rawdevices Command in Linux

---

---

The rawdevices command in Linux is used to manage raw devices, which provide direct access to the underlying storage device without any buffering or caching provided by the operating system. This command is particularly useful for applications that require low-level I/O operations on storage devices, such as databases and high-performance computing applications.

Table of Contents

Here is a comprehensive guide to the options available with the rawdevices command −

• Understanding rawdevices Command
• Syntax of rawdevices Command
• rawdevices Command Options
• How to Use rawdevices Command in Linux?
• Use Cases of Raw Devices
• Error Handling

Understanding rawdevices Command

This command enables users to read from and write to the device at the lowest level possible, bypassing higher-level abstractions like file systems and device drivers. It's typically used for accessing low-level hardware devices such as hard drives, network interfaces, and serial ports. However, using the rawdevices command requires caution, as improper use can lead to data loss or hardware damage.

Raw devices are character devices that provide direct access to the underlying storage device without any buffering or caching provided by the operating system. This allows applications to perform low-level I/O operations on the storage device, which can be beneficial for certain types of applications, such as databases and high-performance computing.

Syntax of rawdevices Command

The basic syntax of the rawdevices command is as follows −

rawdevices [options] [arguments]

• Options − Various options to control the behavior of the rawdevices command.
• Arguments − The raw device and block device to be managed.

rawdevices Command Options

Here are some common options used with the rawdevices command −

How to Use rawdevices Command in Linux?

The rawdevices command in Linux is used to bind a raw character device to a block device, allowing direct access to the underlying hardware.

Listing All Raw Devices

To list all raw devices and their associated block devices, you can use the following command −

rawdevices -a

This command will display a list of all raw devices and the block devices they are bound to.

Binding a Raw Device to a Block Device

To bind a raw device to a block device, you can use the following command −

rawdevices -b /dev/raw/raw1 /dev/sda1

For example, to bind the raw device /dev/raw/raw1 to the block device /dev/sda1, you would use −

rawdevices -b /dev/raw/raw1 /dev/sda1

This command binds the raw device /dev/raw/raw1 to the block device /dev/sda1, allowing direct access to the underlying storage device.

Unbinding a Raw Device

To unbind a raw device from a block device, you can use the following command −

rawdevices -u /dev/raw/raw1

For example, to unbind the raw device /dev/raw/raw1 from any block device, you would use −

rawdevices -u /dev/raw/raw1

This command unbinds the raw device /dev/raw/raw1 from any block device.

Displaying Help Information

To display help information for the rawdevices command, you can use the -h option −

rawdevices -h

This command displays help information for the rawdevices command, including usage and options.

Use Cases of Raw Devices

Raw devices are useful in various scenarios, such as −

• Databases − Some database applications, such as Oracle and MySQL, can benefit from using raw devices for data storage. By using raw devices, these applications can bypass the operating system's buffering and caching mechanisms, resulting in improved performance and reduced latency.
• High-Performance Computing − In high-performance computing environments, raw devices can be used to achieve low-latency and high-throughput I/O operations. This is particularly important for applications that require direct access to the underlying storage device, such as scientific simulations and data analysis.
• Backup and Recovery − Raw devices can be used for backup and recovery operations, allowing direct access to the underlying storage device for creating and restoring backups.

Error Handling

When using the rawdevices command, you may encounter various errors. Here are some common ones and how to handle them −

• Permission denied − This error occurs if you do not have the necessary permissions to access the raw device or block device. Ensure that you have the appropriate permissions.
• No such file or directory − This error occurs if the specified raw device or block device does not exist. Double-check the device paths and ensure that the devices exist.
• Device or resource busy − This error occurs if the block device is already in use by another process. Ensure that the block device is not being used by any other process before binding it to a raw device.

Conclusion

The rawdevices command is a powerful tool for managing raw devices in Linux. By understanding the syntax, options, and common use cases of the rawdevices command, you can effectively use it to manage and manipulate raw devices. Whether you are a developer, system administrator, or database administrator, the rawdevices command provides valuable functionality for working with storage devices in Linux.

When using raw devices, it is important to be aware of potential security risks. Since raw devices provide direct access to the underlying storage device, they can potentially be used to bypass the operating system's security mechanisms. It is important to ensure that only trusted applications and users have access to raw devices.