One of the Linux’s beauties is that you can control almost everything about it. This gives a system administrator a great control over his system and better utilization of the system resources.

While some might have never thought about doing this, it is important to know that in Linux you can limit how much resource a single user may use and for how long.

Read Also: How to Increase Number of Open Files Limit in Linux

In this short topic, we will show you how to limit the number of processes started by user and how to check the current limits and modify them.

Before we go any further there are two things we need to point:

1. You need root access to your system to modify the user limits
2. You must be extremely careful if you plan to modify these limits

To setup user limits, we will need to edit the following file:

/etc/security/limits.conf

This file is used to apply ulimit created by the pam_module. 

The file has the following syntax:

<domain> <type> <item> <value>

Here we will stop to discuss each of the options:

• Domain – this includes usernames, groups, guid ranges etc
• Type – soft and hard limits
• Item – the item that will be limited – core size, file size,  nproc etc
• Value – this is the value for the given limit

A good sample for a limit is:

@student          hard           nproc                20

The above line sets a hard limit of maximum 20 processes on the "student" group.

If you want to see the limits of a certain process has you can simply “cat” the limits file like this:

# cat /proc/PID/limits

Where PID is the actual process ID, you can find out process id by using ps command. For more detailed explanation, read our article that says – Find Running Linux Processes and Set Process Limits Per-User Level

So here is an example:

# cat /proc/2497/limits

Sample Output

Limit Soft Limit Hard Limit Units 
Max cpu time unlimited unlimited seconds 
Max file size unlimited unlimited bytes 
Max data size unlimited unlimited bytes 
Max stack size 8388608 unlimited bytes 
Max core file size 0 unlimited bytes 
Max resident set unlimited unlimited bytes 
Max processes 32042 32042 processes 
Max open files 1024 4096 files 
Max locked memory 65536 65536 bytes 
Max address space unlimited unlimited bytes 
Max file locks unlimited unlimited locks 
Max pending signals 32042 32042 signals 
Max msgqueue size 819200 819200 bytes 
Max nice priority 0 0 
Max realtime priority 0 0 
Max realtime timeout unlimited unlimited us 

All of the lines are pretty much self explanatory. However if you want to find more the settings you can input in limits.conf file, you can have a look at the manual provided here.

If you have any questions or comments, please do not hesitate to submit them in the comment section below.