How to use the command 'addpart' (with examples)

The addpart command is a Linux utility that serves as a simple wrapper around the add partition ioctl. Its primary function is to inform the Linux kernel about the existence of a specified partition on a storage device. This tool is especially useful for system administrators and power users dealing with disk management tasks in environments where the kernel may not automatically detect partition changes or when managing partitions in scripted or automated setups.

When partition changes are made using utilities like fdisk or parted, those changes may not always be immediately recognized by the kernel, especially in situations where disk partition tables are created or modified outside of the typical system operations. The addpart command can be employed to update the kernel’s partition information without requiring a system reboot.

Use case 1: Tell the kernel about the existence of the specified partition

Code:

addpart /dev/sda 3 204800 1024000

Motivation:

In situations where an administrator has created a new partition on a disk, it is crucial for the system to recognize this new partition so that it can be used effectively for file storage, mounting, or further partitioning. The addpart command comes into play by allowing the user to manually update the kernel’s partition table without the need for a system restart. This can enhance system uptime and allows for disk manipulation in environments where minimizing downtime is a priority.

Explanation:

• /dev/sda: This specifies the storage device on which the new partition exists. /dev/sda is typically the first SCSI disk in a system under Linux. Here, it’s the device on which the user has created or wants to inform the kernel about a new partition.
• 3: This number refers to the partition number on the specified device. In this context, it implies that the third partition on /dev/sda is the subject of this command.
• 204800: This value represents the starting block or sector of the partition. It defines where the partition begins on the disk. 204800 is often used as a starting point for partitions so that they are aligned for optimized performance, especially on SSDs.
• 1024000: This denotes the length of the partition in blocks or sectors. It specifies the partition’s size. In this case, 1024000 blocks would typically translate to around 500MB, depending on the block size defined for the disk.

Example Output:

OK

In this example, seeing a simple output like OK indicates that the kernel has successfully acknowledged the partition and updated its internal partition table to reflect this new information. There may not be additional feedback unless an error occurs.

Conclusion:

The addpart command is a vital tool for any Linux user involved in disk management, enabling real-time updates to the kernel’s partition table without a reboot. Whether you’re setting up a server with complex partition needs or managing a desktop with multiple storage devices, understanding how to apply addpart ensures that your system can adapt swiftly to partition changes, thereby maintaining operational efficiency. By following the examples and explanations above, users can confidently employ addpart in a variety of contexts to enhance their system administration toolkit.