How to Monitor CPU and Memory Usage in Linux

Monitoring CPU and memory usage is essential for managing Linux systems effectively. Linux provides several commands to get a detailed look at resource consumption, helping administrators optimize performance and troubleshoot issues. Here are some essential commands for monitoring CPU and memory usage.

1. Using top Command #

The top command is a popular utility that provides a real-time view of CPU and memory usage.

• To start top:

top

• Key Features:
  • Shows CPU, memory, and swap usage.
  • Displays a list of processes sorted by CPU usage by default.
  • Press M to sort by memory usage. You may want to press shift+m

2. Using htop Command #

htop is an improved version of top with a more user-friendly interface.

• Install htop:

sudo apt install htop # Debian/Ubuntu

sudo yum install htop # CentOS/RHEL

• Start htop:

htop

• Features:
  • Color-coded display for easy reading.
  • Ability to scroll vertically and horizontally.
  • Interactive interface to kill processes directly from the list.

3. Using vmstat Command #

vmstat (Virtual Memory Statistics) reports information about processes, memory, paging, block I/O, and CPU usage.

• Run vmstat with a delay:
  • This will refresh every 2 seconds.

vmstat 2

• Key Columns:
  • r: Number of processes waiting for CPU.
  • free: Amount of free memory.
  • si and so: Swap memory in and out.
  • us, sy, id: CPU time for user, system, and idle.

4. Using free Command #

The free command provides a quick overview of system memory usage, showing total, used, and available memory.

• Run free with human-readable format:

free -h

5. Using sar Command

sysstat’s sar command provides historical data on CPU, memory, and other resource usage over time. This is especially useful for identifying trends.

• Install sysstat

sudo apt install sysstat # Debian/Ubuntu
sudo yum install sysstat # CentOS/RHEL

• Enable Data Collection:
  • The sysstat service should be enabled and configured to collect data periodically.
  • Edit the Configuration File: Open the sysstat configuration file.
  • Set ENABLED to "true": Change the ENABLED line to true so that sysstat collects and logs system statistics.
  • Save and close the file.
  • Restart the sysstat Service: After enabling data collection, restart the sysstat service to apply changes.

sudo vi /etc/default/sysstat

sudo systemctl restart sysstat

You can then check the status

sudo systemctl status sysstat

• View CPU Usage over the past intervals:
  • This example shows CPU usage at 1-second intervals, 5 times.

sar -u 1 5

• View Memory Usage:

sar -r

6. Using iostat Command

iostat is useful for monitoring CPU load and input/output (I/O) statistics on disks.

• Install sysstat (if not already installed):

sudo apt install sysstat # Debian/Ubuntu
sudo yum install sysstat # CentOS/RHEL

• Run iostat:
  • This command shows CPU statistics at 2-second intervals.

iostat -c 2

7. Using ps Command

ps (Process Status) displays information about active processes and can be customized to show specific details.

• View Processes by Memory Usage:

ps aux --sort=-%mem | head

• View Processes by CPU Usage:

ps aux --sort=-%cpu | head

8. Using mpstat Command

mpstat (Multiprocessor Statistics) shows CPU usage per processor, which is valuable for multi-core systems.

• Run mpstat:
  • This will show statistics for each core on the system, helping to identify if any single core is overloaded.

mpstat -P ALL

Summary of Commands #

• General Resource Overview: top, htop
• CPU Usage: top, mpstat, sar -u
• Memory Usage: free, vmstat, sar -r
• Disk I/O: iostat, vmstat

With these commands, Linux administrators have a toolkit for continuous monitoring and diagnostics to manage system resources effectively.