The extended stored procedure, xp_cmdshell in Microsoft SQL Server (not MySQL) allows us to run operating system commands directly from within SQL Server. This latest blog offers a brief insight into the command. Bobcares, as a part of our SQL Server Support offers solutions to every query that comes our way.

Overview

1. The xp_cmdshell in Microsoft SQL Server (not MySQL)
2. How to Enable xp_cmdshell in Microsoft SQL Server (not MySQL)?
3. Usage Examples
4. Main Considerations
5. Conclusion

The xp_cmdshell in Microsoft SQL Server (not MySQL)

xp_cmdshell is an extended stored procedure in SQL Server that allows us to run operating system commands directly through T-SQL. This feature can be incredibly useful for database administrators who need to perform various tasks like file management, system automation, and even integration with cloud platforms. In this article, we’ll explore how to enable xp_cmdshell and shows its usage through practical examples, including file management, executing PowerShell commands, and connecting to Azure.

Prerequisites

Before diving into the examples, make sure we have:

• SQL Server installed (SQL Server 2016 used here, but compatible with earlier versions like SQL Server 2005).

• SQL Server Management Studio (SSMS) for running the commands.

How to Enable xp_cmdshell in Microsoft SQL Server (not MySQL)?

1. To enable xp_cmdshell, we first need to verify if advanced options are activated in SQL Server. Here’s how to check:

USE master;
GO
EXEC sp_configure 'show advanced options';

2. If the value is 0, it shows that advanced options are disabled. To enable them, we must run the following:

USE master;
GO
EXEC sp_configure 'show advanced options', '1';
RECONFIGURE WITH OVERRIDE;

3. Once advanced options are enabled, we can activate xp_cmdshell using:

EXEC sp_configure 'xp_cmdshell', 1;
GO
RECONFIGURE;

This enables xp_cmdshell for running command-line tasks from SQL Server.

Usage Examples

Example 1: Copying Backups Between Folders

A common use of xp_cmdshell is to manage file backups. Suppose we have backups in the c:\backup directory and want to copy them to c:\shared. We can execute the following T-SQL command:

xp_cmdshell 'copy c:\backup c:\shared';

This command will copy all files from the backup folder to the shared folder, automating the backup process.

Example 2: Storing File Paths in a SQL Server Table

To store full paths of files in a SQL Server table, follow these steps:

i. List all file paths in a folder and save them to a text file using:

xp_cmdshell 'dir "c:\images" /s/b>c:\sql\path.txt';

This creates a file (path.txt) containing the paths of all files.

ii. Create a table to store these paths:

CREATE TABLE images(path VARCHAR(80));

iii. Import the file paths into the table using the Bulk Copy Program (bcp):

xp_cmdshell 'bcp AdventureWorks2016CTP3.dbo.images IN c:\sql\path.txt -c -T';

iv. This command imports the paths from path.txt into the images table in the AdventureWorks database. We can verify the imported data using:

SELECT * FROM images;

v. To enhance this, we may want to create a more comprehensive table:

CREATE TABLE [dbo].[pictures](
[id] [smallint] IDENTITY(1,1) NOT NULL,
[path] [varchar](max) NULL,
INT [PK_pictures] PRIMARY KEY CLUSTERED ([id] ASC)
);

vi. We can now insert data:

INSERT INTO pictures (imagename, path)
SELECT REPLACE(path, 'c:\images\', '') AS imagename, path FROM images;

This will extract the image names from paths and store them alongside the full paths.

Example 3: Executing PowerShell Commands in T-SQL

PowerShell offers more flexibility for system management tasks in SQL Server environments. We can run PowerShell commands using xp_cmdshell as follows:

xp_cmdshell 'powershell -command "copy-item C:\sql\source -Destination C:\sql\destination -Recurse"';

This copies all files and folders from the source to the destination directory using PowerShell. We can also run entire PowerShell scripts:

i. Create a script (script.ps1):

copy-item "C:\sql\source" -Destination "C:\sql\destination" –Recurse

ii. Run the script using:

xp_cmdshell 'powershell -command "C:\\sql\\script.ps1"';

Example 4: Connecting to Azure Using xp_cmdshell and sqlcmd

We can use xp_cmdshell in combination with sqlcmd to manage Azure SQL Databases from the local server:

i. Create a SQL script (sqlscript.sql) with the following content:

CREATE DATABASE SQLSHACKDB;

ii. Run the script in Azure using:

xp_cmdshell 'sqlcmd -U username -S sqlshack.database.windows.net -P "yourpassword" -d master -i "c:\sql\sqlscript.sql"';

Replace username, yourpassword, and the server details with user credentials. This command connects to Azure SQL and runs the script to create a database.

Main Considerations

While xp_cmdshell is powerful, it can pose security risks if not managed properly. It allows running OS-level commands, making it a target for malicious attacks if misused. Here are some best practices:

• Restricted Access: Only allow trusted administrators to access and run xp_cmdshell.

• Audit and Monitor: Regularly audit and monitor the usage of xp_cmdshell to detect any unauthorized or suspicious activity.

• Disable When Not in Use: If we don’t need xp_cmdshell for regular operations, we need to disable it to reduce the attack surface:

EXEC sp_configure 'xp_cmdshell', 0;
GO
RECONFIGURE;

• Use SQL Server Roles: Limit access using specific SQL Server roles and permissions to ensure that only authorized personnel can enable and execute xp_cmdshell.

[Need to know more? Click here to reach us.]

Conclusion

xp_cmdshell is a powerful tool in SQL Server, offering extensive capabilities for system integration and automation. From managing files to running PowerShell scripts and connecting to Azure, it opens up many possibilities for database administrators. However, with its power come risks, so it’s crucial to manage it securely, enabling it only when necessary and monitoring its use. By following the examples and best practices outlined here by our Experts, we can effectively leverage xp_cmdshell while minimizing security concerns.