Linux chrt Command with Practical Examples

Introduction

In this lab, you will learn how to use the Linux chrt command to manage the real-time scheduling attributes of running processes. The chrt command allows you to adjust the real-time priority of a process and manage its scheduling policy, which can be useful for optimizing the performance of time-critical applications or ensuring that important processes are scheduled with higher priority.

You will start by understanding the purpose of the chrt command and how to check the current real-time priority of a process. Then, you will learn how to change the real-time priority and scheduling policy of a process using the chrt command. This knowledge can help you optimize system performance and ensure that critical tasks are executed in a timely manner.

Linux Commands Cheat Sheet

Skills Graph

Understand the Purpose of the chrt Command

In this step, you will learn about the purpose of the chrt command in Linux. The chrt command is used to set and retrieve the real-time scheduling attributes of a running process.

The chrt command allows you to:

• Adjust the real-time priority of a process
• Manage the scheduling policy of a process

This can be useful for optimizing the performance of time-critical applications or ensuring that important processes are scheduled with higher priority.

Let's start by checking the current real-time priority of a process. Run the following command to get the real-time priority of the current shell process:

chrt -p $$

Example output:

pid 1234's current scheduling policy: SCHED_OTHER
pid 1234's current scheduling priority: 0

The output shows that the current shell process is using the SCHED_OTHER scheduling policy with a priority of 0. This is the default scheduling policy for most regular processes.

Now, let's try changing the real-time priority of a process. We'll use the sleep command to create a new process and then use chrt to adjust its real-time priority.

sudo chrt -f -p 10 $$

This command sets the real-time FIFO (First-In-First-Out) scheduling policy with a priority of 10 for the current shell process.

Example output:

pid 1234's current scheduling policy: SCHED_FIFO
pid 1234's current scheduling priority: 10

The chrt command allows you to manage the scheduling policies and priorities of processes, which can be useful for optimizing system performance and ensuring that critical tasks are executed in a timely manner.

Adjust the Real-Time Priority of a Process

In this step, you will learn how to adjust the real-time priority of a process using the chrt command.

Real-time scheduling policies in Linux are designed to provide deterministic and low-latency behavior for time-critical applications. The chrt command allows you to set the scheduling policy and priority of a process.

Let's start by creating a new process using the sleep command and then adjust its real-time priority.

## Start a new process
sudo chrt -f -p 10 sleep 60 &

This command starts a new sleep process with the real-time FIFO (First-In-First-Out) scheduling policy and a priority of 10.

You can verify the scheduling policy and priority of the new process using the chrt command:

chrt -p $(pgrep sleep)

Example output:

pid 12345's current scheduling policy: SCHED_FIFO
pid 12345's current scheduling priority: 10

Now, let's try changing the real-time priority of the sleep process to a higher value of 20:

sudo chrt -f -p 20 $(pgrep sleep)

You can verify the updated priority by running the chrt -p command again:

chrt -p $(pgrep sleep)

Example output:

pid 12345's current scheduling policy: SCHED_FIFO
pid 12345's current scheduling priority: 20

The chrt command allows you to dynamically adjust the real-time priority of a running process, which can be useful for optimizing the performance of time-critical applications or ensuring that important processes are scheduled with higher priority.

Manage Scheduling Policies with the chrt Command

In this final step, you will learn how to manage different scheduling policies using the chrt command.

Linux supports several scheduling policies, each with its own characteristics and use cases. The main scheduling policies are:

• SCHED_OTHER: The default scheduling policy for regular processes. It uses a time-sharing approach to distribute CPU time among processes.
• SCHED_FIFO: A real-time, First-In-First-Out scheduling policy. Processes with this policy run until they voluntarily yield the CPU or are preempted by a higher-priority process.
• SCHED_RR: A real-time, Round-Robin scheduling policy. Similar to SCHED_FIFO, but processes are assigned a time slice and are preempted when the time slice expires.
• SCHED_BATCH: A policy designed for CPU-bound, batch-style processes. It gives these processes a slightly lower priority than SCHED_OTHER.
• SCHED_IDLE: A policy designed for low-priority, idle-time processes.

Let's try setting different scheduling policies for a process using the chrt command:

## Set the SCHED_FIFO policy with priority 10
sudo chrt -f -p 10 sleep 60 &

## Set the SCHED_RR policy with priority 15
sudo chrt -r -p 15 sleep 60 &

## Set the SCHED_BATCH policy
sudo chrt -b sleep 60 &

## Set the SCHED_IDLE policy
sudo chrt -i sleep 60 &

You can use the chrt -l command to list all the available scheduling policies:

chrt -l

Example output:

Scheduling policies available:
SCHED_OTHER
SCHED_FIFO
SCHED_RR
SCHED_BATCH
SCHED_IDLE

The chrt command provides a flexible way to manage the scheduling policies and priorities of processes, allowing you to optimize system performance and ensure that critical tasks are executed in a timely manner.

Summary

In this lab, you learned about the purpose of the chrt command in Linux, which is used to set and retrieve the real-time scheduling attributes of a running process. You started by checking the current real-time priority of a process, and then learned how to adjust the real-time priority of a process using the chrt command. This can be useful for optimizing the performance of time-critical applications or ensuring that important processes are scheduled with higher priority.

Linux Commands Cheat Sheet