How do Windows file permissions work?

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Joomla and Windows file permissions - Explanation

For those of you that are either developing or delivering your Joomla! Web-Sites from a Windows environment, it is sometimes difficult to obtain relevant information regarding permissions. Unfortunately, it is a fact that most Web-Serving is offered under Unix and that Unix is pretty well documented within this environment. Hopefully, the following information will go some way to clear up any confusion and provide a little guidance as well.

Windows Web-Servers Overview

Firstly, lets discuss the differences between servers. In general, most Windows folks appear to be using either Apache(Win32) or Microsoft IIS, these two web servers operate very differently and utilize slightly different models of delivery. Apache(Win32) generally runs on the host computer as the User that it was installed under, whereas IIS installs under a specific user but will run under a newly installed user " IUSR_ ".

Permission Defaults

By default, Unix tends to only give full access to the "owning" user to files and directories, in opposition to this approach Windows by default will also assign the Group "Everyone", Full permissions. The first thing any good Windows Administrator will do is to remove the rights of the "Everyone" group, to improve security. For local PC testing, this is probably not necessary, but explains why, if "Everyone" is not removed and you run some form of permissions check script or the Joomla! Pre-Installation check, on the whole you will have Full "Read, Write and Execute" permissions, because you are acquiring the rights of the "Everyone" Group.

Microsoft Internet Information Server (IIS)

IIS comes in two main flavors, PWS (Personal WebServer), and IIS (Internet Information Server). Essentially these are the same application. PWS is just a cut-down version of IIS designed for desktop environments, whereas IIS is designed for Server environments. PWS limits you to a single main website, so your application installations will generally be in sub-directories of the main website. IIS, on the other hand, provides the functionality for Virtual Hosts to be run from these directories, delivering multi-site capability.

Due to the different functionality limitations, PWS does not have the "Permissions Wizard" as it is determined to not be needed. Only one user will be using the PWS Server. In IIS, many users will be using the Server, thus differing permission assignments are needed.

Once the "Everyone" account is removed, Windows IIS is now left with the " IUSR_* " account having top-level rights to the Web-Server directories. A permissions check now should yield different results. Only the IUSR_* account has full permissions and other users should acquire either "Read Only" or no rights. Rights are determined by which other users have been assigned which rights to the IIS directories manually.

Assigning Permissions

Assigning permissions in Windows is reasonably straight forward, but can be a little confusing at times. Right-Click on the appropriate folder or file. Selecting "Properties" or "Sharing and Security" will enter the Windows Security Management pane. Selecting (click once) any user name listed will display the rights that user has in the bottom half of the pane. Some rights might be "greyed" out. These are unavailable, either because the current user (you are logged in as) does not have high enough permissions to alter them, or they are inherited from the directory above and have been set to use that higher level directory's permissions (this is generally the default mechanism).

As you can see, Windows utilizes the following Permissions/Rights scheme:

1.	Full Control	Allows: 1, 2, 3, 4, 5, 6, 7
2.	Modify	Allows: 2, 3, 4, 5, 6
3.	Read & Execute	Allows: 3, 4
4.	List Folder Contents	Allows: 4 (but cannot run programs)
5.	Read	Allows: 5 (Implies: 4)
6.	Write	Allows: 6 (Implies:4 )
7.	Special Permissions	Allows: Combinations

Windows file permissions properties

Windows file permissions can be seen as having similar properties as UNIX or Linux file (Modes) permissions, they are just represented differently. For example, if you are primarily a Unix/Linux user, you are probably used to having permissions represented as 644/666 755/777, instead of being described in the terms above. So, when you are quoted to use 644 this equates to:

   The owner of this file can read and write to it.

   The owner's group can read the file.

   Everyone else can read the file.

* Note: Windows and Unix permissions (Access Control Lists) do not equate exactly, as Windows does not use the "Groups" mechanism in the same manner. However, for this discussion and in regards to the Web-Hosting environment they can be summarily equated. 

Ah, but,  in windows "Groups" are not used and "Everyone" should have been removed.....

So this is where Windows and Unix do not quite equate, but what can be done is to "match" or "correlate" equivalent meanings. So this outline is not really going to provide you with a Windows or an NTFS specific permissions guide but more of an understanding of how the commonly quoted numbered UNIX/Linux style permissions correlate on a machine with an NTFS file system.

 
The files that are placed in the www or public_html root folder, or whatever directory your site (www.domain.com.au or localhost) points to on your hard drive should be owned by your user account, but only if that user is not what is considered as a privileged user like "Administrator" on Windows or "root" on UNIX/Linux. These accounts allow way too much access and should never be used for everyday use.

Best Practices

Commonly used security practices suggest that all FILES should have the following permissions.

       Owner  :  Read & Write

       Group   :  Read Only

       Others : Read Only

    All DIRECTORIES/FOLDERS should have the following permissions.

       Owner  : Read, Write & Execute

       Group   : Read & Execute

       Others : Read & Execute

Arguably, this is not necessarily "optimum" security, but a balance must be struck between security, functionality and maintainability.

Windows, unlike Unix, does not maintain a single ACL for "Execute", but simply provides "Read & Execute" combined, which does not imply "Write". The "Read & Execute" ACL does however imply "List Directory Contents". Therefore, if you have only "Read & Write" permissions on a directory but no "Execute" you will not be able to see the contents of the directory and may also have problems when attempting to run the file through a Web-Browser.

Unfortunately, a little understanding of UNIX/Linux permissions is required to fully equate/correlate them to Windows permissions, the following "cheat-sheet" should assist;

 

Unix Mode	Windows ACL	Comments
7	Modify	Read, Write & Execute, you should be the owner of this file
6	Read & Write
5	Read & Execute	used for most applications
4	Read Only	security through obscurity is not a good practice
3	Write & Execute	not available through windows, unless "Special" Permissions is used, not commonly used
2	Write Only	not available through windows, unless "Special" Permissions is used, not commonly used
1	Execute Only	(not available through windows, unless "Special" Permissions is used, not commonly used)

So as a comparison example to Unix Modes, when you are quoted something like 644, you would now need to break that into three entities:

      6  :  4  : 4

The first number represents the "Owners" permissions, the second represents the "Group" permissions and the third, the "Other" permissions.

So the Windows equivalent would be something like;

  Owner (6) : Read & Write

  Group (4) : Read Only

  Others (4) : Read Only

 

Hopefully, this example provides some insight into how to correlate Unix Modes/Permissions into Windows Permissions/ACL's. This document does not include more complex subjects such as "Effective", "Inherited", or "Special" permissions. Despite Windows ease of use, Microsoft's Permissions and ACL mechanisms are actually reasonably complex and very extensive, but this might just give you a quick reference to try and alleviate some of the confusion surrounding Unix and Windows Permissions translations.