts. Think of it as the identity under which your application pool, and therefore your web application, actually runs. Introduced as a replacement for IIS_WPG in older versions of IIS, IIS_IUSRS is designed for managing permissions for application pools.
When an application pool starts, IIS automatically adds the virtual accounts associated with that pool to the IIS_IUSRS group. This group is primarily used when your application needs to access resources based on the application pool’s identity. For instance, in a .NET application without impersonation enabled, the application will access resources using the identity defined for its application pool, which is part of the IIS_IUSRS group.
IUSR: The Anonymous User Identity
On the other hand, IUSR is the Anonymous User Account. This is the identity that IIS uses to represent users who access your website anonymously – meaning users who are not authenticated with Windows credentials or other forms of authentication. IIS uses IUSR as the default identity when handling requests from users who haven’t provided specific credentials.
The need to “iis enable server directory read iis_user” typically arises because, by default, anonymous access in IIS uses the IUSR account. In scenarios like serving static files or in Classic ASP applications, IIS often operates under the context of the anonymous user (IUSR). This is due to a concept called impersonation, which is always enabled in Classic ASP and for static files.
When impersonation is active, the IIS worker process temporarily adopts the identity of the user accessing the site. In the case of anonymous authentication, this identity is IUSR. Consequently, if your website needs to read files or directories, and anonymous access is enabled, you must grant read permissions to the IUSR account.
Why “iis enable server directory read iis_user” is necessary
The keyword “iis enable server directory read iis_user” directly addresses the scenario where you need to grant read permissions on a server directory to the IUSR account. This is commonly required in situations such as:
- Serving Static Content: If anonymous users need to access HTML files, images, or other static content stored in a specific directory, IUSR needs read permissions on that directory.
- Classic ASP Applications: Classic ASP applications frequently operate under the anonymous user’s context due to default impersonation settings. If these applications need to read data from files or directories, IUSR permissions are essential.
Streamlining Permissions in IIS 7 and Later: Using Application Pool Identity for Anonymous Access
IIS 7 and later versions offer a way to simplify permissions management and potentially reduce confusion between IUSR and IIS_IUSRS. You can configure IIS to use the Application Pool Identity as the anonymous user identity. This means instead of using IUSR, anonymous requests will be handled under the same identity as the application pool itself (which is part of IIS_IUSRS).
By configuring IIS to “reuse the pool identity as the anonymous identity”, you eliminate the need to manage permissions separately for IUSR in many cases. Permissions granted to IIS_IUSRS will then apply to both application pool processes and anonymous access.
Clarifying Identity Usage: Impersonation and Anonymous Access
The following table summarizes how the user identity is determined based on impersonation and anonymous access settings:
| Impersonation | Anonymous Access | Resources Accessed As |
|---|---|---|
| Enabled | Enabled | IUSR_computer (IIS 5/6) or IUSR (IIS 7+) or custom Anonymous User Account |
| Enabled | Disabled | User’s Windows/Domain Identity (Windows Authentication) |
| Disabled | Enabled | NT AuthorityNetwork Service (Application Pool Identity) |
| Disabled | Disabled | NT AuthorityNetwork Service (Application Pool Identity) |
In Conclusion
Understanding the distinction between IIS_IUSRS and IUSR is key to properly configuring permissions in IIS. While IIS_IUSRS manages permissions for application pools, IUSR represents the anonymous user. The need to “iis enable server directory read iis_user” arises when anonymous users require access to directories, particularly for static content or in Classic ASP scenarios where impersonation defaults to the anonymous user. Modern IIS versions offer the flexibility to unify these identities, simplifying permission management by using the application pool identity for anonymous access.
