How to Check and Increase Linux Open File Limits (ulimit, sysctl)

In Linux you can change the maximum number of open files. You can use the ulimit command, which allows you to control resources available to the shell or processes it starts.

Find Linux Open File Limit

# cat /proc/sys/fs/file-max

365004

This value indicates the number of files that can be opened per login session; results may vary across systems.

For example, on a CentOS server the limit is set to 365004 .

Check Hard Limit in Linux

# ulimit -Hn

65535

Check Soft Limit in Linux

# ulimit -Sn

65535

To view hard and soft values for different users, switch users with su and compare.

Example:

# su rumenz
$ ulimit -Sn
1024

$ ulimit -Hn
1024

How to Check System‑Wide File Descriptor Limit

If you run a server, some applications (e.g., MySQL/MariaDB or Apache) may require a higher open file descriptor limit.

You can increase the limit by editing the kernel parameter fs.file-max using sysctl at runtime.

For instance, to raise the limit to 500000 as root:

# sysctl -w fs.file-max=500000

Check the current value with:

$ cat /proc/sys/fs/file-max

These changes persist only until the next reboot; to make them permanent, edit /etc/sysctl.conf and add the line fs.file-max=500000 .

# vi /etc/sysctl.conf

Add the following line:

fs.file-max=500000

You can adjust the number as needed.

# cat /proc/sys/fs/file-max

Users must log out and log back in for changes to take effect; to apply immediately, run:

# sysctl -p

Set User‑Level Open File Limit in Linux

The above examples show how to set a global limit; to apply limits per user, edit /etc/security/limits.conf as root.

# vi /etc/security/limits.conf

Format:

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

Example for user rumenz :

## Example hard limit for max opened files
rumenz    hard    nofile    4096
## Example soft limit for max opened files
rumenz    soft    nofile    1024