CompTIA Linux+ XK0-005 - 4.3 - High CPU Utilization

High CPU utilization can impact system performance and responsiveness in a Linux environment. Analyzing and troubleshooting high CPU utilization is essential for identifying resource-intensive processes and optimizing system performance. This guide aims to provide detailed steps to check for high CPU utilization, including command examples and explanations of command flags/options.

How to Check for High CPU Utilization

To check for high CPU utilization in a Linux environment, follow these steps:

Identify the CPU usage: Use the top command to monitor CPU usage and identify processes consuming the most CPU resources:
```
top
```
The top command displays real-time information about system processes, including CPU utilization. The processes are listed in descending order based on their CPU usage. Look for processes with high CPU percentages.

View CPU usage summary: Use the mpstat command to view CPU usage statistics:

mpstat -P ALL

The mpstat command displays CPU usage statistics for each processor. The -P ALL flag shows statistics for all processors individually. Pay attention to the "%idle" column, which represents the idle percentage of each CPU. Lower idle percentages indicate higher CPU utilization.

Example

Linux 4.18.0-477.10.1.el8_8.x86_64 (redhat-8-install.dtvlinux.home.arpa) 09/06/23 _x86_64_ (2 CPU)

10:16:41     CPU    %usr   %nice    %sys %iowait    %irq   %soft  %steal  %guest  %gnice   %idle
10:16:41     all   17.83    0.03    1.55    0.11    0.82    0.10    0.00    0.00    0.00   79.56
10:16:41       0   16.67    0.02    1.59    0.11    0.81    0.12    0.00    0.00    0.00   80.67
10:16:41       1   19.00    0.04    1.51    0.10    0.82    0.08    0.00    0.00    0.00   78.45

Check process CPU usage: Use the ps command with the --sort=-%cpu flag to list processes sorted by CPU usage:
```
ps aux --sort=-%cpu
```
The ps command with the --sort=-%cpu flag lists all processes, sorted in descending order based on their CPU usage. This helps identify processes that are consuming excessive CPU resources.

Monitor CPU usage over time: Use the sar command to monitor CPU usage at regular intervals:

sar -u 1 5

The sar command with the -u flag displays CPU usage statistics at specified intervals. In the example above, it displays CPU utilization every second for a total of 5 times.

Example

Linux 4.18.0-477.10.1.el8_8.x86_64 (redhat-8-install.dtvlinux.home.arpa) 09/06/23 _x86_64_ (2 CPU)

10:14:47        CPU     %user     %nice   %system   %iowait    %steal     %idle
10:14:48        all      3.06      0.00      0.00      0.00      0.00     96.94
10:14:49        all      5.03      0.00      1.51      0.00      0.00     93.47
10:14:50        all      4.02      0.00      1.51      0.00      0.00     94.47
10:14:51        all      3.54      0.00      1.01      0.00      0.00     95.45
10:14:52        all      5.50      0.00      2.00      0.00      0.00     92.50
Average:        all      4.23      0.00      1.21      0.00      0.00     94.56

Investigate CPU usage by process: Use the pidstat command to analyze CPU usage by individual processes:
```
pidstat -p <PID> -u
```
The pidstat command with the -p <PID> flag provides detailed CPU usage statistics for a specific process identified by its Process ID (PID). The -u flag shows CPU usage information. Replace <PID> with the actual Process ID.
Example
```
$ pidstat -p 1

  Linux 4.18.0-477.10.1.el8_8.x86_64 (redhat-8-install.dtvlinux.home.arpa) 09/06/23 _x86_64_ (2 CPU)

  10:19:08      UID       PID    %usr %system  %guest   %wait    %CPU   CPU  Command
  10:19:08        0         1    0.02    0.06    0.00    0.30    0.08     0  systemd
```
Analyze system logs: Check system logs for any relevant error messages or indications of high CPU utilization. Use the following command to view system logs:
```
dmesg
```
The dmesg command displays the kernel ring buffer, which contains messages and error information from the operating system. Look for any indications of high CPU utilization or related issues.

Conclusion

Analyzing and troubleshooting high CPU utilization in a Linux environment is crucial for maintaining system performance. By following the steps outlined in this guide, you can identify resource-intensive processes, monitor CPU usage, and take necessary actions to optimize system performance.

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