How to Monitor System Performance in Unix

Monitoring system performance is essential for maintaining a healthy Unix environment. Whether you’re checking CPU usage, memory consumption, or disk I/O, understanding how to monitor and troubleshoot your system can help you prevent issues and optimize resource usage.

This blog will guide you through some of the most useful tools and commands to monitor system performance in Unix, including CPU, memory, disk usage, and process monitoring.

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1. How to Check CPU Usage with top and htop

The top command is a powerful tool to display real-time information about running processes, CPU usage, memory usage, and system load. It updates periodically and gives you a snapshot of your system’s performance.

Basic Syntax

top

Once the top command is running, you’ll see a list of active processes and resource usage statistics. The most important columns to watch are:

• %CPU: The percentage of CPU being used by each process.
• %MEM: The percentage of memory being used by each process.
• LOAD: The system load averages for the past 1, 5, and 15 minutes.

You can interact with top using the following keys:

• q: Quit the program.
• P: Sort by CPU usage.
• M: Sort by memory usage.

Advanced: Using htop

htop is an interactive version of top that is more user-friendly and visually appealing. It shows system metrics in a color-coded format and allows you to interact with processes.

To install htop:

$ sudo apt install htop  # On Ubuntu/Debian
$ sudo yum install htop  # On CentOS/Red Hat

To run htop:

$ htop

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2. How to Monitor Memory Usage with free and vmstat

Using free

The free command shows you the current memory usage, including both physical and swap memory. It is a quick and easy way to check your system’s memory status.

Basic Syntax

free -h

The -h option displays memory sizes in human-readable format (e.g., MB, GB).

Example Output:

              total        used        free      shared  buff/cache   available
Mem:           16G          3G         10G         1G          3G         12G
Swap:          4G          0G          4G

• Used: Memory currently used by processes.
• Free: Unused memory.
• Buff/Cache: Memory used for buffering and caching data.
• Available: Memory available for starting new applications without swapping.

Using vmstat

The vmstat (virtual memory statistics) command provides more detailed information about memory, processes, paging, block IO, and system performance.

Basic Syntax

vmstat 1

This will display system statistics every second. Key fields to watch:

• r: The number of processes waiting for CPU time.
• free: Amount of free memory.
• si: Swap in (memory being moved from disk to RAM).
• so: Swap out (memory being moved from RAM to disk).

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3. How to Monitor Disk Usage with df and du

Using df

The df command is used to check disk space usage for mounted filesystems. It gives an overview of the available and used space on each filesystem.

Basic Syntax

df -h

The -h option displays the output in human-readable format (e.g., GB, MB).

Example Output:

Filesystem      Size  Used Avail Use% Mounted on
/dev/sda1       50G   25G   20G  60% /
/dev/sdb1       100G  40G   55G  43% /data

• Size: Total size of the filesystem.
• Used: Amount of space used.
• Avail: Available space.
• Use%: Percentage of disk space used.
• Mounted on: Mount point of the filesystem.

Using du

The du command shows disk usage for directories and their contents. It’s useful when you want to find out how much space a particular directory is consuming.

Basic Syntax

du -sh /path/to/directory

• -s: Show only the total size for the directory.
• -h: Human-readable format.

Example Output:

$ du -sh /home/user
1.5G    /home/user

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4. How to Monitor Process Usage with ps and pgrep

The ps (process status) command displays information about active processes, such as the process ID (PID), memory usage, and CPU usage.

Basic Syntax

ps aux

• a: Show processes of all users.
• u: Show user-oriented format (including memory and CPU usage).
• x: Show processes without a controlling terminal.

Example Output:

USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
user      1234  0.3  1.2  34567 12345 ?        Ss   10:00   0:05 /usr/bin/python3

Using pgrep

The pgrep command allows you to search for processes by name and get their process IDs.

Basic Syntax

pgrep process_name

• Example: Find the PID of all running python processes:

  $ pgrep python

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5. How to Check System Load with uptime and w

The uptime command provides a simple way to check how long the system has been running, along with the current system load averages.

Basic Syntax

uptime

Example Output:

 10:12:34 up 5 days,  2:34,  2 users,  load average: 0.12, 0.10, 0.08

• Load average: The system load averages for the past 1, 5, and 15 minutes.
• Up time: How long the system has been running.

The w command is similar but provides additional information, such as who is logged in and what they are doing.

Basic Syntax

w

Example Output:

 10:12:34 up 5 days,  2:34,  2 users,  load average: 0.12, 0.10, 0.08
USER     TTY      FROM             LOGIN@   IDLE   JCPU   PCPU  WHAT
user     pts/0    192.168.1.1      09:30    1.00s  0.10s  0.01s  w

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6. How to Monitor System Logs with journalctl

The journalctl command is used to query and display logs from the systemd journal, which contains logs for system processes, kernel events, and other system activities.

Basic Syntax

journalctl

Examples:

• View logs from the current boot:

  $ journalctl -b

• View logs related to a specific service:

  $ journalctl -u nginx

• Follow logs in real-time:

  $ journalctl -f

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Practice Time!

1. Monitor CPU and Memory Usage:

• Use top or htop to check CPU and memory usage and monitor processes.

1. Check Disk Space:

• Use df to view available disk space and du to check the disk usage of specific directories.

1. Monitor Processes:

• Use ps to examine active processes and pgrep to find specific processes.

1. Check System Load:

• Use uptime and w to check the system load and logged-in users.

1. Review System Logs:

• Use journalctl to view logs and troubleshoot any system issues.

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Summary

• How to use top and htop to monitor CPU and memory usage.
• How to use df and du to monitor disk space and disk usage.
• How to use ps and pgrep to monitor and manage processes.
• How to use uptime and w to check system load and user activity.
• How to use journalctl to review system logs.