Maximum number of opened files on Ubuntu

To increase the maximum number of opened files on Ubuntu, follow these steps:

1. Check the Current Limit

You can check the current limit for the maximum number of open files using:

ulimit -n

2. Temporary Change (Session Only)

To temporarily change the limit for the current session:

ulimit -n <new_limit>

For example:

ulimit -n 65535

This change lasts only for the duration of the shell session.

3. Permanent Change for a User

To make the change permanent for a specific user:

Step 1: Edit Limits Configuration

Edit the limits configuration file:

sudo nano /etc/security/limits.conf

Add or modify the following lines at the end of the file:

<username> soft nofile 65535
<username> hard nofile 65535

Replace <username> with the actual username.

Step 2: Apply Limits to All Sessions

Ensure PAM modules apply the limits. Check or add the following line in /etc/pam.d/common-session and /etc/pam.d/common-session-noninteractive:

session required pam_limits.so

4. Change System-Wide Limit

To increase the limit system-wide:

Step 1: Edit limits.conf

Update the system-wide limit in /etc/security/limits.d/90-nproc.conf (or similar) by adding:

* soft nofile 65535
* hard nofile 65535

Step 2: Update /etc/systemd Configuration

For services managed by systemd, update its configuration. For example, edit the default limits in:

sudo nano /etc/systemd/system.conf
sudo nano /etc/systemd/user.conf

Add or modify these lines:

DefaultLimitNOFILE=65535

Step 3: Restart System Services

Reload systemd to apply changes:

sudo systemctl daemon-reexec

5. Verify Changes

Restart your system or session and verify the new limits using:

ulimit -n

Or check limits for systemd services with:

cat /proc/$(pgrep -o <service_name>)/limits

Replace <service_name> with the name of the service you're checking.