How to limit CPU usage with CPULimit on Ubuntu Linux

This tutorial describes how to limit CPU usage in Ubuntu. I will use the cpulimit utility for this purpose. Cpulimit is a tool that limits the CPU usage of a process (expressed in percentage, not in CPU time). It is useful to control batch jobs when you don't want them to eat too many CPU cycles. The goal of cpulimit is to prevent a process from running for more than a specified time ratio. It does not change the nice value or other scheduling priority settings but the real CPU usage. Also, it can adapt itself to the overall system load dynamically and quickly.

The used CPU amount is controlled by sending SIGSTOP and SIGCONT POSIX signals to processes. The specified process's children processes and threads will share the same CPU percentage.

1 Preliminary Note

This tutorial has been tested on Ubuntu 22.04, but it also works on the older Ubuntu 18.04 and 20.04 releases. The system should have a static IP address. I use 192.168.1.100 as my IP address in this tutorial and server1.example.com as the hostname.

2 CPULimit Installation

Firstly we need to install cpulimit as follows:

apt update
apt install cpulimit

3 Limiting CPU usage 

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