Adjusting Open File Limits for PortSIP PBX

Sometimes, depending on the default Linux OS configuration, the maximum number of open files (nofile) may be set too low. When this happens, PortSIP PBX may not be able to support a large number of users, especially when many clients connect to the PBX using TCP.

Note: In most deployments, you do not need to change this. The default Linux and Docker settings already allow a sufficiently high number of open files. Only follow this guide if you encounter system warnings or limitations such as “too many open files.”

To ensure stable performance under heavy workloads, it is recommended to increase the maximum open file limit (nofile) at both the Linux system level and the Docker engine level.

This guide provides detailed and safe steps to update these limits.

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1. Check the Current File Limit for Docker

Perform the command below to check whether the Docker service already has a file limit applied:

systemctl show docker | grep LimitNOFILE

If the value is low (for example, 1024, meaning the PBX can open only up to 1024 files/TCP connections), continue with the steps below.

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2. Update the Docker Systemd Service Limit

Perform the command below to open the override configuration for the Docker service:

systemctl edit docker.service

Add the following content:

[Service]
LimitNOFILE=1065535

Save and close the editor.

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3. Apply the Systemd Changes

Perform the commands below to reload Systemd and restart Docker:

systemctl daemon-reload
systemctl restart docker

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4. Configure Docker Daemon File Descriptor Limits

Perform the command below to open the Docker daemon configuration file (ensure you have installed the nano editor):

nano /etc/docker/daemon.json

If the file does not exist, create it.

Add the following configuration (or merge it with existing settings):

{
  "default-ulimits": {
    "nofile": {
      "name": "nofile",
      "soft": 565535,
      "hard": 565535
    }
  }
}

Save the file and exit the editor.

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5. Restart Docker to Apply the New Limits

Perform the command below:

systemctl restart docker

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6. Verify the Limits Inside the PortSIP PBX Container

Perform the command below to enter the PortSIP Call Manager container:

docker exec -it portsip.callmanager /bin/bash

Perform the commands below to check the soft and hard limits:

ulimit -Sn
ulimit -Hn

Expected output:

565535
565535

If both values match, the configuration has been successfully applied.