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Home Forums How do you set file permissions or access control lists (ACLs) in C#? – MindStick
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1 Answers

Anubhav Sharma
Anubhav Sharma 26 May 2025
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To set file permissions or Access Control Lists (ACLs) in C#, you use classes from the System.Security.AccessControl namespace.

Example: Grant Read and Write Permissions to a Specific User

using System.IO;
using System.Security.AccessControl;
using System.Security.Principal;

public class FilePermissionHelper
{
    public static void SetFilePermissions(string filePath, string userName)
    {
        FileSecurity fileSecurity = File.GetAccessControl(filePath);

        // Create a new rule granting read and write access
        FileSystemAccessRule accessRule = new FileSystemAccessRule(
            userName,
            FileSystemRights.Read | FileSystemRights.Write,
            AccessControlType.Allow
        );

        // Add the rule and apply it
        fileSecurity.AddAccessRule(accessRule);
        File.SetAccessControl(filePath, fileSecurity);
    }
}

Usage

string file = @"C:\secure\file.txt";
string user = @"DOMAIN\UserName"; // or use Environment.UserName

FilePermissionHelper.SetFilePermissions(file, user);

Key Concepts

Class Purpose
FileSecurity Represents the ACL for a file
FileSystemAccessRule Defines access rules (who, what rights)
AccessControlType Allow or Deny
FileSystemRights Enum for specific rights (e.g. Read, Write, Modify, FullControl)

To Remove or Modify Permissions

Use RemoveAccessRule, ResetAccessRule, or SetAccessRule on the FileSecurity object.

Notes

  1. Your application needs permission to change ACLs (run as administrator if needed).
  2. Works on NTFS file systems where ACLs are supported.
  3. Use DirectorySecurity and Directory.SetAccessControl for folders.
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