There can be cases when your server performance can slow down when even a single process uses all of your server CPU capability. Such usage will cause issues for other processes to work properly on your VPS instance. Since when one process is using all of the resources, other processes have to wait in the queue to start their tasks. This can be solved by limiting CPU resource usage with CPULimit software.
The main purpose of CPULimit is to set a restriction on the specific process on how much CPU it can use. When the limitation is implemented, there is no influence on the nice value or the settings on priorities, but on real CPU usage instead.
0. Requirements:
Root or sudo.
nano or another text editor.
1.1 Installation if using Ubuntu/Debian:
sudo apt-get install cpulimit
1.2 Installation if using CentOS/Fedora:
Firstly, it will be required to install the EPEL repository if it was not done previously:
sudo yum install epel-release
Afterward, the installation can be initiated:
sudo yum install cpulimit
or
sudo dnf install cpulimit
2. Usage of CPULimit:
To check the effectiveness of CPULimit, let's create a process (usecpu.sh) that will consume all of your server's CPU:
Enter the following code into the usecpu.sh file:
#!/bin/bash
while :; do :; done;
Save the code on your file. This code will create a loop that will consume all of the server's CPU. When the file is created, set executable permission for it:
The created process can be started using:
After initiation, you will receive a result of process id, for example, 1887:
If everything is correct, the new process should use all of the server's CPU. You can check the usage of your CPU by using the top command:
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
2912 root 20 0 12512 896 792 R 99.9 0.0 0:18.38 usecpu.sh
2893 root 20 0 39688 3660 3092 R 0.3 0.2 0:00.02 top
1 root 20 0 37912 6000 4004 S 0.0 0.3 0:01.52 systemd
2 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kthreadd
3 root 20 0 0 0 0 S 0.0 0.0 0:00.05 ksoftirqd/0
5 root 0 -20 0 0 0 S 0.0 0.0 0:00.00 kworker/0:0H
6 root 20 0 0 0 0 S 0.0 0.0 0:00.10 kworker/u2:0
7 root 20 0 0 0 0 S 0.0 0.0 0:00.49 rcu_sched
8 root 20 0 0 0 0 S 0.0 0.0 0:00.00 rcu_bh
9 root rt 0 0 0 0 S 0.0 0.0 0:00.00 migration/0
10 root rt 0 0 0 0 S 0.0 0.0 0:00.01 watchdog/0
11 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kdevtmpfs
12 root 0 -20 0 0 0 S 0.0 0.0 0:00.00 netns
13 root 0 -20 0 0 0 S 0.0 0.0 0:00.00 perf
14 root 20 0 0 0 0 S 0.0 0.0 0:00.00 khungtaskd
15 root 0 -20 0 0 0 S 0.0 0.0 0:00.00 writeback
16 root 25 5 0 0 0 S 0.0 0.0 0:00.00 ksmd
As you can see from the table, the usecpu.sh process uses 99.9% of server CPU. Such CPU usage will prevent other processes from working successfully and can finally result in server OS inactivity. This is where CPULimit comes to usage.
If you wish to limit the process to use only 30% of your server total CPU, initiate the following command:
- -l 30 will set the limit to the provided number of %. In this case 30%.
- -p 2892 is used to identify the process by it's PID, as seen in the first column from top command.
Now, when the process is limited by CPULimit let's check the results again by initiating top command:
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
2912 root 20 0 12512 996 896 T 31.6 0.0 0:29.76 usecpu.sh
2915 root 9 -11 8612 1544 1428 S 0.3 0.1 0:00.02 cpulimit
1 root 20 0 37912 6000 4004 S 0.0 0.3 0:01.53 systemd
2 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kthreadd
3 root 20 0 0 0 0 S 0.0 0.0 0:00.06 ksoftirqd/0
5 root 0 -20 0 0 0 S 0.0 0.0 0:00.00 kworker/0:0H
6 root 20 0 0 0 0 S 0.0 0.0 0:00.11 kworker/u2:0
7 root 20 0 0 0 0 S 0.0 0.0 0:00.52 rcu_sched
8 root 20 0 0 0 0 S 0.0 0.0 0:00.00 rcu_bh
9 root rt 0 0 0 0 S 0.0 0.0 0:00.00 migration/0
10 root rt 0 0 0 0 S 0.0 0.0 0:00.02 watchdog/0
11 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kdevtmpfs
12 root 0 -20 0 0 0 S 0.0 0.0 0:00.00 netns
13 root 0 -20 0 0 0 S 0.0 0.0 0:00.00 perf
14 root 20 0 0 0 0 S 0.0 0.0 0:00.00 khungtaskd
15 root 0 -20 0 0 0 S 0.0 0.0 0:00.00 writeback
16 root 25 5 0 0 0 S 0.0 0.0 0:00.00 ksmd
Now the usecpu.sh process CPU consumption will be limited to 31.6% of CPU (can be +/- 5% deflection).
If you wish to use process name instead of PID for the limitation, you can form your command from such example:
cpulimit -l 25 ./usecpu.sh &
