ionice

Ionice is a command-line tool that allows users to prioritize disk I/O for a given process or command under Linux. It works by manipulating the ionice values associated with processes, which determines their I/O priority.

The tool provides three different I/O classes that can be assigned to processes: idle, best-effort, and real-time. The idle class provides the lowest priority to the process, allowing it to use disk resources only when no other process is requesting them. The best-effort class is the default and provides a balanced allocation of disk I/O resources to processes. The real-time class gives the highest priority to the process, allowing it to access disk I/O resources with higher preference.

Each class, except idle, has eight different priority levels ranging from 0 to 7, with 0 being the highest and 7 the lowest. The higher the priority level, the more access the process will have to the disk I/O resources.

Ionice is usually used with the 'ionice' command followed by the priority level and command to be executed. For example, 'ionice -c2 -n0' sets the process to the highest best-effort priority level.

Using ionice can be particularly useful when running demanding tasks in the background without affecting the responsiveness of the system, as it allows users to allocate disk I/O resources more efficiently. This is particularly important in scenarios where multiple processes are competing for disk access.

Ionice is part of the util-linux package and is available by default on most Linux distributions. It is a powerful tool that can optimize disk I/O operations and improve system performance by fine-tuning process priorities.