How to limit CPU usage with CPULimit on Ubuntu Linux

The cpulimit command is designed to restrict the CPU usage of a specific process on Linux, ensuring that it does not exceed a defined threshold. This can be particularly useful for managing system resources and preventing a single process from monopolizing CPU time, which could degrade overall system performance. By specifying the desired CPU usage limit as a percentage, users can apply constraints to running processes or initiate new ones under controlled CPU consumption. The tool sends SIGSTOP and SIGCONT signals to the target process, pausing and resuming them to maintain the set usage limit.

1 Preliminary Note

This tutorial has been tested on Ubuntu 24.04, but it also works on the older Ubuntu releases.

2 CPULimit Installation

Firstly, we need to install cpulimit as follows:

sudo apt update
sudo apt install cpulimit

3 Limiting CPU usage 

Now, we will check the utility for limiting CPU usage. For this, we will first check the CPU usage without CPUlimit and then implement CPUlimit to evaluate it. Let's make it clear with an example.

1. Here is an example of how to utilize your CPU with an application in single-core CPU:

dd if=/dev/zero of=/dev/null &

Then, we will check the CPU usage with the command:

top

top - 11:24:18 up 49 min,  1 user,  load average: 0.94, 1.02, 1.79
Tasks: 249 total,   2 running, 247 sleeping,   0 stopped,   0 zombie
%Cpu(s): 13.4 us, 11.6 sy,  0.0 ni, 74.9 id,  0.0 wa,  0.1 hi,  0.0 si,  0.0 st
KiB Mem:   1010540 total,   271652 used,   738888 free,    21760 buffers
KiB Swap:  1048572 total,        0 used,  1048572 free.   158204 cached Mem

  PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND                    
 1850 root      20   0    7224    616    520 R 100.0  0.1   1:20.33 dd                         
 1851 root      20   0   24952   1756   1180 R   0.3  0.2   0:00.03 top                        
    1 root      20   0   33480   2776   1456 S   0.0  0.3   0:05.31 init                       
    2 root      20   0       0      0      0 S   0.0  0.0   0:00.01 kthreadd        

As we can see that, CPU usage has gone to 100%. Now, we will use the cpulimit to limit CPU usage. We can bring up this process to the foreground using fg command and cancel it with CTRL+C

fg

Now we can test cpulimit to see if it does what it should. Let's test it as follows:

cpulimit -l 30 dd if=/dev/zero of=/dev/null &

Now we will check the CPU usage with top command:

top

Now you can see that the CPU usage has decreased from 100% to 33.8%, almost 30%. So we have successfully checked the utility cpulimit, which can limit the usage of CPU consumption in a single-core Ubuntu distro.

2. Here is an example of how to utilize your CPU with an application in multiple core CPU:

To check your CPU core, use the command:

nproc   

 In my case, it is CPU core count was 4.
Now we will proceed to check the CPU usage without cpulimit in all 4 cores for the application as follows:

for j in `seq 1 4`; do dd if=/dev/zero of=/dev/null & done

It will run the command utilizing all the cores and yeild the output as:

Now check the CPU usage with the top command:

top

The dd command consumes almost 100% CPU of all the cores.  Next, we will check the command with the cpulimit utility. For this, kill previous traces for the dd command as follows:

killall dd

Now use cpulimit with the same command as follows:

for j in `seq 1 4`; do cpulimit -l 20 dd if=/dev/zero of=/dev/null & done

Now check the CPU usage wit the cpulimit utility.

top

As you can see above, CPU usage is limited from 100%  to 20% almost for multiple-core CPUs.

Congratulations! We have successfully tested the cpulimit for limiting the CPU usage in Ubuntu.

4 Links

•     Ubuntu : http://www.ubuntu.com/
•     cpulimit : https://github.com/opsengine/cpulimit