ulimit command is used by the administrator to limit hardware resources in a pool share and is mainly used by shared hosting providers to curb unwanted hardware resource usage by other tenants.

There are two types of limits that you can set on your Linux machine.

• Hard Limit
• Soft Limit

Both limits have different usage. One can be overridden by root or sudo privilege, and the second one can be overridden by normal users within the threshold that the root account has set.

Ulimit is a built-in command located under /bin or /usr/bin. It can be found easily on all Linux distributions, whether it is Debian, Ubuntu, Arch Linux, Fedora, or any other RHEL-based distros.

So, let’s see how you can enforce limitations on physical hardware for other users and what types of limitations you can implement on them.

Type of Limit

Although we have mentioned that ulimit has two types of limits hard limit and soft limit, we will now discuss them separately in the following sections.

What is the hard limit?

A hard limit is set by a privileged user to limit hardware resources for other users, and it can be set through the configuration “/etc/security/limits.conf”, which can be modified by the root user.

Once you have specified the limits in “limits.conf”, you need to restart your system for the changes to be applied.

What is the soft limit?

A privileged user also sets the “soft limit” to limit hardware resources for other users, but there are slight changes compared to the hard limit.

Standard users can also override soft limits within capped resources by root users.

You can manipulate soft limit resources through your terminal, but for persistent changes, you need to contact your administrator to remove the cap limit.

To set a soft limit on a current shell, use the -S option along with the ulimit command.

$ ulimit -S

Ulimit Command Syntax

The basic command syntax of ulimit is shown below.

$ ulimit [-OPTIONS] -[TYPE-OF-LIMIT]

System resources on which you can set limit

If you open the /etc/security/limit.conf configuration file, you will find the following list of items on which you can apply limitations:

These are listed below, and use the specific resource keywords when you want to apply changes throughout the system using limit.conf.

core		limits the core file size (KB)
data  		max data size (KB)
fsize 	 	maximum filesize (KB)
memlock  	max locked-in-memory address space (KB)
nofile  	max number of open file descriptors
rss  		max resident set size (KB)
stack 	 	max stack size (KB)
cpu  		max CPU time (MIN)
nproc 	 	max number of processes
as  		address space limit (KB)
maxlogins  	max number of logins for this user
maxsyslogins  	max number of logins on the system
priority  	the priority to run user process with
locks 	 	max number of file locks the user can hold
sigpending  	max number of pending signals
msgqueue  	max memory used by POSIX message queues (bytes)
nice  		max nice priority allowed to raise to values: [-20, 19]
rtprio  	max realtime priorit
chroot	 	change root to directory (Debian-specific)

How to find a detailed report about the current user

To check for any limitations on your account, you can invoke ulimit with the -a option, which will generate a report of the current logged in user.

$ ulimit -a

For better understanding, we have changed the default output a bit.

You can also generate a completely separate report for hard and soft limits assigned to your account or system by specifying -H (Hard limit) and -S (Soft limit).

$ ulimit -Ha
$ ulimit -Sa

How to check and change the max locked memory limit in Linux

To check the max locked memory limit, you can use the -l option along with the ulimit command.

$ ulimit -l

The output of the above command

From the above output, I have discovered I do have some limitations on Memory locked on my system. To change a limit, you can use -l along with the limitation value.

Let me change the memory-locked value of my current shell.

ulimit -l 15000
ulimit -l

The output of the above command

How to check and change the virtual memory limit in Linux

To check the virtual memory limit, you can use the -v option along with the ulimit command.

$ ulimit -v

From the above output, I have discovered I don’t have any limitations on virtual Memory. To set a limit, you can use -v along with the limitation value.

Let me set virtual memory limitations on my current shell.

$ ulimit -v 20000
$ ulimit -v

The output of the above command:

How to check and change open file limit in Linux

To check the open file limit, you can use -n option along with the ulimit command.

$ ulimit -n

The output of the above command

From the above output, I have discovered that I do have some limitations on the number of files that can be open on my system. To change a limit, you can use -n along with the limitation value.

Let me increase the limit on the number of open files in my current shell.

$ ulimit -n 2000
$ ulimit -n

The output of the above command:

 How to check and change the file size limit in Linux

To check the file size limit, you can use -f option along with the ulimit command.

$ ulimit -f

The output of the above command

From the above output, I have discovered I don’t have any limitations on individual file size . To set a limit, you can use -f along with the limitation value.

Let me set a file size limitation on my current shell.

$ ulimit -f 5000
$ ulimit -f

The output of the above command:

How to check and change the max user process limit in Linux

To check the max user process limit, you can use -u option along with the ulimit command.

$ ulimit -u

The output of the above command

From the above output, I have discovered I do have some limitations on the number of processes a particular user can create. To change a limit, you can use -u along with the limitation value.

$ ulimit -u 500
$ ulimit -u

The output of the above command:

How to check and change the CPU time limit in Linux

To check the CPU time limit, you can use the -t option along with the ulimit command.

$ ulimit -t

The output of the above command

From the above output, I have discovered I don’t have any limitations on CPU time. To set a limit, you can use -t along with the limitation value.

$ ulimit -t 4
$ ulimit -t

The output of the above command:

How to check and change max memory size limit in Linux

To check the physical memory size limit, you can use the -m option along with the ulimit command.

$ ulimit -m

The output of the above command

From the above output, I have discovered I don’t have any limitations on physical Memory. To set a limit, you can use -m along with the limitation value.

Let me set max memory limitation on my current shell.

$ ulimit -m 4096
$ ulimit -m

The output of the above command:

Save changes ulimit changes permanent in limit.conf

The above change that you have made will be applicable till the shell is running, and once it is closed, every changes will be elapsed. To persist changes throughout the system, you must modify the /etc/security/limit.conf file.

To edit /etc/security/limit.conf, you need to have sudo privileges. One important point is that whatever changes you make to limit.conf can affect your users, and it can also crash your system when you are not sure about the value.

Therefore, I recommend that you modify the file only if you are sure about what you are doing.

To modify the limit.conf file, open your terminal using any command-line editor with sudo.

$ sudo nano /etc/security/limit.conf

While scrolling, you will find a suggested format to use to save changes.

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

• <domain>: specify user, group, and you can also use (* or %) wildcard
• <type>: Declare which type of limit you are assigning: “hard” or “soft”
• <item>: Specify the resource on which you want to set a limit.
• <value>: Define limit value

For example, if I want to set a soft file (fsize) limit for trendoceans, then I need to append this line to limit.conf file

trendoceans soft fsize 500

Suggestion for you: How to fix file size limit exceeded

Once you have modified “limit.conf”, you will need to reboot your system for the new changes to apply.

Wrap up

That’s all for ulimit command usage in Linux