Ulimits file in linux

Working with ulimit in Linux [Beginners Guide]

ulimit is a Linux shell command that allows to view or limit the amount of system resources consumed by local Linux users.

The ulimit command comes with shell(bash,sh,zsh etc) packages on Linux systems. The default shell in most Linux distribution is bash. As with most operating systems, it is installed during installation. Ulimit usage, may vary depending on the shell (bash, sh, zsh, csh etc.) used. Parameters can be named more or less differently.

Changes made with Ulimit are temporary. The /etc/security/limits.conf file is pointed to for permanent limits. However, it is recommended to proceed by creating a new configuration file under the /etc/security/limits.d directory.

Understanding ulimit usage

If you haven’t used the ulimit command before, run the following command in terminal to see your local user limits:

[foc@rocky9 ~]$ ulimit -a real-time non-blocking time (microseconds, -R) unlimited core file size (blocks, -c) 0 data seg size (kbytes, -d) unlimited scheduling priority (-e) 0 file size (blocks, -f) unlimited pending signals (-i) 5694 max locked memory (kbytes, -l) 64 max memory size (kbytes, -m) unlimited open files (-n) 1024 pipe size (512 bytes, -p) 8 POSIX message queues (bytes, -q) 819200 real-time priority (-r) 0 stack size (kbytes, -s) 8192 cpu time (seconds, -t) unlimited max user processes (-u) 5694 virtual memory (kbytes, -v) unlimited file locks (-x) unlimited 

You can see that some values have unlimited and some values have a certain limit.

List what you can do with ulimit by typing the following command in the terminal:

[foc@rocky9 ~]$ ulimit --help ulimit: ulimit [-SHabcdefiklmnpqrstuvxPT] [limit] Modify shell resource limits. Options: -S use the `soft' resource limit -H use the `hard' resource limit -a all current limits are reported -b the socket buffer size -c the maximum size of core files created -d the maximum size of a process's data segment -e the maximum scheduling priority (`nice') -f the maximum size of files written by the shell and its children -i the maximum number of pending signals -k the maximum number of kqueues allocated for this process -l the maximum size a process may lock into memory -m the maximum resident set size -n the maximum number of open file descriptors -p the pipe buffer size -q the maximum number of bytes in POSIX message queues -r the maximum real-time scheduling priority -s the maximum stack size -t the maximum amount of cpu time in seconds -u the maximum number of user processes -v the size of virtual memory -x the maximum number of file locks -P the maximum number of pseudoterminals -R the maximum time a real-time process can run before blocking -T the maximum number of threads 

When you run these parameters in plain form with the active user, it shows the value of that parameter. For example, with the max user process -u parameter:

you can learn the max locked memory limit of that user with the -l parameter:

Hard ( -H ) and soft ( -S ) limits are given for each value to be limited. Parameters are written side by side to display values such as hard-soft:

[foc@rocky9 ~]$ ulimit -Hu 5701 [foc@rocky9 ~]$ ulimit -Hl 64

The soft limit is the limit allocated for the actual processing of users. The hard limit is an upper (final limit) limit of the soft limit values.

Limiting different types of resource limits with ulimit

One thing to consider when changing the limit is that the soft limit should not be more than the hard limit. The rule is expressed as:

Increase ulimit values for 5 frequently used values.

Example -1 Modify File Size Limit

To increase the file size value, a new value must be written after the -f parameter:

In the last case file size:

Example -2 Modify Max Memory Size

To increase max memory size:

Example -3 Modify Open File Limit

Open files previous value:

Example -4 Modify Max User Processes Limit

To change the maximum number of processes the user can create:

Let’s take the final state:

Example -5 Modify Virtual Memory Limit

Finally, let’s increase the virtual memory value:

Let’s look at the virtual memory value:

We shared examples of increasing 5 values above.

Bonus Tip

These values will return to default when the user logs out and re-enters.

You can write these values to .bashrc file for automatic application when user login.

[foc@rocky9 ~]$ nano ~/.bashrc ulimit -f 2050 ulimit -m 2024 ulimit -n 2280 ulimit -u 2096 ulimit -v 10240

Save and exit the file. Let’s user logout and login. View the limits:

[foc@rocky9 ~]$ ulimit -a file size (blocks, -f) 2050 max memory size (kbytes, -m) 2024 open files (-n) 2280 max user processes (-u) 2096 virtual memory (kbytes, -v) 10240

How to modify ulimit permanently?

In the previous section we applied ulimit changes to individual users via terminal which we know is non-persistent. To make them persistent we added the changes to individual user’s .bashrc file. But instead of that it is recommended to add all custom ulimit changes inside /etc/security/limits.d file which will automatically be considered every time a user with matching ruleset logs in to the server.

Let’s create an example configuration file for the following values:

• — core — limits the core file size (KB)
• — data — max data size (KB)
• — fsize — maximum filesize (KB)
• — stack — max stack size (KB)
• — nproc — max number of processes
• — maxlogins — max number of logins for this user
• — maxsyslogins — max number of logins on the system

Apply ulimit to users

Create a file named user_limits.conf :

[foc@rocky9 ~]$ sudo nano /etc/security/limits.d/user_limits.conf

#For foc user foc soft core 1024 foc soft data 4096 foc hard fsize 1048576 foc soft maxlogins 4 foc hard maxsyslogins 6 foc soft stack 512 #For faruk user faruk soft core 2048 faruk soft data 3072 faruk hard fsize 1048576 faruk soft maxlogins 2 faruk hard maxsyslogins 3 faruk soft nproc 1200

For example, we added hard and soft limit lines for users. To see the changes, you must do one of the following:

Changes in limits.conf do not require reboot. You just need to close your active session and start a new session to pick the new changes.

Show limits for foc and faruk users. For foc user:

[foc@rocky9 ~]$ ulimit -a core file size (blocks, -c) 1024 data seg size (kbytes, -d) 4096 file size (blocks, -f) 1048576 stack size (kbytes, -s) 512

[foc@rocky9 ~]$ su - faruk Password: Last login: Mon Oct 3 23:11:30 +03 2022 on pts/0

[faruk@rocky9 ~]$ ulimit -a core file size (blocks, -c) 2048 data seg size (kbytes, -d) 3072 file size (blocks, -f) 1048576 max user processes (-u) 1200

Try logging in more than the specified value from different terminals for the max login value. You will encounter the following warning:

foc@fedora:~$ ssh -l foc 192.168.122.238 foc@192.168.122.238's password: There were too many logins for 'foc'. Last login: Mon Oct 3 23:26:30 2022 from 192.168.122.1 Connection to 192.168.122.238 closed. 

foc@fedora:~$ ssh -l faruk 192.168.122.238 faruk@192.168.122.238's password: There were too many logins for 'faruk'. Last login: Mon Oct 3 23:26:30 2022 from 192.168.122.1 Connection to 192.168.122.238 closed.

Apply ulimit to groups

We defined it for users, let’s create an example file for user groups:

[foc@rocky9 ~]$ sudo nano /etc/security/limits.d/group_limits.conf #For worker group @worker hard rss 10000 @worker soft as 12000 #For test01 group @test01 hard rss 11000 @test01 soft as 13000

The foc user is in the worker group, and the faruk user is in the test01 group. You can define different limits according to the groups that users belong to. In this way, you do not have to make separate definitions for each user.

In the last case, the values in KB can be seen with the following command.

[faruk@rocky9 ~]$ cat /proc/$(ps -uax | grep faruk | head -1 |awk )/limits Limit Soft Limit Hard Limit Units Max resident set 11264000 11264000 bytes Max address space 13312000 unlimited bytes 

[foc@rocky9 ~]$ cat /proc/$(ps -uax | grep foc | head -1 |awk )/limits Limit Soft Limit Hard Limit Units Max resident set 10240000 10240000 bytes Max address space 12288000 unlimited bytes

Each value you set is now permanent. You can now increase limit using the opportunities offered by ulimit.

Summary

Increasing user limits may be appropriate for short-term access. Permanent limit increase is usually used by users who manage the application. In systems with central user management, these actions will not be needed.

We recommend that you try the limit increase experience on test systems first.

References

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How do I change the number of open files limit in Linux? [closed]

When running my application I sometimes get an error about too many files open . Running ulimit -a reports that the limit is 1024. How do I increase the limit above 1024? Edit ulimit -n 2048 results in a permission error.

I just went through this on Centos 7 (same on RHEL) and made a blog post covering it because I had so much trouble even with all these posts: coding-stream-of-consciousness.com/2018/12/21/…. Often along with open files, you need to increase nproc which actually resides in multiple settings files. and if you use systemd/systemctl that has its own separate settings. It’s kind of nuts.

4 Answers 4

You could always try doing a ulimit -n 2048 . This will only reset the limit for your current shell and the number you specify must not exceed the hard limit

Each operating system has a different hard limit setup in a configuration file. For instance, the hard open file limit on Solaris can be set on boot from /etc/system.

set rlim_fd_max = 166384 set rlim_fd_cur = 8192 

On OS X, this same data must be set in /etc/sysctl.conf.

kern.maxfilesperproc=166384 kern.maxfiles=8192 

Under Linux, these settings are often in /etc/security/limits.conf.

There are two kinds of limits:

• soft limits are simply the currently enforced limits
• hard limits mark the maximum value which cannot be exceeded by setting a soft limit

Soft limits could be set by any user while hard limits are changeable only by root. Limits are a property of a process. They are inherited when a child process is created so system-wide limits should be set during the system initialization in init scripts and user limits should be set during user login for example by using pam_limits.

There are often defaults set when the machine boots. So, even though you may reset your ulimit in an individual shell, you may find that it resets back to the previous value on reboot. You may want to grep your boot scripts for the existence ulimit commands if you want to change the default.

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